Effect of Hydrogen Bonding Interaction on Rheological Properties of Hydroxyl-terminated Hyperbranched Polyesters

Based upon 1,1,1 -trimethanol propane (TMP) as core and 2,2-bis(hydroxymethyl) propionic acid (DMPA) as branched monomer, the first to the fifth generation of hydroxyl-terminated aliphatic hyperbranched polyesters were synthesized through melt polycondensation. The effect of hydrogen bonding interaction on rheological properties of hydroxyl-terminated hyperbranched polyesters was studied by rotational rheometer. The results showed that the onset of nonlinear viscoelastic region occurred at lower strains for hydroxyl-terminated hyperbranched polyesters of lower generations compared with those of higher generations in the dynamic strain sweep experiments. Relaxation times calculated from dynamic rheological parameters indicated that the lower generations relaxed much slower than their higher generation counterparts. Hydroxyl-terminated hyperbranched polyesters of the first and the second generations showed shear-thinning behavior of pseudoplastic fluid but the third to the fifth generations of hyperbranched polyesters showed Newtonian fluid behavior in both oscillatory and steady shears within the deformation rates investigated. The Cox-Merz rule was found to be not obeyed by all the polymers studied. The degree of crystallinity was higher for low generations compared with high generations detected by temperature sweep experiments. These phenomena appeared in the rheological experiments are closely related to intermolecular hydrogen bonding interaction.