Micellization Of Temperature- And PH-sensitive P(AA-g-NIPAM) And Synthesis Of Core Cross-linked Nanoparticals

A number of poly(acrylic acid-g-N-isopropyl acrylamide) (P(AA-g-NIPAM)) copolymers were synthesized via copolymerization of AA and oligo-NIPAM, which had been synthesized by utilizing a macromonomer technique. The phase behavior and conformation change of P(AA-g-NIPAM) in aqueous solutions were investigated by UV-vis transmittance measurements, fluorescence probe and fluorescence quenching techniques. The results demonstrated that the P(AA-g-NIPAM) copolymers had temperature- and pH-sensitivities, and these different composition graft copolymers had the different lower critical solution temperature(LCST) and critical phase transition pH values. The LCST of graft copolymer decreased with increasing the PNIPAM content, and the critical phase transition pH values increased with increasing PNIPAM content. The P(AA-g-NIPAM) graft copolymers in dilute aqueous solutions (0.001%(w)) was a loose conformation within a pH range of 3.0 to 10.0. For the P(AA-g-NIPAM) aqueous solutions, the transition from coil to globular was an incomplete reversible process. The unique properties of the graft copolymer may be used in design and synthesis of novel sensitive gels and nanocomposite materials.The complexation between poly (acrylic acid-g-N-isopropylacrylamide) (P(AA-g-NIPAM)) and poly (N-isopropylacrylamide) (PNIPAM) in aqueous solution was studied by UV-vis transmittance measurements, fluorescence probe and fluorescence anisotropy techniques. It was found that an interpolymer complex formed between the two polymers through hydrogen bonding interactions. Moreover, the complex formation showed the dependence on pH values and the AA contents in the graft copolymers. The complexation became stronger with increasing AA contents in the graft copolymers and decreasing the solution pH value. This interaction made the polymer backbones shrink, meanwhile, the complex system exhibit,; hydrophobic properties, and its hydrophilic character is weakened. The alteration may be taken as bases for the design and synthesis of novel sensitive gels and self-assembly of stimuli-responsive polymers.On the basis of the studies above, the pH-induced micelles of P(AA-g-NIPAM) were formed. Core-crosslinking of the PAA chains in the P(AA-g-NIPAM) micelles in acidic medium resulted in stable nanoparticles. The size and shape of the core-linking micelles were observed by TEM.