Mechanisms of cationic polymerizations of lactones

Abstract

AbstractIt is demonstrated by means of 1H NMR spectra in combination with IR spectra that the reaction of δ‐valerolactone with an alkylating reagent results in alkylation of the exocyclic oxygen. The propagation of the resulting cyclic dioxocarbenium ion involves cleavage of the alkyl‐oxygen bond. Initiation and propagation mechanisms induced by Lewis acids such as boron bromide, aluminum bromide, titanium(IV) and zirconium (IV) bromide, tin(IV) bromide and zinc bromide are discussed. It is demonstrated by means of IR and NMR spectroscopy that complexation of the lactones at the exocyclic oxygen is followed by cleavage of the alkyl‐oxygen bond and halogen transfer, so that ω‐bromocarboxylic acids are obtained (after hydrolytic work up). In the case of aluminum, tin and zinc the intermediately formed metal‐oxygen bond initiates rapid polymerization via a nonionic insertion mechanism which is characterized by cleavage of the acyl‐oxygen bond.