Ring-expansion metathesis polymerization of cycloolefins to highly pure cyclic polymers

Abstract

The means to produce cyclic polymers in high purity and at large scale remains an elusive goal. Although ring-closure methods have been successful in producing rings free of linear chains, scalability is an unavoidable obstacle. We report a ring-expansion method for synthesizing cyclic polyalkenamers in high purity and at scale ( > 25 g / reaction) using a recyclable heterogeneous ruthenium-based olefin metathesis catalyst. This ring-expansion metathesis polymn. (REMP) catalyst is an analog of the 2nd Generation Hoveyda-Grubbs catalyst and is covalently bound to a silica surface via dual tethers from the N-heterocyclic carbene (NHC) and benzylidene. Cyclic polyalkenamers were synthesized from a variety of cycloolefins, including cyclopentene and cyclooctadiene. Their purity from linear species was detd. using rheol., hightemp. HPLC (HT-HPLC), solid-state NMR, size-exclusion chromatog. (SEC), and differentional scanning calorimetry (DSC). This synthetic methodol. was shown to be a robust means to produce cyclic polymers in high purity and at large scale.