PNIPAM-b-PDMAEA double stimuli responsive copolymers: Effects of composition, end groups and chemical modification on solution self-assembly

Abstract

Doubly temperature- and pH-responsive HOOC-poly(N-isopropylacrylamide)-b-poly(2-(dimethylamino)ethyl acrylate)-C12H25 (HOOC-PNIPAM-b-PDMAEA-C12H25) and HOOC-poly(2-dimethylamino)ethyl acrylate)-b-poly(N-isopropylacrylamide)-C12H25 (HOOC-PDMAEA-b-PNIPAM-C12H25) diblock copolymers were successfully synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. Hydrophilic COOH groups and hydrophobic C12H25 groups were selectively placed at the chain end of either the thermoresponsive or the pH-responsive block. The amine precursor diblocks were converted to strong, cationic block polyelectrolytes by quaternizing the tertiary amine groups of PDMAEA block with methyl iodide. The self-assembly behavior of amine-based and quaternized diblock copolymers was investigated in aqueous media of varying pH and temperature by utilizing light scattering techniques and fluorescence spectroscopy. The novel diblock copolymers formed nanoassembled structures at temperatures above the nominal lower critical solution temperature (LCST) of the PNIPAM block. However, the amine-based and quaternized block copolymers form loose aggregate structures even at room temperature, due to the existence of the hydrophobic C12H25 terminal groups. Moreover, the solution pH was found to affect the self-assembly behavior of the amine-based diblock copolymers because of the presence of the PDMAEA block.