Polymerization-induced self-assembly driving chiral nanostructured materials†
To prepare chiral nanostructures coated with bioactive molecules, a side-chain amino acid containing macromolecular chain transfer agent (macroCTA), poly(Boc-L-alanine methacryloyloxyethyl ester) (PBLAEMA), has been used as the steric stabilizer for the reversible addition–fragmentation chain transfer (RAFT) mediated dispersion polymerization of benzyl methacrylate (BzMA) in methanol at 65 °C. Gel permeation chromatography (GPC) analysis confirmed an efficient and well-controlled block copolymerization. A full spectrum of morphologies spanning spherical micelles, worm like micelles, fibres and vesicles could be attained by tuning (i) the length of the solvophobic block and (ii) the total solid content at which the block copolymerization is performed. Interestingly, a purely fibre phase morphology formed a thermoresponsive gel at room temperature above a critical fibre entanglement concentration, which underwent degelation upon heating because of the morphological transformation from anisotropic fibre to isotropic sphere. In actual fact, twisted nano-fibres have been formed through the hierarchical self-assembling of polymerization induced self-assembly (PISA) generated macromolecules in the gel state. Circular dichroism (CD) spectroscopy was used to elucidate chiroptical properties. Additionally, a high demanding wrinkle surface has been constructed preliminarily from this copolymer dispersion solution. Successful Boc-group expulsion facilitates the disassembly of vesicles to either worms or spheres with an appreciable cationic character below pH 7.0 as revealed by aqueous electrophoresis studies. Though the creation of nano-objects through PISA is well-known, fabricating chiral nanostructures with reactive handles and their hierarchical self-organization to have functional architectures is a less explored area. In this present work we were able to hybridize PISA, chirality and hierarchical self-assembling.