Steric bulk prevents the formation of strong bonds between Lewis acids and bases in frustrated Lewis pairs (FLPs), where latent reactivity makes these reagents transformative in small molecule activations and metal-free catalysis. However, their use as a platform for developing materials chemistry is unexplored. Here we report a fully macromolecular FLP, built from linear copolymers that containing either a sterically encumbered Lewis base or Lewis acid as a pendant functional group. The target functional copolymers were prepared by a controlled radical copolymerization of styrene with designer boron or phosphorus containing monomers. Mixtures of the B- and P-functionalized polystyrenes do not react, with the steric bulk of the functional monomers preventing the favorable Lewis acid base interaction. Addition of a small molecule (diethyl azodicarboxylate) promotes rapid network formation, cross-linking the reactive polymer chains. The resulting gel is dynamic, can self-heal, is heat responsive, and can be reshaped by postgelation processing.

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 polymerization of short-chain alkyl glycidyl ethers (SCAGEs) enables the synthesis of biocompatible polyethers with finely tunable hydrophilicity. Aliphatic polyethers, most prominently poly­(ethylene glycol) (PEG), are utilized in manifold biomedical applications due to their excellent biocompatibility and aqueous solubility. By incorporation of short hydrophobic side-chains at linear polyglycerol, control of aqueous solubility and the respective lower critical solution temperature (LCST) in aqueous solution is feasible. Concurrently, the chemically inert character in analogy to PEG is maintained, as no further functional groups are introduced at the polyether structure. Adjustment of the hydrophilicity and the thermoresponsive behavior of the resulting poly­(glycidyl ether)­s in a broad temperature range is achieved either by the combination of the different SCAGEs or with PEG as a hydrophilic block. Homopolymers of methyl and ethyl glycidyl ether (PGME, PEGE) are soluble in aqueous solution at room temperature. In contrast, n-propyl glycidyl ether and iso-propyl glycidyl ether lead to hydrophobic polyethers. The use of a variety of ring-opening polymerization techniques allows for controlled polymerization, while simultaneously determining the resulting microstructures. Atactic as well as isotactic polymers are accessible by utilization of the respective racemic or enantiomerically pure monomers. Polymer architectures varying from statistical copolymers, di- and triblock structures to star-shaped architectures, in combination with PEG, have been applied in various thermoresponsive hydrogel formulations or polymeric surface coatings for cell sheet engineering. Materials responding to stimuli are of increasing importance for “smart” biomedical systems, making thermoresponsive polyethers with short-alkyl ether side chains promising candidates for future biomaterials.

Dedicated to Brigitte Voit on the occasion of her 60th birthdayIn-depth understanding of copolymerization kinetics and the resulting polymer microstructure is crucial for the design of materials with well-defined properties. Further, insights regarding the impact of solvents on copolymerization kinetics allows for precisely tuned materials. In this regard, in situ 1 H NMR spectroscopy enables precise monitoring of the living anionic ring-opening copolymerization (AROP) of ethylene oxide (EO) with the glycidyl ethers allyl glycidyl ether (AGE) and ethoxy vinyl glycidyl ether (EVGE), respectively. Determination of reactivity ratios reveals slightly higher reactivity of both glycidyl ethers compared to EO, emphasizing a pronounced counterion chelation effect by glycidyl ethers in AROP. Implementation of density functional theory (DFT) calculations further illustrates the complexation capability of ether-containing side groups in glycidyl ethers, in analogy to crown ethers ("crown ether effect"). Investigation of the copolymerization in i) THF-d 8 and ii) DMSO-d 6 shows an increasing disparity of reactivity ratios for both glycidyl ethers compared to EO, clearly related to decreasing solvent polarity.

Statistical copolymers of linear glycerol (linG) and ethyl glycidyl ether (EGE) show tunable thermoresponsive behavior. The cloud point of the highly biocompatible copolymers is tailored by polymer composition and concentration.