Copolymerization of acrylamide with sulphur dioxide. Determination of the effect of copolymerization temperature on the monomer sequence distribution by 13C n.m.r.

Abstract

Acrylamide was copolymèrized with sulphur dioxide at temperatures from −78° to 60°C. The bulk monomer composition was fixed at 60 mol % sulphur dioxide, and both azobisisobutyronitrile and 60Co gamma radiation were used as initiators. The ratio R of acrylamide to sulphur dioxide in the copolymers increased as the copolymerization temperature was raised; for example R was 1.97 at −78°C and 29.3 4at 60°C. The microstructure of the copolymers was determined by 13C-{ 1H} n.m.r. The carbonyl resonances were the most sensitive to structure, and they were assigned to monomer sequence pentads and configurational sequence dyads and triads. Only the backbone carbon resonance areas were quantitatively reliable under the observing conditions. The methine and methylene carbons revealed monomer sequence triad structure, and their relative areas allowed the monomer sequence distribution to be obtained as a function of temperature. A propagation-step mechanism was proposed to account for the effect of temperature on the monomer sequence distribution. No 1:1 alternating sequences were formed above 0°C, and this result suggested that depropagation of the sulphonyl radical was particularly facile when there was a pen-penultimate sulphone unit in the terminal chain sequence. The results were compared with those from other systems which form variable-composition polysulphones.