Module 2, Unit 3: Polymers PDF

Unit 3 Polymers UNIT LEARNING OUTCOMES TLO 6: Apply appropriate concepts of polymerization and nanotechnology for engineering materials. ENGAGE Giant molecules called polym...

Unit 3 Polymers UNIT LEARNING OUTCOMES TLO 6: Apply appropriate concepts of polymerization and nanotechnology for engineering materials. ENGAGE Giant molecules called polymers are made up by the linkage of simpler molecules (monomers) by a polymerization reaction into essentially endless chain structures. Polymers occur naturally, but the majority which are used commercially are manufactured from simple monomers. The most well known natural polymers are proteins (polymers of amino acids), nucleic acids (polymers of ribose or deoxyribose sugars with attached purine or pyrimidine bases), and the polymers of glucose (starch, glycogen, cellulose). Synthetic polymers were originally derived from these natural polymers. The first commercially successful synthetic polymer was cellulose nitrate (Celluloid, 1869) which was first practically molded as a substitute for ivory in billiard balls. Nitration of cellulose, [C6H7O2(OH)3].xH2O, produces mixtures of cellulose trinitrate, called guncotton, and cellulose dinitrate, called pyroxylin. John Wesley Hyatt discovered that pyroxylin, when mixed with camphor, becomes a thermoplastic, a substance which can be molded when heated. Unfortunately, cellulose nitrate is also an explosive and its use in motion picture film and in billiard balls occasionally produced spectacularly inflammable incidents. Cellulose acetate, discussed in a following section, soon replaced it. The second development was that of casein-formaldehyde plastics (A. Spitteler, 1899) made using formaldehyde (H2C=O) and casein obtained from milk. These polymers are no longer of industrial significance. Phenol (C 6H5OH)-formaldehyde resins (Bakelite, 1909) were developed in the United States by the Belgian-born chemist Leo Baeckeland while searching for a substitute for varnish shellac. Heating these resins under pressure gave soft solids which could be molded and then hardened; they were both safe and economical. These early polymers have now been replaced by others based on simpler monomers. The polymer industry is normally divided into three areas on the basis of the type of product manufactured: synthetic plastics, man-made textile fibers, and synthetic rubber. Some polymers have properties which permit their use in more than one of these areas. Prepared by: Engr. N. L. Escalante 40 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  EXPLORE What are Polymers?  Polymer is a molecule, made from joining together many small molecules called monomers.  Polymer can be broken down into “poly”, which means “many”, and “mer”, which means “unit”. A polymer is a large molecule or a macromolecule which essentially is a combination of many subunits. The term polymer in Greek means „many parts‟. Polymers can be found all around us. From the strand of our DNA which is a naturally occurring biopolymer to polypropylene which is used throughout the world as plastic. Polymers may be naturally found in plants and animals (natural polymers) or may be man- made (synthetic polymers). Different polymers have a number of unique physical and chemical properties due to which they find usage in everyday life. Polymers are all created by the process of polymerization wherein their constituent elements called monomers, are reacted together to form polymer chains i.e 3-dimensional networks forming the polymer bonds. The type of polymerization mechanism used depends on the type of functional groups attached to the reactants. In biological contexts, almost all macromolecules are either completely polymeric or are made up of large polymeric chains. Classification of Polymers: Polymers cannot be classified under one category because of their complex structures, different behaviours, and vast applications. We can, therefore, classify polymers based on the following considerations. Prepared by: Engr. N. L. Escalante 41 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  A. Classification of Polymers based on origin 1. Natural Polymers: They occur naturally and are found in plants and animals. For example proteins, starch, cellulose, and rubber. To add up, we also have biodegradable polymers which are called biopolymers. 2. Synthetic Polymers: These are man-made polymers. Plastic is the most common and widely used synthetic polymer. It is used in industries and various dairy products. For example, nylon-6, 6, polyether‟s etc. B. Classification of Polymers based on chemical structure 1. Homopolymer – polymer which consists of one type of monomer Examples: polyethelyne, polystyrene, etc. 2. Copolymer – a polymer which is derived from more than one type of monomer. Examples: polyethelyne-vinyl acetate (PEVA), Acrylonitrile Butadiene Styrene (ABS) C. Classification of Polymers based on polymeric structure 1. Linear Polymers: The structure of polymers containing long and straight chains fall into this category. PVC, i.e. poly-vinyl chloride is largely used for making pipes and electric cables is an example of a linear polymer. Prepared by: Engr. N. L. Escalante 42 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  2. Branched-chain Polymers: When linear chains of a polymer form branches, then, such polymers are categorized as branched chain polymers. For example, Low- density polythene. 3. Cross-linked Polymers: They are composed of bifunctional and trifunctional monomers. They have a stronger covalent bond in comparison to other linear polymers. Bakelite and melamine are examples in this category. D. Classification of Polymers based on arrangement of monomers 1. Block polymer – consists of relatively long sequences of identical monomer units Prepared by: Engr. N. L. Escalante 43 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  2. Graft polymer – branched polymer whose backbone is formed from one type of monomer and branches are formed from other type of monomer E. Classification of Polymers based on tacticity Tacticity – it is the orientation of monomer units in a polymer molecule with respect to the main chain 1. Isotactic polymer – side groups of the polymer lie on the same side of the chain 2. Syndiotactic polymer – side groups of the polymer are arranged in an alternate manner 3. Atactic polymer – side groups are arranged in an irregular or random manner around the main chain Prepared by: Engr. N. L. Escalante 44 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  F. Classification of Polymers based on thermal behavior 1. Thermoplastics – polymers which are easily softened upon heating Examples: Acrylic, PVC, Polypropylene, Polystyrene, Teflon 2. Thermosets – polymers which change irreversibly into hard and rigid materials on heating and cannot be reshaped Examples: Melamine Formaldehyde, Bakelite, Epoxy Resin G. Classification of Polymers based on molecular forces 1. Elastomers – polymers which can be easily stretched by applying small stress Examples: Natural rubber (Polyisoprene), Synthetic rubbers 2. Fibers – polymers which have strong intermolecular forces between the polymer chains Examples: wool, cashmere, cotton, rayon, polyester, nylon H. Classification of Polymers based on modes of synthesis 1. Addition polymers – these polymers are formed when same monomers are added – these monomers are usually alkenes (hydrocarbons that contain double bonds) 2. Condensation polymers – these polymers are formed when two monomers react with the elimination of smaller molecule (usually water, ammonia, methanol, or hydrogen chloride) Prepared by: Engr. N. L. Escalante 45 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  How Can We Differentiate Natural Polymers from Synthetic Polymers? NATURAL POLYMERS Sources of natural polymers  Plants  Cellulose – polymer made up of long strands of glucose, which is also called the “polysaccharide”. It is abundantly found in plants which give plants their sturdy structure.  Starch – another polymer made up of glucose monomer units. Starch is made up by plants for them to store energy. It is a combination of “amylose” and ”amylopectin”.  Rubber – natural rubber is a polymer that is obtained as a milky white fluid known as latex from a tropical rubber tree. It is made up of Isoprene monomer units.  Animals  DNA (Deoxyribonucleic Acid) – Polymer made up of monomer units called “nucleotides”. DNA is found in nearly all living cells. 4 Nucleotides (nucleic acid) that form our DNA (a) Thymine (b) Cytosine (c) Guanine (d) Adenine Genes – section of the DNA that codes for a protein is called the genes − Genes make all the enzymes needed to carry out the reaction in our bodies  Proteins – polymers made up of amino acids bonded together to create a long chain. Proteins make up our hair and muscles. 10 Essential Amino Acids (a) Arginine (f) Methionine (b) Histidine (g) Phenylalanine (c) Isoleucine (h) Threonine (d) Leucine (i) Tryptophan (e) Lysine (j) Valine Prepared by: Engr. N. L. Escalante 46 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Silk – a kind of protein produced by silkworms to make their cocoon. − it is used for the production of the silk cloth. Other Natural Polymers  Lignin – a polymer found in trees, together with cellulose, makes trees rigid.  Chitin – a polymer which composes the exoskeleton of crustaceans such as crabs and shrimps. − It is also found in the cell wall of fungi like mushrooms. SYNTHETIC POLYMERS - These polymers are mostly derived from petroleum/crude oil, and manufactured in factories. Synthetic polymers include fibers, elastomers, and the most commonly encountered are PLASTICS.  PLASTICS – comes from the Greek word “plastikos”, which means “to grow or form”. 7 Types of Plastics (1) Polyethylene Terephthalate (PET or PETE) Use: Containers of beverages (2) High-Density Polyethylene (HDPE) Use: Detergent bottles, Household cleaners for bottles (3) Polyvinyl Chloride (PVC) Use: Pipings, Wiring cables (4) Low-Density Polyethylene (LDPE) Use: Plastic bags, Packaging for computer hardware, plastic wraps (5) Polypropylene (PP) Use: Food containers (6) Polystyrene (PS) Use: Styrocups, styrofoam (7) Other (e.g. Polycarbonate (PC), and other plastics not included in 1-6) Use: Polycarbonate – alternative roofing, spectacle lenses Other Synthetic Polymers  Polyvinyl Acetate (PVA) – used in regular glue  Ethylcyanoacrylic – used in superglue (stronger than PVA) Prepared by: Engr. N. L. Escalante 47 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.   Polyactic Acid (PLA) – used to make a biodegradable plastic, also termed as “bioplastic” Structure of Polymers Most of the polymers around us are made up of a hydrocarbon backbone. A Hydrocarbon backbone being a long chain of linked carbon and hydrogen atoms, possible due to the tetravalent nature of carbon. Hydrogen Carbon Many common classes of polymers are composed of hydrocarbons, compounds of carbon and hydrogen. These polymers are specifically made of carbon atoms bonded together, one to the next, into long chains that are called the backbone of the polymer. Because of the nature of carbon, one or more other atoms can be attached to each carbon atom in the backbone. There are polymers that contain only carbon and hydrogen atoms. Polyethylene, polypropylene, polybutylene, polystyrene and polymethylpentene are examples of these. Polyvinyl chloride (PVC) has chlorine attached to the all-carbon backbone. Teflon has fluorine attached to the all-carbon backbone. Other common manufactured polymers have backbones that include elements other than carbon. Nylons contain nitrogen atoms in the repeat unit backbone. Polyesters and polycarbonates contain oxygen in the backbone. There are also some polymers that, instead of having a carbon backbone, have a silicon or phosphorous backbone. These are considered inorganic polymers. One of the more famous silicon-based polymers is Silly Putty®. Properties of Polymers Physical Properties ▪ As chain length and cross-linking increases the tensile strength of the polymer increases. ▪ Polymers do not melt, they change state from crystalline to semi-crystalline. Prepared by: Engr. N. L. Escalante 48 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Chemical Properties ▪ Compared to conventional molecules with different side molecules, the polymer is enabled with hydrogen bonding and ionic bonding resulting in better cross-linking strength. ▪ Dipole-dipole bonding side chains enable the polymer for high flexibility. ▪ Polymers with Van der Waals forces linking chains are known to be weak, but give the polymer a low melting point. Optical Properties ▪ Due to their ability to change their refractive index with temperature as in the case of PMMA and HEMA: MMA, they are used in lasers for applications in spectroscopy and analytical applications. Some Polymers and their Monomers ▪ Polypropene, also known as polypropylene, is made up of monomer propene. ▪ Polystyrene is an aromatic polymer, naturally transparent, made up of monomer styrene. ▪ Polyvinyl chloride (PVC) is a plastic polymer made of monomer vinyl chloride. ▪ The urea-formaldehyde resin is a non-transparent plastic obtained by heating formaldehyde and urea. ▪ Glyptal is made up of monomers ethylene glycol and phthalic acid. ▪ Bakelite or polyoxybenzylmethylenglycolanhydride is a plastic which is made up of monomers phenol and aldehyde. Types of Polymerization Reactions The process of combining a large number of small molecules to form a single macromolecule is known as polymerization. The small molecules that act as the building blocks of polymers are called monomers. Based on the kinds of reactions involved, polymerisation is divided into two groups known as addition polymerization and condensation polymerization. Addition polymerization is the process of repeated addition of monomers that possess double or triple bonds to form polymers. Condensation polymerization is a process that involves repeated condensation reactions between two different bi-functional or tri-functional monomers. Give below in a tabular column is the difference between addition and condensation polymerization. Addition Polymerization This is also called as chain growth polymerization. In this, small monomer units joined to form a giant polymer. In each step length of chain increases. For example, Polymerization of ethane in the presence of Peroxides Condensation Polymerization In this type small molecules like H 2O, CO, NH3 are eliminated during polymerization (step growth polymerization). Generally, organic compounds containing bifunctional groups such as idols, -dials, diamines, dicarboxylic acids undergo this type of polymerization reaction. For example, Preparation of nylon -6, 6. Prepared by: Engr. N. L. Escalante 49 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Addition Polymerization Condensation Polymerization Monomers must have either a double Monomers must have two similar or bond or triple bond different functional groups Produces no by-products By-products such as ammonia, water and HCl are produced The molecular weight of the resultant The molecular weight of the resultant polymers is a multiple of monomer‟s polymer is not a multiple of molecular weight monomer‟s molecular weight Lewis acids or bases, radical initiators The catalysts in condensation are catalysts in addition polymerization are catalysts in polymerization condensation polymerization. Common examples of addition Common examples of condensation polymerization are PVC, polyethene, polymerization are nylon, bakelite, Teflon etc. silicon, etc. What is Copolymerization? In this process, two different monomers joined to form a polymer. Synthetic rubbers are prepared by this polymerization. For example, BUNA – S. Uses of Polymers Here we will list some of the important uses of polymers in our everyday life. ▪ Polypropene finds usage in a broad range of industries such as textiles, packaging, stationery, plastics, aircraft, construction, rope, toys, etc. ▪ Polystyrene is one of the most common plastic, actively used in the packaging industry. Bottles, toys, containers, trays, disposable glasses and plates, tv cabinets and lids are some of the daily-used products made up of polystyrene. It is also used as an insulator. ▪ The most important use of polyvinyl chloride is the manufacture of sewage pipes. It is also used as an insulator in the electric cables. ▪ Polyvinyl chloride is used in clothing and furniture and has recently become popular for the construction of doors and windows as well. It is also used in vinyl flooring. ▪ Urea-formaldehyde resins are used for making adhesives, moulds, laminated sheets, unbreakable containers, etc. ▪ Glyptal is used for making paints, coatings, and lacquers. ▪ Bakelite is used for making electrical switches, kitchen products, toys, jewellery, firearms, insulators, computer discs, etc. Prepared by: Engr. N. L. Escalante 50 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Commercial Uses of Polymers Polymer Monomer Uses of Polymer Isoprene (1, 2-methyl 1 – 1, 3- Making tyres, elastic Rubber butadiene) materials BUNA – S (a) 1, 3-butadiene (b) Styrene Synthetic rubber (a) 1, 3-butadiene (b) Vinyl BUNA – N Synthetic rubber Cyanide Non-stick cookware – Teflon Tetra Flouro Ethane plastics (a) Ethylene glycol (b) Terylene Fabric Terephthalic acid (a) Ethylene glycol (b) Phthalic Glyptal Fabric acid Plastic switches, Mugs, Bakelite (a) Phenol (b) Formaldehyde buckets PVC Vinyl Cyanide Tubes, Pipes Melamine Formaldehyde (a) Melamine (b) Formaldehyde Ceramic plastic material Resin Nylon-6 Caprolactum Fabric EXPLAIN To be able to translate your understanding of metals, do the following activity. Activity 1: Polymers in the Engineering Field Self-Assessment No. 1 Based on your field of interest (e.g. mechanical engineering, civil engineering, chemical engineering, etc.), what are the commonly used polymers and what are their uses? To be submitted in Google classroom on: ELABORATE & EVALUATE Activity 2: Materials Selection: Polymers Vs. Metals Self-Assessment No. 3 Compare and contrast polymers and metals, and come up with different scenarios where polymers are most likely used than metals or scenarios polymers may substitute metals. To be submitted in Google classroom on: Prepared by: Engr. N. L. Escalante 51 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.