Switching between Thermal Initiation and Photoinitiation Redirects RAFT-Mediated Polymerization-Induced Self-Assembly

Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA) is an in situ growth method of growing interest for the preparation of well-defined block copolymer nano-objects at high solids (10-50%). Synthesis and self-assembly of block copolymers occur simultaneously during PISA, making the mechanism of PISA much more complicated than the traditional solution self-assembly method. Herein, we demonstrate that switching between thermal initiation and photoinitiation can redirect RAFT-mediated PISA in both polymerization kinetics and self-assembled structures. Taking advantage of the temperature-insensitive property of photoinitiated PISA (photo-PISA), both thermally initiated PISA and photo-PISA were performed at 70 degrees C to eliminate the disturbance of temperature. Higher-order morphologies are likely to form by thermally initiated PISA, while kinetically trapped spheres are likely to form by photo-PISA, although compositions of block copolymers are the same. It was found that the difference in polymerization kinetics between thermally initiated PISA and photo-PISA was the main reason for the morphological difference. The relatively low polymerization rate of thermally initiated PISA provides sufficient time for block copolymers to relax and reorganize from spheres to worms and vesicles. Finally, a new strategy by combining thermal initiation and photoinitiation was developed to tune polymerization kinetics, and therefore allows further control over morphologies of block copolymer nano-objects. We expect the current study will not only give more mechanistic insights into the process of PISA but also provide a facile platform to finely tune morphologies of block copolymer nano-objects.