Polyimides (PIs) exhibit excellent thermal stability, mechanical, dielectric, and chemical resistance properties due to their heterocyclic imide rings and aromatic rings on the backbone. Due to these advantageous properties, PIs have found diverse applications in industry. Most PIs are insoluble because of the nature of the high chemical resistance. Thus, they are generally used as a soluble precursor polymer, which forms complexes with solvent molecules, and then finally converts to the corresponding polyimides via imidization reaction. This complexation with solvent has caused severe difficulty in the characterization of the precursor polymers. However, significant progress has recently been made on the detailed characterization of PI precursors and their imidization reaction. On the other hand, much research effort has been exerted to reduce the dielectric constant of PIs, as demanded in the microelectronics industry, through chemical modifications, as well as to develop high performance, light-emitting PIs and liquid crystal (LC) alignment layer PIs with both rubbing and rubbing-free processibility, which are desired in the flat-panel display industry. This article reviews this recent research progresses in characterizing PIs and their precursors and in developing low dielectric constant, light-emitting, and LC alignment layer PIs.

In this study we investigated bacterial and cell adhesion to poly(propylene carbonate) (PPC) films, that had been synthesized by the copolymerization of carbon dioxide (a global warming chemical) with propylene oxide. We also assessed the biocompatibility and biodegradability of the films in vivo, and their oxidative degradation in vitro. The bacteria adhered to the smooth, hydrophobic PPC surface after 4 h incubation. Pseudomonas aeruginosa and Enterococcus faecalis had the highest levels of adhesion, Escherichia coli and Staphylococcus aureus had the lowest levels, and Staphylococcus epidermidis was intermediate. In contrast, there was no adhesion of human cells (cell line HEp-2) to the PPC films, due to the hydrophobicity and dimensional instability of the surface. On the other hand, the PPC films exhibited good biocompatibility in the mouse subcutaneous environment. Moreover, contrary to expectation the PPC films degraded in the mouse subcutaneous environment. This is the first experimental confirmation that PPC can undergo surface erosion biodegradation in vivo. The observed biodegradability of PPC may have resulted from enzymatic hydrolysis and oxidative degradation processes. In contrast, the PPC films showed resistance to oxidative degradation in vitro. Overall, PPC revealed high affinity to bioorganisms and also good biodegradability.

There are two beamlines (BLs), 4C1 and 4C2, at the Pohang Accelerator Laboratory that are dedicated to small angle X-ray scattering (SAXS). The 4C1 BL was constructed in early 2000 and is open to public users, including both domestic and foreign researchers. In 2003, construction of the second SAXS BL, 4C2, was complete and commissioning and user support were started. The 4C2 BL uses the same bending magnet as its light source as the 4C1 BL. The 4C1 BL uses a synthetic double multilayer monochromator, whereas the 4C2 BL uses a Si(111) double crystal monochromator for both small angle and wide angle X-ray scattering. In the 4C2 BL, the collimating mirror is positioned behind the monochromator in order to enhance the beam flux and energy resolution. A toroidal focusing mirror is positioned in front of the monochromator to increase the beam flux and eliminate higher harmonics. The 4C2 BL also contains a digital cooled charge coupled detector, which has a wide dynamic range and good sensitivity to weak scattering, thereby making it suitable for a range of SAXS and wide angle X-ray scattering experiments. The general performance of the 4C2 BL was initially tested using standard samples and further confirmed by the experience of users during three years of operation. In addition, several grazing incidence X-ray scattering measurements were carried out at the 4C2 BL.

PMDA-ODA and BPDA-PDA polyimides in 10-50 Atrn thick films were prepared from the respective poly(amic acid) precursor by thermal imidization for 1-10 h at various temperatures over 230-400C. Their water sorption behaviours were studied in detail by gravimetry. Water sorption in both PMDA-ODA and BPDA-PDA followed a nearly Fickian process in spite of the morphological heterogeneity due to the ordered and less ordered phases. Water clustering or plasticization was very weakly evident on the water uptake versus humidity plots. Water sorption in both polyimides was highly dependent upon imidization history. Both diffusion coefficient and water uptake are decreasing functions of imidization temperature and time. This resulted mainly from the enhancement of overall crystallinity by high-temperature imidization because of their high-rT nature. The diffusion coefficient and water uptake were (1.0-3.0) x 10-9 cm2 s-1 and 0.4-4.5 wt% for PMDA-ODA and (0.9-3.0)x 10-cm2s-' and 0. I2-2.40wt%, depending on humidity,/iihidization history and film thickness. The differences between the water sorptions of the p'olyimides are interpreted by considering the differences in their morphologies and chemical affinities to water.

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Various zinc dicarboxylate catalysts were synthesized by the reaction of zinc oxide with eleven different glutaric acid derivatives, and their coordination characteristics were investigated by infrared spectroscopy. The electronic nature and steric hinderance of substituents influenced the coordination of the carboxylate and the zinc metal ion. The coordination characteristics were classified into three categories: i) compounds exhibiting bridging bidentate coordinating bonding modes, such as syn-anti and syn-syn bridging: ii) compounds with only unidentate coordination: and iii) compounds with mixed coordinations of unidentate and

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Five poly (amic acid) solutions based on PMDA‐PDA, PMDA‐ODA, PMDA‐6F, ODPA‐ODA, and 6FDA‐ODA were prepared in N‐methylpyrrolidone at a polymer concentration of ca. 10 wt %. From these five poly (amic acid) solutions, six different binary blends were prepared: PMDA‐PDA/PMDA‐ODA, PMDA‐PDA/PMDA‐6F, PMDA‐ODA/6FDA‐ODA, PMDA‐ODA/ODPA‐ODA, PMDA‐PDA/ODPA‐ODA, and PMDA‐PDA/6FDA‐ODA. These blends were then characterized with respect to miscibility in the ternary state (polyamic acid‐1/polyamic acid‐2/N‐methylpyrrolidone), the condensed state (ca. 70 wt % polymer), and the fully imidized state. All blends except for PMDA‐PDA/PMDA‐6F yielded homogeneous mixtures in the ternary solution of 10 wt % polymer concentration. The PMDA‐PDA/PMDA‐6F mixture eventually became homogeneous after 10 days of mixing at room temperature. Upon solvent evaporation (condensed state) and full cure (imidized state) two blends incorporating ODPA‐ODA as one of the components exhibited apparent miscibility as evidenced by optical microscopy. The remaining blends exhibited large‐scale phase separation upon solvent evaporation with no significant differences in the overall morphology between the condensed and imidized state. However, as in the case of the PMDA‐PDA/PMDA‐6F ternary system, the morphology in the condensed and imidized state was strongly dependent on the mixing time of the precursor poly(amic acid) components; the phase‐separated domain size decreased with increasing mixing time, eventually leading to complete miscibility. These results are discussed with respect to the proposed “polymer‐monomer” reequilibration reaction as well as its implications with respect to the preparation of polyimide molecular composites.