Hierarchical nanostructures of tunable shapes through self-aggregation of POSS end-functional polymer and poly(ionic liquid) hybrids

Abstract

Herein, the synthesis of polyhedral oligomeric silsesquioxanes (POSS) end-functional poly(1-vinyl imidazole) (POSS-PVim) hybrid using thiolated POSS in combination with AIBN as the radical initiator is described. Owing to its amphiphilic nature, such a hybrid could self-aggregate into primary micelles with PVim corona and a core containing POSS crystalline aggregates in water. POSS-PVim hybrid molecules also self-assemble to form micelles in DMF. These primary micelles further associate into compound micelles (nanospheres) through secondary ionic interactions in water (pH 6) and in DMF as established by FESEM and DLS. Interestingly, the formation of hierarchical nanostructures of different shapes such as cube, pyramid and chain-like morphology is observed due to different mode of aggregation of primary micelles upon tuning the pH of the medium. The addition of Zn(II) ion also induces aggregation of primary micelles into dendritic nanostructures. The formation of crystalline POSS aggregates is confirmed from XRD and HRTEM. Zeta-potential measurement reveals ionic interactions among PVim chain of micelles that lead to the formation of anisotropic hybrid nanostructures. POSS-poly(ionic liquid) (POSS-PIL) hybrid can be easily prepared from POSS-PVim hybrid via post-grafting modification of pendent imidazole group with 1-bromoalkanes of different alkyl chain length, which again undergoes self-aggregation into cube-shaped nanostructures in water.