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 A₂ + B₃ stepwise polymerization. TI is defined as the ratio of terminal units of an A₂ + B₃ type highly branched polymer to those in its perfect hyperbranched counterpart. TI is concisely represented as T/(D + L), which can be conveniently calculated from a quantitative NMR spectrum. The model of soluble A₂ + B₃ 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 A₂ + B₃ 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 + B₃ polymerization.