Synthesis and Thermo-/pH- Dual Responsive Properties of Poly(amidoamine) Dendronized Poly(2-hydroxyethyl) Methacrylate
journal contributionposted on 11.05.2010, 00:00 by Min Gao, Xinru Jia, Yan Li, Dehai Liang, Yen Wei
The first and second generation poly(amidoamine) dendronized poly(2-hydroxylethyl) methacrylate (PGn-macro (n = 1, 2)) were synthesized by the macromonomer approach. The structures and molecular weights of the obtained polymers were characterized by 1H NMR, FTIR, and GPC. UV−vis turbidity measurements revealed that all the resultant polymers were thermo-responsive, exhibiting the LCSTs in the range of 16−33 °C. The polymers also showed pH sensitive for the existence of the tertiary amino groups in the interior of the pendent dendrons. It was found that the generation of the dendrons, the molecular weights of the polymers, the concentrations, and the pHs showed great influence on the lower critical solution temperatures (LCSTs) of the polymer solutions. The higher LCST could be achieved either by increasing the generation of the dendrons or by decreasing the molecular weight. The dilute polymer solution with lower pH displayed the higher LCST. For example, the LCST of PG1-macro solution increased significantly with the pH decreased below 7.0, but the decrease of LCST was much slower at pH ≥ 7.0. DLS experiments at variable temperatures demonstrated that the polymer chains spontaneously aggregated to form large size particles as increasing the temperature above LCST due to the dehydration of the peripheral butylamide groups and the enhanced hydrophobic interactions. The morphology of aggregates was directly visualized by optical microscopy, and uniform spherical aggregates with the diameter of 3−7 μm were observed.