Multi‐center nature of heterogeneous Ziegler–Natta catalysts: TREF confirmation

Abstract

A new approach to detailed Tref analysis of ethylene/α‐olefin copolymers prepared with multi‐center polymerization catalysts is developed. It is based on resolution of complex Tref curves into elemental components described with the Lorentz distribution function. This approach was applied to the study of a series of ethylene/1‐butene copolymers prepared with a supported Ti‐based catalyst. The analysis showed that the copolymers, which, on average, contain from 6.5 to 3.5 mol % of 1‐butene, consist of seven discrete components with different compositions, ranging from a completely amorphous material with a 1‐butene content of > 15–20 mol %, to two highly crystalline components with 1‐butene contents < 1 mol %. A comparison of these Tref results with the data on the molecular weight distribution of the copolymers (based on resolution of their GPC curves) shows that Tref and GPC data provide complimentary information on the properties of active centers in the catalysts in terms of the molecular weights of the material they produce and their ability to copolymerize α‐olefins with ethylene. Tref analysis of copolymers produced at different reaction times showed that the active centers responsible for the formation of various Tref components differ in the rates of their formation and in stability. The centers that produce copolymer molecules with a high 1‐butene content are formed rapidly but decay rapidly as well whereas the centers producing copolymer molecules with a low 1‐butene content are formed more slowly but are more stable. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4351–4362, 2005

Recent Advances in High-Temperature Fractionation of Polyolefins

“…Therefore it is concluded by them that the rate of thermo-oxidative degradation will increase systematically with the increase of meso sequences in the chain. Kissin et al [16] developed a new approach for the detailed TREF analysis of ethylene/a-olefin copolymers prepared with multi-centre heterogeneous Ziegler-Natta catalysts. Their approach was based on the deconvolution of complex TREF curves into elemental components described with a Lorentz distribution function.…”

Application of Monte Carlo simulation method to polymerization kinetics over Ziegler–Natta catalysts

“…Ziegler-Natta catalysts, particularly those based on titanium, have multiple active centers that considerably differ in kinetic features [1][2][3][4][5][6][7]. For one thing, some centers are more stable and therefore they make a higher contribution to the final polymer.…”

Simultaneous Deconvolution of the Bivariate Distribution of Molecular Weight and Chemical Composition of Polyolefins Made with Ziegler‐Natta Catalysts

“…[3] Recently, Kissin et al have applied an empirical method to quantify CRYSTAF profiles based on resolution of CRYSTAF curves into elemental compositions, each of which represents a fraction of polymer with the same copolymer content. [4,5] The objective of this paper is to develop a model to deconvolute the MWD and CCD of ethylene/a-olefin copolymers simultaneously, considering the room temperature soluble fraction. To the best of our knowledge, this is the first time this type of deconvolution procedure has been used for polyolefins.…”