CHAPTER-15  POLYMERS

Polymer:   It is a very large molecule having molecular mass 103 - 107 g mol-1. They are formed by joining together repeating structural units called monomers.

 Classification of Polymers: (a) Based On Source:

(i) Natural: Found in plants and animals, e.g. Proteins, cellulose, natural rubber, silk, wool.

(ii) Synthetic: Man-made e.g. Nylon, polyester, neoprene, Bakelite, Teflon, PVC, polystyrene.

(ii) Semi-synthetic: Rayon, vulcanized rubber and gun cotton

(b) Based On Structure:

(i) Linear Polymers: This consist of long and straight chain repeating units e.g. Polythene (HDPE),          PVC, nylon, polyester.

(ii) Branched Polymers: This contain linear chains having some branches e.g. amylopectin, glycogen etc.

(iii) Cross Linked Polymers: Strong covalent bonds are present between various linear polymer chains. E.g. Bakelite, urea- formaldehyde polymer, melamine, formaldehyde polymer etc.

(c) Based On Mode Of Polymerization:

(i) Addition Polymers: These are formed by the repeated addition of monomer molecules possessing multiple bonds, e.g., polythene, polypropene, polystyrene, PMMA (polymethyl metha crylate)

(ii) Condensation Polymers: These are formed by the repeated condensation reaction of different bifunctional or trifunctional monomers, with the elimination of small molecules like water,HCl,NH3, alcohol etc. e.g. Bakelite,nylon,polyster,urea- formaldehyde resin.

(d) Based On Molecular Forces:

(i) Elastomers: Forces of interaction between polymer chains is weakest, e.g. natural rubber, neoprene, vulcanized rubber.

(ii) Fibers: Strong hydrogen bonds are present between the polymer chains. They have high tensile strength e.g., nylon.polyster, silk, wool, orlon, rayon etc.

(iii) Thermoplastics: They are linear/slightly branched chains molecules capable of repeated softening on heating and hardening on cooling,e.g., polythene,PVC, polystrene, polypropene.

(iv) Thermosetting Plastics: They are cross-linked or heavily branched molecules, which on heating undergo extensive cross-linkages and become infusible, e.g., bakelite,urea formaldehyde resin.

(e) Based On Growth Of Polymerization: Depending upon the mechanism of Polymerization, polymers are classified as

(i) Addition Polymers Or Chain Growth Polymers:

They follow mostly free radical mechanism.

(ii) Condensation Polymers or Step Growth Polymers because they are formed in gradual steps.

Polymer

Monomer

Uses

(i) Polyethene

Ethene

Insulation of wires,

(ii) Polytetra

Fluroethene(Teflon)

Tetrafluoroethene

Oil seal and Gasket

(iii) Polyarcylonitrile

Acrylonitrile

Synthetic wool

(iv) Terylene or

Decron

Glycol + Terephthalic

Acid

Ropes, safety belts

(v) Nylon-6,6

Hexamethylenediamine +

Adipic acid

ropes,Parachutes,

(vi) Nylon-6

Caprolactum

Tyre-cords,

(vii) Novolac

Phenol + Formaldehyde

binding glue, laminated

(viii) Phenol

Formaldehyde resin

Formaldehyde + Phenol

Combs,records

(ix) Melamine

polymers

Melamine + Formaldehyde

unbreakable

crockery

(x) Buna-S

Copolymer

1,3-Butadiene + Styrene

Autotyres floor,

(xi) Natural rubber

2-methyl-1,3-butadiene

(Isoprene)

Used for tyres

(xii) Neoprene

2-chloro-1,3-butadiene

(chloroprene)

Conveyor belts

(xiii) Buma-N

1,3-butadiene + acrylonitrile

oil seals,tank linings

(xiv) (PHBV) poly-β hydroxybutyrateco-

β- hydroxyl valerate

(biodegradable)

3-hydroxybutanoic acid +

3-hydroxypantanoic acid

Packaging

(xv) Nylon-2-nylon-6

Glycine + aminocaproic acid

biodegradable step growth

Polymer

(xvi)Poly(glycolicacid)

Poly(lactic acid)

(dexton)

(biodegradable)

Glycolic acid + lactic acid

stitching wounds.

Biodegradables

 

  1. Natural elastomer.=>Natural rubber.
  2. Synthetic polymer which is an amide. =>Nylon 6 or Nylon 6,6.
  3. Write the monomer units of Bakelite.  =>  Phenol and formaldehyde.
  4.  Name of monomer of  Nylon 6.  => Aminocaproic acid
  5.  Copolymer.:   =>   The polymers made by addition polymerisation from two different   monomers are termed as copolymers, e.g., Buna-S, Buna-N, etc.
  6.  Write one use of PVC. => Manufacture of rain coats& vinyl flooring.
  7.  Give an example of thermoplastics.  => Polythene, polystyrene, polyvinyls
  8. Monomers  in terylene=> Ethylene glycol and terephthalic acid.
  9.  Role Sulphur in vulcanisation of rubber=> Slphur introduces sulphur bridges.So it is become more tensile strength,elasticity and resistance to abrasion etc.
  10. Arrange the following polymers in increasing order of their intermolecular forces.(i) Nylon 6,6, Buna-S, Polythene.(ii) Nylon 6, Neoprene, Polyvinyl chloride. Ans. (i) Buna-S  < Polythene<Nylon 6,6         (ii)Neoprene < Polyvinyl chloride< Nylon 6.
  11. Classify the following as addition and condensation polymers: Terylene, Bakelite,   Polyvinyl chloride,  Polythene. Ans. (i) addition polymers :Polyvinyl chloride, Polythene.        (ii) condensation polymers: Terylene , Bakelite.
  12.  What is a biodegradable polymer ? Give an example of a biodegradable aliphatic polyester.     Ans. Polymers which disintegrate by themselves over a period of time due to environmental degradation by bacteria,etc.are called biodegradable polymers. e.g. PHBV
  13. How can you differentiate between addition and condensation polymerization.  Ans. In addition polymerization the molecules of the same monomer or diferent monomers add together on a large scale to form a polymer. The monomers used are unsaturated compounds, e.g., alkenes, alkadienes and their derivatives.  Condensation  polymerisation generally involves a repetitive condensation reaction between two bi-functional monomers. These polycondensation reactions may result in the loss of some simple molecules as water, alcohol, etc., and lead to the formation of high molecular mass condensation polymers. e.g. , Nylon 6,6.
  14. What is meant by PTFE ?Give its popular name. Ans.Polytetrafluoroethylene.it is called Teflon.
  15. Write chemical name of (Ziegler-Natta catalyst).  Ans:   Triethylaluminium and titanium tetrachloride
  16. Write down the two differences between thermoplastic and thermosetting plastic and examples. Ans: Thermoplastic are the linear or slightly branched long chain molecules  capable of repeatedly softening on heating and hardening on cooling. These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres. Some common thermoplastics are polythene, polystyrene, polyvinyls, etc.  Thermosetting plastic polymers are cross linked or heavily branched molecules,which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins, etc.
  17. Differentiate Novolac and Bakelite on the basis of structure.  Ans: A linear product of Phenol - formaldehyde polymer is Novolac, used in paints. Novolac on heating with formaldehyde undergoes cross linking to form an infusible solid mass called bakelite. It is used for making combs, phonograph records, electrical switches and handles of various utensils.
  18.  Distinguish between the terms homopolymer and copolymer and give an example of each. Ans: the addition polymers formed by the polymerisation of a single monomeric species are known as homopolymers, e.g., polythene. The polymers made by addition polymerisation from two different monomers are termed as copolymers, e.g., Buna-S, Buna-N, etc.
  19. How will you differentiate between LDP and HDP?  Ans: Low density polythene: It is obtained by the polymerization of ethene under high pressure of 1000 to 2000 atmospheres at a temperature of 350 K to 570 K in the presence of traces of dioxygen or a peroxide initiator (catalyst). Low density polythene is chemically inert and tough but flexible and a poor conductor of electricity.e.g., squeeze bottles, toys and flexible pipes. High density polythene: It is formed when addition polymerisation of ethene takes place in a hydrocarbon solvent in the presence of a catalyst Ziegler-Natta catalyst at a temperature of 333 K to 343 K and under a pressure of 6-7 atmospheres. HDP  consists of linear molecules and has a high density due to close packing. It is more tougher and harder. It is used for manufacturing buckets, dustbins, bottles, pipes, etc.
  20. What is the main constituent of bubble gum?  Ans - Styrene  - butadiene copolymer (SBR).
  21. What is a plasticizer?  Ans; The substances which are added to increase the softness of hard  polymers.
  22. Draw the structures of the monomer of PAN.    Ans: CH2=CH-CN
  23. Give the name of polymer which is used for making non- stick utensils. Ans: Teflon(CF2=CF2)
  24. What is the % of sulphur using during in vulcanization of rubber ? Ans: 3% to  5%
  25. Give the common and the IUPAC name of the monomer of natural rubber.  Ans: cis-Isoprene  & 2-methyl-1,3-butadiene
  26. Discuss the two main purpose of  vulcanization of rubber. Ans: (i)It makes the rubber hard.       (ii)It is more elastic.        (iii)It has more wear and tear resistance.
  27. Why should one always use purest monomer in free radical polymerisation?        Ans: Impurities of other substances if present,may inhibit or hinder the chain  propagation.
  28. .How is dacron obtained from ethylene glycol and terephthalic acid?  Ans: It is the condensation product of ethylene glycol and terephthalic acid  Carried out at 420 to 460K in the presence of catalyst mixture of zinc acetate  and antimony trioxide.
  29.  Why is Bakelite a thermosetting polymer? Ans: It is a cross-linked polymer. On heating it sets permanently into a solid.It  can not be remoulded by heating again. A regular copolymer of ethylene and vinyl chloride contains alternate monomers of each type.What is the weight percent of ethylene in this copolymer?