Jeong-Cheol Kim

Synthesis and characterization of colorless polyimide nanocomposite films containing pendant trifluoromethyl groups

A series of colorless polyimide (PI) nanocomposite films were synthesized from 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) with various organoclay contents by solution intercalation polymerization to poly(amic acid)s, followed by thermal imidization. The variation with the organoclay content of the thermomechanical properties, morphology, and optical transparency of the hybrids was examined at organoclay loadings ranging from 0 to 1.0 wt%. The hybrid films showed high optical transparency and almost no color, with cut-off wavelengths ranging from 352 and 356 nm and very low b* values of 1.19–1.77. The hybrid PI films showed good thermal properties with a glass transition temperature of 280–287 °C. Most films did not show any significant thermal decomposition below 490 °C. The addition of only a small amount of organoclay was sufficient to improve the tensile properties of the PI films with maximum enhancement being observed at 0.25 wt% organoclay. Moreover, these PI hybrids also had low coefficients of thermal expansion (CTE).

Quaternary copolyimides with various monomer contents: Thermal property and optical transparency

Several quaternary copolyimides (Co-PIs) were prepared using various molar ratios of two dianhydrides and two diamines: 4,4’-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride) (PMDA), 2,2’-bis(trifluoromethyl)benzidine (TFB), and trans-1,4-cyclohexanediamine (CHDA). Copolymerization of the monomers afforded poly(amic acid)s (PAA), which were solution-cast onto glass plates and subjected to thermal imidization to yield the Co-PI films. These Co-PI films showed no significant decomposition below 500 °C in a N2 atmosphere. Finally, the films were colorless and exhibited high optical transparencies, with UV-vis. absorption edges of 342-367 nm and low yellow index (YI) values of 1.72–5.09.

Optically transparent and colorless polyimide hybrid films with various clay contents

AbstractPoly(amic acid) (PAA) was prepared by the reaction of 4,4-(hexafluoroisopropylidene)diphthalic anhydride with m-xylylenediamine in N,N-dimethylacetamide. Hybrid films were obtained from solutions of the precursor polymer blended with varying amounts of pristine saponite (SPT) clay (0–25 wt%). The cast PAA film was heat-treated at different temperatures to create polyimide (PI) hybrid films, which showed excellent optical transparencies and were almost colorless. The wide-angle X-ray diffraction and transmittance electron microscopy results for the PI hybrid films showed a substantial increase in the agglomeration of the clay particles as the clay loading was increased from 10–25 wt%. This finding suggests that in hybrid materials with low clay contents, the clay particles are better dispersed in the matrix polymer and do not agglomerate significantly. The addition of some amount of clay was sufficient to improve the thermal and oxygen barrier properties of the PI, with a maximum improvement observed at 20 wt% SPT.

High gas barrier properties of poly(vinyl alcohol) nanocomposite films with various equibiaxial stretching ratios

Abstract

Flexible clay hybrid films with various poly(vinyl alcohol) contents: Thermal properties, morphology, optical transparency, and gas permeability

AbstractClay hybrid films were obtained by the solution blending of saponite (SPT) with various amounts of poly(vinyl alcohol) (PVA). Variations in the thermal properties, morphology, optical transparency, and gas permeability of the clay hybrid films with PVA content in the range 0–10 wt% were examined. With increasing PVA content, the thermal transition temperatures of the hybrids decreased. However, the values of the coefficient of thermal expansion (CTE) increased gradually. The values of the yellow index (YI) and oxygen transmission rate (O2TR) of the clay hybrid films remained constant regardless of their PVA content.

Effect of Silica Nanotube Surface Modification on the Physical Properties of Nanocomposites with Poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA)/silica nanotube (SNT) nanocomposites were prepared by a melt dispersion method using a twin screw extruder and a chloroform-based solvent dispersion method. After removing the template by calcination or organic solvent treatment, the SNT surface was modified by methacryloxypropyl trimethoxysilane (MPMA). The effects of SNT template removal, surface modification, and nanocomposite preparation method on the physical properties of PMMA/SNT nanocomposites were analyzed. The dispersion of SNTs in PMMA was analyzed using transmission electron microscopy. The thermal properties were evaluated using differential scanning calorimetry and thermogravimetric analysis. The mechanical properties of the nanocomposites were analyzed using a universal testing machine and the light transmittance of the nanocomposites was measured using UV-VIS-NIR spectrophotometry. As the SNT increased, the flexural modulus of SNT/PMMA nanocomposites increased. In particular, the surface modified SNT nanocomposite with 5% content by solvent dispersion method showed 49% improvement in flexural modulus compared to virgin PMMA. The tensile strength of nanocomposites decreased with the increase of SNT content. Nanocomposite containing surface modified SNT was higher in tensile strength than that of SNT without surface modification. The dispersion of SNT in the nanocomposite was better by surface modification of SNT, regardless of the preparation method (melt or solvent) of the nanocomposite. However, the light transmittance was more dependent on the SNT template removal method than the SNT surface modification, and ethanol extraction showed higher light transmittance than the calcination method.