Photostability and radiation resistance of polyurethane

Polyurethane synthesized from aromatic isocyanate (such as TDI and MDI) is easy to oxidize and turn yellow when exposed to ultraviolet light, which is caused by the bridge bond structure of aromatic biuret. Under UV irradiation, it is easy to oxidize to form a quinone like structure. Aliphatic urethane bond is more stable than aromatic urethane bond and is not easy to be oxidized. Even if it is oxidized and decomposed into fatty amines, it is not easy to change color like aromatic amines. Because there is no benzene ring conjugation as a chromophore. Although XDI has benzene ring, the urethane is not directly connected to the aromatic ring, and there is methylene separation in the middle to prevent the formation of conjugation, so it does not turn yellow. The yellowing resistant additives on the market can improve the yellowing performance of TDI and meet the requirements of TDI for coatings.

In the synthesis of polymer materials, polyurethane is very good in high energy ray resistance. It still has satisfactory performance under the radiation dose of 105-106gy. However, for light or transparent elastomers, discoloration will occur under the action of radiation, similar to that observed in hot air or atmospheric aging tests.