Polyurethane blends usually thicken up during the polymerization, but unexpected drop in viscosity could be occasionally observed [1]. In this study, an oligomeric ether-ester macro diol (EEMD of 2700 g/mol) [2] was diluted with polyethylene glycols (PEG of 200 g/mol or 400 g/mol). The polyols were mixed with a trifunctional adduct of hexamethylene -1,6- diisocyanate (HDI3, CAS 3779-63-3) at 1.4 mol excess to initiate addition reactions and assure eventual gelation. Within 1 min of mixing dynamic viscosity η was measured using Anton Paar MCR 302 rheometer and a concentric cylinder system. The spindle was lowered leaving 1 mm gap between cylinders and assuring the absence of air bubbles. Viscosity was measured at 3 different shear rates: 1 s-1, 10 s-1, 100 s-1, see fig 1. The theoretically predicted viscosities are somewhat higher than measured. During early stages of polymerization the viscosity is highly dependent on shear, but later the trends become Newtonian-like [3]. Despite ongoing polymerization, viscosity seems to drop initially, or at least stagnate. It remains unclear what causes such unusual tendencies of viscosity dependence on polymerization

Abstract and poster from the conference. The same abstract can also be found on pg 175 within the proceedings website https://www.ebooks.ktu.lt/eb/1561/advanced-materials-and-technologies-book-of-abstracts-of-23rd-international-conference-school/