Real-time crystallization and melting of poly(n-octadecyl methacrylate) induced by temperature and pressure - A dielectric spectroscopy investigation

We have studied the crystallization and melting of poly(n-octadecyl methacr ylate) (PNODMA) by performing temperature and pressure jump experiments fro m the melt to the final semicrystalline state. The evolution of the crystal lization process is studied in real time by recording the changes in the di electric spectrum. The single cu process in the melt upon crystallization l ooses intensity and a new slower alpha ' process appears, reflecting the dy namics of the restricted amorphous phase. The effect of pressure on increas ing the crystallization temperature is stronger than the increase of the me lt glass transition temperature, i.e. dT(c)/dP approximate to 2.3dT(g)(m)/d P. The isothermal/isobaric crystallization experiments induced by T and P j umps give rise, respectively, to stretched exponential and to typical nucle ation and growth kinetics of the Avrami type. The different crystallization kinetics induced by T and P reflect the 'paradoxical' situation of increas ing mobility with increasing pressure. From the equivalence of the dynamics we concluded that undercooling of 1K corresponds to an overpressure of 20 MPa, ie. deltaT/deltaP approximate to 50 K/GPa.