Positron annihilation and phase separation phenomena in polyurethane crosslinked coatings with different polyether segments

Eight model polyurethane crosslinked coatings were obtained from different compositions of polyisocyanurates of hexamethylenediiso-cyanate (HDI) and i sophoronediisocyanate (IPDI) with polypropylenglycol (PPG) and perfluoropol yether macrodiols (PFPE), both having M-n 1000. The polyurethanes were char acterized by Differential Scanning Calorimetry (DSC) and Positron Annihilat ion Spectroscopy (PAS). The DSC analysis showed that PPG based polyurethane s are monophasic materials having one glass transition temperature T-g incr easing with the density of crosslinking and related to the T-g of the start ing polyisocyanurate. On the other hand PFPE containing polyurethanes are p olyphasic with segregation of fluorinated moiety and presence of urethane p hases with highly diversified T-g values. It is found that PAS is sensitive to the phase segregation; furthermore, ortho-positronium lifetimes are cor related to the T-g. From the analysis of PAS spectra the size distributions of the nanoholes forming the free volume was obtained. (C) 2001 Elsevier S cience Ltd. All rights reserved.