Terminal Index: A New Way for Precise Description of Topologic Structure of Highly Branched Polymers Derived from A2 + B3 Stepwise Polymerization

Terminal index (TI) was presented as a new characteristic parameter for quantitative description of branched and cyclic topology of highly branched soluble polymers derived from A(2) + B-3 stepwise polymerization. TI is defined as the ratio of terminal units of an A(2) + B-3 type highly branched polymer to those in its perfect hyperbranched counterpart. TI is concisely represented as TAD + L), which can be conveniently calculated from a quantitative NMR spectrum. The model of soluble A(2) + B-3 type polymers is suggested as an intermediate between multicyclic polymers and perfect hyperbranched polymers. The TI ranges between 0 and 1 where a higher TI indicates a perfect hyperbranched topology while a low TI indicates a multicyclic structure. The analysis of soluble A(2) + B-3 type polyesters and polycarbosilanes as model polymers demonstrates that TI as a more precise parameter, along with degree of branching, can be generally applied to understand the fine topology of highly branched polymers derived from A(2) + B-3 polymerization.