Synthesis and conformational behaviour of luminescently labelled poly[styrene‐graft‐(N‐isopropyl acrylamide)] copolymers

The synthesis and characterization of poly(N‐isopropyl acrylamide) (PNIPAM), which has been grafted to polystyrene, are described. Despite the fact that these copolymers contain around 20 % of the hydrophobic monomer styrene, they still retain water solubility below 32 °C. Such observations imply that altering the polymer topography provides an alternate strategy for manipulation of the lower critical solution temperature (LCST). The fluorescence characteristics of the polarity probe, pyrene, have been used to provide information regarding the thermoresponsive behaviour of the grafted copolymer samples. On the basis of these measurements, a model is proposed which suggests that a hydrophobic styrene core exists at all temperatures between 5 and 60 °C, which is stabilized by a hydrophilic ‘corona’ formed by the PNIPAM grafts. The LCST marks a conformational ‘collapse’ of the grafts onto the styrene core, which results in the formation of a compact globular species. The fluorescence data also provide evidence that the PNIPAM graft chain‐length influences the nature of the globule.