Ethylene sequence length distribution

Figure 22 Sequence length distributions for ethylene-propene copolymers (Karssenberg et al. [130]). Top normalized ethylene sequence length distribution bottom normalized propylene sequence length distribution. Reproduced from Karssenberg et al. [130]. Copyright 2006, John Wiley Sons, Inc. Reprinted with permission of Wiley-Liss, Inc., a subsidiary of John Wiley Sons, Inc.

The previous sections in this chapter have tried to stress upon the significance of distribution of sequence lengths in polyethylene-based copolymers. The sequence length of interest in a system of ethylene-octene copolymers would be the number of methylene units before a hexyl branch point. As was discussed, this parameter has a greater impact on the crystallization behavior of these polymers than any other structural feature like branch content, or the comonomer fraction. The importance of sequence length distributions is not just limited to crystallization behavior, but also determines the conformational,... 

In some very recent work by Karssenberg et al. [130], attempts have been made to improve the analytical ability of a technique like NMR spectroscopy to effectively predict the distribution of sequence lengths in polyethylene-alkene copolymers. They analyzed the entire [ C-NMR spectrum for homogeneous ethylene-propene copolymers. They used quantitative methods based on Markov statistics to obtain sequence length distributions as shown in Figure 22 [130]. The... 

We proposed a modified Monte Carlo model [57] based on the distribution of average ethylene sequence lengths, which was found to better represent the Crystaf profiles for a wider range of ethylene/1-olefin copolymers. Figiu e 49 compares the experimental Crystaf profiles with results from the proposed... 

Fig. 12.2. Dependence of crystalline fraction (/c) in ethylene-propylene rubbers on composition. The wide spread of results is ascribed to compositional heterogeneity and variations in sequence length distributions. Data collected by Baldwin and VerStrate from various sources. (Reprinted with permission from Rubber Chem. TechnoL, 45, 709 (1969). Copyright by the American Chemical Society.)...

We will introduce this approach in the case of the 2D CLD/DBD computation for mixed-metallocene polymerization of ethylene. Subsequently, we present applications of the approach to the 3D problems of radical polymerization of vinyl acetate (CLD/DBD/number of terminal double bonds distribution), AB radical copolymerization (CLD/comonomer composition distribution/sequence length distribution), and finally the 2D problem of radical polymerization of polyethylene, where random scission is a complicating factor. 

Ethylene- tetrafluoroethylene, perfluoro butylethylene Py-GC Sequence length distribution [255]... 

Hosoda (1988) also studied Z-N-LLDPE. The MW and MWD were determined using SEC with a refractometer and LALLS. The SCB was calculated from FT-IR spectra, while SAXS provided information on the crystalline lamellar thickness. C NMR spectra of LLDPE solutions in o-dichlorobenzene (ODCB)/perdeuter-iobenzene provided the triad sequence distribution, average sequence length, and run number in ethylene/ -butene copolymer. There are many ways to display the plethora of results, but the most interesting is the global cross-plot of MWD and composition the authors called this the bird s-eye view presented in Fig. 18.6. 

Fig. 7.4. Overall distribution of n-sequences for random polyethylene/olefin copolymers (a) polyethylene/hexane copolymer (b) polyethylene/butane copolymer. The arrows indicate the critical length of ethylene sequences which is in equilibrium with undercooled melt at given Tc...

A structure of C34F23 (C14F 22)11 C14H23 is proposed, where n = 0, 1, or 2 for the dimer, trimer, or tetramer, respectively. Ethylene-propylene copolymers can contain up to four types of sequence distribution of monomeric units. These are propylene to propylene (head-to-tail and head-to-head), ethylene to propylene, and ethylene to ethylene. These four types of sequence and the average sequence lengths of both monomer units, i.e., the value of w in the structures opposite, can be measured by the Tanaka and Hatada [48] method. 

The IR determination of the content and sequence distribution of ethylene units in propylene/ethylene (P/E) copolymers has received considerable attention over many years [e.g. 89-97]. Many of these studies have concerned the rocking-mode absorption band for -(CH2)n-, the position of which depends on the value of n, i.e. the sequence length of methylene units. Absorption bands... 

Thermal fractionation employs a temperature routine (either programmed step cooling or a series of heating and cooling cycles) that is designed to produce a distribution of lamellar crystals whose sizes reflect the distribution of methyl sequence length (MSL) that are present in the ethylene/a-olefin copolymer [33]. The experiment is performed in a conventional DSC. 

This catalyzed ethylene-1-butene system shows ideal behavior is large while rs is small, and the product of the reactivity ratios is near unity. The copolymer has a random distribution with short sequence lengths of each monomer. 

Pyrolysis products such as benzene, toluene, styrene, and naphthalene were observed. The amount of these aromatic compounds formed directly reflects the concentration of chlorine atoms and their distribution in the CPE. The composition and structure calculations were based on those degraded trimer peak intensities obtained by Py-GC. This Py-GC method can be used to quantitatively determine the chlorine content in CPE. The same method can also explore the microstructure through number-average sequence length (NASL) of ethylene and vinyl chloride monomers. Other structure-related terms, such as the percentage of grouped vinyl chloride monomers, i.e., the percentage of chlorine atoms structured as polyvinyl chloride (PVC)-like structures, can also be calculated. 

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