Effects of alicyclic moiety incorporation on the properties of polyimide/silica hybrid films

Polyimide (PI)/silica hybrid films were prepared from tetraethyl orthosilicate (TEOS) using a sol-gel process as well as pyromellitic dianhydride and 4,4-oxydianiline. 1,4-Cyclohexanedicarboxylic acid (1,4-CHDA) was added as a coupling agent. The PI/silica hybrid films were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, differential scanning calorimetry and wide-angle X-ray diffraction. The thermal, tensile and dielectric properties of the hybrid films were measured. The results showed that the tensile and dielectric properties of the hybrid films improved with increasing silica concentration and 1,4-CHDA content in the PI matrix. Covalent ester bonds were formed between SiOH groups of silica and carboxyl groups of 1,4-CHDA. As a result, the silica particle size was reduced and dispersed homogeneously in the PI matrix, leading to increased tensile strength and tensile modulus of the typical hybrid film with 1,4-CHDA (PI-2), when compared with the PI/silica hybrid film without 1,4-CHDA at the same silica contents. The presence of an alicyclic moiety containing silica in PI reduced the dielectric constant considerably to 2.83, which was lower than that of pristine PI. Copyright (c) 2016 John Wiley & Sons, Ltd.