Synthesis of Bottlebrush Polymers by Z‑/E‑Specific Living Ring-Opening Metathesis Polymerization, Exhibiting Different Thermal Properties

Synthesis of bottlebrush polymers (BBPs) and block copolymers by Z-/E-specific living ring-opening metathesis polymerization (ROMP) of N-substituted-norbornene-2,3-dicarboximides containing long alkyl chains (n-octadecyl, n-tetradecyl, etc.) has been attained by the vanadium(V)–alkylidene catalysts V(CHSiMe₃)(ArN)[OC(CF₃)₃](PMe₃)₂ [Ar = 2,6-Cl₂C₆H₃ (1), C₆F₅ (2)] and V(CHSiMe₃)(2,6-F₂C₆H₃N)(OC₆Cl₅)(PMe₃)₂ (3). The ROMPs using 1 afforded the BBPs with exclusive Z selectivity (98 to >99% cis) even at high temperature (up to 80 °C) in the presence of PMe₃, whereas the ROMPs using 3 gave the BBPs with high E selectivity (90% trans). These ROMPs proceeded in a living manner (even at 80 °C using 1), affording various (amphiphilic) block copolymers while maintaining high E/Z selectivity. The resultant Z- and E-selective BBPs especially prepared from N-(n-octadecyl)norbornene-2,3-dicarboximide possessed different melting temperatures due to different degrees of interpolymer alkyl side chain interaction (side chain crystallization).