Relaxation behaviour of semirigid chains in the amorphous state

Dielectric and mechanical behaviour of two polymers having severe restrictions on the conformational versatility of the backbone, namely poly(monocyclohexylmethylene itaconate) (PMCMI) and poly(dicyclohexymethylene itaconate) (PDCMI), have been studied. Both polymers present a weak glass-rubber relaxation named α and two stronger absorptions in the glassy state that, in increasing temperature order, are called β- and γ-relaxations. Both mechanical and dielectric β-peaks are located in the same region of the spectra and have the same activation energy, which suggest that both relaxations are caused by the same molecular mechanisms. The analysis of the dipole moments of both polymers suggest that they behave as freely joint chains as far as their polarity is concerned. The dipolar correlation coefficients in the sub-glass region were calculated by assuming that the dielectric activity is only produced by reorientations of the side groups with respect to the frozen main chains. The fact that the values of the coefficients thus calculated are somewhat larger than the experimental values suggests that dipolar intermolecular interactions cannot be neglected in the analysis of the dielectric behaviour of these polymers.