Polymerization-induced self-assembly (PISA) is a powerful and versatile technique for the rational synthesis of concentrated dispersions of block copolymer nano-objects of controllable size, shape and surface chemistry. In essence, an insoluble block is grown from one end of a soluble block in a suitable solvent. Once the former block reaches a certain critical degree of polymerization, micellar nucleation occurs and the latter block then acts as a steric stabilizer. Unreacted monomer diffuses into the copolymer cores, which leads to a relatively high local concentration and hence a significant rate acceleration. The final copolymer morphology is typically spheres, worms or vesicles, although other morphologies can also be accessed. The design rules for PISA are generic: it may be conducted in water, polar solvents or non-polar solvents using reversible addition-fragmentation chain transfer (RAFT) polymerization.<br/><br/>One important aqueous PISA formulation involves the RAFT aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA), which enables the rational design of thermoresponsive diblock copolymer worms and vesicles. Recently, we have explored using 4-hydroxybutyl acrylate (HBA), which is a structural isomer of HPMA (see <b>Figure 1</b>). The former monomer has significantly higher aqueous solubility and the corresponding PHBA homopolymer is more weakly hydrophobic than PHPMA homopolymer. Moreover, the lower glass transition temperature exhibited by PHBA enables diblock copolymer nano-objects to be designed that exhibit much greater thermoresponsive character. These aspects are explored when employing various steric stabilizer blocks for such aqueous PISA formulations.

RAFT aqueous dispersion polymerization of 4-hydroxybutyl acrylate

ACS Spring 2022

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