Anionic polymerization of 4‐methyl‐2‐oxetanone (β‐butyrolactone)

Abstract

Polymerization of 4‐methyl‐2‐oxetanone (1) initiated with potassium acetate‐dibenzo‐18‐crown‐6 complex (2) in THF as solvent, was studied. Transfer reactions, leading to both crotonate anions and carboxylic acid formation, have been observed. Two kinetic effects of these reactions, hampering the living polymerization, have been established. The first results from reinitiation with the crotonate anions and thereby lowers the polymer molecular weight. The second is the decrease in the overall polymerization rate due to complexation of the growing carboxylate anions with carboxylic acid moieties. Kinetic scheme of polymerization involves propagation accompanied by transfer followed by slow reinitiation. This scheme, including complexation of the active species has been solved numerically. The apparent rate and equilibrium constants (kp, ktr, kri, and Kass and respectively) have been determined. Although these kinetic parameters depend strongly on the polymerization conditions, but the ratio of the rate constants kp : kt : kri is fairly constant and equal to 10−4 : 10−6 : 10−6, respectively (at 20°C). Conditions of the controlled anionic synthesis of the amorphous poly(4‐methyl‐2‐oxetanone) with \documentclass{article}\pagestyle{empty}\begin{document}$\bar M_n$\end{document} as high as 1.7 × 104 and \documentclass{article}\pagestyle{empty}\begin{document}${{ \le \bar M_n } \mathord{\left/ {\vphantom {{ \le \bar M_n } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} \le 1.20$\end{document} have also been elaborated.

Ring-Opening Polymerization of Lactones Initiated with Metal Hydroxide-Activated Macrocyclic Ligands: Determination of Mechanism and Structure of Polymers

“…Nucleophilic substitution with ring opening in alkyl-oxygen position and elimination of protonated base (with amines or phosphines [7] ) . Nucleophilic substitution with ring opening in alkyl-oxygen position (with potassium acetate- [8] or potassium benzoate-activated dibenzo-18C6 [7] ) . Nucleophilic substitution with ring opening in acyl-oxygen position (with potassium methoxide-activated 18C6 [9] ) .…”

“…[8] On the other hand, the only known method of anionic polymerization of e-caprolactone (e-CL) is nucleophilic substitution with ring opening in the acyl-oxygen position. The rate constant of proton abstraction (chain transfer to monomer) for b-BL was found to be relatively high compared to propagation.…”

Thermodynamics, Kinetics, and Mechanisms of Cyclic Esters Polymerization

“…Namely, kjk* = 4-10 4 for β-propiolactone (CH 2 C1 2 solvent, 20°C), and kp/K <; 2.0· 10 2 for β-butyrolactone (THF solvent, 20°C) propagation to transfer rate constants ratios were determined (29). Both electronic and steric effects of the methyl group are responsible for a lower value of the kp/k^ ratio in β-butyrolactone, when compared to β-propiolactone and this is at least partially because of the differences in the rate constants of propagation (4-10" 3 and 10" 6 mol'^L-s" 1 at 20°C in THF solvent, respectively).…”

Ring-opening copolymerization of (R,S)-β-butyrolactone and ε-caprolactone using sodium hydride as initiator

“…Therefore, several attempts to use a catalyst based on much less toxic metal compounds are being undertaken [2,6,11,[22][23][24][25][26][27]. The anionic polymerization of β-butyrolactone had been widely studied [27][28][29][30][31][32][33][34][35][36][37][38][39][40], and in general polymers with low molecular weight were obtained. Relatively low toxic alkali metal hydrides are among the initiators used for this purpose [27], nevertheless, they have not been used so far for the synthesis of copolymers of (R,S)-BL and CL.…”