Synthesis of PEG-PNIPAM-PLys hetero-arm star polymer and its variation of thermo-responsibility after the formation of polyelectrolyte complex micelles with PAA

Abstract

A hetero-arm star polymer, poly(ethylene glycol)-poly(N- isopropylacrylamide)-poly(L-lysine) (PEG-PNIPAM-PLys), was synthesized by "clicking" the azide group at the junction of PEG-b-PNIPAM diblock copolymer with the alkyne end-group of poly(L-lysine) (PLys) homopolymer via 1,3-dipolar cycloaddition. The resultant polymer was characterized by gel permeation chromatography, proton nuclear magnetic resonance, and Fourier transform infrared spectroscopes. Surprisingly, the PNIPAM arm of this hetero-arm star polymer nearly lose its thermal responsibility. It is found that stable polyelectrolyte complex micelles are formed when mixing the synthesized polymer with poly(acrylic acid) (PAA) in water. The resultant polyelectrolyte complex micelles are core-shell spheres with the ion-bonded PLys/PAA chains as core and the PEG and PNIPAM chains as shell. The PNIPAM shell is, as expected, thermally responsive. However, its lower critical solution temperature is shifted to 37.5°C, presumably because of the existence of hydrophilic components in the micelles. Such star-like PEG-PNIPAM-PLys polymer with different functional arms as well as its complexation with anionic polymers provides an excellent and well-defined model for the design of nonviral vectors to deliver DNA, RNA, and anionic molecular medicines. © 2009 Wiley Periodicals, Inc.