Preparation and Thermosensitivity of Poly(N-Isopropylacrylamide) Hydrogels with Graded Structure

Abstract

A novel graded hydrogel based on poly(N-isopropylacrylamide) (PNIPAM), which is characterized with both ends of slightly cross-linked PNIPAM chains being grafted onto cross-linked PNIPAM chains, has been successfully prepared in a three-step process by a method of sequential synthesis for the first time in this paper. In the preparation of the graded hydrogels, with decreasing the crosslinker dosage, the swelling ratio of the hydrogel increased. The graded hydrogel displays faster and hydration/dehydration dynamic response to temperature cycling owing to slightly cross-linked PNIPAM chains to form big-hole structure. The proposed hydrogel structure provide a new mode of the phase transition behavior for thermo-sensitive "smart" or "intelligent" monodisperse micro-actuators, which is highly attractive for targeting drug delivery systems, chemical separations, sensors and so on.