Rheological properties of concentrated solutions of aliphatic hyperbranched polyesters

Abstract

The rheological investigation of concentrated solutions of aliphatic hyperbranched polyesters (AHBP) in N-methyl-2-pyrrolidinon (NMP) is presented. Two series of hydroxy-functional AHBP were synthesized using pseudo-one-step and one-step procedure. Three commercial (Boltorn(R)) AHBP were also investigated. In the examined temperature region (10-50 degrees C), AHBP solutions (c <= 45 wt.-%) exhibited Newtonian behavior. The same was observed for 50 and 55 wt.-% solutions at T >= 40 degrees C. However, at T < 50 degrees C, solutions of AHBP of higher concentrations (50 and 55 wt.-%) showed shear thinning behavior. Values of the flow activation energies were calculated for all examined AHBP. The influence of the procedure for the synthesis, concentration and temperature on rheological behavior of AHBP solutions in NMP is discussed.