Jin Chul Jung

Synthesis and characterization of polyimides from imidazole-blocked 2,5-bis[(n-alkyloxy)methyl]-1,4-benzene diisocyanates and pyromellitic dianhydride

From imidazole-blocked 2,5-bis[(n-alkyloxy)methyl]-1,4-benzene diisocyanates and pyromellitic dianhydride a series of new rigid-rod polyimides (C n -PY-PI ; n = 4, 6, 8) having linear and flexible (alkyloxy)methyl (-CH 2 OC n H 2n+1 ; n = 4, 6, 8) side chains were prepared and characterized and their properties were measured and discussed with regard to effects of side chains. Incorporation of the side chains onto the rigid main chain greatly enhanced the solubility and fusibility of the polymers, and melting point of C 8 -PY-PI was determined to be 277°C. The UV-VIS absorption behavior was independent of side-chain length. TGA thermograms revealed a two-step pyrolysis behavior, in which the side chains split off separately at lower temperatures. X-ray diffractograms showed that all the polyimides are crystalline at room temperature. Sharp reflections in small-angle region obviously indicated the presence of a layered crystal structure.

Structure and phase behaviour of polyazomethines having flexible (n-alkyloxy)methyl side chains

Abstract Structure and phase behaviour of a series of thermotropic polyazomethines having ( n -alkyloxy)methyl side chains (-CH 2 O- n -C m H 2m+1 , m = 4, 6, 8, 12) have been studied by wide-angle X-ray scattering, differential scanning calorimetry (d.s.c.) and polarizing optical microscopy. In d.s.c. thermograms the samples showed basically three transitions. The first transitions were ascribed to solid-solid transitions resulting from a large increase in disorder of the side chains. The second ones were assigned to crystal-mesophase transitions arising from melting of the side chain crystals. The third ones were attributed to mesophase-isotropic melt transitions. All the samples showed layered structures in the mesophase as well as in the crystalline phase, in which the side chains were fully interdigitated. In the crystalline phase the repeat units of rigid main chain were found not to align parallel with those of neighbouring main chains, but slipped by 49°. In the mesophase the side chain crystals were molten and the layer spacings increased proportionally with increasing side chain length. The structural regularity in the slipped repeat unit disappeared in the polymers bearing long side chains, whereas it was retained in those having short side chains. A unidirectional shearing made the layer plane align parallel on the surface.

Sequence of Rubbing-Induced Molecular Segmental Reorientations in the Nanoscale Film Surface of a Brush Polymer Rod

Poly(p-phenylene-3,6-bis(4-(n-butoxy)phenyloxy)pyromellitimide) (C4-PMDA-PDA PI), a well-defined model brush polymer composed of a rodlike polymer backbone with two bristles per repeat unit, was the first reported polyimide to align liquid crystals perpendicular to the rubbing direction at the rubbed film surface. In the present study, we used polarized infrared (IR) spectroscopy and 2D correlation analyses of the resulting IR spectra to study nanoscale films of C4-PMDA-PDA PI rubbed at various rubbing densities. The results of these studies allowed us to establish the nature and sequence of the rubbing-induced segmental reorientations that occur in the polymer molecules at the film surface. The rubbing process was found to reorient the fully rodlike polymer backbones and the n-butyl bristle end groups such that they lay parallel to the rubbing direction. In contrast, rubbing caused the phenyloxy bristle units to reorient to a direction perpendicular to the rubbing direction. These reorientations of the polymers main chain and bristles became more pronounced with increasing rubbing density, and the rubbing process had a greater effect on the polymers main chains than on the bristles. The rubbing-induced reorientations of the polymer segments were found to follow the sequence PDA (phenyl ring), imide ring, phenyloxy unit, imide C-N bond, and n-butyl group. It was additionally evident that the rubbing process reorients the imide rings biaxially, that is, both along the rubbing direction and out of the plane. This biaxial reorientation was found to be accompanied by a biaxial reorientation of the bristles chemically bonded to the PMDA unit that includes the imide rings. In particular, increasing the rubbing density enhanced the out-of-plane reorientation of the imide rings. In contrast, no rubbing-induced inclination of the reoriented imide rings (i.e., the polymers main chains) was detected.

Micropatterning of a single layer of nanoparticles by lithographical methods with diblock copolymer micelles

We have demonstrated micropatterning of a single layer of nanoparticles by combining a self-assembly of diblock copolymer micelles with conventional and soft lithographical methods. On a photoresist micropattern fabricated by conventional photolithography, a single layer of diblock copolymer micelles containing precursors of nanoparticles was spin-coated. By plasma and lift-off processes, nanoparticles with the preservation of a pseudo-hexagonal order of micelles were synthesized in the micropattern without their aggregation. In addition, soft lithography of the microcontact printing technique was combined with the process of diblock copolymer micelles to produce micropatterns of nanoparticles. As an ink of the microcontact printing process, a single-layered film of diblock copolymer micelles was spin-coated directly onto the stamp and then transferred on the substrate by stamping. Formation of a single layer of nanoparticles in the micropattern was carried out by plasma treatment.

Thermal and physical properties of poly(phenylene oxide) blends with glass fiber reinforced syndiotactic polystyrene

Abstract Melt blends of poly(phenylene oxide)(PPO) with glass fiber reinforced syndiotactic polystyrene(GFRsPS) were prepared using a single screw extruder. DSC and dynamic mechanical measurements indicate that the PPO/GFRsPS blends are miscible in amorphous state as shown by the existence of a single Tg whose values are blend composition-dependent. From the mechanical test results, it is shown that the tensile and flexural modulus increase, but the tensile and flexural strength do not improve as the GFRsPS content increases. An increase in the melt flow index (MFI) as GFRsPS contents increase implies that the processing problem of neat PPO is improved.

Novel polypyromellitimides and their liquid crystal aligning properties

Various aromatic poly{3,6-bis[(4-n-alkyloxy)phenyloxy]-pyromellitimide}s {poly(Ar-C m -PMDA)s, m = 1, 4, 8, 12] were prepared in film form by routine two-step condensation of 3,6-bis[(4-n-alkyloxy)phenyloxy]pyromellitic dianhydrides (C m -PMDAs) with various aromatic diamines. After characterization of their chemical structures their solution, thermal and liquid crystal (LC)-aligning properties in terms of pretilt angle at various rubbing densities were measured and discussed with respect to their backbone structures. All polyimide films showed excellent thermal stability and homogeneous LC alignment, but the poly(p-phenylene-C 12 -PMDA) exhibited completely homeotropic alignment while the pretilt angle values of poly(p-phenylene-C 8 .-PMDA) varied with varying rubbing density.

Synthesis and properties of polyimides derived from N-[4-(4-aminophenyloxy)phenyl]-4-aminophthalimide

Abstract A new phthalimide-containing diamine N -[4-(4-aminophenyloxy)phenyl]-4-aminophthalimide was synthesized and polymerized with various aromatic tetracarboxylic acid dianhydrides via one-step polycondensation in p -chlorophenol to produce high molecular weight polyimides. In comparison with the polymers based on 4,4′-oxydianiline (ODA), the polymers prepared in this work had comparable or slightly higher solubility in spite of the presence of one more rigid phthalimide group in the repeat unit. They showed much higher glass transition temperatures (263–338°C) and enhanced thermal stabilities observed from the temperatures (575–631°C) at 5% weight loss. Some of the polymers exhibited crystalline transitions even though they have bent groups and non-symmetric chain structure leading to irregular repeating sequences.

Rubbed Thin Films of Well-defined Brush Polyimides for Flat-Panel Liquid Crystal Displays: Surface Morphology, Molecular Orientation, and Liquid Crystal Alignability

A series of well-defined brush polyimide (PI) composed of two 4-n-alkyloxyphenyloxy bristles per repeat unit on a semi-rigid poly(4,4′-methylenyldiphenylene pyromellitimide), Cm-PMDA-MDA PIs, were synthesized and their nanoscale thin films prepared by conventional spin-coating of their soluble poly(amic acid) precursor solutions and subsequent drying and thermal imidization in a nitrogen atmosphere. All the PIs were determined to be a positively birefringent polymer. The surface morphology and molecular orientation of each PI in films before and after rubbing were investigated in detail by atomic force microscopy, optical retardation analysis, and linearly polarized infrared spectroscopy. The sequence of the rubbing-induced polymer segmental orientations was further investigated in detail. In addition, the liquid crystal alignment and pretilt ability of the rubbed PI films were examined, and their thermal stability investigated. The present study provides important information on the sequence of the polymer segmental orientations induced by rubbing and additionally the mechanisms of the alignment and pretilt of liquid crystal molecules in contact with the rubbed PI film surface.

Polarity effect near the surface and interface of thin supported polymer films: X-ray reflectivity study.

Four homopolymer films (poly(methyl methacrylate) (PMMA), poly(4-vinylpyridine) (P4VP), polystyrene (PS), and poly(alpha-methyl styrene) (PAMS)) with different interactions with native Si oxide on Si wafers and three random copolymer films (PS-ran-PMMA) with different mole fractions were investigated with the X-ray reflectivity (XRR) method. The electron density profile of each film was obtained by fitting the results of the XRR measurements. A new data correction technique that uses the vertical real beam profile and a fitting method that uses the distorted wave Born approximation were combined to overcome the sensitivity limitations of XRR analysis. The results show that the chemical structures of polymer pendant groups and the interactions between the polymer films and the native Si oxide layer are strongly correlated with the density profiles of the films near the surfaces and interfaces. Two general types of electron density profiles were found that are characterized by the polarity of the pendant group of the polymer. The reproducibility and credibility of the fitting technique were also thoroughly tested.

High Temperature Size Exclusion Chromatography

High temperature size exclusion chromatography (SEC) has been used widely for the characterization of crystalline polymers, for which high temperature operation above the polymer melting temperature is required to dissolve the polymers. However, this high temperature operation has many advantages in SEC separation in addition to merely increasing polymer solubility. At high temperature the eluent viscosity decreases, which in turn decreases the column backpressure and increases the diffusivity of the analytes. Therefore, many reports on the high temperature operation of high performance liquid chromatography (HPLC) have focused on shortening the analysis time and enhancing the resolution. However, the application of high temperature SEC analysis to exploit the merits of high temperature operation is scarce. In this article, therefore, we report on a new apparatus design for high temperature SEC.