LAURA MADALINA POPESCU, ROXANA MIOARA PITICESCU, TINCA BURUIANA THE INFLUENCE OF PRESSURE ON ACID POLYURETHANE STRUCTURE Acid polyurethane of hard type was prepared to be further treated in hydrothermal conditions at high pressures of 20, 40, 60 and 80 atm. The influence of pressure on chemical structure and morphology of macromolecular chains have been investigated using Fourier transform Infrared Spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC). Three endothermic peaks appear in hydrothermally treated polyurethanes, being related to conformational changes due to polymer shrinking, decomposition and melting. Their corresponding enthalpies increase with pressure, probably due to a more compact polymer structure at high pressure. Under the influence of pressure, macromolecular chains modify their conformation and approach each other, leading to an increased density of the hydrogen bonds. Stretching vibrations of the –C=O group are shifted from 1746 to 1724 cm-1. There is an optimum pressure (60-80 atm) range where the polyurethane presents an increased capacity of interaction through carbonyl groups (r1 =1.295 at 60 atm) which is favorable for further composite synthesis.
Keywords: acid polyurethane, high pressure, hydrothermal process, IR spectroscopy, DSC