ABSTRACT
Telechelic polymers are usually bifunctional linear polymers having reactive groups at their extreme positions — chain ends. An analogy of formation of hard segment sequences in linear polyurethanes is possible in branched and cross-linked polyurethanes. It is well-known that the allophanate and biuret formation is utilized in practice for intentional modification of the polyurethane properties. The chapter discusses the spanning-tree approximation of post-gel cyclization and deals with polyurethane networks. The network build-up is simulated by chemical kinetics. The theories of network build-up describe the changes of structural parameters brought about by formation of chemical bonds. The existing branching theories fall into two major categories: graph-like models not directly associated with the dimensionality of space, and network models generation in n-dimensional space. The systems macrotriol-or macrotetrol-diisocyanate, or macrodiol-triisocyanate can serve as model systems in network formation and elasticity studies.
