Property‐structure relationships in poly‐urethanes: Infrared studies

Temperature dependent infrared studies have been carried out on three series of poly‐urethanes previously synthesized and characterized. The repeat units of the three series may be schematically represented as follows: magnified image In each case n varies from 2 to 10. The H and DP series are partially crystalline while the 4M series is entirely amorphous. It was possible to draw several conclusions concerning the hydrogen bonded NH and Cbond;O groups in these polymers. These conclusions are: (1) The aromatic polyurethanes of the DP and 4M series are hydrogen bonded in the amorphous phase below the glass transition temperature, (T g ) , to the extent of 75% or less whereas the aliphatic H series is completely hydrogen bonded below T g . (2) Both the DP and H series are completely hydrogen bonded in the crystalline phase below the melting point, ( T m ), regardless of the value of n . (3) A temperature dependent equilibrium between free and hydrogen bonded NH groups occurs in the amorphous phase above T g in all three series. (4) The temperature dependences of the total area of the NH stretching bands exhibit transitions corresponding to T g , T m , and, in the case of the H series, to a first order crystal‐crystal phase transition, T t . (5) The temperature dependences of the frequencies of the hydrogen bonded NH stretching vibration also exhibit transitions corresponding to T g and T m .