Additives to Modify Polymer Chain Structures

Polycondensation polymers such as polyesters or polyamides carry functional end groups, which can be used to build up the molecular weight by reaction with suitable additives that are capable of reacting with these end groups. As there are ideally two end groups per chain, a linear 

As an example of molecular weight increase of polyamides, the decrease of the MVR (increase in molecular weight) in relationship to the reactive additive concentration is shown for diepoxides, catalyzed by a phosphonate (Fig. 11.23) [43]. 

As an alternative to organic peroxides, carbon-carbon (CC) initiators, for example, dimethyl diphenylbutane, hydroxylamine esters [51], or unsymmetric azo compounds [47] can be used for crosslinking reactions especially at higher processing temperatures. 

Concentrations of crosslinking agents depend on the required crosslinking density, the application, and the production process, and vary between 1% and 10%. 

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