Studies in cyclocopolymerization. IV. Evidence of charge‐transfer complexes as intermediates in cyclocopolymerization of 1,4‐dienes with alkenes

Charge‐transfer complexes in solutions of comonomers such as divinyl ether and maleic anhydride have been identified by use of ultraviolet spectroscopy. Equilibrium constants and molar extinction coefficients were determined for several of these complexes. It appears reasonable that the cyclic units formed in these copolymers result from free‐radical initiation of the charge‐transfer complex, which preorients the comonomers into a conformation favorable for formation of copolymer in the observed comonomer ratio of 1:2. Copolymers prepared and studied were those of divinyl ether with N‐substituted maleimides having the following substituents on nitrogen: (a) hydrogen, (b) methyl, (c) ethyl, (d) n‐propyl, (e) isopropyl (f) n‐butyl, (g) isobutyl, (h) benzyl, (i) α‐naphthyl, (j) phenyl, (k) p‐methoxyphenyl. These copolymers were characterized by elemental analyses to establish the comonomer ratios and by viscosity measurements and in certain instances by determination of molecular weights by the vapor‐pressure osmometry method. The copolymer of divinyl ether and maleic anhydride has been found to be an effective antitumor agent by the Cancer Chemotherapy National Service Center, National Institutes of Health. Consequently, these copolymers were also submitted for evaluation in this program, and several have been found to possess favorable inhibiting action on tumor growth.