Polyethylene , structure

9 Characterization of Reactivity Ratios in Multi-site Mg/Ti Catalysts 

Solvent extraction methods were used by Y. V. Rissin to fractionate ethylene/1 -hexene copolymers prepared with the Mg/Ti catalyst described above [64] in which ethylmagnesium chloride and TiCl were used to prepare high-activity catalysts with and without silica. 

Each catalyst was evaluated in ethylene/1-hexene copolymerization reactions at 80°C in the presence of the cocatalyst TEAL at various 1-hex-ene/ethylene ratios. The ethylene reactivity ratio r was determined for each catalyst from the simplified copolymerization equation [65]. 

The catalyst prepared on silica exhibited very high reactivity with 1 -hexene as indicated by a r value of 26, whereas the catalyst prepared without silica exhibited a r value of 125. Hence, the silica-supported catalyst reacts approximately five times better with 1-hexene than the catalyst prepared without the silica. 

In addition, the copolymer produced from each of these catalysts was fractioned into five different fractions using hexane, heptane and octane and the comonomer content was determined for each fraction. The results are shown in Table 2.12. 

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While not overcrowded, the polyethylene structure uses space with admirable efficiency, the atoms filling the available space with 73% efficiency. For contrast, recall that close-packed spheres fill space with 74% efficiency, so polyethylene does about as well as is possible in its utilization of space. 

Peacock, A. J. Handbook of Polyethylene Structures, Properties and Applications. (2000) Marcel Dekker, New York. 

Andrew Peacock is a Development Associate with Tredegar Film Products, Richmond, Virginia. Previously he worked as a Senior Research Chemist with Exxon Chemical Company, Baytown, Texas. Publications include the Handbook of Polyethylene - Structures, Properties and Applications , nine patents in the field of polymer science, and numerous journal articles. Dr. Peacock received a B. Sc. in Chemistry from the University of London, England, an M. Sc. in Polymer Science and Technology from Lancaster University, England and a Ph. D. in Chemistry from the University of Southampton, England. 

Under the same py.-f.i.m.s. experimental conditions, compounds with normal and branched alkyl chains up to C32 were easily detected in natural waxes (15). Thus, the present results indicate that long alkyl compounds are not major constituents of the coal and discussing the FID signals of coal in terms of its "polyethylene structures" (B. C. Gerstein in reference 8) is not correct for the coal studied and may be not correct for other coals. 

Fig. 17.6. Maps of in-plane crystallographic orientation of the orthorhombic cell in the crystalline part of the polyethylene structure (a) short-term and (b) longterm implanted acetabular cups (cf. the central photographs). Compare the average direction of c-axis orientation and the motion direction shown on the respective maps and on the photographs of the acetabular cups, respectively...

Peacock AJ (2000) Handbook of polyethylene, structures, properties, and applications. Dekker, New York... 

Jalali-Arani A, Katbab AA, Nazockdast H (2003) Preparation of thermoplastic elastomers based on silicone rubber and polyethylene by thermomechanical reactive blending Effects of polyethylene structural parameters. J Appl Poly Sci 90(12) 3402-3408... 

Recent developments in ADMET polymerization and its use in materials preparation have been presented. Due to the mild nature of the polymerization and the ease of monomer synthesis, ADMET polymers have been incorporated into various materials and functionaUzed hydrocarbon polymers. Modeling industrial polymers has proven successful, and continues to be appUed in order to study polyethylene structure-property relationships. Ethylene copolymers have also been modeled with a wide range of comonomer contents and absolutely no branching. Increased metathesis catalyst activity and functional group tolerance has allowed polymer chemists to incorporate amino acids, peptides, and various chiral materials into metathesis polymers. Sihcon incorporation into hydrocarbon-based polymers has been achieved, and work continues toward the application of latent reactive ADMET polymers in low-temperature resistant coatings. 

Hydrogenation pyrolysis has been applied to the determination of the composition of copolymers of a-olefins, the sequence of monomer units and the manner in which they are added (head-to-head and head-to-tail) [253]. Mikhailov et al. [251] used Py—GC to investigate the structure of low- and high-density polyethylenes and copolymers of ethylene with propylene. The pyrolysis products were hydrogenated. The method made it possible to examine alkanes up to Cjo, which facilitates the investigation of the polymer chain structure. The isoalkanes identified corresponded to the branched polyethylene structure. It has been established that the ethyl and butyl side-chains occur most frequently in polyethylenes. 

Figure 1 Polyethylene structure-activity dependence upon imido group for compounds of the formula Ti(NR)(Me3[9]aneN3)Cl2. Reproduced by permission of The Royal Society of Chemistry.

General Description Ethylene Vinyl Acetate (EVA) Copolymer is a copolymer resin ranging in vinyl acetate content from 7.5 wt% to 33 wt%. DuPont Elvax and Equistar Ultrathene grades vary by vinyl acetate content. Some grades are available with antiblock and slip additives. The vinyl acetate units in the copolymer modify the basic polyethylene structure and its properties. The addition of vinyl acetate to polyethylene provides lower sealing temperature, increased flexibility, improved optical properties, greater adhesion, increased impact, and puncture resistance. 

A. Peacock, Handbook of Polyethylene Structures Properties, and Applications (CRC Press, Cleveland, 2000)... 

Figures. The 1510 cm-i (C=C stretch) band of a stretched poly(S-octylthiophene)/ polyethylene structure, for infrared light polarized parallel (E( ) and perpendicular (Ej ) to the stretch direction. The stretch ratio 1 / 1q = 3.

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