Reactive blending and transesterification-induced degradation of isosorbide-based polycarbonate blends

We report the reaction of bio-renewable isosorbide-based polycarbonate (IcC-PC) with poly(bisphenol A carbonate) (BPA-PC) by melt-blending in the presence of dibutyltin dilaurate (DBTDL). The blends formed copolymers and transformed into transparent alloys with a single Tg after melt-blending. A remarkable reduction in molecular weight was observed in the reactively blended products. 1H NMR and 13C NMR results showed that the carbonate group of IcC-PC is less vulnerable to nucleophilic attack than that of BPA-PC and that transesterification is initiated by the exchange reaction between the laurate ligands of DBTDL and the carbonate groups of BPA-PC. Tin-containing BPA-PC chains were proposed to react with the carbonate group of IcC-PC via a coordination-insertion mechanism to produce the (IcC-PC)-(BPA-PC) copolymer. The hydroxyl end-groups of IcC-PC were also involved in transesterification under the catalysis of dibutyltin compounds and converted into low-reactive phenolic end-groups of BPA-PC. Degradation in the IcC-PC/BPA-PC blends after adding DBTDL was mainly caused by the exchange reaction between DBTDL and BPA-PC, hydrolysis, and phenolysis of IcC-PC and BPA-PC under the catalysis of dibutyltin compounds. Among these reactions, hydrolysis played the major role and occurred mostly at the BPA-PC chains. •Transparent IcC-PC/BPA-PC alloys were obtained by reactive blending in the presence of dibutyltin dilaurate.•1H NMR and 13C NMR results show that IcC-PC is less vulnerable to nucleophilic attack than BPA-PC.•Tin-containing BPA-PC (IcC-PC) chain is the real active species in the transesterification of IcC-PC and BPA-PC.•Mechanism of degradation in IcC-PC/BPA-PC blends after adding dibutyltin dilaurate was proposed.