Effect of nonterminal monomer units on the reactivity of polymeric free radicals

Certain abnormalities in the compositional relationship of styrene/maleic anhydride copolymers indicate that nonterminal monomer units in a polymer radical (principally the penultimate unit) can detectably influence radical reactivity, through electrostatic interactions with reacting monomer molecules. This effect should be particularly pronounced for monomers of type CHXCHX, where X is a dipole. Several examples from the literature are cited to show that abnormal dependences of copolymer composition on monomer concentration ratio can be explained along these lines. It is suggested that the recently observed variation of cross‐termination velocity coefficients with composition of the monomer mixture is attributable to a similar cause.