Effect of pressure on the side-chain crystallization of poly(n-octadecyl methacrylate) studied by dielectric spectroscopy

Abstract

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.