Synthesis, Response And Application Of Novel Poly (N - Isopropylacrylamide) Copolymer

Stimuli-responsive polymers, whose behavioral characteristics depends strongly on environmental conditions such as pH, temperature, ionic strength, light, and so on, have aroused increasing interest for their wide applications in latex stabilisers and emulsifers, nanoreactors, biomedical field. Poly(N-isopropylacrylamine) (PNIPAM) can exhibits volume phase transition at approximately 32℃ in aqueous solution. Thus PNIPAM-based copilymers were widely investigated.In this paper, a series of copolymers, poly(acrylic acid)-b-poly(N-isopropylacrylamide)-b-poly (acrylic acid) (PAA-b-PNIPAM-b-PAA) with varying PNIPAM block lengths, were successfully synthesized by reversible addition-fragmentation chain transfer radical polymerization using BDATC as chain transfer agent. The resulting polymers were characterized in detail by 1H NMR and FT-IR. The thermo-and pH-induced behaviors were investigated by means of UV-vis spectroscopy, dynamic light scattering and transmission electron microscopy(TEM). It was found that the lower critical solution temperatures (LCSTs) of the triblock copolymers in aqueous solution could be tuned by altering the length of PNIPAM chains, the concentrations and pH of micelle solution. At pH 6.0 and 45℃, the block copolymer self-assembled into spherical core-shell micelles with hydrophobic PNIPAM segments as the core and hydrophilic PAA segments as the shell. However, with decreasing the pH and temperature, the block copolymer self-assembled into flower-like micelles with a core of collapsed hydrophobic PAA blocks, a corona of some petal-like hydrophilic PNIPAM segments.We have demonstrated a novel method that using PAA-b-PNIPAM-b-PAA copolymers as nanoreactors for RAFT-mediated polymerization of styrene to produce the polystyrene nanoparticles. This novel process allowed the production of nanoreactors of desired size (130-240nm). The influnce of the mounts of styrene(St), nanoreactors, ammonium persulfates (APS) on the particle size and size distribution were investigated by means of dynamic light scattering. FT-IR confirmed the incorporation of PAA-b-PNIPAM-b-PAA. Core-shell structure of the polystyrene polynanoparticles was recorded by Transmission electron microscopy (TEM). The thermo- and pH-sentivity of nanoparticles was confirmed by DLS. Moreover, the polystyrene nanoparticles grafting the PNIPAM and the PAA segments remained stable for 3 months under alkaline conditions.