Polymer cubosomes of block copolymers having cross-linkable soft hydrophobic blocks

Abstract

Inverse bicontinuous cubic mesophases of block copolymers are an emerging class of mesoporous structures consisting of block copolymer bilayers, in which well-defined reticulated pore networks are intertwined in a long-range crystalline order. Polymer cubosomes, colloidal particles consisting of inverse cubic mesophases of block copolymers may find applications in ultrafiltration and affinity-based separation if the physical properties of their self-assembled structures could be optimized to maintain their structural integrity under physical and chemical stresses. In particular, highly ordered triply periodic mesoporous structures showing reversible swelling can be directly synthesized via solution self-assembly of block copolymers into polymer cubosomes and their subsequent cross-linking. Here we report a series of block copolymers synthesized by joining two structural modules, a branched poly(ethylene glycol) (PEG) hydrophilic block and linear/branched polyisoprene (PI) hydrophobic blocks. In addition to the block ratio and architecture of the block copolymer, PEG-b-PI, we suggest the length of the hydrophobic PI chain by adjusting its microstructure as a key structural parameter for the self-assembly of PEG-b-PI to form inverse cubic mesophases. The polymer cubosomes of these block copolymers can be covalently stabilized by the photo-radical-induced cross-linking of PI chains, resulting in the formation of rubbery hydrophobic domain. In contrast to uncross-linked polymer cubosomes, the cross-linked structures retained their structures under ambient conditions without water, and exhibited reversible swelling-deswelling upon exposure to organic solvents.