Gas-phase polymerization of ultra-high molecular weight polyethylene with decreased entanglement density

It is well known that ultra-high molecular weight polyethylene (UHMWPE) is a polymer with long chains and very high molecular weight that poses difficulties in terms of processability due to the presence of chain entanglements. In many cases is thus necessary to treat the material in different ways after the polymerization to minimize the amount of entanglements and improve the processability. Based on observations that the use of inert condensing agents (ICA) had a noticeable impact on molecular weight and crystallinity, it was decided to develop a gas-phase polymerization process with addition of ICA for UHMWPE with a high fraction of disentangled chains. For the optimization of this process, the comparison with slurry is important for the understanding the improvement. Thus, a clear difference between slurry and gas phase is observed in terms of crystallinity and the lamellar thickness of the crystals, molecular weight and entanglements. Characterization techniques are developed to measure the properties of the reactor powder and understand the impact of the alkanes in situ. Using solid-state drawability, the entanglement degree of the reactor powder is analyzed. From the small-angle x-ray scattering and wide-angle x-ray scattering techniques, it is possible to find a correlation of entanglements and lamellar thickness. Moreover, crystallization kinetics measurements of the polymer in presence of ICA constitutes a powerful method to explain the phenomena of entanglement and crystal formation.

Automated summary

Ultra-high molecular weight polyethylene (UHMWPE) with long chains and high molecular weight is difficult to process due to chain entanglements. By using inert condensing agents (ICA), the gas-phase polymerization of UHMWPE was developed to minimize entanglements and improve processability. Comparison with slurry revealed notable differences in crystallinity, lamellar thickness, molecular weight, and entanglements. Characterization techniques were used to measure reactor powder properties and analyze the impact of alkanes. Solid-state drawability analysis and scattering techniques provided insights into the entanglements and crystal formation.