Rubber Molecular weight

Compatibility and Corrosion. Gas turbine fuels must be compatible with the elastomeric materials and metals used in fuel systems. Elastomers are used for O-rings, seals, and hoses as well as pump parts and tank coatings. Polymers tend to swell and to improve their sealing abiUty when in contact with aromatics, but degree of swell is a function of both elastomer-type and aromatic molecular weight. Rubbers can also be attacked by peroxides that form in fuels that are not properly inhibited (see Elastomers, synthetic Rubber, natural). 

The exact mechanism of polymer initiation is unknown. Initiation of rubber synthesis has been studied in several plants and a common finding is that the end groups found in low molecular weight rubber (such as rubber from goldenrod and H. brasiliensis leaves) are not made up of c/x-isoprene units, unlike the bulk of the rubber [259, 260]. Structural studies [261, 262] have led to the suggestion that the Cl5 FPP may be the most common initiator in vivo, at least in H. brasiliensis. 

As modifiers, low molecular weight rubbers with carboxyl terminal reactive groups are more effective. As hardeners, we recommend phenolic Mannich bases, such as dimethylaminomethyl phenols for hot curing and ethylene di aminomethyl phenols for cold curing. 

Silicone rubber, developed by Dow Corning company, is one of the few polymers developed for medical use. The repeating unit is dimethyl sUoxane which is polymerized by a condensation polymerization. Low molecular weight polymers have low viscosity and can be cross-linked to make a higher molecular weight, rubber-like material. Medical grade silicone rubbers contain stannous octate as a catalyst and can be mixed with a base polymer at the time of implant fabrication. 

HCR heat-cured rubber HMWR high-molecular-weight rubber... 

The third category of natural rubbers are the specialty materials, which include liquid low molecular weight rubber, methyl methacrylate grafted polymers, oil-extended natural rubber, deproteinized natural rubber, epoxidized natural rubber, and superior-processing natural rubber. 

PROPERTIES OF SPECIAL INTEREST BMI resins are generally brittle. They can be toughened with additives such aromatic diamines (chain extension via Michael Addition reaction), divinylbenzene or bis (ally Iphenyl) compounds (chain extension via Diels-Alder reaction and ene reaction, respectively), benzocyclobutene derivatives (chain extension via Diels-Alder reaction), low molecular weight rubber, and thermoplastics. Certain bismaleimides are liquid crystalline. ... 

UP-637 and ED-20 cured by UP-0639 with and without addition of the low-molecular-weight rubber. As in systems based on diene oligomers, the integration of the rubber into oligomers based on UP-637 results in a peak in the temperature relationship of tan 6 at 213 K. Increase of the rubber content produces increase of the peak intensity only, without any practical change in the temperature at which tan 6 is maximal. 

Recently Nitto Denko developed a battery separator made by a wet process that had high puncture strength and high heat rupture resistance. They used a polyolefin resin with a high-molecular-weight rubber as its main component materials and cross-linked through oxidation in air. The melt rupture temperature, as measured by thermomechanical analysis, was over 200°C in this material. They also tried cross-linking UHMWPE with electron-beam and ultraviolet irradiation, but this had the... 

However, dispersion of high-molecular weight rubbers into the monomeric or prepolymer mixtures of the thermosetting resin matrix is usually difficult due to a viscosity mismatch and a lack of solubility or compatibility. 

Thus, in brief, a successful pressure-sensitive adhesive not only has low resistance to small strain deformation in order to facilitate wetting, but also it can resist large strains without flowing apart easily. Certain neat elastomers such as acrylate-based PSAs possess these features and are intrinsically tacky without additives. Other PSAs are formulated by diluting high molecular weight rubbers with special resins called tackifiers. 

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