Synthesis and Characterization of BPA-free Polyesters by Incorporating a Semi-rigid Cyclobutanediol Monomer

The ability of diol monomers, such as 1,4-cyclohexanedimethanol (CHDM) and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD), to replace the potentially hazardous BPA in the production of polyesters and polycarbonates with excellent thermal, optical, and mechanical properties has not only gained considerable academic interest but has also garnered significant commercial success. Herein, we report a novel strategy to synthesize a semi-rigid diol, trans-1,3-cyclobutane dimethanol (CBDO-1), a versatile building block which may also serve as a phenol-free BPA replacement. It was synthesized using a facile photoreaction and subsequent reduction. Specifically, an initial photodimerization of trans-cinnamic acid using a 365 nm blacklight was carried out to form a trans-1,3-cyclobutane diacid, CBDA-1, which was then reduced with either NaBH4 in the presence of I2, or by catalytic hydrogenation using CuO–CrO3, to give the desired CBDO-1 in excellent yield. To highlight the potential application of this useful primary diol, CBDO-1 and various diacids were used to synthesize novel polyesters via conventional melt polymerization. The thermal properties of this new series of polyesters were studied, including the glass transition temperature, which ranged from 33 to 114 °C, and the decomposition temperature, which ranged from 381 to 424 °C. The ease of synthesis of this cyclobutane-containing CBDO-1 monomer, coupled with its desirable properties, will not only help in the development of alternatives for the widely used BPA, but will also lead to novel and useful materials that are not accessible employing thermal reactions alone.