Abstract

In the current work, a series of black polyimide (PI) films with excellent thermal and dimensional stability at elevated temperatures were successfully developed. For this purpose, two aromatic diamines including 4,4′-iminodianline (NDA) and 2-(4-aminophenyl)-5- aminobenzimidazole (APBI) were copolymerized with pyromellitic dianhydride (PMDA) to afford PIs containing imino groups (–NH–) in the molecular structures. The referenced PI film, PI-ref, was simultaneously prepared from PMDA and 4,4′-oxydianiline (ODA). The introduction of imino groups endowed the PI films with excellent blackness and opaqueness with the optical transmittance lower than 2% at the wavelength of 600 nm at a thickness of 25 μm and lightness (L*) below 10 for the CIE (Commission International Eclairage) Lab optical parameters. Meanwhile, the introduction of rigid benzimidazole units apparently improved the thermal and dimensional stability of the PI films. The PI-d film based on PMDA and mixed diamines (NDA:APBI = 70:30, molar ratio) showed a glass transition temperature (Tg) of 445.5 °C and a coefficient of thermal expansion (CTE) of 8.9 × 10−6/K in the temperature range of 50 to 250 °C, respectively. It is obviously superior to those of the PI-a (PMDA-NDA, Tg = 431.6 °C; CTE = 18.8 × 10−6/K) and PI-ref (PMDA-ODA, Tg = 418.8 °C; CTE: 29.5 × 10−6/K) films.

Highlights

  • Aromatic polyimide (PI) films represent a class of high-performance polymer films characterized by excellent engineering properties, including extraordinary thermal and extreme cold resistance, good chemical and radiative stability, good electrical and thermal insulating properties, and good flame retardancy [1,2,3]

  • Discussion precursors, poly(amic acid)s (PAAs) were synthesized, which can be illustrated by the synthesis of PI-d

  • The number average molecular weights (Mns) of the PAAs decreased with the increasing contents of the APBI in the polymers as follows: PI-a > PI-b > PI-c > PI-d

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Summary

Introduction

Aromatic polyimide (PI) films represent a class of high-performance polymer films characterized by excellent engineering properties, including extraordinary thermal and extreme cold resistance, good chemical and radiative stability, good electrical and thermal insulating properties, and good flame retardancy [1,2,3]. The lone pair electrons on the nitrogen atoms in imino unit are attracted toward the electron-deficient carbonyl groups in the dianhydride moiety, leading to an enhanced charge migration and flow in the molecular chains of the NDA-PIs, which is beneficial for the coloration of the NDA-PI films according to the CTC theory. These two factors endowed the NDA-PI films excellent blackness and opaqueness. The influence of the introduction of benzimidazole units on the thermal and optical properties of the PI films was studied in detail

Materials
Characterization
PI Synthesis and Film Preparation
Results
Optical
Optical Properties investigated by by the theUV-Vis
Thermal Properties
Thermogravimetric
Conclusions
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