A Strategy for the Preparation of UHMWPE Featuring Self-Retardant Properties Catalyzed by a Functionalized N/P-Containing Metallocene Catalyst through In Situ Coordination Polymerization

Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) exhibits excellent properties such as impact resistance and abrasion resistance, but it is highly flammable and difficult to process. Traditional flame-retardant modification methods suffer from poor dispersion uniformity in the UHMWPE matrix. This study proposes an approach by designing and synthesizing metallocene catalysts containing N, P, and F elements, which not only catalyze ethylene polymerization but also act as flame retardants. The catalysts were synthesized using phenyl dichlorophosphine as a bridging group and various aniline derivatives. Strong electron-withdrawing groups (e.g., fluorine) enhanced both catalytic activity and polyethylene molecular weight. The catalyst 2d exhibited the highest activity, up to 9.24 × 105 g·(mol·Ti)−1·h–1 and produced UHMWPE with a weight-average molar mass of 1.76 × 106 g·mol–1 under atmospheric pressure of ethylene. The residual methylaluminoxane (MAO) and the catalyst precursors formed a flame-retardant system in situ, improving the limiting oxygen index (LOI) of the UHMWPE from 17.3% to 20.3% and forming a dense char layer upon combustion. This work provides a method for in situ preparation of a composite flame-retardant system in a UHMWPE matrix and a solution to the challenge of traditional flame-retardant modification of UHMWPE.