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 bothends of solvophilicpolymers produces BAB triblock copolymers in solution. The self-assemblyof the extending solvophobic blocks may lead to network formationand gelation. This process, referred to as polymerization-inducedself-assembly (PISA) in triblock copolymers, is a topic of significantinterest. The underlying mechanism, however, has been poorly understoodin comparison to that of PISA in diblock copolymers. In this study,we used two independent in situ time-resolved techniques-small-angleX-ray scattering and oscillatory rheology-to monitor the PISAand gelation process of triblock copolymers for the first time. Wediscovered that the gelation proceeds instantaneously after an inductionperiod and is distinct from conventional gelation processes that involvethe polycondensation or cross-linking reactions of polymers. Thisstudy sheds light on the entire process of PISA and network formationduring the synthesis of triblock copolymers.