Influence of an ionic comonomer on polymerization-induced self-assembly of diblock copolymers in non-polar media

A series of poly(stearyl methacrylate)-poly(benzyl methacrylate) (PSMA-PBzMA) diblock copolymer nano-objects has been synthesized via reversible addition-fragmentation chain-transfer (RAFT) dispersion polymerization in n-dodecane at 20 wt%. This polymerization-induced self-assembly (PISA) formulation was modified by the incorporation of an anionic monomer, tetradodecylammonium 3-sulfopropyl methacrylate ([NDod ₄] ⁺[SPMA] ^-) into the oil-insoluble PBzMA block. According to the literature (M. J. Derry, et al., Chem. Sci., 2016, 7, 5078-5090), PSMA ₁₈-PBzMA diblock copolymers only form spheres using this formulation for any core degree of polymerization. Unexpectedly, incorporating just a small fraction (<6 mol%) of [NDod ₄] ⁺[SPMA] ^- comonomer into the structure-directing block resulted in the formation of non-spherical diblock copolymer nano-objects, including pure worm-like and vesicular morphologies. However, only spherical micelles could be formed using a longer PSMA ₃₄ stabilizer. These diblock copolymer nano-objects were characterized by transmission electron microscopy, small-angle X-ray scattering, and dynamic light scattering. The bulky nature of the ionic comonomer appears to make it possible to avoid the kinetically-trapped sphere morphology. This study reveals a new approach for tuning the morphology of diblock copolymer nano-objects in non-polar media.