Influence of Organoboron Compounds on Ethylene Polymerization Using Cp2ZrCl2/MAO as Catalyst System

Luis Alexandro Valencia López,Florentino Soriano Corral,Ricardo Mendoza Carrizales,Ramón Enrique Díaz De León Gómez,Adali Castañeda Facio,Francisco Javier Enríquez-Medrano

doi:10.1155/2014/519203

Luis Alexandro Valencia López, Florentino Soriano Corral + Show 4 more

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https://doi.org/10.1155/2014/519203

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Abstract

Organoboron compounds of nonionic and ionic nature, tris(pentafluorophenyl)borane, and N,N-dimethylanilinium tetra(pentafluorophenyl)borate were evaluated to act in conjunction with MAO as activators on ethylene polymerization by using the catalyst Cp2ZrCl2. A decrease on the catalytic activity was observed in both cases in relation with a reference polyethylene which was synthesized in absence of any organoboron compound. An increase on the crystallinity degree and molecular weight, as well as an improvement in thermal and dynamic-mechanical properties, was observed in polyethylenes synthetized in presence of tris(pentafluorophenyl)borane. A low density polyethylene with improved thermal stability was obtained when N,N-dimethylanilinium tetra(pentafluorophenyl)borate was employed as activator.

Highlights

Due to the increasing current demand of polyethylene (PE), since the last decades some strategies have been developed in order to reduce the production costs and the quantity of impurities in the final products, as well as improve the final properties of the obtained polymers
As it was previously exposed, organoboron compounds can be classified according to their ionic nature in nonionic or ionic compounds [8,9,10], where nonionic are constituted by an only species (mainly tris(pentafluorophenyl)borane) [11, 12] which abstracts one of the methyl groups of the catalyst leading to the formation of two ionic species, an “activated” cationic metallocene ([Cp2ZrCH3]+), which proceed to be coordinated by an ethylene molecule, beginning the polymerization, and an anionic boron compound of general formula [CH3B(C6F5)3]−
It is noticeable how the addition of B either of ionic or nonionic nature significantly decreased the catalytic activity, in the way that by incorporating tris(pentafluorophenyl)borane (B1) into the reaction system (PE-2) the catalytic activity diminished in 42.36% and in 72.79% by adding N,N-dimethylanilinium

Summary

Introduction

Due to the increasing current demand of polyethylene (PE), since the last decades some strategies have been developed in order to reduce the production costs and the quantity of impurities in the final products, as well as improve the final properties of the obtained polymers. One disadvantage of these compounds as cocatalysts is their noncapacity of alkylating halide metallocene catalysts such as Cp2ZrCl2, for using these compounds on these kinds of systems, a necessity of being combined with an alkyl-aluminum such as MAO is required where, besides of alkylating the Zr catalyst, acts as scavenger during the polymerization; in the literature there is very few information reported about the influence wielded on the final properties of the materials by using a mixture of organoboron compound and MAO, and depending on the ionic nature of the organoboron compound As it was previously exposed, organoboron compounds can be classified according to their ionic nature in nonionic or ionic compounds [8,9,10], where nonionic are constituted by an only species (mainly tris(pentafluorophenyl)borane) [11, 12] which abstracts one of the methyl groups of the catalyst leading to the formation of two ionic species, an “activated” cationic metallocene ([Cp2ZrCH3]+), which proceed to be coordinated by an ethylene molecule, beginning the polymerization, and an anionic boron compound of general formula [CH3B(C6F5)3]−.

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