Dynamics of amorphous and semicrystalline 1,4-trans-poly(isoprene) by dielectric spectroscopy

Abstract

We have studied the dynamics of amorphous 1,4-trans-poly(isoprene) (trans-PI) with different molecular weights using broadband dielectric spectroscopy over a wide range of temperature ∼Tg − 70 K to Tg + 130 K, and frequencies (10−1 to 106 Hz). Avoiding crystallization by quenching, three dielectric processes (global chain, segmental and local relaxations) were observed in order of decreasing temperature. Both the segmental and local relaxations of the here studied trans-PI, were found to be markedly different compared with the corresponding processes in cis-PI. In contrast, the temperature dependence of the relaxation time related to the global chain mode was found to be independent of the chain configuration. However, its relaxation strength was 1 order of magnitude lower in trans- than in cis configuration indicating a small parallel component of the dipole moment in trans configuration. In addition we also studied the dielectric spectra of trans-PI upon crystallization. The kinetics during crystallization as observed by dielectric spectroscopy results independent of molecular weight. During isothermal crystallization the dielectric spectra can be analyzed by a combination of three processes: the αm-relaxation related with the modified amorphous phase, the so-called αCAP-relaxation induced by crystallization and the β-relaxation, the two later only varying in relaxation strength. At the end of isothermal crystallization a percentage of crystallinity about 30% was estimated.