The photolytic decomposition in air of a polyimide film based on a dianhydride and a diary lamine with hexafluoroisopropylidene 6F bridging groups is extremely rapid, leading to efficient chain cleavage and subsequent photooxidative decomposition. Only relatively short photolysis times with an unfiltered mediumpressure mercury lamp are required to give a clean photoablation of the 6F-6F polyimide films in air. IR difference spectroscopy shows the appearance of anhydride groups on photolysis in air, indicating a photooxidation process via decomposition of the arylimide linkage. A photophysical and photochemical analysis of several model N-arylphthalimides indicates that both solvent polarity and electron-withdrawing/ donating substituents can greatly alter the efficiency of the photolysis process. The formation of the triplet state is also dependent on the substituents and solvent polarity. In general, an increase in the CT character of the excited state by either substituent or solvent effects leads to a reduction in both the photolysis and intersystem crossing quantum yields.
SYNOPSISPolyimides based on a hexafluorinated dianhydride decrease in thermal and thermal-oxidative stability upon photolysis with an unfiltered medium pressure mercury lamp source in air. Additionally, the glass transition of photolyzed polyimides containing the hexafluorinated moiety is lowered with increasing photolysis time. By contrast, pyromellitic-dianhydride-based polymers are relatively thermally stable even after prolonged photolysis under similar conditions.
Polymide films made from diarylanhydrides with oxygen, carbonyl, and hexafluoroisopropylidene 6F bridging groups are photolabile when irradiated with unfiltered light from a medium‐pressure mercury lamp. The presence of oxygen is necessary to the photolytic degradation process, which results in the ultimate oxidative ablation of thin polyimide films. Films based on the 6F dianhydride containing a hexafluoroisopropylidene hinge group are the most unstable. However, photolysis of 6F dianhydride based polyimides in an inert atmosphere with either the unfiltered medium pressure mercury lamp or an electron beam results in no detectable changes even after long exposure times.
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