Molecular mobility of unfilled and carbon-black-filled isoprene rubber: proton NMR transverse relaxation and diffusion
In an attempt to understand the effect of intense ultrasound on the devulcanization of unfilled and filled isoprene rubber (IR), melts and networks, non spectroscopic solid state NMR proton transverse relaxation (T2) and pulsed gradient diffusion measurements were performed. At 70.50C, the T2 relaxation decay of the unfilled and 35phr carbon black filled was successfully described by two-component four-parameter model. The long component mainly arose from the unentangled sol, dangling ends and oligomers, and the short component was due to the entangled sol and crosslinked network. Sonication increased intermolecular mobilities, while curing reversed this effect. The long and short T2 components in CB filled IR without processing oil increased with increasing sol generated, while no such increase was observed in the IR extended with oil. Thus, processing oil significantly altered the dependence of both T2 components on the sol fraction. The high melt molecular weight (M) without a low M tail precluded diffusion measurements. The IR melts were then degraded ultrasonically with and without subsequent vulcanization. It lowered and broadened the molecular weight distribution. This made it possible to conduct pulsed gradient diffusion experiments; the diffusion spectrum is bimodal. Here the T2 decays are consistent with a three- component model with six parameters. The additional component here is the intermediate T2 component. The results obtained were quantitatively related to earlier work in natural rubber.
Isayev, Avraam, "Molecular mobility of unfilled and carbon-black-filled isoprene rubber: proton NMR transverse relaxation and diffusion" (2007). Polymer Engineering Faculty Research. 84.