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Ultra-Low CTE and Improved Toughness of PMDA/PDA Polyimide-based Molecular Composites Containing Asymmetric BPDA-type polyimides

¹ Department of Chemistry, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
² Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan

^* To whom correspondence should be addressed.

	Abstract

A completely amorphous polyimide (PI) derived from 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) with 4,4'-oxydianiline (4,4'-ODA) (i.e. a-BPDA/ODA) was used as a matrix polymer for a rod-like polyimide structure derived from pyromellitic dianhydride (PMDA) with p-phenylenediamine (PDA) (i.e. PMDA/PDA) to improve the toughness without sacrificing its ultra-low coefficient of thermal expansion (CTE) characteristics. A matrix effect of a-BPDA/ODA was investigated by comparing with an isomer PI system, s-BPDA/ODA (s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride). Neither of the PMDA/PDA-based blend systems with a minor fraction of these flexible PIs showed any distinct glass transitions during dynamic mechanical thermal analysis. The unique fluorescence behavior of perylenetetracarboxydiimide (PEDI), which became almost non-fluorescent by intimate intermolecular contact with the PMDA/PDA chains, was applied to study the miscibility of the PMDA/PDA-based blend systems. For this purpose, a- and s-BPDA/ODA was labeled by copolymerization using a trace amount of difunctional PEDI. The results revealed that the a-BPDA/ODA-containing blend system was miscible over the entire blend composition whereas the s-BPDA/ODA-containing counterpart was essentially immiscible. The a-BPDA/ODA was much more effective as a flexible component than s-BPDA/ODA for reducing the crystallinity of PMDA/PDA and, as a result, significantly improved the film toughness. Blending of only small amounts of a-BPDA/ODA (5–10 wt.%) into PMDA/PDA caused an unexpected further decrease in the ultra-low CTE (2.8 ppm/K) of homo PMDA/PDA film. A mechanism is proposed to reasonably explain the results obtained in the present study. The blend system composed of PMDA/PDA (90 wt/%) and a-BPDA/ODA (10 wt.%) achieved an ultra-low CTE of 0.9 ppm K^–1 in addition to sufficient film flexibility.

Key Words: 2, 3, 3', 4'-biphenyltetracarboxylic dianhydride (a-BPDA)-type polyimides, PMDA/PDA, ultra-low CTE, polyimide/polyimide blend miscibility

First published on November 28, 2008
High Performance Polymers 2008, doi:10.1177/0954008308096624


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