Polymer

Introduction to Polymers 1

What are polymers, monomers and

Polymerizations? What are polymer and polymerization types?

The addition-condensation system The chain growth-step growth system

Nomenclature of polymers Homopolymer vs. copolymer

Classification of polymers depending on their

structureThermosets vs. Thermopalstics


Polymers are macromolecules built up by the linking together of large numbers of much smaller molecules.


The small molecules which combine with each other to form polymer molecules are termed monomers.



Let CH2-CH2 ≈ 1 inch


Ethylene Polyethylene

Consider only a 200 Consider only a 200 - mer, M- mer, Mww ≈ 5600 ≈ 5600

This ends up with a chain of approximately 1/4 inch (6.4 mm) This ends up with a chain of approximately 1/4 inch (6.4 mm) in diameter and 1/2 mile (805 m) long.in diameter and 1/2 mile (805 m) long.

Molecular weights of 1,000,000 are not uncommon for PE …!Molecular weights of 1,000,000 are not uncommon for PE …!

Classification of Polymers

Polymer StructurePolymerization

Mechanism

Step- Polymerization

Chain- Polymerization

Condensation Polymers

Addition Polymers


The condensation takes place between two polyfunctional molecules to produce one larger polyfunctional molecule with the possible elimination of a small molecule such as water. The reaction continues until one of the reagents is used up.


Polymer StructurePolymer Structure

The addition-condensation systemThe addition-condensation system


Adipoyl chloride

Hexamethylene diamine

Nylone 6/6



Addition polymers are those formed from monomers without the loss of a small molecule.


What are addition polymers?What are addition polymers?

Y Y

The major addition polymers are those formed by polymerization of monomers containing carbon-carbon double bond; such monomers are called vinyl monomers or substituted ethylenes.





Usually in this type of polymerization, vinyl monomers react with themselves to form

polymers

What about polyurethane, is it condensation or addition polymer?


OCO CONHester amide

Condensation polymers (New definition)


Polymers whose repeating units are joined Polymers whose repeating units are joined together by functional units such as ester together by functional units such as ester (-OCO-), amide (-NHCO-), urethane (-OCONH-), (-OCO-), amide (-NHCO-), urethane (-OCONH-), sulfide (-SOsulfide (-SO22-) and other linkages. -) and other linkages.

-R-Z-R-Z-R-Z-R-Z-R-Z--R-Z-R-Z-R-Z-R-Z-R-Z-

R is aliphatic or aromatic grouping and Z is functional unit.R is aliphatic or aromatic grouping and Z is functional unit.



There are two major differences between the two mechanisms:

1. The nature of the species that can react with each other.

2. The relationship between polymer molecular size and polymerization conversion.


Polymerization MechanismPolymerization Mechanism

The step-chain polymerizationThe step-chain polymerization

The characteristic of chain polymer is that polymer growth takes place by monomer reacting only with the reactive centers. Monomer does not react with monomer and the different-sized species such as dimer, trimer, and n-mer do not react with each other. Polymerization ceases when the active centre destroyed by termination reaction(s).


Chain polymerizationChain polymerization


Chain polymerization – anionic polymerization of Chain polymerization – anionic polymerization of styrenestyrene

But, the following is NOT possible

In step polymerization each polymer formed can react further with monomer or other polymers. Each dimer, trimer, etc. is just as reactive as monomer. By this mechanism, the size of the polymer molecules increases slowly.


Step polymerizationStep polymerization


Step polymerization – the production of poly Step polymerization – the production of poly (ethylene terephthalate) (PET)(ethylene terephthalate) (PET)


Step polymerization – the production of poly Step polymerization – the production of poly (ethylene terephthalate) (PET)(ethylene terephthalate) (PET)

Next steps:

Or……..


Most simple and frequently used It is applicable to polymers synthesized from

a single monomer as in addition and ring-opening polymerizations.

How to name: simple monomers: add monomer name to

the prefix poly without space or hyphen.


Nomenclature based on sourceNomenclature based on source

simple monomers



EthyleneEthylene Polyethylene Polyethylene

AcetaldehydeAcetaldehyde Polyacetaldehyde Polyacetaldehyde

Monomers have multiword name or abnormally long name: parenthesis are placed around its name following the prefix poly



3-methyl-1-pentene3-methyl-1-pentene Poly (3-methyl-1-pentene)Poly (3-methyl-1-pentene)

Propylene oxidePropylene oxide Poly(propylene oxide)Poly(propylene oxide)

ClorotriflouroethyleneClorotriflouroethylene Poly(clorotriflouroethylene)Poly(clorotriflouroethylene)

Note: condensation polymers synthesized from single reactants are named in a similar manner.



6-aminocaproic acid6-aminocaproic acid Poly(6-aminocaproic acid) Poly(6-aminocaproic acid)

Homopolymers are polymers composed of only one repeating unit in their molecules.


What are homopolymers?What are homopolymers?

What are copolymers?What are copolymers?Copolymers are polymers composed of two different Copolymers are polymers composed of two different

repeating units in their molecules.repeating units in their molecules.

Such asSuch as

StyreneAcrylonitir

leBe careful !!!


Types of copolymer systemsTypes of copolymer systems

Random copolymer Random copolymer -AABABBBABBAAAA--AABABBBABBAAAA-

Alternating copolymer Alternating copolymer -ABABABABABABAB--ABABABABABABAB-

Block copolymer Block copolymer -AAA-BBBBBB-AAAA-BB- -AAA-BBBBBB-AAAA-BB-

Graft copolymer Graft copolymer

Linear polymers


What if polymerization conditions are changed or What if polymerization conditions are changed or different monomer is used, e.g. ethylene vs. different monomer is used, e.g. ethylene vs. butadiene?butadiene?

Branched polymers


What is the effect of branching on polymer properties?Crystallinity

Is it branched polymer?!!!

Cross-linked polymers


Using appropriate monomersChemical reactions

Polymer molecules are connected together at points other than their ends

Crosslinked polymers do not dissolve but can be swelled by liquids.

Light crosslinking improves elasticity properties

polymer is used as rubber

High degree of crosslinking gives high rigidity and thermal stability (high melting point).

BOTH CROSSLINKED POLYMERS CANNOT BE RECYLED OR REPOROCESSED


Examples


Show the polymer formed by the reaction of the following monomers.

Is the resulting polymer linear or branched/cross-linked? Solution


Examples


Show the polymer formed by the reaction of the following monomers.

Is the resulting polymer linear or branched/cross-linked? Solution

What are thermoset polymers?


Polymers that will not flow when heated. Thermosets Polymers that will not flow when heated. Thermosets have cross-linked structure. Examples are phenolic have cross-linked structure. Examples are phenolic

and epoxy resins.and epoxy resins.

What are What are thermoplasticthermoplastic polymers? polymers?

Polymers that soften, without chemical change, and take Polymers that soften, without chemical change, and take new shapes by the application of heat and pressure new shapes by the application of heat and pressure and harden when cooled. Thermoplastics have linear and harden when cooled. Thermoplastics have linear and branched structures. Examples are PP, PVC and and branched structures. Examples are PP, PVC and NylonNylon


Plastics

Thermosets Thermoplastics

Amorphous CrystallineHighly

cross-linkedLightly

cross-linked

Classification of polymers – polymer structureClassification of polymers – polymer structure


phenol formaldehyde Phenol-formaldehyde


Is this a homopolymer or copolymer? Why?Is this a homopolymer or copolymer? Why?

The monomer composed of more than one structural unit


Branched polymerBranched polymer

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