A catalyzed interfacial phosgenation process with controlled feed ratios and controlled reaction pH levels allows for the formation of high heat polycarbonate random copolymers having high loadings of bis (4-hydroxyphenyl)-2-phenylisoindolin-1-one (“PPPBP”) or a structurally related comonomer. The process produces a polycarbonate copolymer having improved hydrolytic stability.