STPUs are block copolymers composed by a soft segment (SS), formed by the medium- to high-molecular weight (500-4000 g/mol) diol and a hard segment (HS), formed by the diisocyanate and a low-molecular weight diol as the chain extender.
The aim of the work was to investigate the effect of the ratio of hard to soft segment components and the diisocyanate nature on the synthesized STPUs as well as changes in microstructure after subjecting the material to mechanical testing.
Attenuated total reflectance infrared (ATR-FTIR) spectroscopy was used to characterize the functional groups of the synthesized STPUs and also to investigate the hydrogen-bonding formation.
DSC thermograms of the synthesized STPUs and the PTEG were obtained on a Mettler Toledo DSC 822e calorimeter by cooling the sample from room temperature to -100[degrees]C by liquid nitrogen and then heating the sample to 250[degrees]C at a heating rate of 20 [degrees]C/min, under an inert nitrogen atmosphere.
It is known that in MDI-based STPUs the free carbonyl groups of the urethane bond show absorbance bands at 1731-1733 [cm.sup.-1], whereas the hydrogen-bonded carbonyl groups show absorbance bands at 1713-1718 [cm.sup.-1] in the less ordered amorphous regions and at 1685-1706 [cm.sup.-1] in ordered crystalline regions [22, 23].
In the absorption range of carbonyl group (C=0), the urethane carbonyl band appears at different wavenumbers, depending on whether the free electron pair of the amine group is conjugated with the [pi] bond of the carbonyl group in HDI-based STPUs (1682 [cm.sup.-1]) or with the aromatic ring in MDI-based STPUs , Sample PU-HDI-40 showed a higher relative intensity between the hydrogen-bonded carbonyl groups (1682 [cm.sup.-1]) and the free carbonyl groups (1723 [cm.sup.-1]), indicating that the urethane groups in HDI are more able to associate by hydrogen bonding and result in highly phase-separated polyurethanes .
In general, synthesized STPUs showed properties comparable to petroleum derived polyurethanes [28, 36].