Non‐Phosgene Polycondensation and Molecular Structure Regulation of Polycarbonate–Polydimethylsiloxane Copolymers

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Polycarbonate–polydimethylsiloxane (PC–PDMS) copolymers were synthesized via a melt transesterification process, and the effects of PDMS chain length, end‐group, and polymerization degree on molecular structure and optical clarity were systematically investigated. The results demonstrate that the formation of the PDMS–PDMS sequence, which causes optical opacity of the copolymer, is synergistically governed by thermodynamic compatibility between PC and PDMS blocks and the dynamic covalent nature of carbonate groups. A shorter PDMS chain length or longer polyether‐modified termini enhances the compatibility among monomers and oligomers, thus suppressing PDMS–PDMS accumulation during the polymerization. We found that the formation of the PDMS–PDMS sequence is triggered at the polycondensation stage. Furthermore, reactive blending of a PDMS–PDMS‐free PC–PDMS copolymer with alkali metal catalysts derives high amounts of PDMS–PDMS segments, accompanying a gradual transition from optical transparency to opacity. AFM imaging revealed that PDMS blocks aggregate into large domains as PDMS–PDMS content increases. We further confirmed that the PDMS–PDMS content is saturated at a given ratio that is independent of the total PDMS loading and catalyst activity.