Cross-linking curing

The multiepoxy functionality of the epoxy novolaks (2.2 to >5 epoxy groups per molecule) (3) produce more tightly cross-linked cured systems having improved elevated temperature performance and chemical resistance than the difunctional bisphenol A-based resins. 

In the energy domain, new and efficient uses in gas lines, electric cable ducts and the like, will promote surface stabilization and endurance as well as complex stress capability of various extruded or cast systems. Such reactants as acetylene terminated polymers have yielded cross-linked cured, networks of exceptional density and durability. A diimide dianhydride combined with (3) ethynylaniline yields an acetylene terminated tetraimide. On further polymerization at 250°C, the cross-linked structure derived can be used continuously at about 230°C. When this is combined with polymer carbon fibers or filaments, an exceedingly refractory and tough binder is produced. 

Fluoroelastomers based on polyvinylidene fluoride (VDF) can be cross-linked by ionic mechanism. However, if the polymer has been prepared in the presence of a cure site monomer (CSM) it can be cross-linked (cured) by a free radical mechanism. 

After inactivation treatment, the catalyst is removed, and phenolic antioxydants and other stabilizers are added. Cross-linking curing is realized on unsaturated pendant groups. Peroxides are avoided because they cause chain scission and therefore systems with sulfur as cross-linker and zinc oxide, 2-mercaptobenzothiazole and tetramethylthiuram monosulfide as accelerators are used. 

The spun fibers were cross-linked (cured) by air oxidation and pyrolyzed to give silicon-carbide-type fibers. Yajima et al. (7) reported further that heteroatoms such as titanium could be incorporated into the polymers and ceramic fibers to enhance their stability (equation 3). 

The polymeiization/cross-linking/curing process, or processes, for the component base polymer, including any chemical additives employed. 

Chicken feathers can be converted to fibers for use in diapers.140 Each chicken produces 0.5 1.0 lb of feathers. Feathers, hides, hoofs, and hair all contain proteins containing cystine cross-links. Cured rubber containing disul-... 

Cross-linking (cured rubber, thermosetting cesins)... 

By adjusting postpolymerization temperature and cross-linking (curing) time, the mechanical properties, degradation profiles, and surface energies of the cross-linked polyester networks, POC can be tuned to fit a wide range of tissue engineering applications (see Table 16.2) [2,16-18,35,50-56]. An increase in postpolymerization temperature and cross-... 

The University of Florida, in collaboration with 3M, has developed a potentially lower cost, dry spun polymer-derived analogue of Hi-Nicalon fiber. It appears that this process can produce the same microstructural evolution that produeed the high-performance Nicalon/Hi-Nicalon family of SiC fibers. Processing costs may be lower because this fiber does not require a separate thermal cross-linking (cure) step. This advantage may, however, be somewhat offset by the controlled evaporation and recovery of solvent, which is inherent in the dry spinning process. 

C temperatures gave similar products. It should be noted that it was not necessary to react all available hydroxyls with glycidyl methacrylate. Intermediate levels, i. e., 25, 50 and 75 percent may be reacted if desired to control the final properties of the cross-linked cured polymer. 

Chopped strands several inches long can be loosely bound as a mat that is porous and in which the strands are randomly oriented in two dimensions. This form is suitable for impregnation by a liquid polymer. After polymerization or cross-linking (curing) under pressure, the composite will comprise a polymer-network matrix in which the individual strands are embedded. 

The second-stage cross-linking (cure) reaction is initiated by organic peroxides MEK peroxide for room-temperature cure, and benzoyl peroxide or t-butyl perbenzoate or other stabler peroxides for higher-temperature cure processes. Peroxide action may be speeded by heat and/or activators such as cobalt soaps and tertiary amines. (Nonchemists are apt to use the terms catalyst and activator ratber loosely, which can he confusing or even dangerous in practice.)... 

Primary and secondary amines react very readily with epoxy resins (Fig. 3.28). Polyethylene polyamines H2N(CH2CH2NH) H with n = 2 to 4 are particularly useful, because every N-H group reacts with a different epoxy group to produce a highly cross-linked cured thermoset product. They are particularly useful for fast room-temperature cure reactions of coatings and adhesives. 

FIGURE 3.56 Benzocyclobutene cross-linking cure reactions. 

A polymer in which initially linear macromolecules are joined by a covalent bond or a short sequence of chemical bonds either during the polymerization [e.g., poly(styrene-co-divinylbenzene)] or in a postpolymerization cross-linking reaction (cross-linking, curing, or vulcanization). The cross-linked materials are insoluble and they do not flow when heated. 

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