Cross-linking mechanisms for

The observed spectral changes suggest the following photochemical cross-linking mechanism for oligoorganoepoxystannanes ... 

Both disilazanes A and B, which are readily prepared and isolated, may be cocondensed with other polymeric polysilazanes. By cocondensation, the controlled introduction of either (or both) vinyl and silyl hydride groups can be accomplished readily. In turn, these groups provide a convenient cross-linking mechanism for these polymers via platinum catalysis or thermal inducement of hydrosilation. This method eliminates the need for cross-linking via hydrolysis or oxidation, which introduces undesirable oxygen bonds. Other advantages will be treated in a later section. 

The prevulcanization of natural rubber in latex form has also been a subject of much investigation. The cross-linking mechanism is not yet fully understood, but the water apparently plays a major role in it. Irradiation results in the cross-linking of the rubber molecules and in coarsening of the latex particles. A process of cross-linking of natural rubber latex has been developed to the point that it can be used for an industrial-scale application. The irradiation is performed in aqueous media by electron beam without a prorad (sensitizer) at a dose of 200 kGy (20 Mrad) or in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur cured (vulcanized) film. As an alternative, the addition of a variety of chloroal-kanes makes it possible to achieve a maximum tensile strength with radiation doses of less than 5 Mrad (50 kGy). ... 

These different casein monomers combine with calcium phosphate to form discrete particles on the nano-size scale. The phosphoserines of the caseins are seemingly clustered for the purpose of linking within the micelle to putative calcium phosphate microcrystallites, also known as nanoclusters (Holt, 1992 Home, 1998, 2002, 2003, 2006 Holt et al., 2003 Home et al., 2007). Structural evidence for the existence of such nanoclusters has come from neutron and X-ray scattering (de Kruif and Holt, 2003 Holt et al., 2003 Pignon et al., 2004 Marchin et al., 2007). The presence of nanoclusters allows native casein micelles to be effective natural suppliers of essential calcium salts in the human diet in a readily assimilated functional form. Protein-nanocluster interactions are the central concept of the cross-linking mechanism in Holt s model of casein micellar assembly (Holt et al., 2003 de Kruif and Holt, 2003). Any analogy with conventional soap-like micelles is considered to be... 

Isocyanates also can react with each other to produce carbodiimides with the loss of carbon dioxide. This reaction requires high temperatures unless catalyzed by specific phosphorus compounds. Formation of carbodiimides normally is not an important cross-linking mechanism in polyurethane adhesives. However, carbodiimides are sold by Dow Chemicals (Ucarlnk ), Nisshinbo Industries (Carbodilite ), and Stahl USA (XR-2569). They have been recommended as water scavengers, crosslinkers, and stabilizers for carboxyl functional polyurethanes. The carbodiimide can react with water to give a urea, which still can react with additional isocyanate to produce a biuret. 

Besides the continuous fibers, application of metallorganic polymers to heat-resistant coatings, dense ceramic moldings, porous bodies, and SiC matrix sources in advanced ceramics via polymer infiltration pyrolysis (PIP) have been developed. Novel precursor polymers have been synthesized and investigated for ceramics in addition to PCS (Table 19.1). For SiC ceramics, various Si-C backbone polymers have been synthesized. Their polymer nature (e.g., viscosity, stability, cross-linking mechanism, and ceramic yield) are, however, fairly different from PCS. On the other hand, polysilazane, perhydropolysilazane, polyb-orazine, aluminum nitride polymers, and their copolymers have been investigated... 

Thymine-based polymers are advantageous for several reasons. First, they are water-soluble, which avoids the need for organic solvents, an environmentally beneficial objective on its own. Second, a polymerization reaction is not necessary. These water-soluble non-toxic polymers are already polymerized. The photoreaction initiates a cross-linking mechanism by which neighboring strands are tied together (Figure 10). The formation of networks in this way makes them insoluble. 

Figure 4 shows the proposed mechanism for the metabolism of phenolic and diphenolic compounds to quinonoid cross-linking agents for macromolecules in the outer portions of dark brown cuticle from... 

Thermosetting acrylics can be produced from a variety of monomers in varying percentage compositions the systems utilize a variety of cross-linking mechanisms (Table IV). A typical thermosetting acrylic can be prepared from 15-80% styrene, 15-18% alkyl acrylate, and 5-10% acrylic acid (27). Acrylic acid provides the functionality for cross-linking with epoxy resins. 

The reason for these surprising results is postulated by utilizing a concept of immobilization in the cross-linking mechanism of epoxy resins. The aliphatic di- and polyamines react rapidly at ambient conditions. At the higher temperature, these systems are... 

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