Alternating polymer

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Alternating copolymers are polymers which have properities intermediate to those of the corresponding homopolymers A and B. The alternating copolymer has the formula: -A-B-A-B-A-B-A-B-A-B-, or -(-A-B-)_n-. The molar ratios of the monomer in the polymer is close to one, which happens when the reactivity ratios r₁ & r₂ are close to zero, as given by the Mayo-Lewis equation (also called the copolymerization equation):

<math>\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)}</math>

where r₁ = k₁₁/k₁₂ & r₂ = k₂₂/k₂₁

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Example

An example is maleic anhydride and stilbene, with reactivity ratio:

Maleic anhydride (r₁=0.08) & cis-stilbene (r₂=0.07)
Maleic anhydride (r₁=0.03) & trans-stilbene (r₂=0.03)

Both of these compounds do not homopolymerize (i.e. k₁₁ and k₂₂ are close to zero). Instead, they react together to give exclusively alternating copolymer.

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