Study on Temperature-Controlled Branching Behavior with Self-Condensing Atom Transfer Radical Copolymerization of Latent Inimer and Styrene

The synthesis of well-defined branched polymers remains a challenge in macromolecular engineering. In the present study, we designed well-defined branched polystyrenes (BPS) by combining self-condensing atom transfer radical copolymerization (ATRP) and Diels-Alder (DA)/retro-Diels-Alder (r-DA) reactions. This “one-pot” strategy for the structure-controlled synthesis of BPS was performed through programmed heating of a “latent” inimer (FBiBPMI), containing a furan-protected maleimide monomer with a haloalkane initiator. When the polymerization temperature increased from 50 to 110 °C, the end groups (furan and maleimide addition from FBiBPMI) of linear polystyrenes were converted to “real” macromonomers after releasing maleimide (MI) via r-DA reaction, and then they were copolymerized with styrene by self-condensing ATRP. Results showed that BPS exhibited well-controlled long branching chains with a higher degree of branching (g′ = 0.18) and lower R_g/R_h compared to random branched polystyrene. Due to the dynamic characteristic of the r-DA reaction, the release of naked MI and the subsequent copolymerization can be regulated by the reaction temperatures of 70, 90, and 110 °C. Thus, the control of polymer morphologies such as branched polystyrene with controllable long branched chain, random branched polystyrene, and star-shaped branched polystyrene was successfully realized through temperature induction. Interestingly, the various morphologies of BPS obtained at different temperatures exhibited distinctive rheological behaviors in the melt and solution. BPS with the more spherical, three-dimensional structure showed a lower viscosity and faster relaxation time due to reduced entanglement between chains, thereby significantly reducing the viscosity of linear resins.