Phenoxy-imine Catalyst Research Articles

Functionalized phenoxy-imine catalyst for synthesizing highly crystalline nascent UHMWPEs: 2: The non-isothermal crystallization kinetics towards the nascent less entangled UHMWPEs

The morphologies and molecular weight characteristics of nascent UHMWPEs were reported in our previous work. In order to understand the effect of entanglement state on non-isothermal crystallization behaviors and kinetics of the nascent UHMWPEs, a comprehensive thermal analysis was implemented. The nascent UHMWPEs were confirmed as nascent less entangled UHMWPEs from annealing-crystallization-melting cycles. Jeziorny and Mo methods were applied to describe the non-isothermal crystallization kinetics of the UHMWPEs. The effects of entanglement density (molecular weight) and cooling rate on the crystallization temperature and rate were investigated. The crystallization temperature was seldom affected by molecular weight, but decreased with increasing cooling rate. The crystallization enthalpy showed an increasing trend with decreasing molecular weight or cooling rate. The crystallization rate increased with increasing cooling rate or decreasing molecular weight.

Functionalized Phenoxy-Imine Catalyst for Synthesizing Highly Crystalline Nascent UHMWPEs. 1. Molecular Weight Characteristics and Polymer Morphologies

Based on the established achievements, a novel phenoxy-imine catalyst [2-C(CH3)3-4-(OCH2CH=CH2)-6-(2,3,4,5,6-C6F5-N=CH)C6H3O)]2TiCl2 was synthesized by introducing both tert-butyl and alloxy substituents to the ligand skeleton. The catalyst demonstrates an extremely high activity towards ethylene polymerization, and gives access to UHMWPE with adjustable molecular weight just by changing either reaction time or temperature. In order to acquire molecular weight characteristics on multiple levels, a hyphenated HTSEC-LALS-RI-VIS triple detection array (HTSEC-TDA) technique has been applied. By coupling the three detectors, we obtain the averages and distributions of molecular weight, macromolecular size, conformation plots and Mark-Houwink plots of the UHMWPEs. Through a detailed analysis, the nature of molecular weight characteristics and macromolecular structure of the UHMWPEs are disclosed. Further characterized by DSC and SEM, the polymer morphologies for the nascent UHMWPEs will be clarified thereinafter.

Titanium-based phenoxy-imine catalyst for selective ethylene trimerization: effect of temperature on the activity, selectivity and properties of polymeric side products

A thermal switch of selectivity for a phenoxy-imine titanium catalyst was studied by combining kinetic studies and a “polymer-to-catalyst” approach.

Probing the Most Stable Isomer of Zirconium Bis(phenoxy-imine) Cation: A Computational Investigation.

The possibility of coexistence of multiple isomers for zirconium bis(phenoxy-imine) catalyst has been systematically studied by computational approaches. The energetics among the five different isomers of neutral Zr-catalyst have been assessed quantum mechanically. The results suggest that isomer cis-N/trans-O/cis-Me is the most stable among the five isomers in accordance with the general observations of these kinds of phenoxy-imine catalyst. However, for the polymerization reaction, the active species is known to be the cationic form of the Zr-catalyst. The Zr-cation can exist in three different isomers, viz., cis-N/trans-O (A), cis-N/cis-O (B), and trans-N/cis-O (C), and the presence of flexible ligands makes the modeling considerably challenging to determine the most preferable isomers. For the efficient modeling, altogether 80 different structures for each of the three cationic isomers have been generated by using molecular dynamics simulations, and subsequently, the quantum mechanical optimization of these structures has been performed to obtain the most preferable conformation for each isomer. The existing probability derived from the obtained free energy values suggests that isomer C is comparable with isomer A. Even more, isomer A of the cation can be present in two different conformations, where the orientation of side groups is altered at the imine nitrogen atoms. The transition state calculations also confirm that the Zr-cation can exist as a mixture of three structures, "up-down" and "down-down" orientations of the isomers A along with isomer C's "up-up" orientation. However, by varying the substituents at imine nitrogen atoms, one could modulate multimodal to unimodal polymerization behavior of the Zr-catalysts. We believe that this study should provide a starting point for theoretically exploring the mechanistic pathway of the complicated polymerization reactions.

Catalysts for UHMWPE and UHMWPE-copolymers

Classic inorganic and more recent organometallic compounds capable of polymerizing ethylene to ultra high molecular are compared. Activated catalysts showed varying degrees of productivity when challenged with co-monomers. The general activity trend followed TiCl 3 < Mg/Si–TiCl 3 < metallocenes. A new phenoxyimine catalyst complex N-(3,5-diiodosalicylidene)cycloheptylamine titanium dichloride was useful in making UHMWPE and compared to previously reported phenoxyimine catalyst structures capable of living polyolefin polymerizations.

Formation of Polyolefin‐block‐polystyrene Block Copolymers on Phenoxyimine Catalysts

AbstractSummary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation. magnified image

Living random and block copolymerization of ethene and propene on a tailor-made phenoxyimine catalyst and characterization of the resulting high molecular weight PE-block-P(E-co-P) block copolymers

The phenoxyimine catalyst (bis-(N-(3′,5′-diiodo-salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride) was tailored to enable random and block copolymerisation of propylene and ethylene with compositions covering the entire feasible composition range. Well-defined high molecular weight diblock copolymers of the type PE-block-P(E-co-P), consisting of a semi-crystalline polyethylene and a soft P(E-co-P) block, were prepared and evaluated with respect to propylene content and the block lengths. The characterisation by means of AFM, CRYSTAF data and high temperature chromatographic elution provided the experimental evidence that no homo-polyethylene and less than 5% of the random copolymer are formed as by-products.

The synthesis and X-ray structure of a phenoxyimine catalyst tailored for living olefin polymerisation and the synthesis of ultra-high molecular weight polyethylene and atactic polypropylene

A phenoxyimine catalyst (bis-( N-(3′,5′-diiodo-salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride has been synthesised. The ligand as well as the complex have been fully characterised. An X-ray structure of the titanium complex was obtained. After activation with MAO, it was used as highly active catalyst in living olefin polymerisation of ethylene and propylene. Ultra-high molecular weight polyethylene and atactic polypropylene of low polydispersity were obtained. The living character of the polymerisation was shown by online polymerisation kinetics and linear growth of number-average molar mass with polymerisation time. In addition, the influence of hydrogen as a chain transfer agent was studied in living olefin polymerisation.

Living Olefin Polymerisation and Block Copolymer Synthesis in the Presence of a Single‐site Catalyst Containing a Phenoxyimine Ligand

AbstractA new phenoxyimine catalyst (Bis‐(N‐(3′,5′‐diiodo‐salicylidene)‐2,6‐difluoroaniline)‐titanium(IV)‐dichloride) has been synthesised and characterised. After activation with MAO, it was used as highly active catalyst in living olefin polymerisation of ethylene and propylene. Ultra‐high molecular weight polyethylene and atactic polypropylene of low polydispersity were obtained. The living character of the polymerisation was shown by on‐line polymerisation kinetics and linear growth of number‐average molar mass with polymerisation time. A block copolymer of the type PE‐block‐P(E‐co‐P) was prepared and characterised by CRYSTAF analysis and AFM micrographs.