HPAR／HDIT聚氨酯材料的热降解动力学

Thermal Degradation Kinetics of HPAR/HDIT Polyurethane Material

用热重-红外联用和动态力学热分析法研究了羟基丙烯酸树脂与六亚甲基二异氰酸酯三聚体反应生成的聚氨酯材料（PU）在254nm紫外线（UV）照射加速老化前后的热降解动力学，结果表明在N2氛中硬链段热降解成含-NCO的化合物，而软链段热降解成含-COOR或-CO-的化合物，热降解是一级反应．在4个不同温度阶段，热降解反应的活化能（E）和频率因子随温度的变化而变化．UV照射前，PU硬链段的E在40．4～43．7kJ／mol，软链段的E在144．5～163．4kJ／mol，硬链段的热稳定性比软链段差．经UV照射8500h后，硬链段的E在43．3～50．6kJ／mol，软链段的E在136．5～157．2kJ／mol，PU的最大热降解速率温度降低了2～7K．UV照射虽劣化了软链段的热稳定性，但也使PU进一步发生聚合，玻璃化转变温度有所提高．

The thermal degradation of the polyurethane material （PU） before or after 254 nm ultraviolet （UV） irradiation, which was prepared from hydroxyl polyacrylic resin reacting with hexamethylene-diisocyanate trimer, was investigated with a thermogravimetricfourier transfer infrared analyzer and a dynamic mechanical thermal analyzer. The results showed that the hard segments in PU generated some compounds containing --NCO groups during the thermal degradation in an atmosphere of Nz; whereas the soft segments generated --COOR or --CO-- group compounds. The thermal degradation reactions were first order. In the 4 different thermal degradation periods, their activate energy （E） and frequency factors changed with the change of the thermal temperature. Before UV irradiation, the E of the hard and soft segments was in the range of 40. 4～43.7 k J/mol and 144.5～163.4 k J/mol, respectively. The thermal stability of the hard segment was worse than the soft segment. Whereas after UV irradiation for 8 500 h, the E of the hard and soft segments was in the range of 43.3～50.6 k J/mol and 136.5～157.2 k J/mol, respectively; and the temperature corresponding to the maximum rate of the PU thermal degradation decreased by 2～7 K. UV irradiation deteriorated the thermal stability of soft segment of PU, but this increased its glass-transition temperature by initiating some further polymerizations in PU.