Self-assembly of poly(lauryl methacrylate)-b-poly(benzyl methacrylate) nano-objects synthesised by ATRP and their temperature-responsive dispersion properties

Self-assembling poly(lauryl methacrylate)-b-poly(benzyl methacrylate) (PLMA_x-PBzMA_y) diblock copolymers were synthesised for the first time using solution atom transfer radical polymerisation (ATRP). The PLMA degree of polymerisation (x) was fixed at 14 and the PBzMA degree of polymerisation (y) was varied from 34 to 74. Post-polymerisation transfer of this new series of diblock copolymers from chloroform into n-dodecane (a poor solvent for PBzMA) resulted in self-assembly of polymeric nano-objects. The morphologies for the latter (spheres, worms and vesicles) were controlled by y. The observed morphologies generally agreed with those reported for related PLMA_x-PBzMA_y diblock copolymers (x ≥ 16) prepared by polymerisation induced self-assembly (PISA) via reversible addition-fragmentation chain transfer (RAFT) polymerisation (Fielding et al., J. Am. Chem. Soc., 2014, 136, 5790). However, a number of differences were observed such as de-gelation behaviour and the phase boundary positions compared to those expected from Fielding et al. Variable-temperature dynamic light scattering studies for the PLMA₁₄-PBzMA₃₄ spheres revealed that the aggregation number was unaffected by a temperature increase over the range of 20-90 °C, which differed markedly from the behaviour observed for PLMA₁₄-PBzMA₆₄ worms. This difference is a new observation with mechanistic importance for the worm-to-sphere breakdown mechanism. We show that concentrated PLMA₁₄-PBzMA_y dispersions (20% w/w) in n-dodecane can be prepared using post-polymerisation transfer. The dispersion with a mixed spherical and worm-like copolymer phase exhibited reversible de-gelation when heated. Surprisingly, the dispersions containing only the worm phase remained as gels (which were white) at temperatures up to 90 °C. Our new ATRP approach for preparing temperature-responsive non-aqueous nano-object dispersions presented here decoupled chain growth and self-assembly and will apply to other copolymer dispersions.