PCL-PEC-PCL TRIBLOCK COPOLYDIOL-BASED WATERBORNE POLYURETHANE .1. EFFECTS OF THE SOFT-SEGMENT COMPOSITION ON THE STRUCTURE AND PHYSICAL-PROPERTIES

This article examines the effects of the soft-segment composition on t he structure and physical properties of waterborne polyurethane (WBPU) based on polycaprolactone-poly(ethylene glycol)-polycaprolactone (PCL -PEG-PCL) triblock copolydiol as the soft segment. The molecular weigh t of PEG in the soft-segment composition and soft-segment content(SSC) are varied in this study. The water-vapor permeability (WVP) for the WBPU-coated nylon fabric is also studied. The results showed that the glass transition temperatures (T-g's) of the soft segment decreased an d its temperature range (Delta T-g's) narrowed with increase of SSC up to 63 wt % and decrease of the PEG molecular weight. The dynamic mech anical analysis results showed that the alpha-peak height of the soft segment increased with SSC when the SSC was less than 63 wt %. However , when SSC was more than 63 wt %, the alpha-peak height became smaller with increasing SSC due to the crystallization of the soft segment. A t the same SSC, the number of spherulites was reduced and the spheruli tes become larger with decrease of the PEG molecular weight. As for th e mechanical properties of the WBPU cast film, the breaking stress dec reased and the breaking elongation increased with increasing SSC or de creasing PEG molecular weight. For the WBPU-coated nylon fabrics, eith er higher SSC or higher PEG molecular weight improves the WVP. (C) 199 7 John Wiley & Sons, Inc.