Jian Chen

Disentangled ultra-high-molecular-weight polyethylene (d-UHMWPE) solves the problem of the difficult processing of traditional UHMWPE caused by entanglements between molecular chains. In this review, we look into the innovative realm of nascent disentangled UHMWPE, concentrating on the recent advances achieved through the in situ polymerization of ethylene by single-site catalysts. The effect of single-site catalysts and polymerization conditions on the molecular characteristics is discussed in detail from the perspective of mechanism and DFT calculations. The key factors to low entanglement are revealed, which have instructive implications for the development of new single-site catalytic systems that can generate d-UHMWPE more efficiently and become closer to industrial production. The progress in the preparation for nascent d-UHMWPE with homogeneous and heterogeneous single-site catalysts is systematically reviewed. Rheology and DSC can be used to characterize the degree of entanglement. High-modulus and high-strength biaxial films, tapes, and fibers are obtained by the solid-state processing of these nascent d-UHMWPE.

Metallocene catalysts have attracted much attention from academia and industry for their excellent catalytic activity in the field of olefin polymerization. Cocatalysts play a key role in metallocene catalytic systems, which can not only affect the overall catalytic activity, but also have an obvious influence on the structure and properties of the polymer. Although methylaluminoxane (MAO) is currently the most widely used cocatalyst, its price increases the production cost of polyolefin materials. Ammonium tetrakis(pentafluorophenyl)borate has shown excellent performance in polymerization, being one of the best substitutes for the traditional cocatalyst MAO. Compared with the main catalyst, whose composition and structure are relatively complex, the research on cocatalyst is very limited. This review mainly introduces the research history, preparation methods, and application progress in polymerization of ammonium tetrakis(pentafluorophenyl)borate, deepening our understanding of the role of cocatalyst in polymerization, with the hope of inspiring brand-new thinking on improving and enhancing the overall performance of catalyst systems.

The development of catalysts has significantly advanced the progress of polyolefin materials. In particular, group 4 (Ti, Zr, Hf) non-metallocene catalysts ligated with [N,N] bidentate ligand(s) have garnered increasing attention in the field of olefin polymerization due to their structurally stability and exceptional polymerization behaviors. Ligands containing nitrogen donors are diverse and at the core of many highly active catalysts. They mainly include amidine, guanidinato, diamine, and various N-heterocyclic ligands, which can be used to obtain a series of new polyolefin materials, such as ultrahigh molecular weight polyethylene (UHWMPE), olefin copolymers (ethylene/norbornene and ethylene/α-olefin) with high incorporations, and high isotactic or syndiotactic polypropylene after coordination with group 4 metals and activation by cocatalysts. Herein, we focus on the advancements and applications of this field over the past two decades, and introduce the catalyst precursors with [N,N] ligand(s), involving the effects of ligand structure, cocatalyst selection, and polymerization conditions on the catalytic activity and polymer properties.