A Hemi-metallocene Chromium Catalyst with Trimethylaluminum-Free Methylaluminoxane for the Synthesis of Disentangled Ultra-High Molecular Weight Polyethylene

Abstract

Recently, it has been shown that by using a single-site catalytic system having titanium as a metallic center, it is possible to tailor the entanglement density in the amorphous region of a semi-crystalline ultra-high molecular weight polyethylene (UHMWPE). This route provides the possibility to make high-modulus, high-strength uniaxially and biaxially drawn tapes and films, without using any solvent during processing. In this publication, it is shown that a single-site catalyst having chromium as metallic center, proposed by Enders and co-workers, can also be tuned to provide control on the entanglement density during synthesis of the UHMWPE. However, to achieve the goal some modifications during the synthesis are required. The synthesized polymers can be processed in the solid state below the equilibrium melting temperature, resulting in uniaxially drawn tapes having tensile strength and modulus greater than 3.5 N/tex and 200 N/tex, respectively. Rheological studies have been performed to follow the increase in entanglement density in melt state with time.

The effect of processing conditions on the rheological properties of blends of ultra high molecular weight polyethylene with high‐density polyethylene

“…One plausible way to circumvent the problem of slow dissolution is to use a “disentangled” UHMWPE, which is a metastable state in which the long chains are not as entangled as in conventional UHMWPE and therefore could have lower melt viscosity and higher self‐diffusion coefficient than entangled UHMWPE. Disentangled UHMWPE is synthesized using homogeneous or supported single site catalyst in dilute solution wherein individual growing chains crystallize at a rate faster than the rate of polymerization thereby avoiding entanglements until they precipitate out of solution . Disentangled UHMWPE is known to show improved processability because of its lower elasticity and viscosity.…”

Novel SiO2‐Supported Chromium Oxide/Chromocene Dual Site Catalysts for Synthesis of Bimodal UHMWPE/HDPE in Reactor Alloys

“…[ 14 ] To improve the processability of UHMWPE, a lot of methods for reducing the chain entanglement were developed. Romano et al [ 15 ] proved that the synthesis of disentangled UHMWPE produced by half‐metallocene chromium catalyst could be achieved through the control on reaction conditions. Nonsymmetrical phenoxyimine chelate ligands combined with group IV transition metals catalysts (FI catalysts) were developed to produce disentangled UHMWPE through the dilute solution method by Rastogi and co‐workers.…”

Titanium(III, IV)-Containing Catalytic Systems for Production of Ultrahigh Molecular Weight Polyethylene Nascent Reactor Powders, Suitable for Solventless Processing—Impact of Oxidation States of Transition Metal

“…This methodology, which was begun by Smith et al [2,3], received considerable development by Rastogi et al [4,5]. However, not only metallocenes [6] or nonmetallocene catalysts [4,5,7,8] allow us to obtain UHMWPE with a reduced number of entanglements.…”