The preparation and characterisation of a novel, water-proof, irreversible, reusable, UV-activated, O(2) sensitive, smart plastic film is described. A pigment, consisting of a redox dye, methylene blue (MB), and a sacrificial electron donor, DL-threitol, coated onto an inorganic support with semiconductor functionality, TiO(2), has been extruded in low-density polyethylene (LDPE). The blue-coloured indicator is readily photobleached in <90 s using UVA light (4 mW cm(-2)), whereby MB is converted to its colourless, leuco form, leuco-methylene blue (LMB). This form persists in the absence of oxygen, but is re-oxidised to MB in ~2.5 days in air under ambient conditions (∼21 °C, ~65% RH) within the O(2) smart plastic film. The rate of recovery is linearly dependent upon the ambient level of O(2). At the lower temperature of 5 °C, the kinetics of the photobleaching activation step is largely unchanged, whereas that of recovery is markedly reduced to t(1/2) = 36 h at 5 °C (cf. 9 h at 21 °C); the activation energy for the recovery step was calculated as 28 kJ mol(-1). The O(2)-sensitive recovery step was found to be moderately dependent upon humidity at 21 °C, but not significantly dependent upon humidity at 5 °C. The possible application of this type of indicator in food packaging is illustrated and discussed briefly.

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Bulk condensation polymerization of (dimethylmethoxy)-m-carborane and (dichlorodimethyl)-silane occurs in the presence of an M xþ Cl x Lewis acid catalyst. In the literature, FeCl 3 is commonly used as the catalyst of choice but little is known about the activation energy and entropy of this polymerization. By monitoring using 1 H-NMR the reaction of a methoxy-terminated poly(dimethylsiloxane) and (dichlorodimethyl)silane the rate determining step in the FeCl 3 catalyzed system is determined. The activation energy was calculated to be þ43.6 kJ mol À1 and the entropy of the reaction was also calculated. The calculated large entropy of reaction indicates that the transition step is highly ordered. The formation of the electrophile intermediate species in the first step of the reaction has also been investigated using cyclic voltammetry. To the cyclic voltammetry data Randles-Sevcik fits have been applied to the oxidation peaks to determine the diffusion coefficients for the oxidation of Fe 2þ to Fe 3þ . Also, the initial prediction of a reversible reaction Step 1 was shown to be incorrect as the normalized reduction peak maxima increase with scan rate, indicative of an electron transfer-chemical reaction mechanism.