A method of determining the active centers in cationic polymerization, applied to polymerization of dioxolane, trioxane, and formaldehyde

Abstract

AbstractIn order to determine the concentration of active centers, polymerizations are terminated by addition of sodium alkoxide. This yields alkoxy endgroups which after acid hydrolysis of the isolated and purified polymers are determined by gaschromatography of the produced alcohol.In cationic polymerization of anhydrous formaldehyde at −78°C under certain reaction conditions a fast and quantitative initiation reaction and no kinetic chain termination have been observed. Presumably living polymers are obtained. The unexpected decrease in the rate of polymerization after a certain conversion is ascribed to hindrance of monomer diffusion in the crystalline polymer in which the active centers are imbedded.Cationic chainends have been detected in the 60Co γ‐ray induced polymerization of crystalline trioxane. This proves a cationic mechanism of chain propagation in the radiation‐induced polymerization of trioxane.In polymerization of 1.3‐dioxolane by HClO4 at 20°C a gradual but quantitative initiation reaction and no kinetic termination reaction have been observed. Termination by addition of alkoxide and determination of alkoxy endgroups also helped to distinguish between several different mechanisms of chain propagation proposed in the literature. It is assumed that the active center in dioxolane polymerization is a tertiary oxonium ion which propagates by an SN 2 reaction with monomer.