A biaxially stretched film of BEK, a new engineering plastic with high heat resistance (T
g: 181° C, T
m: 364° C) and chemical resistance, was developed as a base film for flexible printed circuit boards. Its heat shrinkage percentage at 260° C and the coefficient of thermal expansion below T
g were decreased to below 0.1%, and 3.3×10-5/° C, respectively. The process of determining stretching and heat setting conditions for film formation with a role stretcher and a tenter is reported.
Relaxation behaviors of BEK, a new engineering plastic with high heat resistance (T
g: 181° C, T
m: 364° C), were investigated. Dielectric relaxation peaks were observed at -83° C and 51° C in 9.8 Hz, and their activation energies were 7 kcal/mol and 19 kcal/mol, respectively. The relaxation peaks were also observed in mechanical measurements. The `chemical structure-relaxation behavior' relationship in BEK and its related polymers suggests that the origins of the high temperature relaxation peak of BEK are crankshaft type chain motions while those of the low-temperature relaxation peak are wigglings of benzonitrile or phenyl groups.
The characteristic ratio of Biphenylene-Ether-Ketone (BEK), a newly developed engineering plastic with high heat resistance (T
g: 181°C, T
m: 364°C), was calculated using rotational isomeric state theory.
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