Dynamics of twist glass transition of a pi-conjugated polymer investigated by NMR relaxation spectroscopy: poly(p-phenylene)

TL;DR

This study investigates the twist glass transition in poly(p-phenylene) using NMR relaxation spectroscopy, revealing critical dynamics consistent with the 3D XY universality class and providing insights into polymer backbone motion.

Contribution

It is the first to identify the twist glass transition in PPP and characterize its critical dynamics using NMR relaxation spectroscopy.

Findings

Observation of glass transition at 295K via DSC.

Identification of one-dimensional backbone motion from frequency dependence.

Critical dynamics consistent with the 3D XY universality class.

Abstract

Dynamics of Yamamoto-type poly(p-phenylene)[PPP] was investigated by differential scanning calorimetry(DSC) and proton solid-state NMR relaxation spectroscopy. The DSC chart shows the baseline jump without latent heat at 295K, which is due to the glass transition of the polymer. From the variable temperature proton longitudinal relaxation time(T1) measurements, relatively short T1 is observed over the wide temperatures range from 250K (closed to Vogel-Fulcher-Tamman temperature) to 360K, inferred the existence of cooperative critical slowing down associated withthe glass transition. The frequency dependence of proton longitudinal relaxation time at 295K shows R1 ~ w^-0.5 dependence, which is due to the one-dimensional diffusion-like motion of the backbone conformational modulation. The frequency dependence is held at least up to 360K. From these experiments, we were able to observe the twist glass transition of the backbone of PPP, of which critical dynamics has a universality class of the three-dimensional XY model.