Organocatalytic Alternating Copolymerization of Isothiocyanate and Trifluoropropylene Oxide: Fluorine-Enhanced...

Heteroatom incorporation is a general strategy toward advanced polymer properties. We report here efficient synthesis of polymers containing, site-specifically, at least four different heteroatoms (O, N, S, F) by copolymerization of isothiocyanate (ITC) and trifluoropropylene oxide (TFPO). Unlike the regular non-fluorinated epoxides for which Lewis pair catalysts are needed, the superior activity of TFPO allows the use of only organobases, even the relatively mild ones, to reach high/complete monomer conversion in hours at room temperature and low catalyst loadings (0.01-0.1 mol.%). With optimal initiator structure and monomer feed ratio (1/1), alternating copolymers, i.e. fluorinated polythioimidocarbonates (^FPTCs), with controlled molar mass and low dispersity are obtained. Copolymerization with alkyl and allyl ITCs are remarkably more chemoselective, which is ascribed to the alleviated nucleophilicity of the oxyanionic species and expedited S-to-O crossover. While thermostability of the aromatic PTC is evidently improved and adhesive strength unaffected by the CF₃ groups, depolymerization becomes much easier under basic conditions, selectively forming a five-membered cyclic thioimidocarbonate.