Abstract
The effect of molecular weight of polyol (soft segment) and the concentration of urethane (hard segment) in segmented polyurethane elastomers on their photodegradation was investigated. Polyurethane elastomers have been prepared from 4.4′-dipheylmethane diisocyanate (MDI) and poly(oxytetramethylene) glycol (PTMO) of 1000 and 2000 molecular weight at NCO OH ratios of 2 1 and 4 1 . Purified 1,4-butanediol (BD) was used as the chain extender. Mechanical, thermal, dynamic mechanical and Fourier Transform Infrared Spectroscopy (FTIR) measurements have been used for mechanical and structural studies of PUR elastomers before and after UV irradiation, for a better understanding of the role of the concentration of hard segments (urethane) and molecular weight of soft segments (polyol) in PUR. It was found that the molecular weight of soft segments as well as the NCO OH ratios have an influence on the UV stability of the examined elastomers. The photooxidative degradation is more prevalent in elastomers with lower hard segment concentration and with higher soft segment molecular weight. The correlation between the compositions of the investigated elastomers and mechanical properties, dynamic mechanical properties, physical transitions, as well as intensities of the changes of these properties after irradiation were established. The results show that with an increase of hard segment concentration in all examined polyurethane elastomers, the glass transition temperature ( T g ) of the soft segment increased, the tensile strength increased and the elongation at break decreased. In irradiated polyurethane elastomers based on PTMO (1000) with the higher hard segment concentration T g of the soft segment decreased, the opposite effect was obtained in PUR elastomer with lower hard segment concentration. Resistance to photooxidative degradation was enhanced with increase of the hard segment concentration in polyurethane elastomers based on PTMO (1000). The photooxidative degradation is more prevalent in polyurethane elastomers based on polyether with higher molecular weight PTMO (2000), than those based on polyether of molecular weight PTMO (1000), even at higher hard segment concentration.
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