Impact of Backbone Amide Substitution at the Meta- and Para-Positions on the Gas Barrier Properties of Polyimide.

Qian Wen,Chengliang Chen,Jinghua Tan,Yiwu Liu,Chunguang Xiao,Duxin Li,Ao Tang

doi:10.3390/ma14092097

Abstract

This study designed and synthesised a meta-amide-substituted dianiline monomer (m-DABA) as a stereoisomer of DABA, a previously investigated para-amide-substituted dianiline monomer. This new monomer was polymerised with pyromellitic dianhydride (PMDA) to prepare a polyimide film (m-DABPI) in a process similar to that employed in a previous study. The relationship between the substitution positions on the monomer and the gas barrier properties of the polyimide film was investigated via molecular simulation, wide-angle X-ray diffraction (WXRD), and positron annihilation lifetime spectroscopy (PALS) to gain deeper insights into the gas barrier mechanism. The results showed that compared with the para-substituted DABPI, the m-DABPI exhibited better gas barrier properties, with a water vapour transmission rate (WVTR) and an oxygen transmission rate (OTR) as low as 2.8 g·m−2·d−1 and 3.3 cm3·m−2·d−1, respectively. This was because the meta-linked polyimide molecular chains were more tightly packed, leading to a smaller free volume and lower molecular chain mobility. These properties are not conducive to the permeation of small molecules into the film; thus, the gas barrier properties were improved. The findings have significant implications for the structural design of high-barrier materials and could promote the development of flexible display technology.

Highlights

Polyimide (PI) is a class of polymeric material with excellent comprehensive performance [1,2]
Dinitro-intermediate m-DABN was obtained by reacting m-nitrobenzoyl chloride and m-nitroaniline as raw materials at room temperature for 1 d. m-DABN was catalytically reduced using Pd/C and hydrazine hydrate to yield the dianiline monomer m-DABA with high purity
The synthesis route is shown in Scheme 1. m-DABA and the intermediate were characterised by NMR, FT-IR, elemental analysis, and mass spectrometry, and the results verified the success of the monomer synthesis

Summary

Introduction

Polyimide (PI) is a class of polymeric material with excellent comprehensive performance [1,2]. PI demonstrates outstanding thermal and mechanical properties, good dimensional stability, and excellent electrical insulation due to its unique imide ring structure [3]. The dianiline/dianhydride monomer of polyimide can be designed and synthesised flexibly and [4]. Their raw materials are diverse and inexpensive, leading to PI’s excellent structural designability. The advancement of new technologies within microelectronics has posed increasingly high requirements for the properties of polymeric materials. The polymeric substrate materials used in the packaging of flexible organic light-emitting devices (OLED)

Methods

Results

Conclusion