Dielectric relaxations and electrical conductivities of poly(alkyl methacrylates) under high pressure

Abstract

Abstract Dielectric properties of four methacrylate polymers (methyl, ethyl, n ‐butyl and n ‐octyl) were studied in the frequency range 0.0001 cps–300 kcps at temperatures above and below the glass transition temperature and at various pressures up to 2500 atm. At temperatures well above T g a single relaxation peak (α′ peak) was observed in the case of the higher n ‐alkyl methacrylates. However, this peak was split into two peaks, α and β, with decrease in temperature or increase in pressure. The molecular motions corresponding to the α and the β relaxation processes are the micro‐Brownian motions of amorphous main chains and of flexible side chains, respectively. From the temperature and the pressure dependence of the average dielectric relaxation time of these polymers the single relaxation process (the α′ process) was attributed to the micro‐Brownian motion of the main chain coupled with that of the side chain. The effects of temperature and pressure on the d.c. conductivity of these polymers were also studied.