Measurement of diffusivity and solubility of olefins in polypropylene by gas chromatography

The classical gas chromatographic technique is applied to measure the solubility and diffusivity of ethylene and propylene in polypropylene. The polymer particles were used as supplied by the producers to pack the chromatographic columns. This allows a direct measurement of the interested properties in a particle with the same morphology obtained at the reactor outlet. Moreover, the apparatus was adapted to carry out measurements at pressures and temperatures close to those typical of the reaction conditions. The measured values of solubility and diffusivity compare favorably with those predicted by literature relationships for semicrystalline polymeric matrices, Moreover, the estimated diffusivities indicate the diffusion in the polymer microparticles as the rate determining step and a diffusive characteristic length comparable with the particle diameter, i.e., larger than expected in the frame of a multigrain particle schematization. (C) 2000 John Wiley & Sons, Inc.