Thermoplastic elastomers by hydrogen bonding 1. Rheological properties of modified polybutadiene

Polybutadiene of narrow molecular weight distribution was modified using 4-phenyl-1, 2,4-triazoline-3,5-dione. The degree of modification was 1% and 2% with respect to the repeating units. Hydrogen bonding between the highly polar urazole groups thus incorporated into the polymer gives rise to the formation of a thermoreversible elastomeric network. Dynamic mechanical measurements in the temperature range between 220 and 330 K support the picture of the thermoreversible hydrogen bond interaction. The rubber elastic plateau is shifted to higher temperatures and lower frequencies. The increase in the plateau modulus cannot be attributed solely to the contribution of the network structure but is mainly a consequence of the broadening of the relaxation time spectrum in the modified samples. From the temperature dependence of the shift factors log(a_T) it is concluded that the general WLF approach fails. The strong temperature dependence of the apparent activation energy of flow is a consequence of the temperature dependence of the hydrogen bond interaction.