ORIENTATION GRADIENTS AT POLYMER SURFACES .1. DESCRIPTION OF METHODS

A method capable of quantitative predictions of orientation gradients at the surface of polymers is proposed. It is based on the transformation of variable-angle attenuated total reflected infrared intensities to absorption coefficients versus depth from the surface. Two alternate approaches have been used to demonstrate the viability of the method: computer simulation and sample analysis. Exact reflected intensities from anisotropic layered systems have been calculated with Fresnel coefficients. The exact intensities are used to reextract the orientation gradient with data transformation. This analysis demonstrates the conditions under which the variable-angle method is expected to optimally perform. Simulation results clearly indicate high accuracy near the interface and low accuracy at remote distances. Thin films of isotropic and uniaxially drawn isotactic polypropylene are prepared and used as layered systems. Step functions in orientation can be accurately predicted only when some information is known prior to the gradient calculation. In uniaxially oriented thick films of polypropylene, the analysis indicates that the crystal phase is highly oriented at the surface and in the bulk. Within the first 2 microns from the surface, both the amorphous and crystal phases show negligibly small gradients in orientation.