Ultrahigh-molecular-weight polymer

Styragel HMW Column for the SEC of Ultrahigh Molecular Weight Polymers... 

Nonsize-exclusion effects caused by the use of small diameter packings are highly dependent on the molecular weight of the polymer and, in fact, severely limit the use of SEC for the analysis of ultrahigh molecular weight polymers as discussed in detail by Giddings (12). 

However, the depressed termination rate is not always a disadvantage. For example, Cr/silica is not well suited to make ultrahigh molecular weight polymer. Molecular weight can be increased by lowering the calcining temperature, reactor temperature, and porosity, etc., but even under the best conditions it is difficult to achieve an inherent viscosity (IV) much higher... 

Determination of Molecular Weight and Size of Ultrahigh Molecular Weight Polymers Using Thermal Field-Flow Fractionation and Light Scattering... 

The open FFF channel is especially suited to fragile materials, and thermal FFF has found a definite niche in its application to ultrahigh-molecular-weight polymers. Furthermore, because samples need not be filtered, thermal FFF is the technique of choice for analyzing gels, rubbers, and other materials that tend to plug SEC columns [7]. Even particles can be analyzed... 

Lyoo used a low-temperature initiator, 2,2 -azobis(2,4-dimethyl-valeronitrile), to polymerize N-vinyl carbazole in a heterogeneous solution in a mixture of methyl and t-butyl alcohols [247]. The polymer that formed has the M molecular weights >3 x 10 . The author emphasized that this method provides ultrahigh-molecular-weight polymer and conversions greater than 80%. 

Polyethylene can be made into a high-strength, high-modulus fiber (tradenamed Spectra by Allied Signal, Inc.) and then into a fabric. The polyethylene is an ultrahigh-molecular-weight polymer. The density of Spectra is the lowest of all fibers, which makes its use in aerospace laminates especially attractive. However, laminates must not be exposed to temperatures over 250°F. Spectra has very attractive electrical properties with low dielectric constant and loss factor. These properties are useful in radomes. Spectra is also used in ballistic applications like helmets and aircraft panels. 

Dole and co-workers have reported yields of alkyl free radicals in polyethylene irradiated at 77 K ranging from 2.7 to 3.7 (141,145,149). Furthermore, Cracco, Arvia, and Dole (49) reported that on warming, alkyl radicals decay by a first-order process, and they attributed this to reactions between alkyl radicals within isolated spurs. The persistent free radicals on warming to room temperature are the allyl radicals II. The impact of long-term stability of radical species on the stability of polyethylene has been underlined by studies of Jahan and co-workers (150-157) of ultrahigh molecular weight polymer used in medical implants. 

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