Whan Gun Kim

Curing reaction of biphenyl epoxy resin with different phenolic functional hardeners

The investigation of cure kinetics and relationships between glass transition temperature and conversion of biphenyl epoxy resin (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl) with different phenolic hardeners was performed by differential scanning calorimeter using an isothermal approach over the temperature range 120–150°C. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of formulations using xylok and dicyclopentadiene type phenolic resins (DCPDP) as hardeners proceeds through a first-order kinetic mechanism, whereas the curing reaction of formulations using phenol novolac as a hardener goes through an autocatalytic kinetic mechanism. The differences of curing reaction with the change of hardener in biphenyl epoxy resin systems were explained with the relationships between Tg and reaction conversion using the DiBenedetto equation. A detailed cure mechanism in biphenyl-type epoxy resin with the different hardeners has been suggested.

Cure Kinetics of Biphenyl Epoxy-Phenol Novolac Resin System Using Triphenylphosphine as Catalyst

The effects of the concentration of triphenylphosphine as a catalyst on the cure reaction of the biphenyl epoxy/phenol novolac resin system were studied. The kinetic study was carried out by means of the analysis of isothermal experiments using a differential scanning calorimeter. All kinetic parameters including the reaction or- ders, activation energy and kinetic rate constants were evaluated. To describe the cure reaction with the catalyst concentration, the normalized kinetic model was developed. The suggested kinetic model with a diffusion term was successfully able to describe and predict the cure reaction of epoxy resin compositions as functions of the catalyst content and temperature.

Contributions of the network structure to the cure kinetics of epoxy resin systems according to the change of hardeners

The cure kinetics of epoxy resin systems was investigated according to the change of curing agents, and analyzed in respect of the network structure. An autocatalytic cure reaction can be shown in the epoxy resin systems with phenol novolac hardener regardless of the kinds of epoxy resin and the epoxy resin systems using Xylok and dicyclopentadiene type phenol resin curing agents follow nth-order kinetic mechanism. The conversion rates of novolac epoxy resins with phenyl and DCPD (dicyclopentadiene) moiety are higher than biphenyl epoxy resin (YX-4000H) and o-cresol novolac epoxy resin (EOCN-1020) systems. All kinetic parameters of each epoxy resin systems were reported in terms of generalized kinetic equation that considered diffusion term, and the network structure of each epoxy resin systems with different curing agents were analyzed using DiBenedetto equation. These kinetic data were interpreted in terms of network structure model in which a curing agent can act as a spacer and control the distances between epoxy resin units.

Kinetic study of the effect of catalysts on the curing of biphenyl epoxy resin

The investigation of cure kinetics of biphenyl epoxy (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl)dicyclopentadiene type phenolic resin system with different kinds of catalysts was performed by a differential scanning calorimeter using an isothermal approach. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of the formulations using triphenylphosphine (TPP), 1-benzyl-2-methylimidazole (1B2MI), and tris(4-methoxyphenyl)phosphine (TPAP) as a catalyst proceeds through an nth-order kinetic mechanism, whereas thatof the formulations using diazabicycloundecene (DBU) and tetraphenyl phosphonium tetraphenyl borate (TPP–TPB) proceeds by an autocatalytic kinetic mechanism. To describe the cure reaction in the latter stage, we have used semiempirical relationship proposed by Chern and Poehlein. By combining an nth-order kinetic model or an auto-catalytic model with a diffusion factor, it is possible to predict the cure kinetics of each catalytic system over the whole range of conversion.

Physical properties of epoxy molding compound for semiconductor encapsulation according to the coupling treatment process change of silica

The change of physical properties of an epoxy-molding compound (EMC) for semiconductor encapsulation according to the coupling treatment process change was investigated. Three different coupling treatment processes were applied in this study: the pretreatment method (PM), the internal pretreatment method (IPM), and the integral addition method (IAM). Especially, we suggested a simple and economic process, the IPM process, in which the drying and powdering process is excluded compared with the PM process. The optimum content range of the coupling agent is 1.0–2.0 wt % based on the weight of the filler, which is about a 1.3–2.5 coating layer. The flexural strength and internal stress of EMC made by the IPM process is almost equivalent to that made by the PM. We applied the model of complex layers of a silane coupling agent at the filler/matrix interface in interpretating the mechanical and thermal properties of EMC and obtaining the relationships between physical properties and the coupling process. It can be concluded that the IPM process is an effective and economic process to be able to obtain a good reliable EMC with strong mechanical strength and low internal stress.

Curing characteristics of o‐cresol novolac epoxy resin modified by bismaleimide

Curing characteristics of o-cresol novolac epoxy resin modified by 4,4-diaminodiphenylmethane bismaleimide (DDM-BMI) using FTIR were investigated and the glass transition temperature was measured. With the addition of DDM as hardener, the relative curing reaction conversion of DDM-BMI increased with equivalent weight ratio [R1 = (equiv wt summation of epoxy and DDM-BMI)/equiv wt of DDM] and weight ratio of epoxy and DDM-BMI (R2 = wt of epoxy resin/wt of DDM-BMI). Using phenol novolac resin (PN) as hardener, the curing reaction conversion of DDM-BMI was hardly changed, but the variation of that in the epoxy resin was observed with R2 change.

Novel Photocrosslinking Nonlinear Optical Polymer Systems

ABSTRACT We designed and synthesized novel photocrosslinking guest-host nonlinear optical (NLO) polymer systems. In the system, guest NLO molecules bearing two photocrosslinking groups such as cinnamate or acrylate double bonds were homogeneously dispersed in the host photocrosslinking polymer matrix. The NLO molecules are then aligned by using the corona poling technique at an elevated temperature and the system was subsequently crosslinked by irradiating UV light. We expect the photocrosslinking keeps the NLO molecules from relaxing to random orientation. Formation of network structure was confirmed by comparing the absorbances of the NLO moiety in the crosslinked film before and after washing the film with methanol or acetone, exhibiting little leaching out of the NLO moiety from the polymer matrix.

Thermally stable photoreactive polymers as a color filter resist bearing acrylate and cinnamate double bonds

Photoreactive polymers as a color filter resist containing both photoreactive acrylate and cinnamate double bonds were synthesized usin two step reactions. The chemical structures of the synthesized polymers were confirmed by1H-NMR and FT-IR spectroscopy. The photoreactive polymers were quite soluble in most common organic solvents and produced excellent quality thin films by spin-coating. The photocuring kinetics of the acrylate and cinnamate double bonds were examined by FT-IR and UV-Vis spectroscopy, which confirmed the excellent photoreactivity of both the acrylate and cinnamate double bonds in the polymers. Upon UV irradiation, photocuring was almost completed within approximately 5 min, irrespective of the type of the prepolymers. The polymers also exhibited superior thermal stability, showing little change in transmittance in the visible region even after heating to 250 °C for one hour. Photolithographic micropatterns could be obtained with a resolution of a few microns.

B‐stage characterization of o‐cresol novolac epoxy resin system using raman spectroscopy and matrix‐assisted laser desorption/ionization mass spectrometry

The B-stage of the o-cresol novolac epoxy resin–phenol novolac hardener–triphenylphosphine (TPP) catalyst system was characterized using Raman spectroscopy and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The consistent decreasing intensities of characteristic epoxy resin peaks in MALDI mass and Raman spectra according to the melt mixing time were observed, which is due to the formation of the epoxy–phenol–TPP complex and the propagation reaction between them and with another epoxy resin. Our microscopic analysis method will provide a useful tool to control the optimum condition of the melt mixing process in the B-stage.

Novel Photocrosslinking Polymers for Liquid Crystal Alignment

Photocrosslinking polymers with optical anisotropy, which may be applied as the alignment layer for liquid crystal display (LCD), were synthesized through reaction between an epoxy compound and several kinds of cinnamic acids. The photocrosslinking polymer film was formed by spin-coating and then exposed to linearly polarized UV light. The optical anisotropy of the polymer film caused by the selective cycloaddition of the cinnamate groups was confirmed from the polarized UV-vis spectra. The polymer films irradiated by unpolarized UV light exhibited isotropic absorbance in the polarized UV-vis spectra, while the polymer films irradiated by the polarized UV light showed anisotropic absorbance. We also confirmed the photocrosslinking polymer film could align liquid crystal (LC). LC cell fabricated using the polymer films irradiated by linearly polarized UV showed anisotropic transmission of the polarized visible light, while the cell fabricated using the polymer films irradiated by unpolarized UV exhibited isotropic transmission.