Polymer Chemistry 4. On the basis of their reactivity ratios (Table 6-5 below),
ID: 964909 • Letter: P
Question
Polymer Chemistry 4. On the basis of their reactivity ratios (Table 6-5 below), predict what types of microstruo- tures (e.g., tendency to alternating, tendency to blocky) you would expect in a free radical copolymerization of the following monomer pairs: (A) acrylamide and acrylonitrile (B) ethylene and methyl acrylate (C) 1,3-butadiene and vinyl stearate (vinyl octadecanoate) (D) chlorotrifluoroethylene and ethyl vinyl ether. (E) styrene/butadiene Assume equimolar concentrations of monomer and also assume you are only examining copolymers produced in the ini tial stages of the reaction.Explanation / Answer
explanation-
A)r1 r2*=1.04*0.94=0.98 =1 (ideal copolymerization)
B)r1*r2=0.2*11=2.2>1(block copolymerization)
C)r1*r2=34.5*0.034=1.2>1 (block copolymerization)
D)r1*r2=0.008*0=0(alternating copolymerization)
E)r1*r2=0.58*1.35=0.9=1 (ideal copolymerization)
Explanation
Copolymerizations are of three types based on the product of the monomer’s reactivity ratios
r 1 r2= unity, < unity, or > than unity.
(K11)
1) M1* +M1M1*
2) (K12)
M1* +M2M2*
3) (K21)
M2* +M1M1*
4) (K22)
M2* +M2M2*
a)Ideal Copolymerization: r1 r2=1 .In Ideal copolymerization the two types of propagating species M1* and M2* show the similar preference for copolymer composition adding any one or the other of the two monomers.
b) Alternating copolymerization, r1 r2= 0, r1 nor r2 are not greater than one.
Two types of alternating behavior—extreme and moderate .In extreme,both r1 and r2 are zero .In this type,the propagating species preferentially adds the other monomer, that is, M1* adds only M2 and M2*adds only M1 .
c)Block Copolymerization: r1>1;r2>1
If both r1 and r2are > than unity (and therefore, also r1r2>1 there is a tendency to form a block copolymer –There exist blocks of both monomers in the chain.