聚碳酸酯的高温剪切降解及其稳定化研究

Degradation and Stabilization of Polycarbonate during High Temperature Shearing

借助傅里叶红外光谱和核磁共振氢谱等分析手段研究了双酚A聚碳酸酯(BPA-PC)在高温剪切混炼过程中的热降解行为,考察了不同抗氧剂对提高PC热稳定性的作用,探讨了PC的热降解黄变机理.结果表明,亚磷酸酯抗氧剂通过抑制碳酸酯键的断链反应,能有效提高PC的色泽稳定性.受阻酚抗氧剂上的酚羟基不利于碳酸酯键的热稳定,易导致其发生断链反应,但却有助于异亚丙基键的热稳定化.此外,探讨了不同降解产物对PC色泽的影响,对比发现,酮类降解产物上的羰基共轭结构可能是引发PC黄变的主要发色基团.

The thermal degradation behavior of bisphenol A polycarbonate （BPA-PC） during high temperature shear mixing was investigated. The effects of different antioxidant systems on improving the thermal stability of PC were compared by using a combination of spectrodensitometer, universal tensile testing machine and Ubbelohde viscometer, while the structural transformation of PC during the degradation process was studied by Fourier transform infrared spectrometer （FTIR） and nuclear magnetic resonance spectroscopy （1H-NMR） analysis. The results show that the addition of phosphite antioxidant and complex antioxidant can greatly improve the thermal stability and delay the extent of reduction of molecular weight as well as mechanical properties during the degradation process. Phosphite antioxidant can effectively enhance the color stability of PC by inhibiting the scission of carbonate linkage. Hindered phenolic antioxidant has opposite effects on the thermal stabilization of carbonate bonds and isopropylidene bonds in PC molecular chains. The phenolic hydroxyl groups of hindered phenolic antioxidant result in chain scission that is against the thermal stability of carbonate bond. Furthermore, hindered phenolic antioxidant contributes to the thermal stabilization of isopropylidene bond, which is superior to phosphite antioxidant. Multiple hindered phenolic antioxidant appears more outstanding thermostability to isopropylidene bonds, and the combination with phosphite can decrease the degradation of carbonate bond, which results in an excellent antioxidant effect. In addition, the effects of different degradation products on discoloration were discussed. It is found that chromophore is not derived from chains terminated with acetophenone. However, the yellow index of PC is proportional to the relative amount of chains terminated with phenolic hydroxyl, and the degree of color deterioration is also correlated with the infrared peak intensity of aliphatic ketone and aromatic ketone. Therefore, ketones could be the main degradation products that cause PC yellowing, while the carbonyl conjugated structure in the molecular chain is the main chromophore.