Sustainable Polycarbonates from a Citric Acid-Based Rigid Diol and Recycled BPA-PC: From Synthesis to Properties

Here we present a series of homopolycarbonates (homo-PCs) and copolycarbonates (co-PCs) based on a novel bicyclic diol octahydro-2,5-pentalenediol (OPD) from naturally occurring citric acid and bis­(hydroxyethyl ether) of bisphenol A (BHEEB), synthesized by melt polycondensation. The recently developed OPD has been shown to be a highly rigid and thermally stable building block suitable for the construction of performance polymers. BHEEB, which was obtained from the chemical recycling of BPA-PC, was used to compensate for the low reactivity of OPD and to modify the brittleness of polycarbonate (PC) solely based on OPD, without compromising other properties. The single crystal of the endo-endo isomer of OPD was deliberately obtained, and its absolute stereochemistry was unambiguously identified by single-crystal X-ray diffraction for the first time. The polymers had M_n in the 10 100–20 000 g mol^–1 range and gradually decreased with increasing OPD content. NMR analyses revealed the random structures of the co-PCs and the molar content of OPD in all cases were lower than its corresponding feeds. Interestingly, in contrast with the semicrystalline poly­(octahydro-2,5-pentalenediol carbonate) (abbreviated as pre-POC) prepared in a different protocol in our previous article, poly­(octahydro-2,5-pentalenediol carbonate) (abbreviated as POC) in this study exhibited amorphous feature with a lower T_g of 74.5 °C. A “ductile–to–brittle” transition occurred with increasing OPD content in the PBC chains, which can be ascribed to their low molecular weights and the low entangled strand density due to the rather stiff polymer chains. This work combines chemical recycling and the biobased polymer together, which would bring a feasible way to satisfy the demands of sustainability.