FT-IR Analysis of Cast Polyurethanes

In order to understand the effect of high MW diols on the formation of amorphous hard segments and their interaction with the crystalline hard segments, FT-IR analysis of the cast polyurethanes was performed. Samples were cast as films on a NaCl plate from a hot dimethyl sulphoxide (DMSO) solution. 

The crystalline structure of polyurethanes is controlled by the formation of hydrogen bonds between NH and C=0 groups of the urethane linkages [28, 29]. From the IR analysis, the hydrogen bonded C=0 present in the crystalline domain can be identified by the peak absorbance at 1699-1706 cm and the non-bonded or free C=0 group shows peaks at 1735 cm and 1748 cm.  

IR analysis also showed a peak at 1736 cm associated with the free C=0 groups of the elastomers. From the IR absorbances of bonded and free C=0 groups, the hydrogenbonding index, R, which is the ratio of c=o/A nonbonded c=o can be calculated [30]. 

The greater the value of R indicates an increase in participation of the C=0 group in the hydrogen bonding. The values of R calculated from the absorbance of hydrogen bonded C=0 (1705 cm ) and free C=0 (1736 cm ) peak values are given in Table 8.13. 

The values clearly suggest an increased hydrogen bonding with HER HP extended material due to high hard segment content. The reason for the higher R value for TG-225 extender is not known at the present time. 

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