Copolymerisation

polymer copolymerisation kinetics

1. COPOLYMERISATION PRESENTED BY , SHUBHAM PRASAD M.SC POLYMER SCIENCE

2. A  copolymer is a polymer formed when two (or more) different types of monomers are linked in the same polymer chain. Example :- nylon 66, polyurethane, PET etc. Copolymer :- Copolymerisation :- In copolymerisation , two or more monomers/monomer pair are polymerised simultaneously and hence the polymer is composed of more than one repeat unit. For example styrene –butadiene rubber (SBR) the firstly commercially made synthetic rubber . It is a copolymer obtained by free radical polymerisation of two monomer , styrene and butadiene.

3. Types of copolymer :- 1. Block copolymer :- Block copolymers consist of two or more strands (blocks) of different polymers chemically attached to each other . 2.Random copolymer :- It is  comprised of more than one kind of repeating unit, in which there is a   random distribution of repeating units. 3. Alternative copolymer :- Alternating  copolymer. are composed of two monomers that alternate   in sequence in the  polymer chain . In an alternating  copolymerization the two monomers M 1  or M 2  are unable to hompolymerize but do copolymerize .

4. 4. Graft copolymer :-   I t is a type of copolymer in which one or more blocks of homopolymer are grafted as branches onto a main chain, meaning it is a branched copolymer with one or more side chains of a homopolymer attached to the backbone of the main chain.

5. Free radical copolymerisation kinetics :- Step 1:-Initiation :-the free radical formed can attack M 1 Or M 2 Step 2 :- propagation

6. Now rate of all four types of propagation :- The basic assumption is that the reactivity of any growing chain depends only on the end monomer unit carrying the free- radicals site not in the no. of monomer units already added to the chain. The rate at monomer M 1 and M 2 are consumed during the course of propagation can be expressed as follows :-

7. Now , assuming a steady state wherein the rate of a particular chain end disappearing is equal to the rate of formation of the same chain end .

8. Combine the all equation

9. The copolymer formed depends on the monomer concentration and their reactivity ratios . Mole fraction of monomer present in copolymer and mole fraction of monomer feed n 1 and n 2 are the mole fraction of monomer M 1 and M 2 respectively , in the copolymer formed . N 1 and N 2 are the mole fraction of the monomer M 1 and M 2 respectively , in the monomer feed .

10. Copolymer equation 1.Mayo lewis method Where , denoted M 1 / M 2 by M , molar concentration ratio the monomer in the feed Denoted m 1 / m 2 by P , molar concentration ratio the monomeric components in the polymer

11. 2.Fineman –ross method :- Fineman ross equation

12. Reactive ratios and copolymerisation behaviour:- When r 1 = r 2 =0 In this case the propagation types 11 and 22 are not possible and hence , a chain ending with M 1 will add only an M 2 and M 2 will add only M 1 and formed alternative compolymer . b) When r 1 = r 2 =1 In this case , all four types of propagation reaction are equally possible . This is ideal copolymerisation and formed random copolymer . c) When r 1 ˃1 and r 2 ˂ 1 in this case , the propagation reaction type 11 and 21 will be preffered to types 12 and 22 and hence , M 1 entering into the copolymer chain is higher as compared to M 2 When r 1 ˂ 1 and r 2 ˃ 1 the copolymer formed will , therefore , be richer in M 2 . e) When r 1 ˃ 1 and r 2 ˃ 1 Such a system does not usually undergo random copolymerisation it form either mixture of two homopolymer or unde r Certain condition , block copolymer having long sequence of M 1 followed by a long sequence of M 2 .

13. Q-e scheme of alfery and price :- The method deals with the resosance stabilisation and polarisation characteristics of a monomer and predicts its reactivity behaviour wit reference to another monomer radical. Assuming that a monomer M 2 adds on to a radical M 1 the rate constant for the propagation reaction . Where , P 1 denotes a factor charactersing the state of the radical M 1 at the growing chain end Q2 indicates the resonance stability and hence the measure of the reactivity of the monomer M 2 e 1 and e 2 is polarisation characteristics of monomer M 1 and M 2 Similarly ,

14. We know r 1 = k 11 / k 12 Q-e scheme suggest Monomers with widely differing Q value do not co polymerise Monomer having widely differing e value have tendency to form alternating copolymers Monomers having roughly equal Q value and almost identical e value will undergo azeotropic copolymerisation .

15. Ionic copolymerisation :- Ionic copolymerisation is same as free radical coplymerisation but reactivity is different as free radical copolymerisation because the reactivity ratio in free radical copolymerisation is dependent on temperature and monomers but while in ionic coploymerisation they are dependent not only on the monomer pair but also on the solvent and the initiator system used and also very much dependent on polarity of the polymerisation system . Free radical polymerisation using benzoyl peroxide yield a copolymer containing roughly 50% styrene. Cationic polymerisation initiated by borontrifluoride etherate copolymer containing more than 95% styrene . Anionic polymerisation with triphenly methyl sodium result in a copolymer having less than 5% styrene .

16. Thank you