Properties cross-linking reaction

The Merrill and Hamrin criterion was derived for a first-order reaction. It should apply reasonably well to other simple reactions, but reactions exist that are quite sensitive to diffusion. Examples include the decomposition of free-radical initiators where a few initial events can cause a large number of propagation reactions, and coupling or cross-linking reactions where a few events can have a large effect on product properties. 

A thermosetting resin converts to an infusible, cross-linked plastic which is insoluble in any solvent after curing. Because of this irreversible cross-linking reaction, excellent physical properties such as heat resistance, creep resistance, mechanical strength, etc., are obtainable through design of the polymer structure. 

Cross-linking reactions can give products with desired increased strength, memory retention, etc. but accompanying such cross-linking can be unwanted increases in brittleness. Throughout the text, cross-linking is an important reaction that allows the introduction of desirable properties. For instance, it is the basis for many of the elastomeric materials. 

When materials are processed using the cross- linking reaction by GA, and especially when the construction of new functions is attempted, the effects of this chemical reaction on the properties of the resultant materials should be kept in mind. Based upon the cross-linking mechanism discussed above, the following effects are expected. 

Chemical cross- linking reaction by GA could alter some properties of the material, besides the physical network formation between the constituent macromolecules. 

Amines produce polyurethanes with better mechanical properties than when diols are used for curing. Amines produce polyurethanes with a lower temperature resistance than when diols are used. The use of catalysts has been found to direct the cross-linking reactions away from the biuret to the allophanate reactions. 

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