Abstract
The polymerization of 5,5‐diethyl‐1,3,2‐dioxathiolan‐4‐one‐2‐oxide has been examined in various solvents at 60–100°C. Kinetic studies have shown that steric hindrance by the C~5~ ethyl substituents prevents the occurrence of a bimolecular propagation reaction involving direct attack by a terminal hydroxyl group on the ring. In dry, nonhydroxylic 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 sulfur dioxide eliminated. This intermediate, which is formally depicted as an α‐lactone, then takes part in a very rapid chain‐propagation process, the individual steps of which govern the molecular weight distribution of the polymer. The values of the activation energy (25–30 kcal/mole) and frequency factor (10^11^−10^13^ sec^−1^) for this polymerization reaction are, therefore, those associated with monomer decomposition and not the chain growth process. The molecular weight of the resultant polymer, poly‐(3‐pentylidene carboxylate) is controlled by adventitious traces of water which produce one carboxyl and one hydroxyl group per chain. Polymers having M̄~n~ ∼ 20,000 are readily obtained; these are materials of moderately high melting point (T~m~ ≃ 200°C) which crystallize from the melt into a banded spherulitic structure.