Development of a Temperature-Responsive Polymer Network with Enhanced Transparency and Volume Shrinkage via Star-Shaped PEG-b-PNIPA Block Copolymer

Abstract

In this study, a temperature-responsive polymer network was successfully synthesized by using a 4-arm star-shaped polyethylene glycol (PEG) derivative as an initiator and polymerizing N-isopropylacrylamide (NIPA) as a secondary acrylamide. The resulting star-shaped block copolymer was used as a building block to prepare a polymer network. Detailed analysis of the polymerization process (including SEC and ¹H NMR) confirmed the successful synthesis and high control over the star-shaped block copolymer structure. The obtained star-shaped block copolymer was crosslinked under semi-dilute conditions via a click reaction, incorporating the hydrophilic PEG into the poly(N-isopropylacrylamide) (PNIPA) network. This network exhibits a lower critical solution temperature (LCST) behavior at 32.5°C in water. The introduction of PEG led to unique properties, such as volume shrinkage upon heating while maintaining optical transparency, due to the effective suppression of phase separation within the network. This advancement overcomes the limitations of conventional PNIPA-based gels and expands their potential applications in optical sensors, actuators, and biomedical devices. The results highlight the promising applications of this polymer network in the development of advanced smart materials.