Enantiopure Isotactic PCHC Synthesized by Ring-Opening Polymerization of Cyclohexene Carbonate

The ring-opening polymerization (ROP) of racemic trans-cyclohexene carbonate (rac-CHC) and enantiopure trans-(R,R)-CHC is successfully carried out with various catalyst systems. Poly(cyclohexene carbonate) (PCHC) with a slight isotactic bias (P-m = ca. 60-76%) is obtained by ROP of rac-CHC catalyzed by zinc diaminophenolate, zinc beta-diketiminate, yttrium bis(phenolate), or 1,5,7-triazabicydo[4.4.0]clec-5-ene (TBD) in combination with an alcohol as a co-initiator. Purely isotactic PCHC is synthesized for the first time via ROP of enantiopure (R,R)-CHC with a zinc/benzyl alcohol catalyst system. All reactions proceed without decarboxylation, affording well-defined PCHCs with M-n,M-NMR up to 17 000 g mol(-1) and D-M = ca. 1.2. Purely isotactic PCHC is semicrystalline, with T-g = 130 degrees C, T-c = 162 degrees C, and T-m = 248 degrees C. DFT computations further highlight the significant favorable impact of the trans-cyclohexane ring-strain to enable the ROP of CHC, as opposed to meso-CHC which is unreactive.