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The chemical modification of PVC films with sodium azide and 4-aminothiophenol was investigated. Using mixtures of a good and a nonsolvent for PVC, reactions took place in a controlled way, and the films remained transparent and smooth. To obtain information about the surface selectivity of the reactions, the degree of modification of the polymer across the film was determined by depth profiling carried out using confocal Raman microscopy. It is shown that the reaction with sodium azide always occurs homogeneously through the film while in the case of aminothiophenol, conditions could be found that allowed the polymer film to be preferentially modified at the surface. The gradient of the degree of modification and the surface selectivity depend on the relationship between the rate constants of the substitution reaction and the diffusion process of the reactant. They are, therefore, functions of reaction time, temperature, and the proportion of solvent/nonsolvent used for the reaction. The measured depth profiles as a function of reaction time have been fitted to a solution of the second Fickian law and combined diffusion/reaction coefficients for the transport of the reactant have been calculated.

A solution-cast poly(vinyl chloride) (PVC) lm of thickness 81 m m was m odi ed with aminothiophenol using surface-selective reaction conditions. After the identi cation of suitable Raman bands characteristic of the modi er (1596 cm 2 1) and the polymer (1425 cm 21), confocal Raman measurements dem onstrated a depth variation of the modi er peak intensity which was consistent with a highly surface-selec tive reaction. Data also showed features clearly attributable to refractive index effects, principally the lack of symmetry in the m odi er depth pro le obtained from the raw data and an underestim ated lm thickness. The lm was cross sectioned under liquid nitrogen to allow conventional lateral Raman measurem ents across its thickness. The depth pro le obtained directly in this way was in good agreement with confocal data after normalization using the polymer peak intensity and an expansion of the thickness scale to the value obtained independently with a micrometer. The nondestructive confocal method has clear advantages in analyzing small samples or where spatial mapping is also required. To sim ulate the effect of sample refractive index, the directly measured cross-sectional depth pro le was used to calculate the confocal depth pro le, using the method of analysis developed by Everall. 1,2 The general features of the pro le were reproduced, assuming a '' ll factor'' for the 1003 microscope objective of 0.63. However, a broadening of features was apparent in the sim ulated pro le. This suggests that direct conventional Raman m easurements of a sectioned lm m ay provide a more sensible approach for the detection of interfaces in polymer lms.