Star-like dextran-graft-pnipam copolymers. Effect of internal molecular structure on the phase transition

Stimuli responsible polymers based on poly(N-isopropylacrylamide) having conformational transition in the range of physiological temperature is discussed last years as novel drug delivery nanosystems. Two star-like copolymers with dextran core and grafted poly(N-isopropylacrylamide) arms were synthesized and characterized by size exclusion chromatography equipped with light scattering, refractometry and viscometry detectors. The copolymers differed in the distance between grafts, that caused various conformation of poly(N-isopropylacrylamide in star-like macromolecule. The influence of the polymer internal structure on the conformational transition temperature range has been studied by Quasi Elastic Light Scattering. It was shown that the thermally induced collapse of end-grafted poly(N-isopropylacrylamide) chains above the Lower Critical Solution Temperature was depended on the grafting density.