Unexpected Random Copolymerization of Propylene Oxide with Glycidyl Methyl Ether via Double Metal Cyanide Catalysis: Introducing Polarity in Polypropylene Oxide

Abstract

The synthesis of amorphous, polar aliphatic polyethers based on the copolymerization of propylene oxide (PO) and glycidyl methyl ether (GME) is described. Copolymers with M n of 1.9−4.5 kg mol −1 , with moderate to low dispersities (D̵ < 1.29) and up to 45 mol % GME content, were obtained via double metal cyanide (DMC) catalysis. An in-depth investigation of the solvent-free copolymerization was conducted by pressure monitoring, in situ 1 H NMR spectroscopy, and 13 C NMR triad analysis. Surprisingly, the results reveal an almost ideally random copolymerization of both epoxides (r PO = 1.40 ± 0.01, r GME = 0.71 ± 0.01). This observation is in pronounced contrast to the well-known preferential incorporation and generally high reactivity of PO in DMC catalysis in comparison to other epoxide monomers as well as the considerably lower reactivity of PO in the anionic ring-opening polymerization compared to glycidyl ethers. The reactivity ratios were evaluated at both 60 and 80 °C, demonstrating the reproducibility of the utilized solvent-free in situ measurement, showing also the temperature independence of the reactivity ratios within this range. Supplementary 13 C NMR triad analysis further supports an almost ideally random copolymerization, confirming an evenly distributed incorporation of polar GME units in the hydrophobic PPO backbone. Turbidimetric measurements demonstrate tunable thermoresponsive behavior and hydrophilicity of the synthesized copolymers with lower critical solution temperatures between 19 and 35 °C. Furthermore, the increase of hydrophilicity is illustrated by contact angle measurements. The random copolymerization of PO and GME by DMC catalysis renders the resulting flexible polyethers an alternative to established ethylene oxide/PO copolymers for flexible polyol components in soft polyurethane foams.

Polyethers Based on Short-Chain Alkyl Glycidyl Ethers: Thermoresponsive and Highly Biocompatible Materials

“…Herein, GME was utilized as a polar but easier and safer to handle alternative to EO, therefore significantly increasing the polarity of such polycarbonates. Recently, our group further capitalized on the aqueous solubility of GME in copolymerization with PO by catalytic copolymerization, using the industrially highly established double metal cyanide (DMC) catalyst (Figure d) . This resulted in polyether copolymers with LCST controlled by the PO content.…”

“…A number of P­(GME- co -EO) copolymers were examined by 13 C NMR triad analysis, revealing preferred incorporation of ethylene glycol units throughout the copolymerization . Explorations concerning the copolymerizations of GME with PO catalyzed by the industrially established double metal cyanide (DMC) catalyst resulted in slight gradient microstructures ( r GME = 0.71, r PO = 1.40, Jaacks) …”

“…In contrast to the reduction of T cp in highly polar polyethers, the incorporation of GME was used to increase the hydrophilicity of otherwise nonsoluble PPO in aqueous solution. The increase resulted in a T cp of 35 °C in random P­(PO- co -GME) copolymers, which is promising for the medical applications in the physiological temperature range . However, in this context the use of DMC catalyst with particles remaining in the polymer may represent a disadvantage considering medical or pharmaceutical applications.…”

“…Recently, our group further capitalized on the aqueous solubility of GME in copolymerization with PO by catalytic copolymerization, using the industrially highly established double metal cyanide (DMC) catalyst (Figure 7d). 105 This resulted in polyether copolymers with LCST controlled by the PO content. The polymerization methods and the specific conditions enabling the preparation of P(SCAGE) are summarized in Figure 8.…”

Borinane Boosted Bifunctional Organocatalysts for Ultrafast Ring-Opening Polymerization of Cyclic Ethers

“…Aluminum-based Vandenberg's catalyst 10 which implies monomer coordination before insertion affords high molar mass PPO but the polymerization is not well controlled. Even zinc/cobalt double metal cyanide (DMC) 11,12,13,14,15 catalyst which is employed for PPO production in industry is not without drawbacks such as long induction time, speci c equipment to meet harsh polymerization conditions (high temperature and pressure build-up during polymerization), high molar mass impurities (100-400 kg/mol), necessity of speci c chain transfer agents (CTAs), and unsuitability for ROP of EO. Other outstanding metallic catalysts have been specially designed for the synthesis of PPO by Coates 16,17,18,19 and De eux, 20,21,22,23 respectively.…”