Temperature-responsive surface-functionalized polyethylene films

Polyethylene-poly(ethylene glycol) co-oligomers were used to surface functionalize polyethylene films via an entrapment process. When immersed in water, the poly(ethylene glycol) groups at these surfaces had solvation behavior that resembled the known inverse temperature-dependent solubility properties of poly(ethylene glycol) in water. The responsiveness of these Films' surfaces was characterized by fluorescence spectroscopy and kinetic studies using pyrene ester labels. Changes in the ratio of the I-1/I-3 peaks in the emission spectrum of the pyrene probe showed that the interface micropolarity was higher at low temperature and lower at high temperature. Repeated heating and cooling (5 degrees C --> 65 degrees C --> 5 degrees C --> 65 degrees C) with the same sample showed that these interface changes were substantially reversible. Interface solvation was measured by comparing I-1/I-3 ratios for pyrene-labelled oligomers in water, ethanol, and toluene solutions with similar labels on films suspended in these same solvents. The results show that interface solvation was independent of temperature in toluene, directly dependent on temperature in ethanol, and inversely dependent on temperature in water. These changes in surface solvation lead to changes in surface reactivity. In water suspensions, these pyrene-labelled poly(ethylene glycol)-functionalized polyethylene films had hydrolysis kinetics that did not follow an Arrhenius relationship.