Strong, Tough, and Heat-Resistant Isohexide-Based Copolycarbonates: An Ecologically Safe Alternative for Bisphenol-A Polycarbonate

Bisphenol-A polycarbonate (BPA-PC) has been widely used, but it has been restricted from use in several food-contact products due to the estrogen-like and antiandrogen effects of BPA. With the aim of developing novel, biobased, and ecologically safe high-performance polycarbonates with the potential to replace BPA-PC, in this work, a series of novel biobased copolycarbonates, viz., poly(isosorbide carbonate-co-isoidide-2,5-dimethylene carbonate) (PIsIeC), were designed and successfully synthesized via melt polymerization. The combination of two isohexide building blocks, the highly rigid isosorbide (IS) and the semirigid isoidide-2,5-dimethanol (IIDML), afforded an optimal candidate (PIsIeC-39) with a nice balance of high Tg (120.5 °C), high tensile strength (72.6 MPa), and also a high elongation at break (75.2%), which are comparable or even surpass the properties of BPA-PC and a few oil-based commercial benchmarks. The SEC/viscosity results and also a DFT simulation jointly revealed that the molecular weights of these copolycarbonates were significantly enhanced when using the two isohexide building blocks together due to a possible autocatalytic effect induced by the hydrogen bonding between IIDML and IS. These polymers were obtained with number-average molecular weights of 27,300–113,200 g/mol and intrinsic viscosities of 54–83 mL/g, which are also comparable to those of BPA-PC. Meanwhile, all copolycarbonates have good transparency similar to BPA-PC and also exhibit similar γ-relaxation and higher biobased content (72–84%). These biobased copolycarbonates with superior thermal and mechanical properties have high potential to be an ecologically safe alternative for BPA-PC.