Industrially-sourced mineral oil and a poly(α-olefin) are used as solvents for the reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) using a poly(lauryl methacrylate) macromolecular chain transfer agent (PLMA macro-CTA) at 90 °C. The insolubility of the growing PBzMA chains under such conditions leads to polymerization-induced self-assembly (PISA), whereby poly(lauryl methacrylate)-poly(benzyl methacrylate) (PLMA-PBzMA) diblock copolymer spheres, worms or vesicles are produced directly as concentrated dispersions. The particular diblock copolymer composition required to access each individual morphology depends on the nature of the oil. Moreover, the solvent type also affects important properties of the physical free-standing gels that are formed by the PLMA-PBzMA worm dispersions, including the storage modulus (G′), critical gelation temperature (CGT) and critical gelation concentration (CGC). Spherical PLMA-PBzMA diblock copolymer nanoparticles can be prepared at up to 50% w/w solids and an efficient ‘one-pot’ protocol involving solution polymerization of LMA followed immediately by dispersion polymerization of BzMA has been developed. The latter formulation enables high BzMA conversions to be achieved, with spherical nanoparticles being produced at 30% w/w solids.