Interplay between chemical structure and ageing on mechanical and electric relaxations in poly(ether-block-amide)s

The molecular relaxations of two poly(ether-block-amides) with different polyamide/polyether ratios were studied to evaluate the effect of the chemical structure on the mechanical and electrical properties and to investigate the modification of these properties by an ageing process at high relative humidity. A specific treatment is designed to simulate an accelerated degradation of the material to evaluate the effect of freezing and melting thermal cycles of residual adsorbed water. The effects of the polyamide/ polyether ratio on the polymer properties and the consequences of the degradation treatment are studied by correlating the results of FT-IR, TGA, DSC, DMA and BES. The analysis of DMA and BES data highlights the presence of various relaxation events: aPA, aPE, bPA, bPE and g, assigned respectively to polyamide (aPA) and polyether (aPE) glass transitions, local fluctuations of the dipole associated with the polyamide (bPA) and the polyether (bPE) chains and local fluctuations of the CH2 groups (g) along the polymer chains. The ageing treatment results in an increased crystallinity in PEBAs with a high polyamide content due to the transition of the polyamide chains from a parallel to anti-parallel b-sheet conformation which forms a stronger hydrogen bonding network. In contrast in PEBAs with high polyether content, the ageing treatment induces the transition of polyamide chains from a parallel b-sheet to an a-helix conformation resulting in the formation of weaker inter-chain interactions.