Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

Summary

A protocol for the high-throughput analysis of polymerization catalyst, chain transfer polymerizations, polyethylene characterization, and reaction kinetic analysis is presented.

Abstract

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel α-diimine ethylene polymerization catalyst. Initial polymerizations with the catalyst lead to optimized reaction conditions, including catalyst concentration, ethylene pressure and reaction time. Using gas-uptake data for these reactions, a procedure to calculate the initial rate of propagation (k_p) is presented. Using the optimized conditions, the ability of the nickel α-diimine polymerization catalyst to undergo chain transfer with diethylzinc (ZnEt₂) during ethylene polymerization was investigated. A procedure to assess the ability of the catalyst to undergo chain transfer (from molecular weight and ¹³C NMR data), calculate the degree of chain transfer, and calculate chain transfer rates (k_e) is presented.

Introduction

Polyolefins are an important class of industrial polymers with uses in thermoplastics and elastomers. Significant advances in the design of single-site catalysts for the production of polyolefins has led to the ability to tune molecular weight, polydispersity, and polymer microstructure, which leads to a wide range of potential applications.^1-3 More recently, chain transfer and chain shuttling polymerizations have been developed to give an additional route to modify the properties of the polymer without having to modify the catalyst.^4-6 This system employs a single-site transition metal catalyst and a chain transfer reagent (CTR), which is typica....

Protocol

Caution: Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in these syntheses are acutely toxic and carcinogenic, while several are pyrophoric and ignite in air. Please use all appropriate safety practices when performing these reactions including the use of engineering controls (fume hood, glovebox) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes). Portions of the following procedures involve standard air-free handling techniques.

1. Preparation of [bis(2,6-dimethylphenyl)-2,3-butanediimine]NiBr₂,^21-25

Results

The ethylene gas consumption versus time is presented in Figure 1 for the different ethylene pressures tested. This data is used to determine optimized reaction conditions. The ethylene gas consumption versus time is presented in Figure 2A for the catalyst alone samples, which is used to calculate the rate of propagation (k_p). Figure 2B shows gel permeation chromatography (GPC) traces for chain transfer polymerizations with 0-1,000 equivalents of diet.......

Discussion

A methyl-substituted cationic [α-diimine]NiBr₂ ethylene polymerization catalyst activated with MAO was examined for its competency for ethylene chain transfer polymerizations. The reactions were monitored via gas uptake measurements to determine the rate and extent of polymerization and catalyst lifetime, and the molecular weight of the resultant polymers were determined via gel permeation chromatography (GPC). Initially, the nickel catalyst was tested over a range of et.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Endeavor Pressure Reactor	Biotage	EDV-1N-L
Blade Impellers	Biotage	900543
Glass Liners	Biotage	900676
2,3-butanedione, 99%	Alfa Aesar	A14217
2,6-dimethylaniline, 99%	Sigma Aldrich	D146005
formic acid, 95%	Sigma Aldrich	F0507
methanol, 99.8%	Sigma Aldrich	179337	ACS Reagent
nickel (II) bromide, 99%	Strem	28-1140	anhydrous, hygroscopic
triethylorthoformate, 98%	Sigma Aldrich	304050	dried with K2CO3 and distilled
1,2-dimethoxyethane, 99.5%	Sigma Aldrich	259527	dried with Na/Benzophenone and distilled
pentane, 99%	Fisher	P399	HPLC Grade *
dichloromethane, 99.5%	Fisher	D37	ACS Reagent *
toluene, 99.8%	Fisher	T290	HPLC Grade *
methylaluminoxane	Albemarle	MAO	pyrophoric, 30% in toluene
diethylzinc, 95%	Strem	93-3030	pyrophoric
1,2,4-trichlorobenzene, 99%	Sigma Aldrich	296104
1,1,2,2-tetrachloroethane-D2, 99.6%	Cambridge Isotopes	DLM-35