Synthesis of ABx and ABxC poly(ester-ether) polymers: polymer sequences and effects of Bx and BxC units on thermal properties

Abstract

Ring-opening copolymerization (ROCOP) of cyclic anhydrides and epoxides has been under intensive investigation as a potential alternative approach for synthesizing tunable polyesters due to a wide range of monomer scopes compared to those of conventional cyclic esters such as lactides or lactones. While most catalytic systems focus on the alternate insertions of cyclic anhydrides (A) and epoxides (B) giving alternating (AB)_n polyesters, the synthesis of AB_x poly(ester-ether) polymers having controllable B_x ether sequences has recently gained significant interest for potential tunable functions. Herein, an AB_x poly(ester-ether) with tunable ether linkages (x = 2.3–5.2) was synthesized conveniently from the ROCOP of cyclic anhydrides (succinic anhydride, phthalic anhydride, 1,8-naphthalic anhydride, terpene-based cyclic anhydride, maleic anhydride and diglycolic anhydride) and epoxides (cyclohexene oxide, cyclopentene oxide and propylene oxide) using commercially available tin(II) 2-ethylhexanoate (SnOct₂) as the catalyst. Exceptionally high purity of AB_x polymers up to 99% was achieved. Kinetic studies revealed the following rate law: rate = k_p[SA][CHO]²[SnOct₂]. The versatility of SnOct₂ was demonstrated and allowed the AB_x polymers to integrate with biodegradable polylactides and polyurethanes in one pot. THF or 1,4-dioxane (C) could be copolymerized as the third component in one pot giving a novel AB_xC poly(ester-ether) with the highest selectivity of up to 74% for THF and 11% for 1,4-dioxane. The presence of B_x or B_xC units was found to significantly accelerate the degradation rates of the polymers compared to conventional alternating (AB)_n polyesters.