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Thermal Degradation of Segmented Polyurethane Elastomers Before and After UV Iradiation

In this work we investigated the thermal degradation behaviour of the segmented polyurethane, PUR, elastomers before and after UV iradiation. Four series of polyurethane elastomers were obtained from poly(oxytetramethylene) glycol, PTMO, of 1000 and 2000 molecular weight and polycaprolactone glycol of 1250 molecular weight (PCL), 4, 4- diphenylmethan diisocynate (MDI) and 4, 4-dicyclohexylmethane diisocyanate (H12MDI) and 1, 4-butanediol as chain extender. The effect of soft segment and hard segment type, soft segment molecular weight and hard segment content on degradation process was measured. The thermal degradation of PUR elastomers was studied over the temperature range of 25-600 oC in an atmosphere of nitrogen using thermal gravimetric analysis (TGA). All investigated PUR elastomers show two step decomposition except PUR elastomer based on cycloaliphatic diisocyanate with higher hard segment content (PUR-ES-W4 elastomer) in which occurred one-step degradation. The first step of degradation corresponds to the hard segment degradation, while in the second step of degradation the soft segment degraded. The PURs show reduced thermostability and their thermal stability dependent on the chemical structure of the polyols and diisocyanates used in their thermal stability dependent on the chemical structure of the polyols and diisocyanates used in their preparation. We found that the PUR elastomers based on polyester polyol and aromatic diisocyanate exhibit better thermal stability than PUR elastomers based on polyether polyol soft segment in both steps of degradation. The thermal degradation is more prevalent in PUR elastomers based on cycloaliphatic diisocyanate. The higher values of temperature of initial decomposition Ti, indicate a higher thermal stability of UV exposed elastomers on the beginning of degradation. This may be due to the formation of crosslinking structure in the presence of UV irradiation.

thermal degradation; UV iradiation; segmented polyurethane elastomers; thermal gravimetric analysis

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