Optically transparent and mechanically strong glass fiber (GF)-reinforced polycarbonate (PC) composites were fabricated via reacting with biorenewable isosorbide (ISB) moiety. While direct copolymerization of ISB and bisphenol A (BPA) by melt transesterification with diphenyl carbonate remained difficult due to the large discrepancy of reactivity and low thermal stability of ISB, we demonstrated in this work that ISB and BPA copolycarbonates with high molecular weight, low discoloration, and excellent optical transparency can be fabricated at 250 degrees C within 2.5 min by reactive blending of commercially available ISB-based PC and BPA-PC. A systematic study of synthesis, thermal degradation, and reactive blending of ISB-containing PCs was performed to distinguish the reactivity between ISB and BPA, elucidate the effect of catalyst on chain scission, and testify the reaction mechanism of the unexpected asymmetrical inner-inner carbonate exchange. We clarified that the hydroxyl group on BPA exhibited a low reactivity and Lewis acid-catalytic transesterification played a key role in preventing from the chain scission during the asymmetrical inner-inner exchange. Another unexpected factor that effectively suppressed the further chain scission was the miscibility of the ISB-based PC with BPA-PC once each chain on average was carbonate exchanged with its counterpart to form a "biblock" PC. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019