Melt Rheology of Aliphatic Hyperbranched Polyesters

Rheological behavior in melt of aliphatic hyperbranched polyesters (AHBP), synthesized using pseudo-one-step and one-step procedure, was investigated in this work. Three commercially available AHBP were also examined. Because of the presence of relatively strong hydrogen bonds between numerous end hydroxyl groups, AHBP of lower generation number, as well as the sample of tenth pseudo generation, show non-Newtonian behavior in the entire investigated frequency and temperature region. However, for other examined AHBP, the slope of the frequency dependence of complex viscosity (eta* = f(omega)) becomes smaller with the temperature increase. Therefore, samples of fourth, fifth, and sixth pseudo generations show Newtonian behavior at temperatures higher than 70 degrees C. Value of glass transition temperature, melt flow activation energy, fractional free volume, and thermal expansion coefficient were determined for the investigated AHBP. The influence of the type of end groups on rheological properties of AHBP was also examined. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2925-2934, 2009