THE MECHANISM OF POLYIMIDE PYROLYSIS IN THE EARLY-STAGE

Pyrolysis mechanism of Kapton-type polyimide was investigated with spe cial attention to the early stage. Two approaches were employed to rev eal the pyrolysis reactions: one is an analysis of evolved compounds, the other is a hydrolysis method that selectively converts polyimide c har into low-molecular-weight compounds. In the initial step of pyroly sis, bond cleavage around imide ring and following hydrogen transfer g enerates various intermediates on aromatic segments in polymer chains. It was derived from the quantitative analysis by the hydrolysis metho d that new linkages between the intermediates are formed efficiently i nstead of the cleaved bonds. Solid C-13-NMR study showed that the pack ing structure of polyimide molecules is little changed by heat-treatme nt at the starting temperature of pyrolysis, though the structure is g radually disintegrated by reconstruction reactions at higher temperatu res. It was also found that the thickness of sample films affects the weight loss and amounts of evolved compounds, while the difference of graphitizability has no appreciable effect.