Amide II and Amide III Bands in Polyurethane Model Soft and Hard Segments

Summary Amide II and III bands in polyurethane (PU) have been often taken as two of the characteristic bands indicating the formation of urethane structure. Since these bands, however, are very complicated, further studies, especially the effect of H-bonds on amide II and III bands in PU, were seldom reported. In the present work, we report a new finding on the correlation of amide II and amide III bands with different H-bonding interactions in PU model soft and hard segments. The PU model soft segment (PUMSS) is based on poly(tetrahydrofuran) (PTHF) and diphenylmethane-4,4’-diisocyanate (MDI) whereas the PU model hard segment (PUMHS) is based on MDI and n-butanol (BO). FTIR results show that the H-bond is formed by NH...carbonyl (C=O) (Type I) in PUMHS while the H-bond is mainly formed by NH...ether(O) (Type II) in PUMSS; the amide II band, however, is more related to the Type II H-bonding interaction while amide III band is more dependent upon the Type I H-bonding interaction.