Studies in Ring Opening Polymerisation: the Interactions of Some Cyclic Esters with a Bimetallic Oxoalkoxide

Abstract

The ring opening reactions of some 1,3, 2-dioxathiolan-4-one 2-oxide (anhydrosulphites) and 1,3-dioxolan-2,4-diones (anhydrocarboxylates) in the presence of bimetallic oxoaikoxide have been studied. The synthesis and purification of these cyclic esters have followed established procedures which have been extended to include the use of a lithium salt. Similarly, the synthesis of the catalyst, a mixed metal oxoalkoxide, followed established methods end presented little difficulty. It has been found that the reactions involving anhydrosulphites yielded very limited amounts of α-ester oligomers, and their reactions were highly sensitive to the degree of substitution on the monomer ring. Reactions involving anhydrocarboxylates were more successful both in terms of α-ester formetion and extent of monomer decomposition. In both cases the reactions have been characterised by the separation of the reaction mixture into two layers, one gelatinous, the other liquid. It has been found that the separation of the reaction mixture and decrease in rate of reaction were parallel events. The kinetics of these reactions have been studied using gas evolution techniques and their products examined by infra red absorption spectroscopy and X-ray diffraction. G.P.C. studies were in general precluded by the lack of solubility of the reaction products in any suitable solvent. Possible mechanisms for the reactions have been considered. It is thought thet reaction proceeds via a four-centred mechanism involving the aluminium-oxygen bond in the catalyst. The mode of addition of the monomer is thought to be sensitive to the degree of substitution on the monomer ring as well as the size and nature of the ring. The present study thus represents the first in which the catalysed decomposition of esters of this kind has not involved an α-lactone intermediate. The studies involving glycollic acid anhydrocarboxylate have been extended to include decomposition in the presence of catalytic amounts of pyridine and also benzyl alcohol, and the results of the former study have been considered in the light of earlier similar studies involving other anhydrocarboxylates.