The nature of photogenerated cross-links in solid poly(vinyl cinnamate) is investigated. Hydrolysis of irradiated films and subsequent chromatography of the hydrolysis products show that the principal matrix reaction is cycloaddition between polymer-bound cinnamoyl groups. The overall quantum yield of the cross-linking reaction decreases during irradiation and the reaction virtually stops while half of the potentially reactive chromophores are still intact. Since all cinnamoyl groups are identical in structure, the lack of reactivity of some must be attributed to their environment. This suggests a description of the matrix in terms of chromophore sites, where the reactive groups are considered together with their immediate surroundings. Sites are characterized by their reaction probability and by geometry. The distribution of site reactivities in the ensemble may be derived from the dependence of the quantum yield of the photoreaction on chromophore conversion. The distribution of chromophore configurations at the sites is inferred from the distribution of cyclic isomers in the final products. Product analysis after cycloaddition may thus be used as a probe into the micromorphology of the polymer matrix.

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A compact optical flow cell for use in aqueous halide determination has been developed. The performance of the cell and optical setup has been tested by studying the halide quenching of fluorescence from thin polymeric films containing a halide-sensitive fluorophore. Aqueous halide is injected into the flow cell and the quenched fluorescence emission observed orthogonal to the plane of excitation after it has undergone total internal reflection within the glass support-an efficient method for observing weak fluorescence intensities. The experimental setup is both a low-cost and an accurate method for use in the determination of aqueous halide ions. The method can very easily be adopted to determine other aqueous anions which quench the fluorescence of dyes incorporated into thin hydrophilic polymer films. The suitability of this method for the continuous measurement of halide 'on-line' rather than a single 'static' measurement is discussed.