Structures and Moisture Permeability of Polyurethane Films

Segmented polyurethane is a block copolymer which consists of hard and soft segments. In this study, moisture permeable segmented polyurethane films with different content of polytetramethyleneglycol (PTMG) and polyethyleneglycol (PEG) as soft segment were used. Three parameters of C1, C2 and higher order term Δh calculated by Mooney-Rivlin plots in the stress-strain relationship were measured. It was clarified that these mechanical parameters had relation with structure of films. Higher order term Δh and hydrogen bond concentration of urethane group by FT-IR measurement decreased with increasing PEG content in soft segment. That is to say, aggregate structure of hard segment decreased with increasing PEG content. Low PEG content samples showed transverse orientation in relation to aggregate structure of hard segment at initial state of elongation process. Transverse orientation has correlation with magnitude of aggregate structure. In the case of soft segment, degree of molecular restraint evaluated by dynamic mechanical analysis decreased with increasing PEG content. Aggregate structure grows through hydrogen bond of urethane group in hard segment. Also, it was clarified that aggregate structure was affected by soft segment and its outgrowth was inhibited.