Structural relaxation of the constrained amorphous phase in the glass transition zone

The idea of two amorphous fractions in polymer is discussed. In order to clarify the influence of specific arrangement of chains on a glass transition, semi-crystalline polymer with various supermolecular structures was studied. It was possible to find two glass transitions well separated. The orientation of the amorphous regions induced by semi-crystallinity results in the appearing of the constrained and unconstrained amorphous structures. Both types of amorphous fractions are distinguished in this paper that give better descriptions of alpha-relaxations. In a serious of experimental studies of chains mobility and free volume, our attention has been given to elucidation of the correlation between the glass transition, the alpha-relaxation and the free volume of polymeric system. Non-Arrhenius and Arrhenius types of temperature dependence of the relaxation times were found for the 'real' and the 'semi-ordered' amorphous fraction, respectively. Differential scanning calorimetry, dynamic mechanical thermal analysis and positron annihilation lifetime spectroscopy were applied.