Synthesis and Characterization of pH-Responsive Block Copolymers with Primary Amine Groups

A new pH-responsive block copolymer, methoxy poly(ethylene glycol)-b-poly[5-methacrylamidopentylamine hydrochloride](mPEG-b-PMAAPA) was synthesized and characterized in this paper. The monomer 5-methacrylamido-pentylamine hydrochloride(MAAPA) and the macroinitiator(mPEG-ACVA) were synthesized, respectively, and mPEG-b-PMAAPA was then obtained by free radical polymerization. The structure and molecular weight of mPEG-b-PMAAPA were confirmed by hydrogen nuclear magnetic resonance(H-1 NMR) spectroscopy and gel permeation chromatography with multiangle laser light scattering(GPC-MALLS) measurements. At a low pH, it is hydrophilic due to the protonation of the primary amine groups. With increasing pH value, deprotonation occurs and the hydrophobicity of PMAAPA block increases. This molecular feature leads to interesting aggregation behavior of mPEG-b-PMAAPA in aqueous solutions at different pH values as revealed by dynamic light scattering(DLS) measurements, transmission electron microscopy(TEM) observations and resonance light scattering(RLS) measurements.