Intramolecular cyclization in A ₂ + B ₃ polymers via step-wise polymerization resulting in a highly branched topology: Quantitative determination of cycles by combined NMR and SEC analytics

In this contribution, we report a convenient expression of average number of cyclic structures (ANC) and cyclic-average molecular weight (M _C) to quantificationally describe the topological defect of intramolecular cyclization in highly branched polymers synthesized via A ₂ + B _n (n ≥ 3) stepwise polymerization strategy by a combination of nuclear magnetic resonance spectrometry (NMR) and size exclusion chromatography (SEC). The ANC and M _C depend on the number ratio of dendritic, linear, terminal units and number-average molecular weight of hyperbranched polymers, which can be derived from NMR and SEC, respectively. The analysis of hyperbranched polycarbosilanes with silicon hydrogen bonds (A) or vinyl groups (B) termini from A ₂ + B ₃ approach indicates that the quantificational description of ANC and MC make it easy to well understand intramolecular cyclic structures resulting in a highly branched topology. Regulating the flexibility and rigidness of internal units in A ₂ monomers is an effective way to control the extent of intramolecular cyclization. Because of the general and convenient nature, the ANC and M _C have potential for the quantificational description of intramolecular cyclization, i.e. one type of topological defect, in a variety of hyperbranched polymers synthesized via A ₂ + B _n strategy.