Aromatic polyimides (PIs) such as pyromellitic dianhydride (PMDA)/4 ,4 ’-oxyd ian i l ine (4 ,4 ’-ODA) and 3 ,3 ,4 ’,4 ’biphenyltetracarboxxylic dianhydride (s-BPDA)/4,4’-ODA are well known for their outstanding thermal and environmental stability attributable to their planar structures, in addition to their rigid wholly aromatic structures [1,2]. However, these advantages include some limitations in their application to molding or fabrication in heat sealing because of their insolubility and infusibility. Among the many methods used for improving the processability of aromatic polyimides, we have reported that the PI derived from an asymmetric aromatic tetra carboxylic acid dianhydride, i.e., 2,3,3’,4’-biphenyltetracarboxylic dianhydride (a-BPDA) and 4,4’-ODA, led to higher Tg than the corresponding PIs from s-BPDA with a symmetric structure. In addition, the asymmetric PIs indicate higher thermoplasticity than that of the corresponding symmetric PIs based on their nonplanar biphenylimide structures inhibiting intermolecular interaction (no ordered structure formation). Consequently, the sterically bent/distorted but rotation-restricted structural unit induced by asymmetric aromatic monomers was strongly anticipated for development of new high-performance polyimides [3,4]. We have also invented asymmetric aromatic addition-type imide oligomers (TriA-PI: a-BPDA/4.4’-ODA/PEPA) having high Tg and good processability [5]. Based on this asymmetric structure chemistry in August 2007, we started developing a heat-sealable polyimide having high space environmental stability for application as a solar sail membrane [6]. This paper presents the development of novel heat sealable asymmetric polyimide thin film (ISAS-Thermoplastic PI: ISAS-TPI) derived from 2,3,3’,4’-oxydiphthalic dianhydride (a-ODPA) and 4,4’-ODA (Figure 1) for application of membrane of Interplanetary Kite-craft Accelerated by Radiation Of the Sun (IKAROS) [7-10].
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