Time-resolved fluorescence anisotropy measurements in the study of poly(N-isopropyl acrylamide)-based systems

In this article we present recent data highlighting the power of (fluorescence) time-resolved anisotropy measurements (TRAMs) in the study of the thermoresponsive behaviour of poly(N-isopropylcrylamide), PNIPAM, and NIPAM-based systems. PNIPAM shows a lower critical solution temperature (LCST) at 32 °C when phase separation occurs as the macromolecule collapses into a globular structure. Manipulation of the conformational switch of PNIPAM results through changing the hydrophobic to hydrophilic balance within the polymer. However, although a degree of control of the LCST is possible through such a strategy, simple free radical copolymerisation serves to reduce the magnitude of the transition. Synthesis of graft copolymers based on NIPAM is offered as a solution to this problem: fine tuning of the thermal response results through control of the entropic term governing the thermodynamics of the process as revealed by TRAMs. Independent fluorescence labelling of both the backbone and the grafts allows the contribution of the chain dynamics from each of these sites to the thermal response to be monitored.