Enhanced crystallinity, mechanical and dielectric properties of biphenyl polyarylene ether nitriles by unidirectional hot-stretching

In this work, biphenyl polyarylene ether nitrile (BP-PEN) was synthesized via a solution nucleophilic aromatic substitution polymerization of biphenyl (BP) with 2, 6-dichlorobenzonitrile (DCBN). BP-PEN films were prepared by solution-casting process and then were unidirectional stretched with different ratios (0, 50, 100, 150 and 200 %) under high temperature (280, 300 and 320 °C) to enhance their crystallinity and degree of orientation. Results showed that the thermal, mechanical, crystallinity and dielectric properties of the BP-PEN films were significantly enhanced after the unidirectional hot-stretching process. The glass transition temperatures (T _g) of the films hot-stretched at 280 °C range from 214.2 to 218.2 °C and melting point was in the range from 330.4 to 346.3 °C. Besides, the percent crystallinity of them was increased from 4.92 to 19.16 %. Moreover the tensile strength and modulus of them increased from 121 to 451 MPa and from 1943 to 4938 MPa, respectively. Compared with BP-PEN films without stretch treatment, the dielectric constant of the film stretched at 280 °C also increased from 4.0 to 6.7 (1 kHz).