Random Copolycarbonates Based on a Renewable Bicyclic Diol Derived from Citric Acid

To address the poor thermal stability of isohexides while at the same time retain rigidity, we developed a novel bicyclic diol octahydro-2,5-pentalenediol (OPD) from naturally occurring citric acid in this study. Owing to the bicyclic skeleton composed of two fused cyclopentane rings, OPD is supposed to have perfect rigidity but higher thermal stability compared to isohexides. Herein, OPD was first converted to octahydro-2,5-pentalenediol bis(methyl carbonate) (OPBMC) by reacting with dimethyl carbonate. The absolute stereochemistry of OPBMC was investigated by 2D 1H NMR and 13C NMR as well as single crystal X-ray diffraction. By polymerization of OPBMC with several aliphatic diols [1,8-octanediol (A8), 1,10-decanediol (A10), and 1,12-dodeacnediol (A12)] and alicyclic diols [1,4-cyclohexanedimethanol (CHDM), 1,2,2-trimethylcyclopentane-1,3-dimethanol (TCDM), and octahydro-2,5-pentalenediol (OPD)], a series of bio-based copolycarbonates (co-PCs) with intriguing properties were synthesized. NMR spectra revealed that the stereochemistry of OPBMC was preserved after polymerization. Both differential scanning calorimetry and wide-angle X-ray diffraction analyses revealed that co-PCs made from A8, A10, A12, and OPD are semicrystalline, while co-PCs based on CHDM and TCDM are amorphous. A relatively high T5% of 276 °C and outstanding high Tg up to 80.4 °C were detected for fully OPD-based co-PC, confirming the excellent thermal stability and rigidity of OPD. This work addresses some critical needs for high performance polymers such as improving the sustainability of raw materials and achieving both high Tg values and thermal stability.