Abstract
Norbornene derivatives (NBEs) are the most common monomers for ring-opening metathesis polymerization (ROMP) because they undergo living polymerization, yielding polymers with low dispersities and diverse functionalities. However, the all-carbon backbone of polyNBEs cannot be degraded. Polymer degradation is highly desired for many applications and has been a major limitation in ROMP chemistry. Here, we report a simple yet powerful method to synthesize controlled, degradable polymers by copolymerizing 2,3-dihydrofuran (DHF) with NBEs. DHF rapidly reacts with the Grubbs catalyst to form a thermodynamically stable Ru Fischer carbene, which is the only detectable active Ru species during the copolymerization, and the addition of NBEs becomes rate determining. This unique Ru Fischer carbene reactivity attenuates NBE homoaddition, which presented a significant challenge to previous copolymerization approaches, allows even incorporation of DHF units (acid-degradable enol ether bonds) throughout the copolymers, and thus enables complete polymer degradation while maintaining the favorable characteristics of living ROMP. We demonstrate the effective copolymerization of DHF with several types of NBEs to synthesize narrow-disperse polymers with tunable solubility, glass transition temperature, and mechanical properties. These polymers can all be fully degraded into small molecule or oligomeric species under mildly acidic conditions. This method can be readily adapted to traditional ROMP of widely used NBEs to synthesize new degradable polymers with tunable properties and facile degradation for various applications and environmental sustainability.
Fischer carbene complexes of cobalt(I): synthesis and structure
