Cross-linked polymers unsaturation

Performance Characteristics Polyester resins undergo a rapid transformation from a viscous Hquid to a soHd plastic state that comprises a three-dimensional cross-linked polymer stmcture. The level of polyester polymer unsaturation determines essential performance characteristics (Table 7), although polymer components can influence subtle features that affect thermal, electrical, and mechanical performance as defined by ASTM procedures. 

Advantages of the electron beam processor are its abiUty to penetrate thick and highly pigmented coatings. It is used to cross-link reactive unsaturated polymers, nonreactive thermoplastic polymers, iasulation, and wire-cable covetings (4,9,16) (see Insulation, electric-wire and cable COVERDIGS). 

Paint Driers and Polymer Additives. Paints based on alkyd resins (qv) dry by the oxidation and cross-linking of unsaturated side chains. Metal catalysts are included in paint formulations to promote this drying. Cerium carboxylates, eg, the naphthenate, are used as through driers, ie, to promote drying in the body of the paint film rather than at the film s surface (44). 

Dialkylperoxides are used as high temperature catalysts for suspension and bulk polymerization as well as hardeners for unsaturated polyester resins and for cross-linking polymers because of their good thermal stability. While the liquid di-tert-butylperoxide is relatively volatile at application temperatures, dicumylperoxide is much less volatile and has the disadvantage of forming decomposition products with intense odors (acetophenone)(Chapter 13). 

Molecular sieve adsorbents have been widely studied and employed to separate saturated, mono- and di-saturated fatty acids or to concentrate them in a mixture. Logan and Underwood (32) patented a method to use zeolite as the adsorbent to separate esters of fatty acids according to their degree of unsaturation. Use of nonionic, hydrophobic cross-linked polymers has also been successful in selective separation of fatty acids (33). The fatty acids are first allowed to adsorb onto the solid bed of a particular adsorbent and then the adsorbed acids may be desorbed by employing a suitable desorbent. 

The cross-linking of unsaturated polymer chains by polymerization with divinyl monomers can be considered to occur in three... 

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