In Situ Monitoring of Polymerization-Induced Self-Assembly and Gelation During the Synthesis of Triblock Copolymers via Time-Resolved Small-Angle X-ray Scattering and Rheology

The polymerization of solvophobic monomers from both ends of solvophilic polymers produces BAB triblock copolymers in solution. The self-assembly of the extending solvophobic blocks may lead to network formation and gelation. This process, referred to as polymerization-induced self-assembly (PISA) in triblock copolymers, is a topic of significant interest. The underlying mechanism, however, has been poorly understood in comparison to that of PISA in diblock copolymers. In this study, we used two independent in situ time-resolved techniques─small-angle X-ray scattering and oscillatory rheology─to monitor the PISA and gelation process of triblock copolymers for the first time. We discovered that the gelation proceeds instantaneously after an induction period and is distinct from conventional gelation processes that involve the polycondensation or cross-linking reactions of polymers. This study sheds light on the entire process of PISA and network formation during the synthesis of triblock copolymers.