Tunable thermoresponsiveness of copolymers with various amine groups in the side chains

Abstract

Thermoresponsive copolymers 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 the introduction of alkyne groups using pentynoic acid, leading to HEMA-alkyne. Different ratios of both 2-azidoethylamine or 2-azido-N,Ndiethylethylamine and 2-azido-N,N-dimethylethylamine were employed to introduce the amine groups to the HEMA-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 5.9×104 to 1.0×105 depending on the molecular architecture. The transmission spectra of the 0.5 wt% aqueous solutions regarding the resulting polymers at 650 nm were measured as a function of temperature. Results showed that the lower critical solution temperature (LCST) could be easily controlled by the different compositions of the amine groups. Open image in new window