An investigation of the copolymerization of EO and PO by in situ1H NMR spectroscopy reveals striking differences in the monomer gradient, depending on the polymerization method.

No abstract

Herein, we demonstrate the application of adducts of various N‐heterocyclic carbenes (NHCs) with CO2 (i.e., NHC–CO2) as precatalysts in the ring‐opening homopolymerization of propylene oxide (PO) onto diethylene glycol as a chain starter to give well‐defined polyether diols. The influence of various NHCs on the structure of the polymers and the mechanism of this reaction were investigated both experimentally and through DFT calculations. With this methodology, copolymers of PO and the monomers ε‐caprolactone and (S,S)‐lactide are accessible.

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.

The combination of hydrophobic polydimethylsiloxane (PDMS) blocks with hydrophilic polyether segments plays a key role for silicone surfactants. Capitalizing on the double metal cyanide (DMC) catalyst, the direct (i.e., statistical) copolymerization of cyclic siloxanes and epoxides is shown to be feasible. The solvent‐free one‐pot copolymerization of hexamethylcyclotrisiloxane and propylene oxide results in the formation of gradient propylene oxide (PPO)‐PDMS copolymers. Copolymers with up to 46% siloxane content with low dispersities (Р< 1.2) are obtained in the molecular weight range of 2100–2900 g mol–1. The polymerization kinetics are investigated by pressure monitoring and in situ 1H and in situ 29Si NMR spectroscopy. Contact angle measurements reveal the impact of siloxane incorporation manifest in strongly increased hydrophobicity of PPO‐PDMS copolymers and a glass transition of −95 °C for 46% SiO content. This unusual copolymerization offers promise for the synthesis of silicone/polyether polyols.