Reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of a range of vinyl monomers enables the convenient synthesis of diblock copolymer spheres, worms or vesicles in various solvents. Such formulations are an example of polymerization-induced self-assembly (PISA). Chain extension of a soluble stabilizer block with a suitable monomer initially produces soluble diblock copolymer chains. Micellar self-assembly occurs at some critical degree of polymerization (DP) for the growing insoluble block. After this nucleation event, sterically-stabilized nanoparticles grow in size. Depending on the precise PISA formulation, various morphological transitions can be observed by time-resolved small-angle X-ray scattering (SAXS). In the present work, poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA31-PBzMA2000) spheres are targeted in mineral oil. Remarkably, the nascent particles that are formed during micellar nucleation are non-spherical (see Figure 1). Systematic variation of this PISA formulation indicated that such anisotropic aggregates are only formed when the monomer concentration is sufficiently high (i.e. when a relatively high insoluble block DP is targeted).

How do diblock copolymer micelles form during polymerization-induced self-assembly?

2019 Fall National Meeting

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