Polyethylene and related polymers

Polyethylene is produced commercially in very large quantities in many parts of the world. The monomer can be synthesized from various sources. Today, however, most of ethylene comes from petroleum by high temperature cracking of ethane or gasoline fractions. Other potential sources can probably be found, depending upon the availability of raw materials. 

Two main types of polyethylene are manufactured commercially. These are low (0.92-0.93 g/cm ) and high (0.94-0.97 g/cm ) density polymers. The low-density material is branched while the high-density one is mostly linear and much more crystalline. The most important applications for the low-density polyethylene are in films, sheets, paper, wire and cable coatings, and injection molding. The high-density material finds use in blow molded objects and in injection molding. 

Free-radical commercial polymerizations are conducted at 1,000-3,000 atm pressure and 80-300°C. The reaction has two peculiar characteristics (1) a high exotherm and (2) a critical dependence on the monomer concentration. In addition, at these high pressures oxygen acts as an initiator. At 2,000 atm pressure and 165°C temperature, however, the maximum safe level of oxygen is 0.075% of ethylene gas in the reaction mixture. Any amount of oxygen beyond that level can cause explosive decompositions. History of polyethylene manufacture contains stories of workers being killed by explosions. Yet, the oxygen concentration in the monomer is directly proportional to the 

Principles of Polymer Chemistry, DOI 10.1007/978-l-4614-2212-9 6, 1st and 2nd editions Kluwer Academic/Plenum Publishers 1995, 2000, 

There is an induction period that varies inversely with the oxygen concentration to the power of 0.23. During this period oxygen is consumed autocatalytically. This is not accompanied by any significant decrease in pressure. A high concentration of ethylene is necessary for a fast rate of chain growth, relative to the rate of termination. Also, high temperatures are required for practical rates of initiation. 

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The pulse radiolysis studies of liquid alkanes have relevance to the radiolysis of polyethylene and related polymers. In liquid alkanes at ambient temperature, the reaction intermediates such as alkane radical-cations, olefin radical-cations, olefine dimer-cations, excited states, and alkyl radicals have been observed after the electron-pulse irradiation [90-93]. According to the nanosecond and subnanosecond studies by Tagawa et al., the observed species were alkane radical cations, excited states, and alkyl radicals in n-dodecane excited states and cyclohexyl radical were observed in cyclohexane, and only radicals in neopentane [91, 93]. Olefin radical-cations were also detected in cyclohexane containing carbon tetrachloride [92],... 

Excellent description of high-pressnre VLE and LLE of systems containing polyethylene and related polymers is obtained. Similarly, good resnlts are obtained for the Henry s law constants for varions solvents in polyethylene. 

Most polyesters (qv) are based on phthalates. They are referred to as aromatic-aliphatic or aromatic according to the copolymerized diol. Thus polyethylene terephthalate) [25038-59-9] (PET), poly(butyelene terephthalate) [24968-12-5] (PBT), and related polymers are termed aromatic-aliphatic polyester resins, whereas poly(bisphenol A phthalate)s are called aromatic polyester resins or polyarylates PET and PBT resins are the largest volume aromatic-aliphatic products. Other aromatic-aliphatic polyesters (65) include Eastman Kodak s Kodar resin, which is a PET resin modified with isophthalate and dimethylolcyclohexane. Polyarylate resins are lower volume specialty resins for high temperature (HDT) end uses (see HEAT-RESISTANT polymers). 

Calculation of the heats of fusion of 100% crystalline polymers from calorimetric data is not clear cut. Because of the partial crystallinity of all polymers (a possible exception are single crystals of polyethylene and other polymers, but these single crystals have not yet been investigated calorimetrically), calorimetric measurements do not yield the true heat of fusion AHf, in calg-1, but only AH where these two quantities are related by the expression... 

SSP [Solid State Polymerization] Also called UOP Sinco SSP. A process for making articles from PET (polyethylene terephthalate) and related polymers. The key step is controlled crystallization of the polymer under optimum conditions. Developed jointly by UOP (United States) and Sinco (Italy) and widely adopted since 1986. 

Surfactants for urethane and related polymer foams are usually silicone-surfactants. These surfactants generally are copolymers of poly(dimethylsiloxane) [-Si(CH3)2-0-] , oxyalkylene chains, e.g., polyethylene oxide chain (EO) , and polypropyene oxide chains, (PO) . The copolymers can be linear, branched or pendant types. The surfactants have different functions, i.e., emulsifying, foam stabilizing, and cell-size control. 

In 1962 Dr. Bovey joined Bell Laboratories as a member of the technical staff, and was appointed to his present position in 1967. He continued his detailed studies of polymer structure and conformation at Bell Laboratories, and extended the scope of his work to include investigations of nuclei other than protons, branch analyses in polyethylene, and determination of defect structures in vinyl and related polymers. He continues to have a vigorous research program in the areas of polymer conformations in the solid state, polymer morphology, and the mechanisms of polymer stabilization and degradation. 

Harris, J.M., Kozlowski, A., Polyethylene glycol and related polymers mono substituted with propionic or butanoic acids and functional derivatives thereof for biotechnical applications, US patent 5672662, 1997. 

Radiation-induced Degradation.—There have been several reports on radiation effects in polymers,288 including single crystals,287 fluoropolymers,288 polyamides,289 polysiloxanes,270 polyethylene and its copolymers,271 polypropylene,272 polyolefins,273 polystyrene and its copolymers,274 poly(vinyl chloride) and related polymers,275 rubbers,278 polysulphones and other sulphur-containing polymers,277 polycarbonate,278 nylon,279 poly(vinylpyridines),280 and wool.281... 

Though there are metals other than copper (such as iron, manganese and cobalt) that can accelerate thermal oxidation of polyolefins and related polymers such as EPDM, in practice, however, the inhibition of copper-catalyzed degradation of polyolefins is of paramount importance because of the steadily increasing use of polyolefin insulation over copper conductors. Among polyolefins, polyethylene is still the most common primary insulation material for wire and cable. In the United States, high-density polyethylene and ethylenepropylene copolymers are used in substantial amounts for communications wire insulation. 

In this section, the correlation between IR/Raman frequencies of functional groups relevant to polymer analysis and polymer microstructures is described. The functional groups considered are the C=C double bond and substituted benzenes. The microstructure featuring the C=C double bond is important because the physical properties of materials such as polybutadiene and related polymers depend on the double-bond content of the overall structure. Also, a small percentage of residual C=C double bonds are formed in polyethylene chains as a result of side reactions. Substituted benzene compounds are used as starting materials such as bis-phenol A, phthalates, and benzoates. 

Heimenz PC, Lodge TP (2007) Polymer chemistry, 2nd edn. CRC, Boca Raton Hiss R, Hobeika S, Lyrm C, Strobl G (1999) Network stretching, slip processes, and fragmentation of crystallites during uniaxial drawing of polyethylene and related copolymers. A comparative study. Macromolecules 32 4390 1403... 

As a result of the work of Ziegler in Germany, Natta in Italy and Pease and Roedel in the United States, the process of co-ordination polymerisation, a process related to ionic polymerisation, became of significance in the late 1950s. This process is today used in the commercial manufacture of polypropylene and polyethylene and has also been used in the laboratory for the manufacture of many novel polymers. In principle the catalyst system used governs the way in which a monomer and a growing chain approach each other and because of this it is possible to produce stereoregular polymers. 

Whilst it is inevitable that polypropylene will be compared more frequently with polyethylene than with any other polymer its use as an injection moulding material also necessitates comparison with polystyrene and related products, cellulose acetate and cellulose acetate-butyrate, each of which has a similar rigidity. When comparisons are made it is also necessary to distinguish between conventional homopolymers and the block copolymers. A somewhat crude comparison between these different polymers is attempted in Table 11.7 but further details should be sought out from the appropriate chapters dealing with the other materials. 

In the polymer filed, new-generation metallocenes, which are currently used in many polyethylene and polypropylene processes, can polymerize proplylene in two different modes alternating blocks of rigid isotactic and flexible atactic. These new developments and other changes and approaches related to polymerization are noted in Chapters 11 and 12. 

In this contribution, in order to illustrate tlie importance of shake-up bands for extended systems, we simulate and compare on correlated grounds the ionization spectra of polyethylene and poly acetylene, the most simplest systems one can consider to represent insulating or semi-conducting polymers. Conclusions for the infinite stereoregular chains are drawn by exU apolation of the trends observed with the first terms of the related n-alkane or acene series, CnH2n+2 and CnHn+2. respectively, with n=2, 4, 6 and 8. Our simulations are also compared to X-ray photoionization spectra (7) recorded on gas phase samples of ethylene, butadiene and hexatriene, which provide a clear experimental manisfestation of the construction of correlation bands (8-12). 

NB Graham. Polyethylene oxide) and related hydrogels. In NA Peppas, ed. Hydrogels in Medicine and Pharmacy, Vol. II Polymers. Boca Raton, FL CRC Press, 1987, pp 95-114. 

The solubility of ethylene in freshly prepared polyethylene, and its diffusion out of the latter were studied in relation to the formation of explosive ethylene-air mixtures in storage. Explosive mixtures may be formed, because the solubility of ethylene in its polymer (e.g. 1130 ppm w/w at 30°C) considerably exceeds the concentration (30 ppm at 30°C) necessary to exceed the lower explosive limit above the gas-containing polymer in closed storage, and the diffusion coefficient is also 30% higher than for aged polymer samples. 

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