Polymer Networks from Precursors of Defined Architecture. Activation of Preexisting Branch Points

A growing group of polyfunctional precursors of polymer networks contains more than one branch point (cross-link). The bonds they extend lead either to another branch point or to a functional group. When such precursors are cross-linked, these branch points are gradually activated to reach the status of elastically active cross-links (EAC), i.e., such cross-links from which three or more bonds extend that have infinite continuation. The contribution of EAC's to the concentration of elastically active network chains (EANC) increases gradually with conversion of functional groups and depends on precursor architecture. Cross-linking of specially assembled precursors, functional dendrimers, and hyperbranched polymers is treated theoretically using the stochastic theory of branching processes based on generation of structures from units in different reaction states. Each bond extending from a branch point is considered as to whether the issuing subtree is finite or whether an infinite continuation exists. Several examples of development of concentration of EANC's and other structural parameters of the network demonstrate the importance of the activation process. It is shown that the branch points of dendritic precursors closer to its center are activated sooner than those at the precursor periphery.