A mechanistic study on the synthesis of branched functional polyethylene through reactive co‐polymer approach

Abstract

The reactive co‐polymer approach is one of the most promising techniques for the synthesis of functional polyolefins. Following this concept, 1‐hexene and p‐methylstyrene are co‐polymerized in the presence of a generic Brookhart‐type catalyst. The microstructures of the co‐polymers imply the tendency of p‐methylstyrene co‐monomers to place at the end of the structural branches formed by the chain walking reaction. The molar masses of the co‐polymers decrease, not only at higher levels of co‐monomer but surprisingly by decreasing reaction temperature. A mechanism consisting of a highly stable η3 metal–benzyl intermediate, which is quantitatively approved by density functional theory calculations, can delicately justify all the aforementioned observations. A series of the produced co‐polymers is selectively functionalized by maleic anhydride at the benzylic position of p‐methylstyrene, under very mild reaction conditions. Such a reactive intermediate opens the path for the introduction of different types of functionalities in polyolefins. Namely, the grafted co‐polymers were further functionalized by a triazole ring, which provides a transient supramolecular network through intermolecular hydrogen bonding.

Control over Branching Topology by Introducing a Dual Catalytic System in Coordinative Chain Transfer Polymerization of Olefins

“…The ideal main polymerization catalyst should not only have an open geometry to reincorporate the released macromers but should also be compatible with the available chain transfer agent to establish a fast and reversible chain transfer reaction. , We utilize an aryl-substituted α-diimine nickel catalyst (Ar–N=C­(An)–C­(An)=Nar)­NiBr 2 ; Ar = 2,6-C 6 H 3 (i-Pr) 2 ) ,, as the main polymerization catalyst due to its reported high comonomer affinity, living characteristics especially at low polymerization temperatures, and its consistency with the desired chain transfer agent. − The living state of the nickel catalyst accompanied by its fast and reversible chain transfer to ZnEt 2 species results in a homogeneous growth of polymer chains on Zn and nickel species. Furthermore, the presence of numerous Zn sites and the possibility of its chain transfer reaction with the desired amount of the Fe catalyst allow us to achieve different extents of released macromers and consequent control over long-chain branching in contrast to the traditional methods of LCB production …”

“…Important and somehow conflicting considerations should be taken into account in selecting the best reaction temperature. Evidently, the selected α-diimine Ni catalyst is more active at low temperatures. , Moreover, the competence of the Fe catalyst highly depends on the reaction temperature. One of the bipyridine ligands of the Fe catalyst forms a weak bond with the Fe center and is expected to reduce the activity of the main polymerization catalyst when added to the polymerization system specifically at high temperatures .…”

“…However, linear ethylenic sequences can simply crystallize at low temperatures, which prevents the transfer of the growing chains to the Zn centers and deteriorates the living features of the reaction. To decrease the possibility of crystallization at lower temperatures, we specifically select the α-diimine Ni catalyst, which provides extensive short-chain branches in the polymerization of ethylene and higher α-olefins by the so-called “chain walking reaction” mechanism , to the extent that none of the produced polymers show a melting point at temperatures above 60 °C as listed in Table .…”

Effects of polymerization parameters on the slow crack growth resistance and rheological properties of bimodal polyethylene resins

“…As a general method, [36][37][38][39][40] all equipment was washed twice by distilled water and dried at 135 C overnight. Before use, all of them were treated with a 25 wt% solution of triethylaluminium (TEA) in hexane and purged with dry nitrogen for several hours.…”

Performance of polyurea formulations against impact loads: A molecular dynamics and mechanical simulation approach

“…Although polyolefins dominate the world's polymer industry due to their very high production volume, the role of elastomers (specially polyurea and polyurethane) in the protective coatings industry is much more prominent. [1][2][3] Thermoplastic-elastomeric polyurea is formed by the reaction between two isocyanate and amine precursors during a condensation polymerization process. 4 The elastomer was synthesized, introduced, and commercialized in the late 1980s.…”