Cross-linking technologies

In this chapter, the big four thermoplastics are covered polyethylene, polypropylene, polyvinyl chloride, and polystyrene. Like most other thermoplastics, they are long-chain polymers that become soft when heated and can be molded under pressure. They are linear- or branch-chained and, except for some exotic copolymers, have little or no cross-linking. Technological advances continue. Research in copolymerization, catalysts, processing, blending, and fabricating continues even as you read this. 

A practical guide to modification and cross-linking technology for research, diagnostics, and therapeutics i Provides useful, detailed, easy-to-follow, step-by-step protocols 0 Contains easy-to-read and easy-to-understand key concepts for making bioconjugates of all types... 

The traditional cross-linking technologies utilized in the coatings market range from hydroxyl functional binders (acrylics or polyesters) cross-linked with melamines (IK) or isocyanates (2K) to drying oils that cure through oxidation of unsaturation in the backbone, to epoxy resins cross-linked with amino resins (amido amines, amines, etc.). 

The benefits of PEX over other plastics has led to a proliferation of cross-linking technologies and, of course, each manufacturer claims the superior quality of its product. Indeed, PEX can be advantageously used in many applications owing to caution in ... 

Class Two. The use of cross-linked PDMS coatings on paper and plastic substrates avoids this thermal variation difficulty. There is also the advantage that such materials are readily available as commercial products primarily to provide release liners for the facile delivery of PSA-coated labels, decals and tapes. Two types of well-understood cross-linking technology are utilized tin-catalyzed systems based on the condensation of silanol and alkoxysilyl functionalities, and platinum-catalyzed systems based on hydrosilylation addition of SiH to vinyl functional siloxanes. 

A unique feature of in situ encapsulation technology is that polymerization occurs ia the aqueous phase thereby produciag a condensation product that deposits on the surface of the dispersed core material where polymerization continues. This ultimately produces a water-iasoluble, highly cross-linked polymer capsule shell. The polymerization chemistry occurs entirely on the aqueous phase side of the iaterface, so reactive agents do not have to be dissolved ia the core material. The process has been commercialized and produces a range of commercial capsules. 

The most commonly used polymers are partially hydrolyzed polyacrylamides (32). The optimum degree of hydrolysis depends on the apphcation, injection water composition, and reservoir conditions (33,34). More salt-tolerant acrylamide copolymers may permit this technology in higher salinity injection water (35). Eield apphcations of cross-linked xanthan gum have also been reported (36). 

Similar types of cross-linking reactions are observed for polymers to which photosensitive molecules ate chemically attached to the backbone of the polymer stmcture (Fig. 7). Radiation curing of polymers using uv and visible light energies is used widely in photoimaging and photoresist technology (Table 8) (58,59). 

Thaumatin. Thaumatin [53850-34-3] is a mixture of proteins extracted from the fmit of a West African plant, Thaumatococcus daniellii (Beimett) Benth. Work at Unilever showed that the aqueous extract contains two principal proteins thaumatin I and thaumatin II. Thaumatin I, mol wt 22,209, contains 207 amino acids in a single chain that is cross-linked with eight disulfide bridges. Thaumatin II has the same number of amino acids, but there are five sequence differences. Production of thaumatins via genetic engineering technology has been reported (99). 

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