Studies in ring-chain polymerisation

The synthesis of anhydrosulphite and anhydrocarboxy derivatives of α-hydroxy acids has been examined together with the decomposition of these compounds by routes which lead to α-polyester formation. The products obtained from the direct reaction of thionyl chloride and several members of the α-hydroxy acid series have been isolated and identified. Possible reaction routes are discussed, together with the effect of α-hydroxy acid structure and reaction conditions on the relative yields of the products obtained. The polymerisation and related reactions of the enhydrosulphites have been studied kinetically using, principally, gas evolution techniques. Two distinct types of behaviour were observed, typified by the anhydrosulphites of lactic and α-hydroxy isobutyric acids. In the former case the anhydrosulphite ring is susceptible to direct attack by alcohols with resulting regeneration of the α-hydroxy group, this reaction forming the basis of a bimolecular propogation step which leads to polymer formation. α-Hydroxy isobutyric acid shows no such reaction, however, the rate of ring opening being kinetically independent of alcohol concentration. The polymerisation of this anhydrosulphite has been studied with the aid of radioactive tracer techniques. Both types of decomposition are discussed, together with the observed reluctance of anhydrocarboxy derivatives of α-hydroxy acids to form high molecular weight polyesters, in terms of ring structure and its effect on possible polymerisation mechanisms. The relationship of these compounds to others showing similar behaviour is also discussed