Mechanism of deformation of thermally stable aromatic polymers studied on the example of polyimide

The mechanism of relaxation (creep) was investigated on films made of polyimide PM subjected to preliminary elongation. New relaxation nuclei were used in the analysis, which take into account the change in entropy accompanying relaxation. Positron annihilation was used as the experimental method. T...

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Bibliographic Details
Published in:Polymer science USSR 1990, Vol.32 (12), p.2560-2568
Main Authors: Askadskii, A.A., Tushin, S.A., Kazantseva, V.V., Kovrina, O.V.
Format: Article
Language:English
Subjects:
Applied sciences
Exact sciences and technology
Mechanical properties
Organic polymers
Physicochemistry of polymers
Properties and characterization
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Summary:The mechanism of relaxation (creep) was investigated on films made of polyimide PM subjected to preliminary elongation. New relaxation nuclei were used in the analysis, which take into account the change in entropy accompanying relaxation. Positron annihilation was used as the experimental method. The results show that deformation leads to a rise of structural microheterogeneity owing to the formation of highly ordered and loosened regions. During the creep period, after stress removal, submicropores formed by deformation coalesce into larger voids. Aromatic polyimide PM exhibits a unique electron structure characterized by high uniformity of the electron density function. This fact apparently lies behind the deformability which aromatic polyimides exhibit over a broad range of low temperatures.
ISSN:0032-3950
1878-268X
DOI:10.1016/0032-3950(90)90434-8