Functionalized cyclic olefin copolymers: chemoselective polymerization of a cyclopropane-containing norbornadiene dimer using a titanium catalyst and post-polymerization modification

Abstract

The synthesis of functionalized polyolefins is important for tuning their properties and expanding their application range. However, the copolymerization of olefins with polar monomers using early transition-metal catalysts remains a formidable challenge. Here, we demonstrate a synthesis strategy through the Ti-catalyzed addition polymerization of a cyclopropane-containing norbornadiene dimer (1), followed by post-polymerization modification (PPM). The polymerization of 1 using a constrained-geometry Ti catalyst afforded poly1 with narrow molecular weight distributions (Đ < 1.3), wherein the molecular weight increased linearly with the monomer conversion. Additionally, the copolymerization of 1 with 1-octene proceeded rapidly, and 1 was consumed faster than 1-octene to form gradient copolymers. The ¹³C nuclear magnetic resonance (NMR) spectroscopic analysis of the polymers indicated that the coordination–insertion of the alkenyl group of 1 occurred selectively without side reactions at the cyclopropane moiety. The polymerizations were highly controlled and chemoselective owing to the lack of cyclopropane coordination to the active Ti species involved in the polymerization. The PPM of poly(1-co-1-octene) via the protic acid-catalyzed ring-opening reaction of the cyclopropane introduced aromatic, acyloxyl, and alkoxy groups in high incorporation ratios without cross-linking reactions. Thus, this work demonstrates a promising procedure for the modification of cyclic olefin copolymers using specific cyclopropane reactivity.