# Alternating polymer

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):

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

where r1 = k11/k12 & r2 = k22/k21

## 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.

## References

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