Copolymerization

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In chemistry, copolymerization is the process of using more than one monomer to produce a copolymer, which will possess properties different to the homopolymer of either monomer. The resulting product may be a random copolymer, an alternating copolymer, or a block copolymer. In the copolymerization between two monomers, M1 and M2, the following reactions may occur:

~~M1* + M1 --> ~~M1M1* (rate constant = k11)
~~M1* + M2 --> ~~M1M2* (rate constant = k12)
~~M2* + M1 --> ~~M2M1* (rate constant = k21)
~~M2* + M2 --> ~~M2M2* (rate constant = k22)

Contents

[edit] Copolymerization Equation

The Mayo–Lewis equation[1] (also called the copolymerization equation) gives the molar ratios of the two monomers in the resulting copolymer as:

\frac {d\left [M_1 \right ]}{d\left [M_2\right ]}=\frac{\left [M_1\right ]\left (r_1\left[M_1\right ]+\left [M_2\right ]\right)}{\left [M_2\right ]\left (\left [M_1\right ]+r_2\left [M_2\right ]\right)}

where r1 and r2 are the reactivity ratios of the individual monomers and r1 = k11/k12 & r2 = k22/k21, i.e. r = the rate of reaction with another monomer of itself / the rate of reaction with a different monomer. r is also called the copolymerization parameter.

k11 and k22 are the rate constants for the homopolymerization of the two monomers. k12 and k21 are the rate constants for the reaction between the two different monomers.

In another form:

F_1=1-F_2=\frac{r_1 f_1^2+f_1 f_2}{r_1 f_1^2+2f_1 f_2+r_2f_2^2}

where F1, F2 are the mole fractions of monomers M1, M2 in copolymer:

F1=1-F2=d[M1]/(d[M1]+d[M2])

and f1, f2 are the mole fractions of monomers M1, M2 in the feed:

f1=1-f2=M1/(M1+M2)

When the copolymer composition has the same composition as the feed, this composition is called the azeotrope.

[edit] Effect of Reactivity Ratios

-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A- (r1 = ∞)
-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B- (r2 = ∞)
  • Random copolymer (or statistical copolymer): favored when r1, r2 close to 1.
-A-A-B-B-A-A-A-B-A-A-B-B-A-B-A-A-A-B-A-A-A-B-B-
-A-B-A-B-A-B-A-B-A-B-A-B-A-B-, or -(-A-B-)n-
-A-A-A-A-A-A-A-B-B-B-B-B-B-B-A-A-A-A-A-A-A-B-B-...

[edit] Examples

acrylonitrile butadiene styrene (ABS) plastic, styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), P(VDF-TrFE).

[edit] External links

[edit] Further reading

  • Odian, G. Principles of Polymerization, 4th Ed., Wiley-Interscience, Hoboken, NJ 2004, Ch. 6. ISBN 0-471-27400-3

[edit] References

  1. ^ Mayo, F. R., and Lewis, F. M., J. Am. Chem. Soc., 66, 1594 (1944). DOI:10.1021/ja01237a052
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