Poly(ethyl methacrylate)-based diblock copolymer nano-objects prepared via RAFT-mediated polymerization induced self-assembly in n-heptane

A series of poly(lauryl methacrylate)-poly(ethyl methacrylate) (PLMA-PEMA) diblock copolymer nano-objects were prepared via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization in n-heptane at 65 °C. By using PLMA with a fixed degree of polymerization (DP) of 18 as a steric stabilizer block, polymerization of EMA at relatively high concentrations (15% w/w solids or above) allowed for the production of nano-objects with morphologies of sphere, worm and vesicle. Interestingly, at lower concentrations, the diblock copolymer could form unusual structures: micrometer-sized rods and nanotubes at 10% and 7.5% w/w solids, respectively. The SEM and TEM characterization suggests that the rods are kinetically trapped aggregates of worms and spheres, and the formation of nanotubes is presumably due to the fusion of ellipsoidal vesicles and then the shear force exerted by stirring which may trigger the elongation of the vesicles to form the nanotubes. Besides, the diblock copolymer worms exhibited thermoresponsive behavior on heating to 90 °C due to the change in nano-object morphology from worms to spheres.