The primary α and the secondary Johari–Goldstein (JG) β relaxations of supercooled glass-forming neat epoxy resin and 2-picoline in mixture with tristyrene are monitored by broadband dielectric relaxation spectroscopy at ambient pressure and elevated pressures. For different combinations of pressure and temperature that maintain the α-relaxation time constant, the frequency dispersion of the α relaxation is unchanged, as previously found in other glass-formers, but remarkably the JG β-relaxation time remains constant. This is more clear evidence of a strong connection between the α- and JG β-relaxation times, a fact that should be taken into account in the construction of a viable theory of glass transition.

We have studied the effect of temperature and pressure on the crystallization of poly(n-octadecyl methacrylate) (PnODMA) by dielectric spectroscopy within the T range from 253 to 363 K and for pressures up to 2.5 kbars. Upon crystallization the spectrum shifts to lower frequencies and broadens considerably towards the low-frequency side. There is a strong increase of pair correlations as we approach the transition from the melt state indicating pretransitional ordering. From the T and P dependence of the relative dielectric intensity the existence of the rigid amorphous phase was documented. From the T and P dependence of the relaxation times the activation energies and activation volumes were obtained and found that the crystal state possess higher activation parameters reflecting the dynamics of the restricted amorphous phase. The effect of pressure on the morphology is to increase the crystal thickness by incorporating additional methylene units to the side-chain crystals.

Dielectric relaxation spectra of two closely related glass formers, dipropylene glycol [H–(C3H6O)2–OH] and dipropylene glycol dimethyl ether [CH3–O–(C3H6O)2–CH3], were measured at ambient and elevated pressures in the supercooled and the glassy states are presented. Hydrogen bonds formed in dipropylene glycol are removed when its ends are replaced by two methyl groups to become dipropylene glycol dimethyl ether. In the process, the primary relaxation, the excess wing, and the resolved secondary relaxation of dipropylene glycol are all modified when the structure is transformed to become dipropylene glycol dimethyl ether. The modifications include the pressure and temperature dependences of these relaxation processes and their interrelations. Thus, by comparing the dielectric spectra of these two closely related glass formers at ambient and elevated pressures, the differences in the relaxation dynamics and properties in the presence and absence of hydrogen bonding are identified.