Statistical Copolymerization of Epoxides and Lactones to High Molecular Weight

Abstract

Copolymerization provides a modular strategy for compositional control of structure−property relationships in polymeric materials. However, this versatility is typically limited to structurally homologous comonomers. To further expand the scope of copolymerization in heterocyclic systems, we explored the copolymerization of structurally distinct lactones and epoxides utilizing the classical Vandenberg catalyst. Copolymerizations were conducted between monomer pairs selected from among two common lactones (DL-lactide, ε-caprolactone) and four epoxides (epichlorohydrin, butylene oxide, propylene oxide, ethylene oxide). The resultant materials had molecular weights of up to 16 Mg/mol. Reactivity ratios were determined for the copolymerization of DL-lactide and propylene oxide, which were consistent with a gradient copolymer with propylene oxide (PO) being the preferred monomer: r PO = 2.81 ± 0.27 and r LA = 0.36 ± 0.02. The copolymerization between ε-caprolactone and propylene oxide was also monitored by 1 H NMR spectroscopy. A greater preference for propylene oxide was evident, but incomplete consumption of the ε-caprolactone under these reaction conditions complicated determination of reactivity ratios. Meyer−Lowry analysis of the time-dependent compositional data provided estimates of r PO = 2.17 ± 0.04 and r CL = 0.08 ± 0.01. Distinct ester−ether dyad signals were observed in the 1 H NMR spectra of the copolymers, and thermal properties of the copolymers were distinct from those of the respective pure homopolymers. The expected hydrolytic degradability of poly[(DLlactide)-co-(ethylene oxide)] was demonstrated under neutral and basic conditions.

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…The copolymerization of aliphatic lactones and epoxides may lead to the formation of copolymers (block/random/gradient) but rarely yields alternating copolymers selectively [113–115] . In contrast, the semi‐aromatic lactone DHC does not undergo ring‐opening polymerisation because of its low ring strain and chain‐end reactivity (Figure 18).…”

The versatile, functional polyether, polyepichlorohydrin: History, synthesis, and applications

“…In 2017, Chwatko and Lynd demonstrated the homopolymerization of lactones and the statistical copolymerization of lactones and epoxides, including ECH. 31 While the Vandenberg catalyst defined the synthesis of PECH at the time, there are still a few drawbacks to this synthetic method. Epoxide polymerizations with Vandenberg's catalyst are marked by limited control over M n and Đ; Polymers are always high molecular weight (M n > 10 6 g/mol) and generally high dispersity (Đ > 2).…”

Heterocycle/Heteroallene Ring‐Opening Copolymerization: Selective Catalysis Delivering Alternating Copolymers

“…Thec opolymerization of aliphatic lactones and epoxides may lead to the formation of copolymers (block/random/ gradient) but rarely yields alternating copolymers selectively. [113][114][115] In contrast, the semi-aromatic lactone DHC does not undergo ring-opening polymerisation because of its low ring strain and chain-end reactivity (Figure 18). One way to overcome this barrier would be if DHC were ring-opened by an alkoxide chain end, such as that derived from epoxide ring opening.…”