Preparation of novel polyimides containing aryl ester side chains end-capped with alkoxy groups and studies on their surface properties

Abstract

A novel diamine containing aryl ester side chains end-capped with alkoxy groups was synthesised and characterised by Fourier transform infrared spectrometry and ¹H-nuclear magnetic resonance. Based on the diamine, a series of copolyimide alignment films were prepared by a one-step process. The effects of side chain content of polyimides on surface energy, surface element components and surface morphology were studied by contact angle measurement, attenuated total reflection Fourier transform infrared spectrometry, x-ray photoelectron spectroscopy and atomic force microscopy. These investigations show that the surface energy decreases linearly with the increase of side chain content in a certain range and then levels off. Side chains with alkyl groups can transfer to the surface spontaneously, which makes the content of side chain on the surface notably higher than that in the matrix. However, when side chain content reaches 60 mol%, further transference stops. The enrichment of side chains on the surface of alignment films could be considered as the reason for the increase of the pretilt angle.

Keywords:

• polyimide
• side chain
• alignment films
• surface energy

Acknowledgements

We are grateful for financial support from the National Natural Science Foundation of China (No. 50773044 and 50433010).