N-BUTYL ACRYLATE ZWITTERIONOMERS OF THE AMMONIOETHOXYDICYANOETHENOLATE TYPE .1. SYNTHESIS

Radical copolymerization of n-butyl acrylate (A) and -1-[2-(2-(acryloy loxy)ethyl)dimethylammonioethoxy] ethenolate (B) initiated at 60-degre es-C by 4,4'-azobis-4-cyanovaleric acid (ACVA) was studied in two comp lementary systems: homogenous phase in dimethylformamide (DMF) and het erogeneous phase in aqueous ethanol (water volume fraction 0.4). In DM F ([A + B] approximately 0.6-1 mol 1(-1), [ACVA]/[A + B] = 5 x 10(-3), molar fraction of monomer B in the comonomer feed f(B) less-than-or-e qual-to 0.7), the copolymerization obeys the terminal unit model and t he two monomers of identical acrylate structure behave as an ideal aze otropic comonomer pair: reactivity ratios r(A) approximately r(B) appr oximately 1. In aqueous ethanol ([A + B] approximately 0.6-2 mol 1(-1) , [ACVA]/[A + B] = 5 x 10(-3), f(B) less-than-or-equal-to 0.8), the un usual composition diagram (apparent reactivity ratios r(A), r(B) > 1) probably results from preferential sorption of either monomer by the i nsoluble growing macroradicals: the experimental data may be reconcile d with the terminal unit model and with invariant 'intrinsic' reactivi ty ratios (r(A) approximately r(B) approximately 1) within the simplif ied framework that stresses the major importance of the ratio of the b inding constants of monomers A and B to the growing chain (K = k(AA)/k (BB) approximately 0.49). Moreover, copolymerization in heterogeneous phase leads to higher molecular weights. The zwitterionic units signif icantly increase the copolymer chain sensitivity towards thermal degra dation: an irreversible and rather slow first-order rearrangement of t he zwitterionic structure occurs for temperatures higher than 150-degr ees-C (K approximately 2.8 x 10(-6) s-1 at 160-degrees-C), well before the initial weight loss observed at about 260-degrees-C under nitroge n.