Manipulating the Thermoresponsive Behavior of Poly(N-isopropylacrylamide). 1. On the Conformational Behavior of a Series of N-Isopropylacrylamide−Styrene Statistical Copolymers

Fluorescence techniques, including time-resolved (fluorescence) anisotropy (TRAMS), have been used to study the effects of hydrophobic modification upon the thermoresponsive behavior of NIPAM-based polymers. Incorporation of styrene, through statistical free radical copolymerization, changes the hydrophobic/hydrophilic balance of the macromolecule and lowers the lower critical solution temperature (LCST) of the system. Unfortunately, although simple copolymerization with styrene can be used to manipulate the system's LCST characteristics, the polymer loses its ability to release solubilized hydrophobic guests below the critical point. This results from the formation of intramolecular aggregates between the styryl residues of the polymer chain, which can accommodate guest solutes. This is a serious limitation to this form of chemical modification if the aim is to produce smart materials for controlled solubilization and release at specific temperatures.