Copolycarbonates Based on a Bicyclic Diol Derived from Citric Acid and Flexible 1,4-Cyclohexanedimethanol: From Synthesis to Properties

Octahydro-2,5-pentalenediol (OPD), is a compelling citric acid-based bicyclic diol with excellent rigidity and thermal stability. Herein, a series of copolycarbonates (co-PCs) were synthesized, starting from OPD, 1,4-cyclohexanedimethanol (CHDM), and diphenyl carbonate (DPC). All polycarbonates are amorphous with glass transition temperatures increased when increasing the content in OPD units. Dynamic mechanical analysis (DMA) revealed the sub Tg β-relaxations at low temperatures originating from the CHDM conformational transition, indicative of the possibility of impact-resistance. Morphological analysis of the fracture surfaces revealed the toughening mechanism under tensile was shear yielding of the matrix triggered by internal cavitation. The incorporation of OPD steadily increased the Young's modulus, from 482 to 757 MPa, with the OPD fraction increased from 0 to 30 mol %. As the OPD content further increased, a "ductile-to-brittle" transition occurred due to the low number-average molecular weight (Mn) and the low entangled strand density (high entanglement molecular weight).