On the α relaxation of the constrained amorphous phase in poly(ethylene)

The idea of coexistence of two different amorphous fractions in semi-crystalline poly(ethylene) (PE) is taken into consideration. Differential scanning calorimetry, dynamic mechanical thermal analysis and positron annihilation were used to study the effect of supermolecular structure on the glass transition associated with ‘semi-ordered’ amorphous phase. The arrangement of chains, located in this phase, is forced internally by the presence of crystalline domains. Influence of drawing, irradiation and annealing on thermodynamic and structural parameters was investigated. In a series of experiments the correlation between the glass transition, the α relaxation and the free volume of a semi-crystalline system was found. In order to better describe the relaxation, existence of two types of amorphous fractions was assumed. The relaxations are treated as a long-scale motion of macromolecule segments located into the ‘semi-ordered’ amorphous regions, or into the ‘real’ amorphous regions, and are labelled as α_c and α_g, respectively. The magnitudes of the loss peaks were quite sensitive to the free volume, which was found to increase by drawing and decrease by irradiation. Two different DSC traces were recorded for both glass transitions.