N-Butyl acrylate zwitterionomers of the ammonioethoxydicyanoethenolate type: 1. Synthesis

Abstract

Radical copolymerization of n-butyl acrylate (A) and 2,2-dicyano-1-[2-(2-(acryloyloxy)ethyl)dimethyl-ammonioethoxy] ethenolate (B) initiated at 60°C by 4,4′-azobis-4-cyanovaleric acid (ACVA) was studied in two complementary systems: homogeneous phase in dimethylformamide (DMF) and heterogeneous phase in aqueous ethanol (water volume fraction 0.4). In DMF ([A + B] ∼ 0.6–1 moll −1, [ ACVA] [ A + B] = 5 × 10 −3 , molar fraction of monomer B in the comonomer feed f B ≤ 0.7), the copolymerization obeys the terminal unit model and the two monomers of identical acrylate structure behave as an ideal azeotropic comonomer pair: reactivity ratios r A ∼ r B ∼ 1. In aqueous ethanol ([A + B] ∼ 0.6–2 moll −1, [ ACVA] [ A + B] = 5 × 10 −3 , f B ≤ 0.8), the unusual composition diagram (apparent reactivity ratios r A, r B > 1) probably results from preferential sorption of either monomer by the insoluble growing macroradicals: the experimental data may be reconciled with the terminal unit model and with invariant ‘intrinsic’ reactivity ratios ( r A ∼ r B ∼ 1) within the simplified framework that stresses the major importance of the ratio of the binding constants of monomers A and B to the growing chain ( K = k AA k BB ∼ 0.49 ). Moreover, copolymerization in heterogeneous phase leads to higher molecular weights. The zwitterionic units significantly increase the copolymer chain sensitivity towards thermal degradation: an irreversible and rather slow first-order rearrangement of the zwitterionic structure occurs for temperatures higher than 150°C ( K ∼ 2.8 × 10 −6 s −1 at 160°C), well before the initial weight loss observed at about 260°C under nitrogen.