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 ([NDod4]+[SPMA]−) into the oil-insoluble PBzMA block. According to the literature (M. J. Derry, et al., Chem. Sci., 2016, 7, 5078–5090), PSMA18–PBzMA diblock copolymers only form spheres using this formulation for any core degree of polymerization. Unexpectedly, incorporating just a small fraction (<6 mol%) of [NDod4]+[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 PSMA34 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.