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

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.

Solution‐processable colorless polyimides with ultralow coefficients of thermal expansion for optoelectronic applications

“…PMDA/ p ‐phenylenediamine ( p ‐PDA) without any bulky side groups), it is very likely that the molecular motion during thermal imidization becomes no longer powerful enough to contribute to the orientational relaxation. Indeed, the PMDA/ p ‐PDA system displayed an extremely high degree of in‐plane orientation by thermal imidization …”

Colorless polyimides derived from 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride, self-orientation behavior during solution casting, and their optoelectronic applications

“…In particular, the use of BAPP and HFBAPP was very effective to enhance the film toughness as suggested from their very high ε b values. Even if the molecular weights were sufficiently high, the combinations of rigid tetracarboxylic dianhydrides and rigid diamines generally lead to brittle PI films owing to insufficient chain entanglement as typically observed in PMDA/p-PDA system (ε b < 3% [51]). Against this general criterion, the H 0 -PMDA/p-PDA system with a stiff/linear backbone structure exhibited sufficient film flexibility as shown in Table 3.…”

Structure and properties of aromatic poly(benzimidazole‐imide) copolymer fibers

“…The key strategy for reducing the CTE value is to choose PI systems consisting of rod‐like backbone structures, thereby drastic chain alignment along the fiber axis can be induced during thermal imidization and heat‐drawing process . The rod‐like PI system prepared from PMDA with a series of diamines shows a considerably low CTE (2.8 ppm/K) . Therefore, introducing PMDA into PI main chains is beneficial to improve corresponding dimensional stability against high temperature.…”