Polymer effect on electron-donating character of polymeric donor. I. Formation of charge-transfer complex between polymers containing N,N-dimethylaniline group and maleic anhydride

The difference in electron-donating character between polymeric and monomeric donors in their charge-transfer-complex formation reactions was studied to clarify the so-called polymer effect in such reactions. Systems containing maleic anhydride and copolymers of N,N-dimethyl-p-aminostyrene (ASt) with styrene, which were prepared by a conventional free-radical polymerization technique, were found to be suitable for this purpose. In correlations between the mean sequence length μ_ASt of the ASt units in the copolymers and the lowest energy of their charge-transfer transition (λ_max) or the association constant of their complex formation K_CT, a bathochromic shift in λ_max and an increase in K_CT with increasing μ_ASt of copolymers are found. Moreover, there is a difference in their modes of μ_ASt dependence. It was concluded from these results that the electron-donating character of the dimethylaniline group increases with increasing number of groups attached on one polymer chain. Also, there is an interaction among neighboring functional groups on one polymer chain. The interaction may be regarded as a kind of polymer effect. In addition, the difference in μ_ASt dependence between λ_max and K_CT and also thermodynamics of the complex formation are discussed.