Effect of a cocatalyst modifier in the synthesis of ultrahigh molecular weight polyethylene having reduced number of entanglements

Abstract

The use of a hindered phenol to trap free trimethylaluminum (TMA) in methylaluminoxane (MAO) solutions has been reported to improve the performance of single-site, homogeneous catalysts for olefin polymerization. In the present study, with the help of rheological analyses, we have investigated and compared the molecular weight, molecular weight distribution and entanglement density of ultrahigh molecular weight polyethylene synthesized with a single-site catalyst activated by MAO and phenol-modified MAO. While the number average molecular weight (M n ) of the obtained polymers remains the same for both activations, a higher yield and a higher entanglement density are found in the initial stages of polymerization on using phenolmodified MAO as the cocatalyst. These results suggest that on using the phenol-modified MAO as activator, a higher number of active sites are obtained. Surprisingly in the presence of untreated MAO, a tail in the higher molecular mass region is produced.

Aluminoxane co-catalysts for the activation of a bis phenoxyimine titanium (IV) catalyst in the synthesis of disentangled ultra-high molecular weight polyethylene

“…In accordance with the earlier findings no chain transfer to the TMA seems to occur when MAO is used as the activator [7].…”

“…Moreover, since most of the entanglements are formed at the beginning of the reaction, the density of entanglements reduces with the synthesis time [4,5]. Studies along this line have been conducted in our research group using a bis(phenoxyimine) Titanium (IV) single site catalyst activated by a methylaluminoxane (MAO) co-catalyst [6,7]. This combination is considered one of the most active in ethylene polymerization [8] and has the additional advantage of being 'quasi-living' [9] (i.e.…”

“…In order to prevent the deactivation processes, it is possible to remove the free TMA by drying the MAO solutions (also known as 'solid MAO' [21]) or to 'trap' it, by adding a hindered phenol, such as 2,6-di-tert-butyl-4-methylphenol (BHT), [6,7,20] that reacts with the free TMA to form sterically hindered aluminum-phenoxide species. In both cases higher catalytic activities are reported [7,21].…”

Stress relaxation in the nonequilibrium state of a polymer melt

“…Reaction time is varied to tailor differences in molar mass and entangled state of the crystals. A more detailed description of the polymer synthesis and molar mass determination by means of linear rheology can be found elsewhere [Romano et al (2013); Talebi et al (2010)]. …”

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.…”