Polymers Chemistry Chapter 15 Notes 2024

Last updated on July 14th, 2024 at 05:53 pm

Polymers

Example:-

• Ethene Polyethene Polymer
• Hexamethylenediamine + Adipic Acid Nylon 6,6

Classification Of Polymer

Based On Source

• Natural Polymers – Found in plants and animals. Example – Proteins, cellulose, starch etc
• Semi-Synthetic Polymer – Cellulose derivatives such as cellulose nitrate and cellulose acetate (rayon) are the examples
• Synthetic Polymer – Man-made polymers are synthetic polymers. Example – Nylon 6,6, Buna-S, polyethylene etc

Based On Structure Of Polymer

• Linear Polymer – Consists of long and straight chains. Example – High density polyethene, polyvinyl chloride (PVC)
• Branched Chain Polymer – Have a linear branched chain. Example – Low density polyethene
• Cross Linked or Network Polymer – Formed from bi-functional and tri-functional monomers containing strong covalent bond among the linear polymer chains. Example – Bakelite, melamine etc.

Based On Mode Of Polymerisation 

Addition Polymers:

• Usually formed from monomers having double or triple bond 
• Additional polymers formed by a single type of monomer are called homopolymers. Example – Ethene to Polyethene
• Addition polymers formed by two different monomers are called copolymers. Example – Buna-S, Buna-N
• Also known as Chain Growth Polymers

Condensation Polymers:

• Formed by repetitive condensation reaction between two different bi-functional and tri-functional monomer units
• Elimination of small molecule like H₂O, alcohol, HCl etc. takes place
• Example – Terylene(dacron), Nylon 6,6, Nylon 6 etc
• Example – Hexamethylenediamine + Adipic acid Nylon 6,6
• Also known as Step Growth Polymers

Based On Molecular Force 

Elastomers:

• Rubber-like solids with elastic property
• Polymer chains are held together by weakest intermolecular forces making them stretchable 
• Crosslinks are introduced between the chains which help the polymer to retract its original position
• Example – Buna-S, Buna-N, neoprene etc

Fibres:

• Thread forming solids having high tensile strength and high modulus
• Consists strong intermolecular forces like hydrogen bonding
• Lead to close packing of chains and causes crystalling nature 
• Example – Polyamides (Nylon 6,6), Polyesters (terylene) etc
• Thermoplastic Polymer
• Linear or slightly branched chain molecules
• Softens of heating and hardens on cooling
• Can be recycled
• Have intermolecular force of attraction lying between a elastomer and fibre
• Example – Polyethylene, polystyrene, polyvinyl etc

Thermosetting Polymer:

• Cross-linked or heavily branched molecules
• Undergo extensive crosslinking in moulds becoming unfusible when heated
• Can’t be reused
• Example- Bakelite, urea-formaldehyde resins etc

Types Of Polymerisation Reaction

1. Addition Polymerisation or Chain Growth Polymerisation

• Molecules of the same or different monomers add up together to form the polymer
• Monomers are unsaturated
• This polymerisation can take place through the formation of free radical ionic species
• Free Radical Mechanism:-
  • Chain Initiating Step
  • Chain Propagating Step
  • Chain Terminating Step
• Preparation of Important Addition Polymers

– Low Density Polyethene (LDP)

• Ethene is polymerised under high pressure (1000-2000 atm) and high temperature (350 k to 750 k)
• Traces of dioxygen and peroxide is used as catalyst
• It is highly branched obtained by free radical addition
• Chemically inert, electrical insulator, tough and flexible
• Used in production of squeeze bottles, insulation of current carrying wires

–High Density Polyethene (HDP)

• Formed when addition polymerisation of ethene takes place
• Reaction takes place in a hydrocarbon solvent
• Ziegler-Natta catalyst (triethylaluminium and titanium tetrachloride) is used 
• Temperature (333-343 k) and low pressure (6-7 atm)
• It have linear molecules and high density due to close packing
• Chemically inert, more tougher, more harder 
• Used for manufacturing of buckets, pipes etc

–Polytetrafluoroethylene (Teflon)

• Chemically inert and resistant to corrosion
• Used in making oil seals and non-stick coated utensils

–Polyacrylonitrile

• Used as a substitute for wool

2. Condensation Polymerisation or Step Growth Polymerisation

• Consists repetitive condensation of two bi-functional monomers
• Simple molecules like alcohols, water is lost
• Called step growth polymerisation because each step produces a distinct functionalized specie and is independent of each other
• Important condensation reaction:
• Polyamides
  • Nylon 6,6 – Used in making sheets, brush bristles
  • Nylon 6 – Used in manufacture of tyre cords, fabrics and ropes
• Polyesters
  • Result of polycondensation products of dicarboxylic acids and diols
  • Prepared by heating a mixture of ethylene glycol and teraphthalic acid
  • Zinc acetate-antimony trioxide used as catalyst
  • Example:- Dacron, terylene etc
  • Dacron is crease resistance and used in blending with cotton, used in safety helmet’s glass

• Phenol-formaldehyde (Bakelite) polymer
  • Oldest synthetic polymers
  • Initial product formed is a linear product – Novolac
  • Novolac is used in paints
  • An infusible solid mass Bakelite is formed when Novolac undergoes cross-linking on reaction with formaldehyde
• Melamine-formaldehyde polymer
  • Used to produce unbreakable crockery

Copolymerisation

• Reaction in which a copolymer is formed by the mixture of more than one monomeric specie
• Copolymer can be formed by both step growth and chain growth polymerisation
• Their property is different from homopolymers
• Example – Butadiene-styrene copolymer is tough and is used as a substitute for natural rubber, used in production of tyres, footwear etc

Natural Rubber

• It’s a natural polymer having elastic property
• Also known as elastomer
• Produced from rubber latex which is a colloidal dispersion of rubber in water
• Chains are held together by weak van der Waal forces and also having a coiled structure, making them stretchable

Vulcanisation of rubber

• Natural rubber becomes soft at high and brittle at low temperature
• Shows high water absolution capacity
• Soluble in non-polar solvents and is non-resistant to attack by oxidising agents
• Vulcanisation is carried out to improve these qualities
• A mixture of raw mixture with sulphur is heated at a temperature from b/w 373-415 K
• After vulcanisation, rubber forms crosslink at the reactive sites of double bond and rubber gets stiffened
• 5% of sulphur is used as a crosslink agent to form tyre rubber

Synthetic Rubber

• Any vulcanised rubber which can be stretched to the twice of its length is synthetic rubber
• Retains its original shape when external force is released

Preparation Of Synthetic Rubber

• Neoprene
  • Formed by free radical polymerisation of chloroprene
  • More resistant than vegetable and mineral oils
  • Used for manufacture of conveyor belts, gaskets etc
• Buna-N
  • Resistant to the action of petrol, lubricating oil and organic solvents
  • Used in making oil seats, tank lining etc

Biodegradable Polymers

• Poly ?-hydroxybutyrate – co-?-hydroxy valerate (PHBV)
  • Used in speciality packaging, orthopaedic materials and in controlled release of drugs
  • Undergoes bacterial degradation in the environment
• Nylon 2-nylon 6
  • An alternating polyamide copolymer of glycine (H2N-CH2-NH2) and amino caproic acid [H2N-(CH2)5-COOH]
  • Biodegradable

Important Polymers, their monomers and uses

Frequently Asked Questions

Final Words

From the above article you must have got idea of polymer. We hope that this note will help you in your exam.

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