Poly(3‐hydroxyoxetane)—an analog of poly(vinyl alcohol): Synthesis, characterization, and properties

Abstract

Abstract The spontaneous polymer formed from 3‐hydroxyoxetane (HO), as first reported by Wojtowicz and Polak, is linear, low molecular weight, water‐soluble, atactic, poly(3‐hydroxyoxetane) (PHO) of high crystallinity with OCH 2 CH(OH)CH 2 OH end units. The highly crystalline nature of this atactic polymer may be related to the crystalline nature of atactic poly(vinyl alcohol) since PHO can be considered a copolymer of vinyl alcohol and formaldehyde. Spontaneous PHO apparently is formed in a cationic polymerization by the carboxylic acids produced by the air oxidation of HO on standing at room temperature for several months. The polymerization can be duplicated by the addition of 2% hydroxyacetic acid to HO. The rate of this unusual cationic polymerization increases greatly with acid strength, e.g., trifluoromethanesulfonic acid reacts explosively with pure HO. A mechanism is proposed for this cationic polymerization. High molecular weight, water‐soluble, linear atactic, and highly crystalline PHO (mp = 155°C) was made by polymerizing the trimethylsilyl ether of HO with the i ‐Bu 3 Al–0.7 H 2 O cationic catalyst followed by hydrolysis. Two 1 H‐NMR methods for measuring the tacticity of PHO were developed based on finding two different types of methylene units at 400 MHz with the methine protons decoupled. Also, an 1 H‐NMR method was developed for measuring branching in HO polymers. High molecular weight, linear PHO with enhanced isotacticity (80%) has been obtained in low yield as a water‐insoluble fraction with T m = 223°C. The low molecular weight PHO prepared previously by the base‐catalyzed, rearrangement polymerization of glycidol is highly branched.