Chain extenders and cross-linkers

Primary and secondary di- and polyamines are used as chain extenders and cross-linkers. Aromatic amines are more reactive than aliphatic ones. 

Use Chain extender and cross-linker, intermediate in organic synthesis of dyes, polymers, especially polyurethanes. 

Raw Materials for Urethane Coatings Isocyanate Components Di- and Polyhydroxy Components Chain Extenders and Cross-linkers Catalysts... 

Chain Extenders and Cross-linkers. In addition to the two principal components of most urethane coatings, isocyanate and polyol components, a number of di- or polyfunctional, active hydrogen components may be used as chain extenders or cross-linkers. The most important classes of compounds for this use are diols or polyols (monomers or oligomers), diamines, and alkanolamines. Typical examples of diols are ethylene, dlethylene, dlpropylene glycol, 1,4-butanedio1, 1,5-hexanediol, neopentyl glycol,... 

Chain extenders and cross-linkers (encountered especially in thermoplastic urethanes) are usually short diamines or diols, such as 1,4-butane-diol or te/rafe/s(2-hydroxypropyl)ethylenediamine. Alkanolamines and triols like glycerol are also used. Most of these can be easily determined by GC. 

As was discussed in Section 3.2, chemistry variables are introduced in the polyurethane structure mainly by chain extenders and cross-linker agents, and polyols and to a less extent by isocyanates. Variables introduced by polyols and chain extenders are ... 

The production of polyurethane involves the controlled polymerization of an isocyanate, a long-chain-backbone polyol and a shorter-chain extender or cross-linker. The reaction rates can be controlled through the use of specific catalyst compounds, well known in the industry, to provide sufficient time to pour or otherwise transfer the mix and to cure the polymer sufficiently to allow handling of the freshly demolded part. The use of blowing agents allows the formation of a definite cellular core (thus the term microcellular elastomer ) as well as a non-porous skin, producing an integral sandwich-type cross section. 

Polyurethane hydrogels are widely used in soft contact lenses, controlled release devices, semipermeable membranes and hydrophilic coatings (66). The properties of polyurethane hydrogels can be varied by variation of their components, such as the polyols, diisocyanate, chain extender, or cross-linker (67-69). Because of the excellent mechanical and physical properties, polyurethanes are widely used in medical applications such as coating for medical devices for preventing protein adsorption (70, 71). 

Telechelic polymers can be used as cross-linkers, chain extenders, and precursors for block and graft copolymers. Moreover, star and hyper-branched or dendric polymers are obtained by coupling reactions of monofunctional and multifunctional telechelics with appropriate reagents. Various macromolecular architectures obtained by the reactions of telechelics are represented in Figure 1. 

Fillers (qv) are occasionally used in flexible slab foams the two most commonly used are calcium carbonate (whiting) and barium sulfate (barytes). Their use level may range up to 150 parts per 100 parts of polyol. Various other ingredients may also be used to modify a flexible foam formulation. Cross-linkers, chain extenders, ignition modifiers, auxiHary blowing agents, etc, are all used to some extent depending on the final product characteristics desired. 

There are regulatory and handling problems in using methylene bis(2-chloroaniline) as a chain extender (curative or cross-linker) for toluene diisocyanate (TDI)-terminated prepolymers, to produce urethane elastomers (1,2). There is, therefore, a strong interest in achieving similar elastomer properties with other curatives and methylene diphenyl diisocyanate (MDI)-terminated prepolymers(3,4). 

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