Application of temperature rising elution fractionation in polyolefins

Xu, Jun‐Ting; Feng, Linxian

doi:10.1016/s0014-3057(99)00143-3

Cited by 82 publications

(67 citation statements)

References 70 publications

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“…Actually, it reflects a typical assembling structure of thermoplastic elastomers and explains why homogeneous copolymers usually show high elasticity, as is the case with low-crystallinity ethylene-1-octene copolymers. 68 The master crystallinity curves as a function of temperature for melting and crystallization can play a role as a phase diagram in fractionation analysis, and hence be useful to clarify the principles of temperature rising elution fractionation (TREF), 69,70 crystallization analysis fractionation (CRYSTAF), 71 and other fractionation methods based on crystallization/dissolution. 1,23 TREF has been widely used to analyze the comonomer distribution within the molecules and to prepare copolymer fractions with narrow-distributed comonomer contents.…”

Section: Discussionmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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We report a numerical study of crystallization and melting in bulk statistical homogeneous (random), homogeneous (slightly alternating), and heterogeneous (produced in a batch reaction) copolymers formed by crystallizable monomers and noncrystallizable comonomers. In our dynamic Monte Carlo simulations of lattice chains, the current model further assumes that the comonomers cannot move into crystalline regions by sliding diffusion of the chains. We find that both the overall composition and the statistical distribution of the monomers affect the phase-transition temperature, the resulting relative crystallinity, and the crystal morphology. However, the final absolute crystallinity of homogeneous copolymers seems insensitive to these parameters. Intramolecular segregation between monomers and comonomers is accompanied by crystallization, demonstrating the concept of sequence segregation or nanophase separation of statistical copolymers with assembling structures like in thermoplastic elastomers. Moreover, if crystallization of homogeneous copolymers has started but not yet completed on cooling, subsequent heating will show cold crystallization before melting, which can be attributed to insertion-mode lamellar growth. For heterogeneous copolymers, intermolecular segregation occurs on cooling before crystallization. On the basis of our observations, a pair of master melting and crystallization curves for the crystallinity of a statistical copolymer as a function of temperature are suggested to reflect the characteristic of the monomer-sequence-length distribution. This suggestion facilitates the clarification to the kinetic disturbance in local temperature regions and to the principle of some fractionation methods, such as temperature rising elution fractionation (TREF).

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Section: Discussionmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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“…To explain the behaviors of Cat-2, Cat3 and Cat-4, the influences of internal donor on the numerical distribution and properties of Addition of internal electron donors to catalysts may change the ratio of lowisospecific active sites and highly isospecific active sites [23]. Xu et al suggested that a part of nonspecific centers are selectively deactivated by the internal donor and a part of them are transformed into isospecific ones [26].…”

Section: Mechanism Of Ethylene-1-hexene Copolymerization By Mgcl 2 /Imentioning

confidence: 99%

Effect of internal electron donor on copolymerization of ethylene and 1-hexene catalyzed by supported Ziegler- Natta catalysts

Fan

Zhang

2008

E-Polymers

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Abstract:The four kinds of TiCl 4 /MgCl 2 type supported Ziegler-Natta catalysts, Cat-1, Cat-2, Cat-3 and Cat-4, were prepared by reaction of MgCl 2 -ethanol adduct with TiCl 4 . Cat-1 contains no internal electron donor (ID), Cat-2 contains diethyl phthalate (DEP) as ID, Cat-3 contains anisole as ID, and Cat-4 contains both DEP and anisole as ID. Ethylene copolymerizations with 1-hexene by these catalysts were compared. Influences of the internal electron donor on catalyst activity, copolymer composition, composition distribution, molecular weight and molecular weight distribution were investigated. Cat-3 showed the largest ability of incorporating 1-hexene into copolymer chains among the four catalysts. Each copolymer sample was fractionated into two fractions: fraction soluble in boiling nheptane (HS) and fraction insoluble in boiling n-heptane (HI). 1-Hexene content of the HS fraction is 6~10 times of that in the HI fractions. Amount of the HS fraction of copolymer by Cat-2 and Cat-4 was much lower than that of Cat-1 and Cat-3. Introduction of internal donor to the catalysts, especially diethyl phthalate (DEP), increased the blockiness of HI fractions. The molecular weight of both fractions increased when there is ID in the catalyst. Addition of anisole reduced the difference in molecular weight between HS fraction and HI fraction, but addition of PA enlarged the difference. The results are discussed based on a mechanistic model of MgCl 2 -supported Ziegler-Natta catalysts.

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“…On the basis of Flory's theory, in the propyleneethylene random copolymer, propylene chains is considered as a long crystallizable chain, however ethylene as no crystallizable comonomer, i.e., they will be excluded from the polypropylene crystal lattice as de- fects. 23 According to Benjamin Monrabal 16 and Robert Brull, 23 the Flory eq 14 32 can be simplified to eq 15, which reveals a relationship between melting temperature and content of comonomer, by assuming that the melting temperature of the copolymer, T m , is close to that of the propylene homopolymer, T 0 m , hence, T m × T 0 m ≈ (T 0 m ) 2 , and also that ∆H u is constant in the considered crystallization temperature range. A straightline relationship between T m and comonomer content is obtained, which is good fit in a range of content of comonomer less than 3.5 mol%.…”

Section: Melting and Crystallization Behaviormentioning

confidence: 99%

“…In order to investigate thoroughly the relationship between performance and macromolecular chain structure, it is necessary to make samples uniform. Temperature rising elution fractionation (TREF) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] has been shown to be a powerful technique to make crystal polyolefins uniform on the basis of their crystallizability and molecular weight. Through TREF experiments, a set of fraction polymers with uniform molecular weight and content of ethylene comonomer can be obtained; hereafter crystallization analysis fractionation (Crystaf) will be used to check the effect of fractionation by analyzing such parameters as σ and R, 16 which can define the broadness of the crystallization temperature distribution of the fraction polymers.…”

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confidence: 99%

Fractionation and Characterization for a Propylene–Ethylene Random Copolymer

Zhang

Zhu

2002

Polym J

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ABSTRACT:A random copolymer of propylene with 3.5 mol% ethylene comonomer is firstly fractionated by temperature rising elution fractionation (TREF). Techniques including 13 C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), gel-permeation chromatography (GPC), crystallization analysis fractionation (Crystaf) and differential scanning calorimetry (DSC) are used to characterize the obtained fraction polymers. The results show that each fraction polymer is composed mainly of isotactic propylene sequence plus a small amount of ethylene comonomer and has uniform molecular weight and ethylene content. The PPP, PPE, and PEP are main part of triad sequence unit. As the elution temperature increasing, ethylene content of the fraction polymers decreases, number average molecular weight increases, and meanwhile number average sequence length of propylene, n P , increases, while that of ethylene, n E , decreases, close to 1. The results show that ethylene content affects linearly the melting temperature (T m ) in a range of ethylene content being as low as less than 10.23 mol%; there is a linear relationship between the reciprocal melting temperature (1000/T m , K −1 ) and reciprocal number average molecular weight (M Polypropylene is a common semi-crystalline synthetic polymer, and its macromolecular chain structure is an important factor to affect such properties of propylene polymers as crystallization behavior, morphologies, melting temperature, degree of crystallization, toughness, and rheological and optical properties. By the way of introducing some comonomers (e.g., ethylene) into its macromolecular chain, the performance of propylene polymers can be improved purposefully and effectively. Because propylene tacticity and ethylene comonomer complicate the macromolecular chain structure, and can farther lead to complex crystallization behaviors and morphologies, it is very important to firstly characterize the macromolecular chain structure well. In order to investigate thoroughly the relationship between performance and macromolecular chain structure, it is necessary to make samples uniform. Temperature rising elution fractionation (TREF) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] has been shown to be a powerful technique to make crystal polyolefins uniform on the basis of their crystallizability and molecular weight. Through TREF experiments, a set of fraction polymers with uniform molecular weight and content of ethylene comonomer can be obtained; hereafter crystallization analysis fractionation (Crystaf) will be used to check the effect of fractionation by analyzing such parameters as σ and R, 16 which can define the broadness of the crystallization temperature distribution of the fraction polymers. [16][17][18][19][20][21][22] Up to now most samples of propylene copolymers on investigation are the impact propylene-ethylene copolymers, a very complex blend. Even though after they have been fractionated by TREF, 3-11 each fraction polymer also consists of PE, ...

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Application of temperature rising elution fractionation in polyolefins

Cited by 82 publications

References 70 publications

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Effect of internal electron donor on copolymerization of ethylene and 1-hexene catalyzed by supported Ziegler- Natta catalysts

Fractionation and Characterization for a Propylene–Ethylene Random Copolymer

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