RAFT synthesis and aqueous solution behavior of novel ph- and thermo-responsive (Co)polymers derived from reactive poly(2-vinyl-4,4- dimethylazlactone) scaffolds

Abstract

Well-defined homopolymers of 2-vinyl-4,4-dimethylazlactone (VDA) and AB diblock copolymers of VDA with N,N-dimethylacrylamide (DMA) and N-isopropylacrylamide (NIPAM) prepared by reversible addition–fragmentation chain transfer (RAFT) radical polymerization are reported. VDA homopolymers reacted with N,N-dimethylethylenediamine (DMEDA), N,N-diethylethylenediamine (DEEDA), and picoylamine (PA) give novel tertiary amine functional polymers that exhibit inverse temperature aqueous solution characteristics in the case of the DMEDA and DEEDA derivatives (provided they are not protonated) and a pH-dependent solubility for the PA species—it is soluble at low solution pH but becomes hydrophobic at ca. pH 4.0. VDA-DMA/NIPAM AB diblock copolymers are also readily modified with DMEDA, DEEDA, and PA to give a novel series of stimulus responsive block copolymers including tunably amphiphilic and schizophrenic species. DMEDA-DMA and DEEDA-DMA/NIPAM block copolymer derivatives undergo reversible temperature induced self-assembly in aqueous media by virtue of the inverse temperature solubility characteristics associated with these tertiary amino species. The aggregation behavior of these species is characterized using a combination of dynamic light scattering (DLS), 1H NMR spectroscopy and transmission electron microscopy (TEM). For the PA derivatives, schizophrenic behavior is demonstrated in AB block copolymers with NIPAM with normal and inverse micelles being readily accessible simply by controlling the solution pH or temperature.Self-assembled species derived from a DMEDA-DMA block copolymer, containing tertiary amino functionality in the core, can be readily core cross-linked, locking the self-assembled structure, using 1,10-dibromodecane as evidenced by DLS. The ability of examples of the ‘smart’ block copolymers to sequester hydrophobic Nile Red upon application of a pH or temperature stimulus from an aqueous environment is also demonstrated. Finally, we show how, if desired, the DMEDA homopolymers can be further modified via the facile reaction with 1,3-propanesultone yielding the sulfopropylbetaine analogous materials.