Enantiopure Isotactic PCHC Synthesized by Ring-Opening Polymerization of Cyclohexene Carbonate
Résumé
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 (Pm = ca. 60–76%) is obtained by ROP of rac-CHC catalyzed by zinc diaminophenolate, zinc β-diketiminate, yttrium bis(phenolate), or 1,5,7-triazabicyclo[4.4.0]dec-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 Mn,NMR up to 17 000 g mol–1 and ĐM = ca. 1.2. Purely isotactic PCHC is semicrystalline, with Tg = 130 °C, Tc = 162 °C, and Tm = 248 °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.