Polyethylene high-molecular-weight

Polyethylene high molecular weight Very slow 0.94. 03 Translncent to opaque... 

Within the family of polyolefins there are many individual families that include low density polyethylenes, linear low density polyethylenes, very low polyethylenes, ultra low polyethylenes, high molecular weight polyethylenes, ultra high molecular weight polyethylenes, polyethylene terephthalates, ethylene-vinyl acetate polyethylenes, chlorinated polyethylenes, crosslinked polyethylenes, polypropylenes, polybutylenes, polyisobutylene, ionomers, polymethylpentene, thermoplastic polyolefin elastomers (polyolefin elastomers, TP), and many others. 

Fig. 4.146 Tensile-relaxation modulus of polyethylene, high molecular weight, at different strain levels for the test temperature of 23 °C [13Gre].

HMT HMTA. See Hexamethylenetetramine HMWHDPE HMWPE. See Polyethylene, high-molecular weight high-density HNBR. See Acrylonitrile-butadiene rubber, hydrogenated... 

Paraffin wax, melting point 74°C Polyethylene, high-molecular-weight, unoxidized Polyethylene wax, slightly oxidized Polyethylene wax, unoxidized... 

There is a second observation which is also directly related to the existing entanglement network A reduction in the entanglement density greatly increases the drawability of samples. One possible route for a reduction is the gel-spinning of polyethylene. High molecular weight polyethylene is dis-... 

Compared to other types of polyethylenes, high molecular weight polyethylenes show improved impact strength, abrasion resistance and environmental stress cracking resistance. HMW-HDPE finds application in film, piping and blow-moulded containers. UHMWPE is used for components of material handling equipment and for container linings. 

In polyethylenes, high molecular weight (MW) HALS are commonly used as the predominant radical quencher. In polypropylme, a combination of low and high MW HALS is the most effective means of optimizing protection of polypropylene and polypropylene copolymer against UV d radation. ... 

Dimerization in concentrated sulfuric acid occurs mainly with those alkenes that form tertiary carbocations In some cases reaction conditions can be developed that favor the formation of higher molecular weight polymers Because these reactions proceed by way of carbocation intermediates the process is referred to as cationic polymerization We made special mention m Section 5 1 of the enormous volume of ethylene and propene production in the petrochemical industry The accompanying box summarizes the principal uses of these alkenes Most of the ethylene is converted to polyethylene, a high molecular weight polymer of ethylene Polyethylene cannot be prepared by cationic polymerization but is the simplest example of a polymer that is produced on a large scale by free radical polymerization... 

Polyethylene. Polymerization of ethylene results in an essentially straight-chain high-molecular-weight hydrocarbon. 

Fig. 1. Stress—strain curves for ionomer and polyethylene resins. Test speed is 5 cm/min. The reference matedal is high molecular weight conventional...

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

Functional polyethylene waxes provide both the physical properties obtained by the high molecular weight polyethylene wax and the chemical properties of an oxidised product, or one derived from a fatty alcohol or acid. The functional groups improve adhesion to polar substrates, compatibHity with polar materials, and dispersibHity into water. Uses include additives for inks and coatings, pigment dispersions, plastics, cosmetics, toners, and adhesives. 

In the United States high molecular weight polyethylene is used, and in the United Kingdom, cross-linked polyethylene with polyvinylchloride is used. 

Polyolefins such as polyethylene and polypropylene contain only C—C and C—H bonds and may be considered as high molecular weight paraffins. Like the simpler paraffins they are somewhat inert and their major chemical reaction is substitution, e.g. halogenation. In addition the branched polyethylenes and the higher polyolefins contain tertiary carbon atoms which are reactive sites for oxidation. Because of this it is necessary to add antioxidants to stabilise the polymers against oxidation Some polyolefins may be cross-linked by peroxides. 

There are a number of polymers which in fact cannot be melt processed because of their high molecular weights. These include PTFE, very high molecular weight polyethylene and most grades of cast poly(methyl methacrylate). In such cases shaping in the rubbery phase is usually the best alternative. 

Since 1900 other methods have been devised for producing polymethylene , including the use of boron trifluoride-diethyl ether catalysts at 0°C. Some of these methods give unbranched linear polymers, often of very high molecular weight, which are useful for comparing commercial polyethylenes which have molecules that are branched to varying extents. 

Polyethylene, in essence a high molecular weight alkane (paraffin), would be expected to have a good resistance to chemical attack and this is found to be the case. 

Very high molecular weight polyethylenes (A/ in the range 1-6 X 10 ) prepared by the Ziegler process have also become available. As might be expected from consideration of Figure 3.1 these polymers cannot be processed easily in the molten state without decomposition and it is therefore often necessary to process in the rubbery phase. 

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