Enhanced relaxation behavior below glass transition temperature in diene elastomer with heterogeneous physical network

- Polyisoprene with heterogeneous physical network formed by quadruple hydrogen bond (PI-UPy).
- The increase of glass transition temperature in PI-UPy.
- A new relaxation process in PI-UPy.

A large number of polymer materials bearing dynamic bond systems have been reported, while the focus is mainly on the macroscopic properties such as self-healing and shape memory. It is well established that dynamic bonds have significant effect on the performance of polymers. In this article, we report the rational design of 2-ureido-4[1H]-pyrimidinone (UPy) units as reversible crosslinking networks introduced into polyisoprene (PI) chains and special consideration has been devoted to the effect of UPy dimers on relaxation behavior of elastomer. The incorporation of UPy dimers into PI chains is corroborated by Fourier Transform Infrared and thermal measurements. As revealed by synchrotron X-ray, the inhomogeneities of modified PI originate from UPy dimers, which resulted in the increased dielectric strength of segmental motion. An additional relaxation process (new mode) has been observed in the samples with high UPy content by broadband dielectric spectroscopy but cannot be found in neat PI. It is evident that this new mode relaxation process behaves as a thermally activated process. However, the dielectric strength of new mode exhibits the opposite trend, compared with that of segmental motion. This anomalous phenomenon could be rationally attributed to the dissociation process of UPy dimers induced by high temperature.