Direct Measurement of Polymer Growth Rate in a Model Ziegler-Natta Polymerization System Using Laser Reflection Interferometry

The polymer growth rate for polypropylene and polyethylene was measured, for the first time, during polymerization on a model Ziegler-Natta catalyst film with a surface area of ~1 cm² by laser reflection interferometry. This technique is based on the difference in the refractive indices of the catalyst and the growing polymer film. A thin film of TiCl_x/MgCl₂ deposited on a polycrystalline gold foil was used as a model catalyst. Polyethylene grew about 30 times faster than polypropylene. The changes in periodicity of the interference fringes indicated a slow decrease in the growth rate with increasing polymer film thickness. This may be due to the monomer diffusion that was controlled by the thickness and morphology of the growing polymer film.