PHOTOSTABILITY OF POLYURETHANE ELASTOMERS BASED ON 2 TYPES OF DIISOCYANATES

The effect of UV irradiation on the mechanical and thermomechanical pr operties of polyurethane (PU) elastomers and their morphology was stud ied. The chemical changes in the PU elastomers exposed to UV radiation were studied by means of Fourier Transform Infrared Spectroscopy (FTI R). The PU elastomers were based on an aromatic isocyanate (4,4'-diphe nylmethane diisocyanate) and a cycloaliphatic isocyanate (4,4'-dicyclo hexylmethane diisocyanate). Poly(caprolactone) glycol of 1250 molecula r weight was the polyol used and 1,4-butanediol was the chain extender . The elastomers were prepared in a two-step procedure. First, prepoly mers were prepared from poly(caprolactone) glycol by reacting with the corresponding isocyanate at NCO/OH ratios of 2/1 and 4/1. The prepoly mers were then chain-extended with 1,4-butanediol and the mixture was press-molded in a platen press at 100 degrees C. The results showed th at the stability of the investigated PU elastomers depended on the che mical structure of the diisocyanate and the hard/soft segment ratio. T he processes of photooxidative degradation are more prevalent in PU el astomers based on cycloaliphatic isocyanate than those based on the ar omatic isocyanate. In the case of PU elastomers based on the cycloalip hatic isocyanate it was found that the photodegradative processes were enhanced with increasing hard segment concentration. The degree of ph otooxidative degradation of PU elastomers, as studied by FTIR, correla ted very well with the extent of morphological changes and changes in mechanical properties. Although PU elastomers based on the aromatic is ocyanate undergo color changes, they exhibited better retention of mec hanical properties compared to those based on the aliphatic isocyanate .