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Poly(stearyl methacrylate) (PSMA) homopolymers, prepared by RAFT radical polymerization, have been employed in the RAFT dispersion polymerization (RAFTDP) of 3-phenylpropyl methacrylate (PPMA) in n-tetradecane. RAFTDPs yielded block copolymers with narrow molecular weight distributions and tunable compositions and allowed for ready access to different polymorphic nanoparticle phases. Polymerization of PPMA at 20 wt %, for a fixed PSMA average degree of polymerization (X̅n) of 19, allowed for the in situ preparation of soft matter nano-objects with spherical, worm, and vesicular morphologies. For a fixed block copolymer composition increasing total solids (from 10 to 40 wt %) favored the formation of nanoparticles with higher ordered morphologies. For block copolymer samples that formed soft physical gels at ambient temperature, a macroscopic thermoreversible degelation–gelation phenomenon was observed. The fundamental reason for this was a worm-to-sphere morphology transition that was facilitated, in part, by the low glass transition temperature of the core-forming PPPMA block and an associated increase in the solvation of the core with increasing temperature. Finally, we note that degelation can also be effected by simple dilution with this macroscopic change now due to simple worm disentanglement and not a fundamental morphology transition.
Pei et al. (Thu,) studied this question.