Chain dynamics in polyisoprene stars with arms linked by dynamic covalent bonds to the central core

Abstract

Although the use of dynamic covalent bonding (DCB) is a promising method to obtain easily recyclable polymer networks, there are many aspects of the incorporation of dynamic covalent bonding into polymer systems that remain poorly understood. In order to gain insight into the fundamentals of these materials, well-controlled model systems are required. Here, we present the synthesis of polyisoprene (PI)-based 3-arm stars containing vinylogous urethane DCBs as linkers of the PI arms to the core of the star. The dynamics of these 3-arm stars, with three different arm sizes, is studied by broadband dielectric spectroscopy. A conventional (static) 3-arm PI star of intermediate size has also been synthesized and studied, and all results are directly compared with those of a linear PI chain. A prominent intermediate relaxation between those identified as the slower normal mode and the faster α-relaxation of PI is found in the stars containing DCBs. This relaxation, which becomes more significant as the molecular mass of the PI arms decreases, seems to originate from the dynamic bond exchange that occurs at the level of the star's core. On the other hand, the arm retraction dynamics responsible for the normal mode relaxation do not show significant differences with respect to that observed in the static star.