Synthesis of highly branched poly(delta-valerolactone)s: a comparative study between comb and linear analogues

A large diversity of tailor-made linear-comb and star-comb poly(delta-valerolactone)s (PVL) have been obtained with hydroxylated polybutadiene (HPB) as a macroinitiator and 1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD) as a catalyst by a simple "one-step" method. The critical content of this research was to explore systematically the differences in the physicochemistry properties between highly branched PVLs and linear PVLs, including the intrinsic viscosity, rheological properties, and crystallization and melting behavior. Studies of solution behavior and melting behavior elucidated that intrinsic viscosities in solution and complex viscosities in the bulk for comb branched PVLs were much lower compared with their linear and star counterparts. Both WAXD and DSC analysis of PVLs with different topological structures indicated that the comb branched architectures do not alter the structures of the PVL crystallites, but markedly improve the crystallization behavior, e.g. higher crystallinities. Moreover, the influence of the molecular weight of a single arm on the thermal properties and crystallization properties of the obtained linear-comb PVLs was explored. The results demonstrated that the crystallization temperatures (T(c)s), melting temperatures (T(m)s) and crystallinities increased with the increase of molecular weight of a single arm. As such, a structure-property correlation is expected to be constructed which is of great practical importance in the syntheses and applications of highly branched polymers (HBPs).