Polyethylene and copolymers

X-ray values may partly be due to the fact that the samples employed in the X-ray and infra-red studies were not identical. Other possible reasons for the discrepancies include the close overlap of the two peaks, the presence of a broad amorphous component (untied at 720 cm which may contribute to both peaks, and the necessity for using thin films which may cause the orientation distribution to deviate somewhat from uniaxial symmetry. Some doubt must therefore exist about the quantitative accuracy of crystal orientation functions evaluated from the 720 and 730 cm peaks. Further X-ray and infra-red studies on identical samples would help to resolve the apparent discrepancies. 

With regard to the amorphous orientation during the initial stages of deformation. Fig. 12 shows some (D—l)l(D+2) = (g values for the same low density material as that used to obtain the data in Fig. 11. 

The peaks at 1078, 1303,1352 and 1368 cm originate entirely from the amorphous phase and the respective D— )/( )-f 2) values were obtained directly. For the 2016 cm peak, which contains both an amorphous and a crystalline component, the ( )—l)/(Z)-i-2) values are appropriate to the amorphous component only. They were obtained from the measured net D values for the 2016 cm peak, in combination with X-ray data and dichroic data on the 1894 cm crystalline band. Details of tte method used for resolving the amorphous orientation function are given by Read and Stein.  

Time dependent dichroic measurements during the stress relaxation of low density polyethylene have been reported by Gotoh et alP and more recently by Fukui et alP and by Uemura and Stein. Fukui and coworkers determined both crystalline and amorphous orientation functions at a constant strain between 2-5 and 5%. At room temperature, values of —f and —f , estimated from data on the 730 and 720 cm bands respectively, increased with time towards steady values which were attained after about 10 s. These time dependencies were considered to largely determine the observed time dependence of the strain-optical coefficient. Values of f from the 1352 cm band showed little time dependence, but the amorphous orientation was estimated to contribute the larger amount to the magnitude of the strain-optical coefficient. 

Dichroic investigations of highly drawn samples of linear polyethylene have been reported by Koenig et alP and more recently by Glenz and Peterlin. In the former study samples were drawn by about 800% 

The material properties of polyethylene vary according to molecular structure and by polymerization mechanism. Since the flow and solution properties of polyethylene are closely related to molecular architecture, it is convenient to consider the SEC characteristics of the various types of polyethylene separately. 

1 High-density polyethylene. The high density and crystallinity arise from linear chains with little or no branching, about 0.5 branches per 10(X)C 

The high degree of crystallinity requires that the polymer be dissolved at high temperatures in solvents such as o-dichlorobenzene (ODCB) and 1,2,4-trichlorobenzene (TCB). It readily crystallizes from solution on cooling, and accordingly SEC determination of molecular mass distribution is carried out at 140°C, and the whole SEC system, from injection to detection, must be maintained at this elevated temperature. 

A major part of the development of SEC in the study of the molecular mass distribution of polyethylene has been concerned with developing effective calibration procedures. This requires correlation of elution volume and molecular weight. There are, however, no well-characterized narrow-distribution linear polyethylene standards for determining the elution 

Two other polymers were fractionated and the fractions similarly studied by SEC and solution viscosity measurements. By this means the mass average molecular mass of the fractions were determined and the calibration of molecular mass against elution volume, V, extended to higher molecular masses. 

The extent of short-chain branching in PE may be quantitatively determined by a variety of techniques including pyrolysis-GC, and y-radiolysis.  

The most definitive information comes from NMR studies. The tj pical 

2 hexyl and longer, 0.5-2.8. The range of values for extent and type of short-chain branches arises because the branching process is extremely dependent on the polymerization conditions. High reaction temperatures and low pressures (monomer concentrations) favor the backbiting process. 

Backbiting also occurs in ethylene copolymerizations with AN, (mctli)acrylatc esters and VAc. jhc structures identified in E-BA 

The incidence of the various structures depends strongly on the comonomer. In copolymerization with acrylates structures 62 and 63 dominate. In copolymerization with VAc structure 61 dominates and 62 and 63 arc not observed. Structure 60 may be present in VAc copolymers to a very small extent but is not observed in acrylate copolymerizations. Structures 62 and 63 arc not observed and cannot be fbnned in methacrylate copolymerizations. The results were interpreted in terms of the PVAc propagating radical having a lesser 

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In Chapter 1, it was mentioned that highly branched low density polyethylene and copolymers made with polar comonomers are produced only by free radical polymerization at very high pressure and temperature. (All other forms of commercially available polyethylene are produced with transition metal catalysts under much milder conditions see Chapters 3, 5 and 6.) In this chapter we will review how initiators achieve free radical polymerization of ethylene. Low density polyethylene and copolymers made with polar comonomers are produced in autoclave and tubular processes, to be discussed in Chapter 7,... 

Thennoplastics are heat softening materials which can be repeatedly heated, made mobile and then reset to a solid state by cooling. Under conditions of fabrication these materials can be moulded (shaped in a mould) by temperature and pressure. Examples of thermoplastics are more numerous than thermosets, e.g. polyethylene, polyvinylchloride, polystyrene, polypropylene, nylon, polyester, polyvinylidene chloride, polycarbonate. Thermoplastics may be further divided into homopolymers which involve one type of monomer, e.g. ethylene polymerised to polyethylene, and copolymers, terpolymers, etc., which involve two or more monomers of different chemical substances. Polymerisation producing thermoplastics and thermoset materials usually follows two basic chemical mechanisms, i.e. condensation and addition polymerisation. 

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. 

GLASS REINFORCED FLUOROPLASTICS NYLON INCLUDING AROMATICS GLASS REINFORCED NYLON CELLULOSICS, POLYETHYLENE AND COPOLYMERS... 

POLYETHYLENE AND COPOLYMERS CHLORINATED PVC IHIGH VOLTAGE) POLYSTYRENE AND COPOLYMERS POLYPROPYLENE OLEFINIC THERMOPLASTIC... 

Figure 3.6 Relationship between density and crystallinity in linear polyethylene and copolymers involving ethylene and a second 1-olefin [10].

The stability of the metal—alkyl bond toward )S-hydrogen abstraction depends on the metal, its valency state and, very importantly, on the ligand environment. Conditions have been found which provide the transition metals of the left-hand end of the transition-metal series with a relatively high stability Ti,V, Cr, Mo can build good polymerization catalysts, and these have found industrial application for the production of polyethylene and copolymers. 

Fig, 55 Valence bands for PTFE, polyvinylidene fluoride, polyethylene and copolymer of ethylene and tetraf1uoroethy1ene,... 

Scheme 12 (a) Process for production of high-pressure polyethylene and copolymers and (b) schematic diagram of tubular reactor with multiple feed points. ... 

Plastic Film, Polyester, Polyethylene Coated (For I.D. Cards) Plastic Tubes and Tubing, Heavy Wall, Teflon TFE Resin Thermoset Epoxy Resin Sheet, Paper Reinforced Insulation Tape, Electrical, Pressure Sensitive, Telfon TFE Resin Plastic Material for Molding and Extrusion, High Density Polyethylene and Copolymers Insulation Sleeving, Electrical, Flexible, Heat-Shrinkable Film Tape, Pressure Sensitive Plastic Sheets, Virgin and Borated Polyethylene Insulation Tape, Electrical, High Temperature, Teflon, Pressure Sensitive... 

Piping, thermal insulation Polyethylene and Copolymers DecaBDE NA Albemarle (2010)... 

Various Types of Polyethylene and Copolymers. There is a wide... 

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