Polymer Chemistry I - Course Overview

Polymer Chemistry I - Course Overview

• Polymers, covered in CHM 317, are large molecules made of repeating structural units (monomers) linked by covalent bonds.
• A more accurate term for the structural units is monomer residues.
• Macromolecules are large molecules, but not all macromolecules are polymers.

Polymer Classification

• Polymers are divided into biological and non-biological types.
• Non-biological polymers include natural and synthetic organic, as well as inorganic variants.
• Synthetic organic materials are adhesives, paints, plastics, rubbers, and fibers.
• Natural polymeric organic materials consist of polyisoprene (natural rubber), protein (adhesives), and polysaccharides.
• Synthetic inorganic polymeric materials include fibers like asbestos.
• Natural inorganic materials include sand, glass, clay, brick, pottery, and cement.

Copolymers

• Homopolymers result when only one species of monomer is used
• Copolymers are formed when chains are composed of two types of monomer units.
• Terpolymers result with three different monomers incorporated.
• Copolymer structures can be random, alternating, block, or graft.
• Random copolymers have random arrangements of monomer units.
• Alternating copolymers have a regular, alternating placement of monomers.
• Block copolymers have substantial sequences or blocks of repeating units.
• Graft copolymers have blocks of one monomer grafted onto the backbone of another.
• Copolymers are increasingly used for achieving special properties, such as increased impact resistance in polypropylene.

Polymerization Processes

• Polymerization converts small molecules into a polymer.
• There are two main types of polymerization: addition and step-growth.

Addition Polymerization

• Addition polymerization involves a chain reaction where a simple molecule (monomer with a double bond) is stimulated to break bonds.
• The resulting free radicals join other molecules.
• The resulting polymer has the same chemical composition as the starting material.
• Ethylene produces polyethylene, and acrylonitrile produces polyacrylonitrile.
• Addition polymerization can be stimulated through free radical or ionic initiators.

Step-Growth Polymerization

• Step-growth polymerization uses monomers with functional groups such as hydroxyl, carboxyl, acyl, or amide.
• This process often involves a series of condensation reactions.
• In step-growth, a small molecule is eliminated during the process.
• For condensation polymerization, organic acids or alcohols must have more than one functional group.
• Linear polymers are formed through reactions between bifunctional organic acids and organic bases, eliminating a small molecule releasing an ester.
• A dimer is an ester with two reactive ends, and which can undergo further reactions to produce trimers, tetramers, and large polymeric chains.
• Step-growth polymerization involves a step-by-step build-up of the polymer chain.
• Reactions may contain other atoms originating from monomer functional groups.
• Two processes (addition and step-growth) are generalized with examples.

Polymerization Through Functional Groups

• This process consists of reactions proceeding between functional groups linked to two different molecules where each monomer must possess at least two reactive functional groups, i.e., step-growth polymerizations.

Nylon 11 and Nylon 6,6

• Nylon 11 has 11 carbon atoms in each repeating unit
• A commercial sample has around 100 units
• Nylon 11 is classifies as a fibre
• In a typical polymerization a mixture of two monomers is used, each with one functional group, such as in the formation of Nylon 6,6.

Polyethylene Terephthalate and Polyurethane

• Polyethylene Terephthalate is an example of polyester formed from ethylene glycol and terephthalic acid.
• Polymerization through functional groups does not always mean a polymer is formed with accompanied secondary products; there are exceptions.

Polymerization Through Multiple Bonds

• This involves joining unsaturated molecules containing multiple bonds.
• A double bond in a molecule is vulnerable to chemical attack.
• The mechanism involves homolytic scission of the double bond to form free radicals.
• The double bond is replaced by a single one, allowing the molecule to extend and form a polymer.
• Polymerization is stimulated by an initiator.
• This kind may be divided to various categories.

Types of Vinyl Polymerizations

Vinyl Polymerization

• The simplest monomer being CH2=CH2- ethylene itself.
• The "n" value has a value of the order of 1000 in a commercial sample.
• An example of polyethylene is leather bags.

Polypropylene

• Examples are plastic bottles, mets, housing for refrigerators etc.

Polystyrene

• Polystyrene is tougher and a little heavier - more expensive
• Are used for plug, sockets (electrical).

Vinyl Chloride Polymerization

• Vinyl Chloride can give Polyvinylchloride (PVC)
• PVC is good for insulation.

Polymethyl methacrylate

• Methyl methacrylate polymerizes to give polymethyl methacrylate (PMMA)

Polytetrafluoroethylene

• Polymerization of tetrafluoroethylene gives polytetrafluoroethylene (PTFE).
• PTFE has a high melting point (350 °C).
• PTFE is used as a lining for non-stick cooking and frying utensils (Teflon).
• Examples given are Vinyl compounds that contain CH2=CH groups, but are referred to as vinyl polymerization.

Vinyl Polymerization Processes

• Vinyl polymerization involves three processes: initiation, propagation, and termination.
• Initiation requires an active species capable of starting the polymerization.
• Propagation involves the continuous addition of the monomer to the active species, leading to high molecular mass polymers.
• Termination deactivates the active species, yielding the final stable polymer.
• Active species in vinyl polymerization: free radicals, anions, or cations, accomplishing polymerization.

Free Radical Polymerization

• Initiation is brought about by light, heat, or the addition of a material which on heating decomposes into a free radical.
• Reroxide and azobisisobutyronitrile (ABIBN) are examples of free radical generators
• Benzoyl peroxide polymerization is catalysed by free radicals.
• General initiators join by a covalent bond which cleaves, when heat is added,
• The next step is the addition of an initiator with fragment radical to a Vinyl monomer molecule.
• The free radical attaches itself to the CH2 group rather than on the substituted R group.
• The abstraction condition depends on the nature of the radical depends on the solvent in which the polymerization is being carried out, and will either be an electron withdrawer or donor.
• Chain transfers involves the termination of a growing chain.

Combination and Disproportionation

• Polymer chains may also occur by transfer.
• Transfer can occur in a Vinyl monomer.
• When two radicals combine, they react and deactivate each other.
• During disproportionation, one radical can abstract out He atom from the other radical.

Termination and Tranfers

Termination of a growing chain

Ionic Polymerization

• In ionic polymerization, consider a Vinyl monomer as the catalyst.
• If the substituent X is electron withdrawing, then the favored initiator is an anion.
• If the substituent X is electron donating, it is initiated by a cation.
• In ionic polymerization, the incoming monomer must fit between the growing chain and an associated ion or complex. Cationic Polymerization

Cationic Polymerization

• In cationic polymerization of vinyl monomers, the active center is a carbanium ion.
• Substances that initiate this type are protonic acids, metal halides, and carbanium salts.
• Acids, such as HCl and H2SO4, are used as initiators.
• The monomer attacks at the C+ ion of the growing chain, but the mechanism is not clearly understood.
• The reaction stops when the monomer is exhausted, or by another material.

Anionic Polymerization

• Here, the active center is a carbanion.
• Substances that initiate this type are of two main kinds that are ionic/covalent.
• Catalysts for anionic polymerization include alkali metals, alkoxide, allyls, cyanide.
• The basic steps of the process involve heterolytic splitting, producing the reaction

Kinetics of Free Radical Addition Polymerization

• Reaction kinetics is the study of how fast a chemical reaction will proceed and what factors affect the rates of reaction.
• This study can be used to control the reaction for specific purposes during the manufacturing process.
• Three reaction steps of free addition are listed with their associated equation.

Termination and Reaction Rates

Termination by combination of the growing chains will be considered.

Reaction Steps

• This sections includes derivation of the rate equation is referred to by derivations involving concentrations and steady state equations

Kinetics of Step-Growth Polymerization

• In addition involves carbonyl reaction mechanism.
• Carbonyl is essentially acid catalyzed.

Important factors to notice

• The reactivity of the functional group is independent of chain length.
• The formation of a polyester from the reaction of dibasic acid and glycol is catalysed by acid.

Molecular Weight of Polymers

• Many polymer properties characterize their long chain lengths, and are reflected in its large molecular mass.
• Length of molecular chains can be obtained simply from measuring of molar masses.

Polymer Mass

• Determining the molar mass is important as chain length can control solubility, elasticity, and other properties.
• Common methods for polymer mass measurements include end group assay and osmotic pressure.
• Viscosity and ultra centrifuge are also used
• Can be classified into relevant or absolute methods depending on complexity.

Average Molar Mass

• The formation of long chain polymers involves varying lengths with the process resulting in chains that differ from others.
• Processes here result in random nature and the quoted values or polymer average

Stereochemistry of Polymers

• Micro structural variations in polymers affects well as the chemical properties in its materials.
• Physical behaviours are very significant.

Stereoisomerisms

• Stereoisomerisms can be represented into four main headers which consist of structural, orientational, configurational, geometrical.

Architectural Isomerism

• Arises from isomeric monomers, stemming from branching and network formation.

Orientational Isomerism

• The method monomer units join influence a free radical reaction, impacting resultant polymer structure and stability, with varied addition modes for asymmetric vinyl monomers. Head-to-Tail structures will form.

Configuration and Isomerism

• This process involves the presence of substituted monomers that arise in the form of head-to-head arrangement.

Configurational Isomerism and Tactic Forms

Configuration

• Planar molecules is given with an impression with a linear molecule.
• Structure is very to be non-planar.
• Forms can exits.
• Structures mentioned.

Isomers

• Molecules are on a side of the chain is defined as isotactic, if not it's a different story.

Geometric Isomerism

• Geometric isomers are obtained when conjugated dienes are obtained.
• Chain growth of monomers proceeds in a number of ways depending, or could lean to isotactic.

Polymer Crystallinity

Structures

• The ratio of unsaturation is represented in the chain.

Crystallinity

• Crystalline material is perfect when it consists of an arrangement of individual atoms.
• Some crystals as not.

Factors Affecting Crystallinity

• A polymer should be easy pack.
• Intermolecular bonding for crystalites need to be strong.

Tactility of Polymer

• Chain symmetry and flexibility will result
• If the chain is rigid the packing tightens.

Branching of Chain

• Picking deficiency will increase.

Methods To Determine Crystal Structure

• Crystal structure is difficult to precisely achieve which is why two methods exist.

1. Liquid Density

• Liquid of with levels of density are injected into a cylinder depending on density rating.

2. IRP

• IRP absorption spectra of polymers can differ depending on the structure.

3. X-Ray Difraction

• Some structure will create different layers.

Structural Classification of Natural Macromolecules

Some Materials

• Several plant materials

Fibres and Proteins

• Proteins have a complex striture.
• Fibre class and Amino Acids include feathers and hails etc.

Polymers

• Rubber is an example of an material.

Invention of "Vulcanization."

• Vulcanization is the process of gross linking.
• Vulcanization creates higher degrees.

Bulk Macromolecules

• Macromolucules effect their shape.

Material State

• Some states can exist that are rubbery.

Crystalline State

• State needs to be hard to enable state transition.
• Can be found in to several different forms or forms.

Elastomers and Plastics

• There is no dividing line between the two materials

There are examples of each:

• Rubber material
• Polymer

Elongation and Tension Values Represented.

• Values presented show the type and elasticity of the material depending on the line.

High Elasticity and Strenght

• High elasticity can represent strength

Fibres

• Fibers can be described with a height versus diameter ratio to represent the type.
• Polymers are important to understand in order to prevent degradation

Temperatures for fibre formations

• Temperatures for fibre formations can be determined and understood

The following must be taken into account

• glass transition temperatures.

Plastics

• These materials are formed with a certain shape to act as a mould.
• Plastics include a vast variety dependent greatly on their individual traits.

Polymers

• Polymers are resistant to specific change

Polymers

• Polymers come from variety of forms and structure