Thermo-induced chain scission and oxidation of isosorbide-based polycarbonates: Degradation mechanism and stabilization strategies

The thermal degradation mechanism and stabilization strategies of isosorbide (ISB)-co-1,4-cyclohexanedimethanol (CHDM) polycarbonate (IcC-PC) and IcC-PC/bisphenol-A polycarbonate (BPA-PC) blends were systematically investigated. IcC-PC is more prone to molecular weight decrease and yellowing than BPA-PC during high-temperature processing. MALDI-TOF-MS and 1H-NMR analysis results show that ISB-PC and CHDM-PC underwent hydrolysis, β-elimination, and ISB-unit oxidation reactions, in which the former two reactions reduced molecular weight, and the latter induced yellowing. The addition of phosphite antioxidants, which have a strong peroxide removal ability, and free radical scavengers with low steric hindrance can inhibit the hydrolysis and ISB-unit oxidation. Accordingly, the thermal stability of IcC-PC is significantly improved. By reducing the reaction time (even if the catalysts loading is increased) and adding antioxidants, the thermal stability of reactive blends can be further improved, and the IcC-PC/BPA-PC transparent alloys close to the PC raw materials were prepared.