Tunable intramolecular cyclization and glass transition temperature of hyperbranched polymers by regulating monomer reactivity

In this work, the dialkynyl-functionalized A₂ monomers with different alkyls and aromatic backbones were synthesized and employed as construction units to produce multi-component A₂ + B₃ type hyperbranched polymers via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The alkyl and aromatic backbones between two alkynyl groups were designed as hexyl (C₆), dodecyl (C₁₂), phenyl (Ar) and diphenyl (Ar₂) to regulate monomer reactivity for investigating its effect on intramolecular cyclization and glass transition temperature (T_g). It was found that both the increase of backbone rigidity and the decrease of backbone length can enhance monomer reactivity. In addition, the differences of monomer reactivity can greatly influence the backbone compositions of hyperbranched polymers. High monomer reactivity can lead to high content of corresponding backbones, which can further control the degree of intramolecular cyclization and T_g of hyperbranched polymers. Thus, regulating monomer reactivity is an effective way to tune hyperbranched topology, backbone composition and physical properties.