Novel Thermoresponsive Polymers Tunable by pH

Thermoresponsive polymers that are pH tunable were successfully synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu(I)-catalyzed 1,3-dipolar cycloaddition of azide and alkynes (click chemistry). ATRP was employed to synthesize poly(2-hydroxyethyl methacrylate) (PHEMA), followed by introduction of alkyne groups using pentynoic acid, leading to PHEMA-alkyne. 2-Azidoethylamine, 2-azido-N,N-dimethylethylamine, and 2-azido-N,N-diethylethylamine were added to the PHEMA-alkyne backbone via click chemistry. Molecular weight, molecular weight distribution, and click reaction efficiency were determined by gel permeation chromatography (GPC) and 1H NMR spectroscopy. The average molecular weight (Mn) of the resulting polymers ranged from 5.6 × 104 to 7.0 × 104 depending on the molecular architecture. The molecular weight distribution was low (Mn/Mn = 1.25−1.35). The transmission spectra of the 0.1 wt % aqueous solutions of the resulting polymers with different pH values at 650 nm were m...