Studies of molecular dynamics in polyurethane networks with hyperbranched polyester Boltorn®H30 as a crosslinker

Several non-conventional polyurethane networks crosslinked with hyperbranched polyester (Boltorn®H30) were synthesised with an aim to determine an influence of the polyurethane linkage length on molecular relaxations in such systems. The polyurethane chain length was regulated by changing the macrodiol length or by changing the number of the repeating macrodiol-diisocyanate units. Molecular dynamics were investigated by dielectric spectroscopy and by dynamic mechanical analysis. It was found that the macrodiol length has a strong influence on the glass transition and the α-relaxation process correlated with it. By contrast, the changes of the repeating unit number practically did not affect the molecular relaxations. This effect was explained by the formation of a physical network by hydrogen bonds between urethane groups, controlling the molecular mobility. The distribution of the hydrogen bonds is controlled by the length of soft segment between the urethane groups. It means that in the polyurethanes based on the same macrodiol the distribution of the hydrogen bonds is similar, and what follows it, the molecular dynamics of such systems is very similar.