Copolymerization

In chemistry, copolymerization is the process of using more than one monomer in the production of a polymer, resulting in a product with properties different to the homopolymer of either monomer.

Copolymerization Equation

The Mayo-Lewis equation (also called the copolymerization equation) gives the molar ratios of the two monomers M₁ and M₂ in the resulting polymer as:

${\displaystyle {\frac {d\left[M_{1}\right]}{d\left[M_{2}\right]}}={\frac {\left[M_{1}\right]\left(r_{1}\left[M_{1}\right]+\left[M_{2}\right]\right)}{\left[M_{2}\right]\left(\left[M_{1}\right]+r_{2}\left[M_{2}\right]\right)}}}$ 

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 or k₂₁ are the rate constants for the reaction between the two different monomers.

In another form:

${\displaystyle F_{1}=1-F_{2}={\frac {r_{1}f_{1}^{2}+f_{1}f_{2}}{r_{1}f_{1}^{2}+2f_{1}f_{2}+r_{2}f_{2}^{2}}}}$ 

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)

Examples

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

See also

• Heteropolymer

References

1. Mayo, F. R., and Lewis, F. M., J. Am. Chem. Soc., 66, 1594 (1944).