Some Aspects of the Synthesis and Polymerisation of 1,3,2-Dioxathiolan -4-one-2-Oxides

Abstract

A number of 1,3,2-dioxathiolan-4-one-2-oxides (a -hydroxy carboxylic acid anhydrosulphites) have been prepared from disubstituted a, ~-hydroxy-carboxylic acids and from a-hydroxy-carboxylic acids. The thermal polymerisation of these compounds has been studied in a variety of solvents below 130°. All of the derivatives show a general pattern of kinetic behaviour. In dry non-hydroxylic solvents the first order rate determining step in the sequence of reactions leading to polymer formation is a primary ring scission reaction in which a reactive intermediate is formed and sulphur dioxide eliminated. This intermediate,which is formally depicted as an a-lactone, then takes part in a very rapid chain propagation process, the individual steps of which govern the molecular weight distribution of the polymer. Molecular weights of the polymers are controlled by adventitious traces of water and chlorinated by-products. The latter can be removed by a suitable combination of purification procedures ‘such that in some cases a desirable level of monomer purity is reached. An unusual feature of this polymerisation is the effect of ring substitution on the rate of polymerisation. In the dialkyl series the rate of polymer formation increases with increasing substituent Size, whilst in the Spirocycloalkyl series an additional substituent effect, conveyed ring strain, causes the cyclobutane derivative to decompose most rapidly. This compound deviates from the general reaction pattern in that the six membered glycollide as well as polymer is a principal product. In addition a bimolecular hydroxyl initiated decomposition is observed to occur. An additional feature is the onset of o first order fragmentation reaction which leads to carbon monoxide, sulphur dioxide and ketone formation. However, this reaction is not significant until temperatures in excess of 150°. Several novel poly a-esters have been prepared and their crystalline anu therm2l behaviour briefly examined.