Silicones for Personal Care, 2nd Edition PDF

Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick Jr. Silicones for Personal Care, 2nd Edition ISBN: 978-1-932633-36-8 Copyright 2008, by Allured Publishing Corporation. All Rights Reserved. Editorial Book Editor: Angela C. Kozlowski Copy Editors: Brian Budzynski, Lois Hince Indexe...

Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick Jr. Silicones for Personal Care, 2nd Edition ISBN: 978-1-932633-36-8 Copyright 2008, by Allured Publishing Corporation. All Rights Reserved. Editorial Book Editor: Angela C. Kozlowski Copy Editors: Brian Budzynski, Lois Hince Indexer: Julie Bess Proofreader: Emily S. Keats Designer: Jennifer J. Kauffman Administration Publisher: Marian Raney Book Manager: Marie Kuta Book Coordinator and Web Support: Anita Singh Disclaimer The contents of this book are for educational purpose only. Readers should do their own research for new and updated information, patents, and government regulations. Neither this book nor any part may be reproduced or transmitted in any form by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage retrieval system, without permission in writing from the publisher. NOTICE To the best of our knowledge the information in this book is accurate. However, in a time of rapid change, it is difficult to ensure that all information provided is entirely accurate and up-to-date. Therefore, the author and the publisher accept no responsibility for any inaccuracies or omissions and specifically disclaim any liability, loss, or risk, personal or otherwise, which is incurred as a consequence, directly or indirectly, of the use and/or application of any of the contents of this book. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Publisher. Allured Publishing Corporation 336 Gundersen Drive, Suite A, Carol Stream, IL 60188 USA Tel: 630-653-2155 Fax: 630-653-2192 E-mail: [email protected]  Table of Contents Preface........................................................................................................vii About the Author/Acknowledgement......................................................... ix 1. Introduction........................................................................11 Silicone........................................................................................................11 Comparing Silicon with Carbon................................................................12 Silicone Compounds..................................................................................14 Silicone from Quartz..................................................................................14 Rochow Process – Chlorosilanes from Silicon..........................................14 Hydrolyzate—Silicone from Chlorosilanes3..............................................17 Reactions of Chlorosilanes.........................................................................19 Silicones Properties....................................................................................20 Silicone Backbone Nomenclature.............................................................23 2. Basic Silicone Materials.....................................................35 Cyclomethicone..........................................................................................35 Molecular Weight of Polymeric Silicones.................................................39 Silicone Fluids............................................................................................42 Silicone on Substrate..................................................................................47 Cosmetic Usage of Silicone Fluids............................................................48 Silanol Compounds....................................................................................49 3. Silicone Antifoam Compounds..........................................55 Mechanism of Antifoam.............................................................................57 Testing Antifoam Performance..................................................................59 4. Emulsion.............................................................................63 Emulsion Terminology2.............................................................................66 Emulsion Stability......................................................................................67 Silicone Emulsions.....................................................................................69 Types of Emulsions....................................................................................70 Deposition of Naturally Derived Hair Color via Reactive Silicone Emulsions.................................................................................72 5. Silicone Surfactants............................................................75 Silicone Molecule Preparation...................................................................80 Equilibration...............................................................................................82 Derivitization..............................................................................................90 iii iv Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. 6. Dimethicone Copolyol Chemistry.....................................93 Reaction......................................................................................................94 Dimethicone Copolyol Properties.............................................................94 Structure Function Study..........................................................................99 Water Solubility........................................................................................105 Water Tolerance.......................................................................................107 Odor..........................................................................................................108 Hydroxypropyl Dimethicone...................................................................116 7. Silicone Esters..................................................................123 Reaction....................................................................................................124 Properties..................................................................................................124 Solubility Properties.................................................................................126 Triglyceride-Derived Dimethicone Copolyol Esters..............................126 Dimethicone Copolyol Meadowfoamate.................................................127 Meadowfoam Silicone..............................................................................128 Ester Structure/Function.........................................................................132 Other Esterification Methods..................................................................138 8. Alkyl Dimethicone Copolyol Compounds.......................143 Orientation at the Interface.....................................................................146 Emulsification Properties.........................................................................148 3D Partition Coefficient...........................................................................155 9. Fluoro Dimethicone.........................................................163 Surface Tension Reduction......................................................................163 Chemistry..................................................................................................163 Low Fluoro Compounds..........................................................................165 High Fluoro Compounds.........................................................................167 Fluoro Alkyl Silicones..............................................................................167 10. Alkyl Dimethicone............................................................171 Typical Physical Properties......................................................................177 Alkyl Dimethicone Orientation on Surfaces...........................................177 Structure/Function Properties.................................................................180 Alteration of Functionalization................................................................180 Melt Point.................................................................................................180 Alteration of Construction.......................................................................181 Physical Properties...................................................................................183 Alteration of Properties............................................................................185 SPF Enhancement...................................................................................188 11. Cationic Silicone Compounds..........................................193 Silanol Groups..........................................................................................198  v Anthony J. O’Lenick, Jr. Silicones for Personal Care, 2nd Edition Amino Groups..........................................................................................198 D Units.....................................................................................................199 Dimethicone Copolyol Amine.................................................................200 Polymerization Process............................................................................201 Applications Evaluation...........................................................................201 12. Carboxy Silicone Complexes............................................209 Energetics of Complex Formation..........................................................211 Mild Conditioning Products....................................................................212 Fatty Quaternary Ammonium Compounds............................................212 Chemistry..................................................................................................215 Desirable Properties of Cationic Silicone Complexes............................216 Silicone/Silicone Complexes....................................................................223 13. Silicone Phosphate Esters................................................227 Emulsifiers................................................................................................231 Water Soluble Emollients........................................................................231 Foaming Agents........................................................................................232 Irritation Reduction of Sodium Lauryl Sulfate.......................................235 Irritation Reduction of Alpha Hydroxy Acids (AHA).............................235 14. Silicone Resins..................................................................243 Chemistry..................................................................................................252 Applications..............................................................................................254 Future Developments..............................................................................260 15. Silicone Phospholipids......................................................261 Phosphobetaines.......................................................................................261 Phospholipids............................................................................................263 Complexation with Anionic Surfactants..................................................264 Silicone Products......................................................................................265 Chemistry..................................................................................................266 16. HLB...................................................................................271 HLB System.............................................................................................271 Applicability of the HLB System to Surfactant Types............................273 Three-Dimensional HLB.........................................................................275 Testing the 3-D HLB System..................................................................279 17. Applying the Three-Dimensional HLB System..............283 The 3-D HLB System..............................................................................283 Compounds...............................................................................................284 Testing.......................................................................................................288 Discussion.................................................................................................290 Emulsifier Kits..........................................................................................293 vi Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. 18. Silicone Quats...................................................................297 Structure...................................................................................................299 Properties..................................................................................................301 Softness.....................................................................................................303 19. Silicone Ester Amido Quaternary Compounds...............309 Formulating..............................................................................................313 Applications Data – Foam........................................................................313 Wet Comb Test.........................................................................................314 20. Silicones for Coating Pigments........................................325 Definitions................................................................................................325 Historical Perspective..............................................................................325 Silicone Coatings for Pigments................................................................326 Pigment Reactive Binding Mechanisms..................................................326 Silicone Structure.....................................................................................328 Chemistry..................................................................................................328 Other Functional Groups.........................................................................330 21. Silicone Surface Tension in Formulation........................341 Silicone in Mixed Systems........................................................................341 Simple Surfactant Systems.......................................................................343 Test Methodology.....................................................................................348 22. Properties of Silicone Compounds..................................351 Refractive Index.......................................................................................351 Surface Tension........................................................................................353 Foam.........................................................................................................355 23. Reactive Silicone Compounds..........................................361 24. Methods in Silicone Chemistry........................................371 Instrumental Methods..............................................................................371 Wetting Test Methodology.......................................................................377 Additional Silicone Information..............................................................381 Optimization of Emulsion........................................................................384 25. Future Trends...................................................................387 Technology................................................................................................387 Appendix A..............................................................................391 Index........................................................................................399  Preface First Edition The intention of this book is to provide a source of information to the cosmetic chemist on the basic chemistry and properties of silicone polymers used in the cosmetics industry. Over the years, these silicone polymers have become more and more important in advanced cosmetic formulations. As these materials have a tendency to be more expensive compared to traditional fatty materials, the benefit that silicones provide to formulations needs to be either more effective at lower concentrations or must provide benefits not attainable with other traditional prod- ucts. While silicone compounds can do both, it is critically important to properly select the right silicone compound, and therefore, understanding the structure of these materials is crucial to successful selection. The book stresses the various steps on the synthesis of silicone compounds: con- struction, functionalization and derivitization. As you will see, each has a profound impact on the performance and each needs to be understood. Many suppliers of these materials do not provide such critical information, which makes using their products in cosmetic formulations much like throwing darts in the dark—you may hit the bull’s-eye, but the odds are highly unlikely. The topic of silicone polymers for personal care is broad in scope and cannot be contained within a single work. It is also a topic in which many new developments are being made, any of which could revolutionize the industry. Each new invention builds upon the work of the previous inventor and the science as a whole advances. It is incredible that, in 1946, the silicone pioneer Rochow, looking at the very im- pressive body of work that he had done, wondered if there was any commercial utility to these products. The commercial reality of silicone technology requires a different skill set—that of the chemist and the engineer. It is the combination of the two contributions that keeps product development moving forward. Second Edition The years have passed rapidly since the first edition. I am most grateful to update this work for a second edition. What is most interesting to me is the rate of growth of the use of silicone compounds in our industry and the collective creativity of the raw material manufacturer, finished product formulator and the consumer product marketer. The raw materials, finished products and substantiated claims that have been developed in the last five years have been truly magnificent. Table P.1 shows the dramatic growth in patents that include the terms “silicone” and “cosmetic.” One US patent was issued in the five-year period 1976–1980. In the last two years, there have been an incredible 6,034 US patents located by the same search. vii viii Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. Both the number of patents and products based upon silicone have grown immensely. It is the goal of this book to provide information that will allow the re- searcher to develop and commercialize new products that meet consumer needs. Table P.1. US Patents Containing Words “Silicone” and “Cosmetic” Period Patents % Issued 1976–1980 1 0.01 1981–1985 11 0.1 1986–1990 28 0.3 1991–1995 69 0.9 1995–1999 131 1.3 2000–2004 3,282 34.3 2004–2006 6,034 63.1 Total 9,556 100.0  The Author Anthony J. O’Lenick Jr. Anthony J. O’Lenick Jr. is president of Siltech LLC, a company he founded in 1989, specializing in organo-functional silicones and specialty chemicals. He has more than 250 patents and 30 years of experience in innovative personal care ingredients. He has held technical and executive positions at Alkaril Chemicals, Henkel Corp. and Mona Industries. Tony has four published books: Patent Peace of Mind (Allured Publishing Corp., 2008); Surfactants—Strategic Personal Care Ingredients (Allured Publishing Corp., 2005); Silicones for Personal Care (Allured Publishing Corp., 2003) and Primary Ingredients (Zenitech, 1998). He has written more than 40 technical articles in scientific and industry journals, including Cosmetics & Toiletries magazine and HAPPI. Additionally, he has authored two book chapters and co-edited Chemistry of Colored Cosmetics (Marcel Dekker). His next books, being published by Al- lured Publishing Corp., include Oils of Nature and Silicones for Personal Care, 2nd Edition. Tony also writes the Comparatively Speaking column for Cosmetics & Toiletries magazine. Tony is the recipient of numerous awards for his research on silicone-based surfactants, including awards from the Soap and Detergents Association and the American Oil Chemists’ Society. His work in developing a three-dimensional HLB system (oil-water-silicone) and its use in formulating emulsions was recognized by the Advanced Technology Group. In 2006, Tony was elected as a fellow of the Society of Cosmetic Chemists (SCC), having served the society as a member of its Committee on Scientific Affairs and Education. He teaches a course for the SCC on silicones and on patents. Additionally, Tony has been an invited speaker at a symposia organized by the Cosmetics Toiletry and Fragrance Association (CTFA), Allured Publishing and HBA. Tony and his wife reside outside of Atlanta. They have three sons (Kevin, Thomas and Andrew), two daughters-in-law (Nicole and Courtney) and two grandsons (Ty and Jackson). Acknowledgements The author gratefully acknowledges his wife, Alice, who has provided him with encouragement during the various phases of his work and throughout the last 30 years. He also acknowledges the contribution of Kevin O’Lenick, for reading the manuscript and making helpful suggestions. ix  Chapter 1 Introduction Since the publication of the first edition of this book, the importance of silicone compounds in a variety of personal care products has continued to grow. New materials have been introduced and the technology has been expanded. Since its original military use to make grease to coat aircraft spark plugs during World War II, the use of silicones has virtually exploded. The ultimate raw material for the preparation of silicone compounds is SiO2. Table 1.1 shows the properties of SiO2. Table 1.1. Properties of SiO2 Molecular Formula SiO2 Molecular Weight 60.1 Grams/ mole CAS Number 14808-60-7 Melting Point 1650°C Boiling Point 2230°C Other Names Silica Silicone dioxide Sand Quartz Glass Amethyst Flint Jasper Opal Silicon Silicon is the 14th element in the periodic table. It rarely occurs naturally in its free state, but it accounts for about 25% of the earth’s crust in its combined form. Pure silicon crystals are only occasionally found in nature as inclusions with gold 11 12 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. and in volcanic material. Silicone compounds are unique materials both in terms of the chemistry and in the wide range of useful applications. In combination with organic moieties, silicon provides unique properties that function in a wide temperature range, making the silicone-based products less temperature sensitive than most organic surfactants. These properties can be attributed to the strength and flexibility of the Si-O (silicon-oxygen) bond, its partial ionic character and the low interactive forces between the nonpolar methyl groups, characteristics that are directly related to the comparatively long Si-O and Si-C (silicon-carbon) bonds. The length of the Si-O and Si-C bonds also allows an unusual freedom of rotation, which enables the molecules to adopt the lowest energy configuration at interfaces, leading to surface tension values substantially lower than those of organic polymers. A review of the periodic chart reveals that silicon and carbon are one over the other (see Figure 1.1)1. This allows one to predict a great number of similar properties between the two elements. Figure 1.1. Periodic Chart Comparing Silicon with Carbon There has been a lot of science fiction interest in the similarity between silicon and carbon. In an episode of Star Trek a life form referred to as a “Horta” was said to have its chemistry based upon silicon. While interesting as science fiction, this is not a scientific possibility in a world where our chemistry applies. Table 1.2 shows the comparison of silicon with carbon. One of the major similarities is the affinity for oxygen exhibited by the two elements, but there are also fundamental differ- ences. The fundamental differences include:  13 Anthony J. O’Lenick, Jr. Chapter 1 The oxides of the two elements are vastly and fundamentally different. CO2 is a gas at room temperature and atmospheric pressure. It consists of simple CO2 molecules, O=C=O. The oxide of silicon SiO2 is a crystalline polymer with a very high melting point. It is difficult to envision a life cycle that replaces CO2 with SiO2, since the latter is a crystal. The hydrides of silicon are called silanes. These analogous compounds in the carbon world are referred to as alkanes. Silanes are very reactive compounds. They react violently with oxygen, and ignite or explode spon- taneously in contact with air. Fortunately, alkanes do not react the same way. It would be equally difficult to envision a world based upon silanes rather than alkanes. Silicon compounds do not form multiple bonds between atoms while carbon compounds do. It’s clear we are not likely to encounter silicon-based life forms in the near future, but the chemistry is interesting and important to the cosmetic chemist. Table 1.22 shows a comparison of the elements silicon and carbon. Table 1.2. Comparison of Silicon and Carbon Property Silicon Carbon Atomic Weight 28.0855 12.000 Phase Solid Solid Melt Point 1414°C 4427°C Boiling Point 3583°C Sublimes Electronegativity 1.90 2.55 Isotopes Si (92.2%) 28 C 98.8% 12 Si (4.67%) 29 C 1.2% 13 Si (3.1%) 30 Provides 29Si NMR Provides 13C NMR Terminology One of the most basic technical errors made by chemists is confusing silicon with silicone. Silicon is used to refer to the elemental material, (Si); silicone to refer to materials in which silicon is bonded to oxygen. Silicon is the most elemental raw material from which all silicone chemistry finds its roots. Since it is not common in the metallic form in nature, the first step is to produce silicon from quartz. The term silicone is actually a misnomer. It was incorrectly thought that the early silicone 14 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. polymers were silicon-based ketones, hence the contraction silicone. Despite this error, the term is still widely used and accepted. Another important nomenclature issue is the difference between silicone and silane. A silicone compound has a Si-O-Si bond while the silane has only one Si atom. Hence, (CH3O)3-Si-CH3 is methyl trimethoxysilane. The difference between a volatile and a cyclic is also an important distinction. The most commonly understood cyclic compound is the D4 and D5. These cyclic compounds are ring structures with alternating Si and O having four and five Si and O atoms, respectively. These compounds are also volatile, meaning they evapo- rate. Cyclic structures that have a higher number of silicon and oxygen atoms, like 20 Si and 20 O, are referred to as D20 and, despite being cyclic, are nonvolatile. For example, hexamethyl disiloxane (MM) is volatile but not cyclic. The structure of hexamethyl disiloxane is: CH3 CH3 | | CH3 -Si-- O --Si- CH3 | | CH3 CH3 Silicone Compounds The commercial process for making silicone compounds is a multistep transforma- tion that converts inorganic quartz, a common mineral, into the multifunctional silicone compounds used in many formulations. This transformation process is shown in Figure 1.2. Silicon from Quartz Silicon is obtained by the thermal reduction of quartz (SiO2) with carbon. The re- action is conducted at a very high temperature and therefore is commonly carried out where there is abundant inexpensive power. The reaction is as follows: 1700°C SiO2 + C ‘ Si + CO2 The resulting silicon is generally at least 99% pure. In addition, certain trace contaminants must also be controlled to obtain a material that is suitable for the preparation of silicone compounds. Since the silicon produced is a solid metallic material, it must be crushed into powder with a particle size of between 100 and 350 nanometers (nm) for use in the next reaction—the Rochow process (a process named after Eugene G. Rochow, the father of silicone chemistry1). Rochow Process2–Chlorosilanes from Silicon The Rochow process technology is complicated and requires high capital for the  15 Anthony J. O’Lenick, Jr. Chapter 1 Figure 1.2. Silicone Transformation fi Quartz Silicon Rochow Process (CH3)2–Si–Cl2 Si + CH3Cl —> (CH3)3–Si–Cl fi CH3–Si–Cl Si–Cl4 CH3HSiCl2 CH3HSiCl Others Silicon Chlorosilanes Rochow Process (CH3)2–Si–Cl2 (CH3)3–Si–Cl Si + CH3Cl —> CH3–Si–Cl Si–Cl4 fi Hydrolyzate CH3HSiCl2 CH3HSiCl Others * Organo-functionals fi ** Cyclic Silicones Gums Hydrolyzate * Dimethicone * Dimethiconol * Silicone Surfactants 16 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. construction of plants suitable to practice the chemistry. As a result, few compa- nies actually carry out the Rochow process. Because silicon is crushed prior to reaction in a fluidized bed, the companies practicing this technology are referred to as “silicon crushers.” This is an elite group of companies; being referred to as a silicon crusher is considered an honor in the silicone world. Figure 1.3 shows a silicone flow chart (Wacker). Figure 1.3. Silicone Flow Chart Commercially, the Rochow process is the most important route for the prepara- tion of silicone compounds. In this process, methyl chloride is reacted with solid silicon metal in the presence of copper catalysts and certain promoters to produce a mixture of chlorosilanes. Simplistically, the overall reaction is as follows:  17 Anthony J. O’Lenick, Jr. Chapter 1 300°C 2 CH3-Cl + Si ‘ Me2SiCl2 Catalyst In fact, a complex mixture of products is actually obtained: Si + 2 CH3Cl ‘ (CH3)2-Si-Cl2 (Predominant) (CH3)3-Si-Cl CH3-Si-Cl3 Si-Cl4 CH3HSiCl2 (CH3)2HSiCl Others The predominant material obtained is dimethyldichlorosilane (approximately 80% by weight). In order of decreasing concentration, the most abundant compounds are methyltrichlorosilane (approximately 12% by weight), followed by trimethyl- chlorosilane (approximately 4%) and methylhydrogendichlorosilane (approximately 3% by weight.). This composition information is very important since it drives the economics of the silicone business. Every pound of chlorosilanes produced results in the distribution of hydrolysis derivatives described. The cost of each derivative must be allocated in proportion to the amount produced as well as its commercial demand. To operate business profitably, every pound of product produced must be sold. This, by definition, makes the basic silicone business a commodity business. Specialty producers, on the other hand, make what they can sell and do not have to balance by-product and co-product streams. Since many silicone surfactants are based upon methylhydrogendichlorosilane, a relatively minor component of the silane stream, the cost of these materials is high in relation to silicone fluids based upon dimethyldichlorosilane. The reaction to make chlorosilanes is quite complex and is carried out at a temperature of about 300°C under pressures of around 3 bars. The mass of start- ing material must be heated to initiate reaction. Once the reaction temperature is reached, the reaction becomes exothermic and, consequently, requires very stringent temperature control. It is a solid/gas reaction carried out in a fluidized bed reactor. To maximize the reaction efficiency, the solid silicon must be low in other metallic components. The fine residue that is extracted from the process is dependant on the quality of the silicon going into the process but is generally made up of Cu, Fe, Al and Ca. Consequently, silicon with low concentrations of these elements is desired for the process. The nomenclature for chlorosilanes is presented in Table 1.3. Hydrolyzate—Silicone from Chlorosilanes3 The preparation of silicone compounds from chlorosilanes is an important synthetic pathway. The hydrolysis process is used to achieve this transformation. During this 18 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. process, the chlorosilane compounds produced in the Rochow process are reacted with water, converting them into a mixture of linear and cyclic compounds. The exact composition of the Rochow products, the conditions of pH, the concentration of water and the temperature of hydrolysis determine the exact composition of the hydrolysis products produced. Table 1.3. Chlorosilane Nomenclature Name Structure Trimethylchlorosilane (CH3)2-Si-Cl2 Dimethylchlorosilane (CH3)3-Si-Cl Methyltrichlorosilane CH3-Si-Cl3 Tetrachlorosilane Si-Cl4 Methyltrichlorosilane CH3HSiCl2 Dimethylchloro silane (CH3)2HSiCl Since the Rochow process produces primarily dimethyldichlorosilane, the reac- tion of that component with water is: Hydrolysis of chlorosilane to produce HCl and siloxanediol (CH3)2SiCl2 + H20 ‘ HCl + (CH3)2Si(OH)2 This results in the formation of hydrochloric acid and a siloxanediol. The by- product HCl must be handled with care to avoid corrosion of the equipment. The following process results in two types of compounds that are used by the in- dustrial chemist: silanol (dimethiconol) and cyclomethicone. The former is used in hair gloss compounds and the latter is commonly used in antiperspirant compositions. Dehydration of siloxanediol to cyclomethicone and silanols (CH3)2Si(OH)2 ‘ H2O + HO-(CH3)2SiO)nH + cylclomethicone In his book, The Chemistry of Silicones (1946), Rochow ends with the statement: “With this in mind, it can only be said that a start has been made in organosilicone chemistry and that perhaps something may come of it.” 56 years later, we can safely assume that a great deal will be done to utilize this chemistry and the development will continue for years to come.  19 Anthony J. O’Lenick, Jr. Chapter 1 Table 1.4 outlines the hydrolysis products of the major chlorosilanes produced in the Rochow process. Table 1.4. Chlorosilane Nomenclature Chlorosilane Name Chlorosilane Structure Silanol Structure Trimethylchlorosilane (CH3)2-Si-Cl2 (CH3)2-Si-OH2 Dimethylchlorosilane (CH3)3-Si-Cl (CH3)3-Si-OH Methyltrichlorosilane CH3-Si-Cl3 CH3-Si-OH3 Tetrachlorosilane Si-Cl4 Si-OH4 Methyltrichlorosilane CH3HSiCl2 CH3HSiOH2 Dimethylchloro silane (CH3)2HSiCl (CH3)2HSiOH Reactions of Chlorosilanes Chlorosilanes are important reactive materials used to make many commercially important silicone derivatives. Some reactions include: 1. Chlorosilanes react readily with alcohols or phenols to produce alkoxy silanes. Octyl trimethoxysilane is then used to hydrophobize zinc oxide and titanium oxide. CH3Si-Cl3 + 3 CH3OH ‘ CH3Si-(OCH3)3 + 3HCl Methyltrichlorosilane Methanol Methyltrimethoxysilane 2. Chlorosilanes react readily with fatty acids to produce acyl derivatives. (CH3)3Si-Cl3 + R-COOH ‘ (CH3)3Si-O-C(O)-R + HCl Trimethylchlorosilane Fatty Acid Acyl Silane 3. Chlorosilanes react readily with ethylene oxide to produce haloethoxysilanes. O / \ (CH3)3Si-Cl + CH2—CH2 ‘ (CH3)3Si-OCH2CH2Cl + HCl Trimethylchlorosilane Ethylene oxide Trimethylchloroethoxysilane 20 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. 4. Chlorosilanes are used to make Q resins (which will be addressed in the resin chapter of this book). 5. Chlorosilanes, produced from quartz, are the major materials from which silicones are produced in subsequent processes. Silicones Properties Silicone compounds are finding increased utilization in personal care products and must offer unique properties relative to other compounds to justify their cost. Silicone compounds can be divided into two different categories: 1. Silicone homopolymers—This class of compounds is made up of polymers that have only the methyl groups and oxygen and silicon atoms. It includes polymers that lack cross-linking such as silicone fluids, cyclics and gums. 2. Silicone heteropolymers—These are polymers that, in addition to the methyl groups and silicone and oxygen atoms, include other functionalities. These materials are amphilic silicone compounds; they have two different groups that lack solubility in each other and consequently are surface active. Silicone compounds are used in personal care applications because of the unique properties they possess. These include: Surface Tension Reduction In the formulation of personal care products, the ability to alter surface tension and other interfacial properties is critical. Almost every cosmetic that is applied to hair and skin must have a low enough surface tension to facilitate spreading. Consequently, surface tension is important. Table 1.5 shows the surface tension of a number of pure materials. Surface tension has a direct impact on spreadability, wettability and cosmetic elegance. In terms of the latter, cushion and playtime are most important. Silicone compounds are interesting materials for use in personal care formula- tions because their surface tension is different from both oils and water. Silicone compounds have a surface tension of around 20 dynes/cm2, compared to a surface tension of around 32 dynes/cm2 for oils and 76 dynes/cm2 for water. Table 1.6 shows the reduction of surface tension achieved by the incorporation of a soluble silicone derivative. Solubility—Group Opposites Silicone polymers are water-insoluble and oil-insoluble. They are hydrophobic (water-hating) and at the same time oleophobic (oil-hating). This key attribute forces us to think in terms of another classification of hydrophobic materials, namely sili- cone loving groups, which we have been called siliphillic materials. It is the lack of solubility in oils and water that makes dimethicone a barrier when applied to skin. The use of dimethicone as a barrier on the skin is very common and is considered a drug application by the United States Food and Drug Administration (FDA). This complexity has resulted in the introduction of the concept of group op- posites shown in Table 1.7.  21 Anthony J. O’Lenick, Jr. Chapter 1 Table 1.5. Surface Tension (Pure Materials) Product Surface Tension (dynes/cm) Mercury 472.0 Water 72.6 Is paraffin (C12-C14) 53.0 Squalane 46.2 Soap Solution (1%) 38.8 Mineral oil 33.1 Dimethicone (20cs) 26.6 Acetone 23.7 Ethyl Alcohol 22.2 Cyclomethicone (D4) 20.6 Diethyl ether 17.0 Table 1.6. Reduction of Surface Tension with Silicone Derivatives Solvent Surface Tension Silicone Added Surface Tension (as is) Dynes/cm2 (0.5% weight) Dynes/cm2 Toluene 28.9 C-26 alkyl dimethicone 25.0 2-butoxy ethanol 29.1 Stearyl dimethicone 22.0 Methanol 23.4 Octyl PEG-8 dimethicone 22.2 Water 72.3 PEG-8 dimethicone 20.1 Table 1.7. Groups Opposites Hydrophobic can be either Siliphilic or oleophillic (Water Hating) (silicone loving) (oil loving) Siliphilic is both oleophobic and hydrophobic (silicone loving) (oil loving) (water hating) Oleophilic is both siliphobic and hydrophobic (oil loving) (silicone loving) (water hating) 22 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. The importance of this classification can be made using two examples: one from the carpet industry and the other from the personal care industry. In the preparation of carpets, it is desirable to have a finish that rejects both oil and water. The ability to repel water is a result of making the surface hydrophobic. If hydrophilicity is achieved by making the product oleophillic (that is putting on an oleophillic finish), the carpet will attract oil. Such a carpet is likely to soil permanently if cooking oil is spilled on it, due to the affinity of the carpet for oil. If the carpet has been rendered hydrophobic (water repelling) by using a silicone coating, (a siliphillic material) both oil and water will be repelled. The personal care application example relates to coated pigments. Almost all pigments have some sort of coating on them (be it an oil coating or a silicone coat- ing). The ability to disperse the pigment efficiently is achieved using the phase in which the coating is most compatible. Consequently, a silicone-coated pigment often gets used in a silicone phase. An oil-coated pigment often gets used in an oil phase. Some pigments are chemically reacted forming covalent bonds between pigment and coating. Others are merely chemisorbed. Those pigments in which the coat- ing is not chemically bonded can be metastable in emulsion systems. Keeping in mind that the materials in an emulsion will go to the phase in which the lowest free energy is achieved, over time, the nonbonded pigment can migrate off the pigment into another phase. The result can eventually appear as emulsion instability. The modification of the emulsifier package will not solve this problem. We recommend testing all pigments for the type of coating and its permanence. Amphilic Materials While it is interesting that silicone, oil and water are mutually insoluble, the synthesis of organofunctional silicones is key to utilization of materials in the personal care market. By having two different insoluble groups in a molecule, the product becomes surface active. Even when soluble in oil or water, amphilic materials accumulate at the interface and/or form micelles depending upon concentration. Surface activity allows amphilic materials to wet, foam, defoam, emulsify, condition, effect transepidermal water loss, lower surface tension and form films depending upon the exact structure. It is these abilities that make organosilicone materials most interesting. Figure 1.4 shows the complex set of conditions that occur when a liquid con- taining a surfactant is spread on a surface. This situation occurs with almost all cosmetic products when they are applied to the body. Silicone Challenges Anyone that has formulated with silicone compounds knows that this important class of compounds can be a bit problematic. Specifically, many formulators ask: 1. Why do silicone compounds fail to act in a predictable way in my formula- tion? 2. Why is there so much trial and error in using silicone compounds? 3. Why do compounds purporting to have the same INCI name act so dif- ferently?  23 Anthony J. O’Lenick, Jr. Chapter 1 Figure 1.4. Dynamic Surface Tension Amphilic Silicone Molecules The answers to the first two questions have been already provided in this chapter. The answer to the third question is that the INCI name does not provide all the information needed to fully understand functionality. The performance of a given silicone is dictated by three equally important factors: Construction is the process by which the polymer backbone is prepared. It determines such important functional attributes as the molecular weight (and consequently surface performance), the ratio of silicone groups to non-silicone groups, and cross-link density. Functionalization is the process by which amphilic silicone compounds are prepared. The specific reaction employed is hydrosilylation, the reaction of a silanic hydrogen polymer made using the construction process with alpha vinyl compounds, to introduce another group of differing solubility. Derivitization is the process by which organic chemistry is carried out on functional groups like hydroxyl groups introduced into the molecule during hydrosilylation. Silicone Backbone Nomenclature Like doctors, lawyers and technical professionals, silicone chemists have invented a language which makes communication between members of the profession easier. At the same time, however, it makes communication to individuals outside our profession more difficult. The silicone chemists’ language is a chemical shorthand developed by Alfred Stock in 19164. The nomenclature is based upon the type of groups present in the backbone of the molecule. The following is a breakdown of that shorthand. 24 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. CH3 | “M unit” is monosubstituted (one oxygen atom on silicon) -O1/2-Si-CH3 | CH3 CH3 | “D unit” is disubstituted (two oxygen atoms on silicon) -O1/2-Si-O1/2- | CH3 - O1/2- | “T unit” is trisubstituted (three oxygen atoms on silicon) -O1/2-Si-O1/2- | CH3 O1/2- | “Q unit” is tetrasubstituted (four oxygen atoms on silicon) -O1/2-Si-O1/2- | O1/2 In cases where organofunctional silicone is desired, a process called hydrosilylation is used. It makes use of the Si-H intermediate made in the Rochow process. In the hydrosilylation reaction a double-bonded material (most commonly alpha double- bonded) is reacted with Si-H to form a new Si-C bond. The points at which the organo group is attached contains a Si-H group and has an “*” added to its designation. CH3 | “M* unit” is monosubstituted (one oxygen atom on silicon) -O1/2-Si-CH3 | H CH3 | “D* unit” is disubstituted (two oxygen atoms on silicon) -O1/2-Si-O1/2- with organofunctionality | H  25 Anthony J. O’Lenick, Jr. Chapter 1 -O1/2 | “T* unit” is trisubstituted (three oxygen atoms on silicon) -O1/2-Si-O1/2- with organofunctionality | H There is no “Q* unit” since there is no possibility of functional groups. After reaction with the double bond in the hydrosilylation reaction, the “H” is transformed into an “R” group, discussed shortly. CH3 | “M* unit” is monosubstituted (one oxygen atom on silicon) -O1/2-Si-CH3 | R CH3 | “D* unit” is disubstituted (two oxygen atoms on silicon) -O1/2-Si-O1/2 - with organofunctionality | R O1/2 | “T* unit” is trisubstituted (three oxygen atoms on silicon) -O1/2-Si-O1/2- with organofunctionality | R Silicone Construction The “backbone” structure of a silicone molecule is referred to as its construction. This is one critical factor in determining the functional attributes of the molecule. There are three types of construction of silicone polymers. They are comb, terminal and multifunctional. 26 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. Comb The “R” groups are internal, resembling a comb. CH3 CH3 CH3 CH3 | | | | CH3 —Si-O——(——Si—O-)-50—( -Si——O-)-10——Si—CH3 | | | | CH3 CH3 H CH3 M D50 D*10 M Terminal The “R” groups are terminal, and there are only two groups possible. CH3 CH3 CH3 | | | H—Si——O—(—Si—O—)-50——Si—H | | | CH3 CH3 CH3 M* D50 M* Multifunctional The “R” groups are both internal and terminal, resulting in a high degree of substitution. CH3 CH3 CH3 CH3 | | | | H——Si-O——(—Si—O—)50—(—Si——O—)-5—Si—H | | | | CH3 CH3 H CH3 M* D50 D*5 M* Among the functional differences between the comb and the terminal structures, one of the most important is the difference in the number of possible substituents. This number is limited to two in the terminal number of (*) substituents (one at each end) while in the comb polymer, the number can be much larger. The reason is the number of substituents in the terminal compounds can be no more than two (one at each end). The number of functionalized groups in a comb compound can be much larger than two. The other major difference between terminal and comb structure involves eco- nomics. The terminal compounds are more expensive than the comb compounds having the same molecular weight. This is a direct consequence of the fact that  27 Anthony J. O’Lenick, Jr. Chapter 1 the raw material for making the terminal products M*M* is not abundant in the Rochow process and is therefore expensive. There has been an interest in developing a terminal polymer with a methyl group on one end and an organofunctional group on the other. M*M* is available; however, since the preparation of the silicone polymer is based on equilibration chemistry, even though MM* is used as a raw material, the resulting polymer is a mixture of two parts monosubstituted monomethyl-terminal polymer, one part fluid (dimethyl terminated) and one part difunctional compound having no methyl terminal group. The fluid is not water-soluble and therefore always present in the reaction mixture. This observation leads to another important concept. To avoid forming a fluid in a polymer equilibration reaction, there must be a certain number of water-soluble functional D* groups in a comb structure relative to D units. The smallest ratio of D* to D can be established experimentally. It is that ratio which leads to a water- soluble product, substantially free of fluid. This observation explains why only a limited number of products in this class are offered commercially. The construction of a silicone molecule can be compared to a knitting machine. The various units M, D, D*, M* and the like are linked together in a backbone with the desired quantity of Si-H groups (the * materials). Since there are no organo groups yet added, the molecule is neither oil-soluble, water-soluble, fluoro-soluble or organo-modified. The ratio of organofunctional to silicone functional groups has been established, as has the total molecular weight. This is one critical step to determining functionality of the molecule. Compounds containing silanic hydrogen groups are used commercially to coat pigments and to waterproof gypsum board. Functionalization The preparation of a silanic hydrogen-containing polymer by the construction process does not alter solubility. The silanic hydrogen pre-polymer assumes its altered solubility only after the functionalization reaction is run. For this reason, silanic hydrogen-containing polymers are considered precursors to organofunctional products. A single silanic hydrogen polymer can give rise to an entire family of analogs depending on which functional group is placed onto the backbone in the functionalization reaction. In order to make these products more easily formulated, organofunctional dimethicone compounds have been developed. These include dimethicone com- pounds with improved oil solubility called alkyl dimethicone compounds; dimethi- cone compounds with improved water solubility, called PEG/PPG dimethicone. There are also a series of compounds in which surfactant groups are grafted onto the backbone to improve virtually all surfactant properties including detergency, conditioning, wetting and emulsification. This ability to provide silicone products with improved applicability in personal care products not only opens the possibility of many high performance products, but also can be a source of frustration to many formulators who have not been given the necessary structure/function relationships to make intelligent choices in picking products. Often the formulator is left to use products recommended by suppliers, rather than to be a participant in choosing 28 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. the optimized product for an application. The key to avoiding this situation is to learn the rules of structure/function related to silicones and apply them to new products, resulting in the most cost-effective products possible. The reaction used to place organofunctionality into silicone compounds is called hydrosilylation. This process is used in the construction part of silicone prepara- tion. The key reaction is one in which a silanic hydrogen (Si-H) is reacted with a terminal double bond resulting in a stable Si-C bond. \ \ -Si-H + CH2 = CH-(CH2)7CH3 ‘ -Si-(CH2)9CH3 / / The shorthand for the construction of reactive compound is as follows: CH3 | M* for monofunctional with regard to oxygen CH3-Si-O1/2 and a reactive H. | H CH3 | D* for difunctional with regard to oxygen O1/2-Si-O1/2 and a reactive H. | H O1/2 | T* for trifunctional with regard to oxygen O1/2-Si-O1/2 and a reactive H. | H Silanic hydrogen containing polymers prepared in the equilibration reaction are hydrosilylated in the functionalization reaction to make organofunctional silicones. The vinyl containing groups that are reacted with silanic hydrogen containing silicone polymers include: Alpha olefin CH2=CH-(CH2)7CH3 Ally alcohol alkoxylates CH2=CH-CH2-O(CH2CH2O)8H Fluoro vinyl compounds CH2=CH-CH2(CF2)8CF3  29 Anthony J. O’Lenick, Jr. Chapter 1 The properties of silicone compounds prepared using these raw materials are discussed in the remaining chapters. Derivatization Once the hydrosilylation reaction has been conducted, and the organosilicone mol- ecule has been prepared, if there are reactive groups present, they can be used for subsequent chemistry. A number of the known and patented dimethicone coplyol derivatives are shown in Table 1.8. Table 1.8. Dimethicone Copolyol Derivatives Raw Material Process Product 2nd Process Product Sulfation Silicone Sulfates Carboxylation Silicone Complexation Silicone Carboxylate Complexes DMC Cyanoethylation Silicone Amphoterics -CH2-OH Amines (End Group) Phosphation Silicone Silicone Phosphates Phospholipid Chloroalkyation Silicone Quats Esterification Silicone Esters Why Amphilic Silicone Compounds? Amphilic silicone compounds are polymers in which there are at least two groups of functionalities that are insoluble in one another in pure form. These groups can include water-soluble, oil-soluble, silicone-soluble and fluoro-soluble. This amphilic nature results in surface active properties. Understanding these properties requires an understanding of what molecules do at surfaces. The basic definitions we use need to be examined more closely when consider- ing amphilic materials. Simplistically, the following definitions apply: 1. A solution is a homogeneous mixture composed of one or more substances, known as solutes, dissolved in another substance, known as a solvent. 2. A suspension is a colloidal dispersion in which a finely divided species is combined with another species, with the former being so finely divided and mixed that it doesn’t rapidly settle out. In everyday life, the most common suspensions are those of solids in liquid water. 30 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. 3. An emulsion is a mixture of two immiscible substances. One substance (the discontinuous phase) is dispersed in the other (the continuous phase). While these are neatly defined, the world of cosmetics is rarely so easy to organize. Consider a fully dissolved 1% solution of sodium chloride in water. This simple system has sodium ions (Na+), chloride ions (Cl-) and water, roughly equally distributed over the entire mass of the system. The solution is clear and homogeneous. Now consider a 1% solution of a surfactant. The surfactant, or surface active agent, has a water-soluble head and a water-insoluble tail. A very well-known sur- factant is sodium lauryl sulfate (CAS 151-21-3). Like NaCl, sodium lauryl sulfate has two opposite ions, but sodium lauryl sulfate in water is very different. The presence of a large fatty portion makes the product surface active. The structure of sodium lauryl sulfate is: O || Na+O-—S—O || O A 1% solution of sodium lauryl sulfate, like that of sodium chloride, is clear but not homogeneous. As one adds sodium lauryl sulfate to water, achieving the lowest overall free energy drives the orientation of the material in the water, in this case minimizing disrupting hydrogen bonding in water. The sodium lauryl sulfate organizes itself at the air/water interface and then begins self-assembly into mi- celles. Figure 1.5 shows this.5 The first box in Figure 1.5 shows pure water, having a surface tension of 72 dynes/cm2. As surfactant is added (second box in Figure 1.5), surface tension is falling as dilute surfactant organizes at the surface. As the surface reaches saturation, a very significant situation develops. The surface tension no longer drops even with additional surfactant. It is at this concentration—critical micelle concentration—that micelles become the dominant form of surfactant (third box in Figure 1.5). The ability to provide low surface tension surfactant properties for cosmetic formulations is a key reason to use silicones in formulations. Since silicone materials are almost never used alone in formulation, the interaction of silicone with other materials in formulation is critical to their utility. Performance of the silicone alone is almost trivial. Specifically, the selection of the proper oil-soluble silicone will lower the surface tension of oil-based systems, in exactly the same way that the proper selection of a water-soluble silicone will lower the surface tension of water-based systems, improv- ing spreadability and cosmetic elegance. Selection of the silicone with the proper solubility and surface tension is critical and an often overlooked key to formulating advanced cosmetic products. An example of surface tension reduction of blends with several ratios of water- soluble silicone (in this case PEG-8 dimethicone) are shown in Table 1.9.  31 Anthony J. O’Lenick, Jr. Chapter 1 Figure 1.5. Surfactant Orientation5 Table 1.9. Surface Tension Reduction Aqueous System Cocamidobetaine PEG-8 Dimethicone Surface Tension (% Weight) (% Weight) (Dynes/cm2) Example 1.1 100% 0% 31.3 Example 1.2 75% 25% 26.0 Example 1.3 50% 50% 23.1 Example 1.4 25% 25% 21.6 Example 1.5 0% 100% 20.1 A few examples of surface tension reduction of blends with several ratios of oil-soluble silicone are shown in Tables 1.10 and 1.11. A few examples of surface tension reduction of using silicone compounds capable of reducing surface tension are blends of water silicone and isopropanol. These are shown in Table 1.12. 32 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. Table 1.10. Surface Tension Reduction Triglyceride System Soybean Oil Cetyl Dimethicone Surface Tension (% Weight) (% Weight) (Dynes/cm2) Example 2.1 100% 0% 31.4 Example 2.2 75% 25% 25.5 Example 2.3 50% 50% 24.8 Example 2.4 25% 75% 24.1 Example 2.5 0% 100 % 23.6 Table 1.11. Reduction Mineral Oil System Mineral Oil Cetyl Dimethicone Surface Tension (% Weight) (% Weight) (Dynes/cm2) Example 3.1 100% 0% 28.3 Example 3.2 75% 25% 26.1 Example 3.3 50% 50% 25.1 Example 3.4 25% 75% 24.5 Example 3.5 0% 100 % 23.6 Table 1.12. Surface Tension Reduction Mineral Oil System Isopropanol PEG-8 Dimethicone Surface Tension (% Weight) (% Weight) (Dynes/cm2) Example 4.1 100% 0% 21.7 Example 4.2 75% 25% 20.8 Example 4.3 50% 50% 20.5 Example 4.4 25% 75% 20.5 Example 4.5 0% 100 % 20.5  33 Anthony J. O’Lenick, Jr. Chapter 1 Why is the cosmetic formulator interested in surface tension? Surface ten- sion affects spreadability and cushion, and the addition of different silicones can dramatically alter surface tension and cosmetic acceptability of formulations. The addition of the proper silicone to a high viscosity ester can improve spreadability without effecting the play time (i.e. the time it takes to spread out). The addition of the proper silicone can also improve wetting time and alter bubble structure. A different silicone can improve spreadability and reduce play time. The result is an ability to alter aesthetics in personal care products by adding low concentrations of silicones. This allows one to significantly alter the cosmetic feel of a product without dramatic alteration in the formulation. Conclusion Occasionally, a technology is developed which dramatically revolutionizes an industry. The development of silicone technology by Eugene Rochow and a handful of other dreamers has transformed our industry over the last sixty years. The development of this technology seems unlikely when one considers that the materials used start from quartz (a very common mineral). Rochow states, “The organic compounds of silicon, which have been the subject of many scholarly researches during the past 80 years, at last show promise of emerg- ing from the laboratory and finding a place in industry. An understanding of the behavior of organosilicon materials is necessary to their intelligent use ….” Products have emerged from laboratory curiosities and we still need a better understanding of the behavior of organosilicon materials to intelligently use them. Please Remember 3 The term “Silicone” as applied to the products used in personal care products describe a very wide class of compounds, having varied solubility, and unique surface tension properties. 3 Silicones, if amphillic ( i.e. containing two or more groups which if mixed in pure form will be insoluble), are surface active, assembling in structures which despite their complication provide the lowest free energy to the solution. 3 Silicone compounds are formulated into multi-component formu- lations, wherein interactions occur, which have an effect on the performance of the silicone. Consequently, evaluation of the pure silicone compound can not only be almost meaningless, but may well lead to false conclusions on performance in mixed systems. 3 When properly used, silicones give unique properties to formulations. 34 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. References 1. http://office.microsoft.com/en-us/templates/TC011843281033. aspx 2. EC Rochow, Chemistry of Silicones, John Wiley and Sons, New York, NY, 19 (1946) 3. KF De Polo, A Short Textbook of Cosmetology, Verlag fur Che- mische Industrie, Stuttgart, Germany, (1998) 4. Alfred, Ber Deutsch.Chem.Ges, 49:108 (1916,) 5. LE Scriven, Coating Process Fundamentals Course, University of Minnesota.  Chapter 2 Basic Silicone Materials The basic raw materials used in the personal care market are either products derived from the chlorosilanes process (including cyclomethicone) or products of construction (see Chapter 1). The materials are homopolymers of silicone, being composed of silicon and oxygen atoms and methyl groups only. This class of compounds is the oldest and most understood. The compounds of this class also cause formulators to be the most reluctant to incorporate new silicones into formulations. These materials are water- and oil-insoluble and consequently are difficult to formulate. We need to have a great deal of respect for the pioneering chemists who created a very versatile set of compounds that have their origin in quartz, a ubiq- uitous mineral. This respect grows even deeper when you look at the steps that were needed to accomplish commercial reality for these products. These pioneers showed insight, persistence and engineering intelligence that allowed for the proper economics for silicones to become the widely accepted products they are today. The basic raw materials, covered in this chapter, were the first steps in achieving commercial reality for silicone compounds. They are the stepping stones for this class of materials. Cyclomethicone Cyclomethicone is distilled from the mixture of products found in hydrolsylate, which is produced by the hydrolysis of the chlorosilanes produced in the Rochow process. The predominant cyclomethicone produced is D4, with lesser amounts of D3 and D5. The ratio of D4 to D5 that is distilled from the hydrolysate reaction is generally 85% D4 to 15% D5. The cyclomethicone mixture distills off the hydrolysis process as an azeotrope. This common azeotrope is the least expensive cyclomethicone composition produced. Since separation of the two from one another requires distillation, the pure D4 is more expensive than the azeotrope and the D5 is even more so. Since D4 has been essentially banned from usea in the personal care market, D5 has become the cyclic silicone of choice. a While still being studied, D4 has been shown to have reproductive effects in several reproductive studies including a two-generation study (Stump et al., 2000). These effects include a reduction in the number of implantation sites, the number of live fetuses, and the mean live litter size at the high- est inhalation exposure concentrations tested (i.e., 500 and 700 ppm, respectively). 35 36 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. The term cyclomethicone refers to a series of cyclic silicone compounds. The structures for D4 and D5 are: D4 Cyclomethicone D5 Cyclomethicone Cyclotetrasiloxane Cyclopentasiloxane CH3 CH3 CH3 CH3 \ / \ / Si Si / \ / \ O O O O / \ / \ (CH3)2-Si Si-(CH3)2 (CH3)2-Si Si-(CH3)2 \ / | | O O O O \ / \ / Si (CH3)2 -Si --O--Si-(CH3)2 / \ CH3 CH3 The term cyclic refers to a structure; the term cyclomethicone refers to a physical property. Cyclomethicone is available in a variety of compositions. Pure D3, D4, and D5 are available as well as a more common lower cost 85% D4/15% D5 composition. D3 and D4 are used as raw materials in our industry now, and D5 is used as a dry solvent. Table 2.1 shows the heat of vaporization for several materials. Water takes a lot of energy to vaporize, which explains why clothes take so long to dry in a drier. Ethanol, a rather easily evaporated material, takes less than half the energy. This explains why alcohol-based aftershave formulations feel cool. Finally, D4 and D5 take considerably less energy than ethanol, making them the easiest to evaporate in the series. This explains why cyclomethicone is often used in antiperspirants. Table 2.1. Heat of Vaporization Material Heat of Vaporization (cal/g) Water (aqua) 539 Ethanol 210 D4 31 D5 31  37 Anthony J. O’Lenick, Jr. Chapter 2 Cyclomethicone requires a low heat for vaporization; additionally, it has low viscosity, a dry skin feel, is easily spread, is noncooling, colorless and essentially odor- less. Table 2.2 shows the assigned INCI names for cyclomethicone compounds. Table 2.2. Cyclomethicone INCI Nomenclature # of Si and O Atoms INCI Name Mixtures Cyclomethicone 3 Cyclotrisolxane 4 Cyclotetrasiloxane 5 Cyclopentasiloxane 6 Cyclohexasiloxane Table 2.3 outlines the properties of the various types of cyclomethicone. The benefits of using cyclomethicone in skin care products include: Imparts a soft and silky feeling to the skin Evaporates at room temperature Possesses excellent spreading quality Leaves no oily residue or buildup Detackification Feels nongreasy Is compatible with a wide range of cosmetic ingredients Has low surface tension Is a transient emollient; improved rub in and spread In hair care, the benefits include: Transient conditioning Lack of build up Improved wet comb Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. Table 2.3. Cyclomethicone Properties INCI Name Cyclotetrasiloxane Cyclopentasiloxane Cyclohexasiloxane Cycloheptasiloxane Common Name D4 D5 D6 D7 Viscosity (cSt) 2.5 4.2 4.2 6.8 Molecular Weight 297 371 371 445 Specific Gravity 0.95 0.95 0.95 0.96 Refractive Index 1.394 1.397 1.397 1.399 Solubility Parameter 7.4 7.4 7.4 7.4 Flash Point (°C) 55 76 76 93 Table 2.4. Volatile Non-cyclic silicones INCI Name Hexamethyl-disiloxane Dimethicone Dimethicone Dimethicone Common Name MM 1 visc fluid 1.5 visc fluid 2 visc fluid Viscosity (cSt) 0.65 1 1.5 2 Molecular Weight 162 236 311 385 Specific Gravity 0.76 0.816 0.85 0.872 Refractive Index 1.375 1.382 1.387 1.389 Solubility Parameter 6.7 6.9 7.0 7.0 Flash Point (ºC) -3 34 56 87 38  39 Anthony J. O’Lenick, Jr. Chapter 2 Cyclomethicone is used in the following types of products: AP/DO Hair sprays Cleansing creams Skin creams and lotions Stick products Bath oils Suntan products Shaving products Makeup Nail polishes Table 2.4 shows noncyclic silicone compounds that are volatile and provide a dry feeling to the skin. Molecular Weight of Polymeric Silicones As one considers silicone polymers, the concept of molecular weight becomes important. Consider pure hexane. The structure is CH3-(CH2)4-CH3. It has six carbon atoms, 14 hydrogen atoms and a molecular weight of 100. If we add another CH2 group we get heptane with a molecular weight of 114. Easily completed. Now consider silicone fluid with a viscosity of 200. If one runs a GPC analysis, a molecular weight of 9430 is obtained. The fluid has the following structure: CH3 CH3 CH3 | | | CH3-Si—(-O—Si —)n—O—Si- CH3 | | | CH3 CH3 CH3 Solving for “n” (the number of repeating units within the parenthesis) we get: Molecular weight of polymer – (molecular weight of the two M units) n= Molecular weight of the D units i.e. “n” or in this case: n = 9,430 – 164 (M groups) = 125.2 74 40 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. What does this mean? Is there really a 0.2 n unit? Of course not; it is a conse- quence of the fact that “n” is an average. The polymer has a range of oligomers in the mixture wherein the average “n” value is 125.5. Oligomer distribution is not unique to silicone compounds. Ethoxylates are also oligomers. An oligomer is a compound with an “n” value that is an integer, in contrast to a polymer that consists of a mixture of many “n” values. The oligomer distribution is determined in part by the chemistry used to make the polymer, and to some extent the catalyst. This is not the only contributor. Blend- ing is a nonchemical operation in which silicones of different molecular weight are mixed together. The resulting blend often has very different cosmetic properties, most importantly skin feel. Blends of high viscosity and low viscosity fluids can have very elegant skin feel. The high viscosity fluid when used alone can be sticky. The low viscosity fluid aids in spreading the high viscosity fluid and a product with a very interesting skin feel results; consequently, the oligomer distribution that is often critical to performance. Gel permeation chromatography (GPC) is a separa- tion technique involving the transport of a liquid mobile phase through a column containing the separation medium, a porous material. GPC, is also called size exclu- sion chromatography or gel filtration. The technique provides a rapid method for the separation of oligomeric and polymeric species1. A typical GPC for a silicone fluid made without blending is shown in Figure 2.1. Figure 2.1. Typical GPC for a Silicone Fluid (made without blending) number average molecular weight viscosity average molecular weight Note: Be careful! On a plot like this, molecular weight often increases from right to left, not from left to right! weight average number molecular weight of molecules molecular weight Now consider what happens when one blends two closely related silicones to- gether to obtain a desired viscosity. Figure 2.2 shows a typical GPC for a silicone fluid made blending two similar molecular weight fluids. One can clearly see the two humps, indicative of the two components.  41 Anthony J. O’Lenick, Jr. Chapter 2 Figure 2.2. Typical GPC for a Silicone Fluid (made blending 2 similar molecular weight fluids) number of molecules molecular weight Now consider a blend of two very different silicone fluids. Figure 2.3 shows a typical GPC for a silicone fluid made by blending two very different molecular weight silicone fluids. It is very interesting to note the average molecular weight, for the blend has essentially no concentration. Figure 2.3. Typical GPC for a Silicone Fluid (made blending 2 different molecular weight fluids) number average molecular weight number of molecules molecular weight 42 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. Why is this of interest to the cosmetic chemist? A blend of two very different silicone fluids will have a different feel on the skin in comparison to a single com- ponent. The viscosity of the fluid can be very confusing if it is the salient analysis used for a specification. Low molecular weight silicone fluids help spread high molecular weight silicones on the skin. The high molecular weight silicones then provide an outstanding feeling to the skin. Blends function very differently com- pared to nonblended silicones in application. Silicone Fluids Synthesis Silicone fluids are synthesized by the equilibration reaction of MM and cyclom- ethicone. The reaction is a ring-opening reaction. Typical of the synthesis of fluids is the following reaction in which one MM is reacted with one D4 compound to make MD4M, a simple silicone fluid. CH3 CH3 CH3 CH3 CH3 CH3 | | | | | | CH3-Si—O—Si-CH3 + -(-Si-O)4 ‘ CH3-Si—(-O—Si —)4—O—Si- CH3 | | | Catalyst | | | CH3 CH3 CH3 CH3 CH3 CH3 MM D4 MD4M The reaction may be run with either an acid or base catalyst. Typically, the reaction is conducted at room temperature for 12 hours with a 2% by weight sul- furic acid as the catalyst, resulting in a mixture of about 10% free cyclic product and 90% linear fluid. If the catalyst is neutralized and the cyclic is stripped off, a stable fluid will result. If the catalyst is not neutralized during stripping, the fluid will degrade back to MM and D42,3. The equilibration process is critical not only to produce stable silicone fluids, but as a means of introducing functional groups into the polymer. This is hydrosi- lylation, a process used to make organofunctional silicone compounds. It is also interesting to note that a “finished silicone fluid” may be placed in contact with D4 and catalyst and re-equilibrated to make a higher viscosity fluid. Conversely, a “finished silicone fluid” may be re-equilibrated with MM and catalyst to make a lower viscosity fluid. Finally, silicone rubber may be decomposed into MM and D4 via stripping of the product in the presence of catalyst. This property of silicone polymers makes them decidedly different from organic compounds. Properties Silicone fluids, also called silicone oils or simply silicones, are sold by their viscosity and range from 0.65 centistokes (cSt) to 1,000,000 cSt. If blending two different viscosity fluids does not make the product, the viscosity is related to molecular  43 Anthony J. O’Lenick, Jr. Chapter 2 weight. The viscosity allows for an approximate calculation of the value of “n” as shown in Table 2.5. Table 2.5. Approximate “n” Value Based on Viscosity (Non-blended) Viscosity 25ºC Approximate Approximate (cSt) Molecular Weight “n” Value 5 800 9 50 3,780 53 100 6,000 85 200 9,430 127 350 13,650 185 500 17,350 230 1,000 28,000 375 10,000 67,700 910 60,000 116,500 1,570 100,000 139,050 1,875 Silicone fluids are classified by their viscosity. 1. Volatile Silicone Fluids (Linear, noncross-linked silicone having a viscosity of less than 5 cSt) 0.65 cSt (CAS# 107-46-0) (MM) 1 cSt (CAS# 107-51-7) 3 cSt (CAS # 63148-62-9) Volatile silicone fluids are used in a wide variety of antiperspirants, skin creams, skin lotions, suntan lotions, bath oils, and hair care products. They possess low surface tensions and exhibit excellent spreadability. 2. Low Viscosity Silicone (Linear, noncross-linked silicone having a viscosity of 5–50 cSt) CAS# 63148-62-9 5 cSt 10 cSt 20 cSt 44 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. Low viscosity silicones are primarily used as an ingredient in a number of per- sonal care products due to their high spreadability, low surface tension and subtle skin lubricity. These fluids are clear, tasteless, odorless and provide a nongreasy feel. They are used in a wide variety of skin creams, skin lotions, suntan lotions, bath oils and hair care products. 3. Regular Viscosity Silicones (Linear, noncross-linked silicone having a having a viscosity of 50–1,000 cSt) CAS# 63148-62-9 50 cSt 100 cSt 200 cSt 350 cSt 500 cSt 1,000 cSt 4. High Viscosity Silicones (Linear, noncross-linked silicone having a viscosity of 10,000–60,000 cSt) CAS# 63148-62-9 10,000 cSt 60,000 cSt 5. Ultra High Viscosity Silicone Fluid (Linear, noncross-linked silicone having a viscosity of over 60,000 cSt) 100,000cSt 500,000cSt 1,000,000cSt Table 2.6 is provided to give meaning to the viscosity values by relating them to everyday materials. Silicone fluids, unlike petroleum based products have very good viscosity sta- bility over a wide range of temperatures. This is important in applications where very cold temperatures are encountered, like lubricants for high altitude planes. The viscosity stability can be seen in Table 2.7. See Figures 2.4 and 2.5 for examples of healthy and damaged hair. Silicones have a low surface tension so they spread well on the hair. They are highly lubricious; therefore, they lubricate damaged dry hair. Hair damage comes from a variety of sources including: Sun damage Mechanical damage  45 Anthony J. O’Lenick, Jr. Chapter 2 Table 2.6. Viscosity Comparison Reference Object Viscosity cSt. water 1 to 5cSt. kerosene 10cSt. transformer oil 20cSt. Sae-5 oil 50cSt. Sae-10 motor oil 100cSt. Sae-30 motor oil 350cSt. Sae-30 motor oil 500cSt. light syrup 1,000cSt. pancake syrup 2,500cSt. honey 10,000cSt. chocolate syrup 25,000cSt. ketchup 50,000cSt. thick molasses 60,000cSt. hot tar 100,000cSt. peanut butter 250,000cSt. paste/caulk 1,000,000cSt. Table 2.7. Viscosity Change at Different Temperatures Silicone Fluid and Petroleum Oil Viscosity (cSt) Temperature (°C) Silicone Fluid Petroleum Oil 100 40 11 38 100 100 -18 350 11,000 -37 660 230,000 46 Silicones for Personal Care, 2nd Edition Anthony J. O’Lenick, Jr. Figure 2.4. Hea