Supported coordination polymerization: a unique way to potent polyolefin carbon nanotube nanocomposites

Covalent Organic Framework-Supported Metallocene for Ethylene Polymerization

The loading of homogeneous catalysts with support can dramatically improve their performance in olefin polymerization. However, the challenge lies in the development of supported catalysts with well-defined pore structures and good compatibility to achieve high catalytic activity and product performance. Herein, we report the use of an emergent class of porous material-covalent organic framework material (COF) as a carrier to support metallocene catalyst-Cp2 ZrCl2 for ethylene polymerization. The COF-supported catalyst demonstrates a higher catalytic activity of 31.1×106  g mol-1  h-1 at 140 °C, compared with 11.2×106  g mol-1  h-1 for the homogenous one. The resulting polyethylene (PE) products possess higher weight-average molecular weight (Mw ) and narrower molecular weight distribution (Ð) after COF supporting, that is, Mw increases from 160 to 308 kDa and Ð drops from 3.3 to 2.2. The melting point (Tm ) is also increased by up to 5.2 °C. Moreover, the PE product possesses a characteristic filamentous microstructure and demonstrates an increased tensile strength from 19.0 to 30.7 MPa and elongation at break from 350 to 1400 % after catalyst loading. We believe that the use of COF carriers will facilitate the future development of supported catalysts for highly efficient olefin polymerization and high-performance polyolefins.

Mechanisms of mechanical reinforcement by graphene and carbon nanotubes in polymer nanocomposites

Polymer nanocomposites reinforced with carbon-based nanofillers are gaining increasing interest for a number of applications due to their excellent properties. The understanding of the reinforcing mechanisms is, therefore, very important for the maximization of performance. This present review summarizes the current literature status on the mechanical properties of composites reinforced with graphene-related materials (GRMs) and carbon nanotubes (CNTs) and identifies the parameters that clearly affect the mechanical properties of the final materials. It is also shown how Raman spectroscopy can be utilized for the understanding of the stress transfer efficiency from the matrix to the reinforcement and it can even be used to map stress and strain in graphene. Importantly, it is demonstrated clearly that continuum micromechanics that was initially developed for fibre-reinforced composites is still applicable at the nanoscale for both GRMs and CNTs. Finally, current problems and future perspectives are discussed.

Reinforcement effects of nanocarbons on catalyst behaviour and polyethylene properties through in situ polymerization

MWCNT (multi-walled carbon nanotube), MWCNT-COOH and xGnP (exfoliated graphene nanoplatelet) were used by in-situ polymerization of ethylene in presence of a binuclear complex (BNC₄).

Metallocene Based Polyolefin Nanocomposites

One of the most efficient and versatile ways to synthesize polyolefin nanocomposites is the in-situ polymerization of olefins in the presence of nano particles by metallocene catalysts. Metallocene/methylaluminoxane (MAO) catalysts are soluble in hydrocarbons and therefore they can be absorbed perfectly in solution onto the surface of particles or fibers and after addition of ethene or propene they can then catalyze a polyolefin film on the surface. Metallocene/MAO and other single site catalysts allow the synthesis of polymers with a precisely defined microstructure, tacticity, and stereoregularity as well as new copolymers with superior properties such as film clarity, high tensile strength and lower content of extractables. The polymer properties can be enlarged by the incorporation of nanofillers. The resulting polyethylene or polypropylene nanocomposites give a tremendous boost to the physical and chemical properties such as dramatically improved stiffness, high gas barrier properties, significant flame retardancy, and high crystallization rates.

Recent developments concerning the dispersion of carbon nanotubes in polymers

The ability to control the dispersion of carbon nanotubes in polymers is key to most applications of nanotube-polymer composites. This feature article describes recent advances in methods used to disperse carbon nanotubes and considers how these methods affect dispersion on different length scales. It is becoming increasing clear that perfect dispersion is not desired for many applications, in particular for electrical conductivity, and controlling the dispersion is key for proper function of the composite in its intended application.