Imidazole Catalyst Research Articles

Effects of Catalysts on the Adhesive Properties for Flip Chip Bonding

The application of flip chip technology has been growing with the trend of miniaturization of electronic packages, especially in mobile electronics. Currently, several types of adhesive are used for flip chip bonding and these adhesives require some special properties; they must be solvent-free and fast curing and must ensure joint reliability against thermal fatigue and humidity. In this study, imidazole and its derivatives were added as curing catalysts to epoxy resin and their effects on the adhesive properties were investigated. Non-isothermal DSC analyses showed that the curing temperatures and the heat of reaction were dependent primarily on the type of catalyst. Isothermal dielectric analyses showed that the curing time was dependent on the amount of catalysts added as well as their type. The die shear strength increased with the increase of catalyst content while the Tg decreased. From this study, imidazole catalysts with low molecular weight are expected to be beneficial for snap curing and high adhesion strength for flip chip bonding applications.

Improvement of the thermal latency for epoxy-phenolic resins by novel amphiphatic imidazole catalysts

Novel amphiphatic imidazole compounds were evaluated as thermal latent catalysts for the polymerization of diglycidyl ether of bisphenol A (DGEBA). Amphiphatic compounds 5–9, two commercially available catalysts 1 and 2, and compounds 3 and 4 were used to cure epoxy resin systems for an investigation of their thermal latency and storage stability. The results from the cure activation energy and viscosity-storage time of the catalysts, the order of thermally latent activity was 3-phenylpropanoic acid (4) > 2-amino-3-phenylpropinoic acid (5) > 2-amino-3-(imidazole-4-yl)-propionic acid (H-His-OH, 8) > N-tert-butoxycarbonyl-histidine (9) > imidazole-4-acrylic acid (6) > 3-(imidazole-4-yl)propionic acid (7) > 1-cyanoethyl-2-ethyl-4-methyl-imidazole (2) > 2-ethyl-4-methylimidazole (1) > histamine (3). From the results, the amphiphatic imidazole catalysts 5–9 showed better thermal latency than commercialized catalysts 1 and 2, basic catalyst 3 and acidic catalyst 4. Concerning the glass transition temperature (Tg), the use of amphiphatic imidazole catalysts 5–9 provided complete or near complete curing systems at temperatures ranging from 152–163 °C, which were similar to two commercially available catalysts (151–152 °C, 1 and 2) and histamine (159 °C, 3). On the other hand, the Tg for compounds 4 and 5 could not be detected at 30–300 °C from the temperature scans because of their weak nucleophilicity and low cross-linking reactivity.

ChemInform Abstract: Design and Mechanistic Studies on a Biomimetic Iron—Imidazole Catalyst System for Epoxidation of Olefins with Hydrogen Peroxide.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Design of and Mechanistic Studies on a Biomimetic Iron–Imidazole Catalyst System for Epoxidation of Olefins with Hydrogen Peroxide

Novel iron catalysts, both defined and in situ generated, for the epoxidation of aromatic and aliphatic olefins with hydrogen peroxide as terminal oxidant are described. Our catalyst approach is based on bio-inspired 1-aryl-substituted imidazoles in combination with cheap and abundant iron trichloride hexahydrate. We show that the free 2-position of the imidazole ligand motif plays a key role for catalytic activity, as substitution leads to a dramatic depletion of yield and conversion. X-ray studies, UV/Vis titrations, and NMR studies were carried out to clarify the mechanism.

Novel, environmentally friendly crosslinking system of an epoxy using an amino acid: Tryptophan‐cured diglycidyl ether of bisphenol A epoxy

AbstractTryptophan, an amino acid, has been used as a novel, environmentally friendly curing agent instead of toxic curing agents to crosslink the diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The curing reaction of tryptophan/DGEBA mixtures of different ratios and the effect of the imidazole catalyst on the reaction have been evaluated. The optimum reaction ratio of DGEBA to tryptophan has been determined to be 3:1 with 1 wt % catalyst, and the curing mechanism of the novel reaction system has been studied and elucidated. In situ Fourier transform infrared spectra indicate that with the extraction of a hydrogen from NH3+ in zwitterions from tryptophan, the formed nucleophilic primary amine and carboxylate anions of the tryptophan can readily participate in the ring‐opening reaction with epoxy. The secondary amine, formed from the primary amine, can further participate in the ring‐opening reaction with epoxy and form the crosslinked network. The crosslinked structure exhibits a reasonably high glass‐transition temperature and thermal stability. A catalyst‐initiated chain reaction mechanism is proposed for the curing reaction of the epoxy with zwitterion amino acid hardeners. The replacement of toxic curing agents with this novel, environmentally friendly curing agent is an important step toward a next‐generation green electronics industry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 181–190, 2007

A Reworkable Epoxy Resin for Isotropically Conductive Adhesive

Electrically conductive adhesive (ECA) is a promising alternative to the toxic eutectic tin-lead solder as an interconnect material. Typical ECAs use epoxy resin as their matrix, which has superior properties over other polymers, such as high adhesion, and low dielectric constant. However, once cured, it is not reworkable. In this study, a liquid diepoxide was designed and synthesized, and used in isotropically conductive adhesive (ICA) formulations. This diepoxide has a molecular structure able to thermally decompose at mild temperature that allows selective individual removal of the bad component without damaging the board and its surroundings. The characterizations including proton and carbon 13 nuclear magnetic resonance, infrared spectroscopy indicated the success of the synthesis. A dual-epoxy system containing this secondary diepoxide and an equivalent bisphenol-A diepoxide were formulated and cured with an anhydride hardener and an imidazole catalyst. Thermal analyses, such as differential scanning calorimetry, thermo-gravimetry analysis (TGA), thermo-mechanical analysis (TMA) and dynamic mechanical analysis (DMA) were employed for the curing kinetics, thermal degradation behavior, glass transition temperature, coefficient of thermal expansion (CTE), and mechanical modulus, respectively. The dual-epoxy system showed two exothermal curing peaks at 140/spl deg/C and 180/spl deg/C, respectively. The thermoset of this dual-epoxy system has a decomposition temperature around 234/spl deg/C, a glass transition temperature around 80 to 90/spl deg/C, and CTEs of 74 ppm//spl deg/C and 225 ppm//spl deg/C below and above its Tg, respectively. The rework test on a surface mount component bonded to copper surface showed this ECA can be easily and quickly removed from the copper surface. The bulk resistance and contact resistance of ICAs were measured before and during an accelerated aging process in a temperature/humidity chamber (85/spl deg/C/85% RH). The ECA showed good bulk resistivity and contact resistance comparable to its control and a commercial ECA on gold and copper surface finishes.

Corrigendum to “Novel palladium imidazole catalysts for Suzuki cross-coupling reactions” [J. Mol. Catal. A: Chemical 206 (2003) 77–82

Corrigendum to “Novel palladium imidazole catalysts for Suzuki cross-coupling reactions” [J. Mol. Catal. A: Chemical 206 (2003) 77–82

Novel palladium imidazole catalysts for Suzuki cross-coupling reactions

Novel palladium imidazole catalytic systems for the Suzuki cross-coupling reaction have been developed from commercially available and inexpensive imidazoles and palladium sources, and exhibit high activity and no homo-coupling.

Compartmentalization of reactants in supercritical fluid micelles

The hydrolysis of acetylsalicylic acid, a model reaction, in sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/supercritical ethane reverse micelles has been studied in the presence of imidazole catalyst using in situ UV-vis spectroscopy. An increase of rate constant by 55 times was observed in AOT/supercritical ethane micellar medium compared to the reaction carried out in aqueous buffer. The reaction had a strong dependence on the water content of micelles, which decelerated to a large extent when the water content of the micelles was increased. The acceleration of the reaction in micelles compared to aqueous buffer and the water content dependence of the reaction rate have been confirmed to be due to compartmentalization of the water-soluble reactant and catalyst in the aqueous core of the micelles. The local concentration of substrate and catalyst increases when they are enclosed in the aqueous core of the micelles, resulting in an increase in the rate constant and shortening of the reaction time, rather than the existence of a diluted solution in the aqueous buffer. No pressure dependence of the reaction has been found in the pressure range of 27 to 44 MPa at 310 K.

The promotion of hydrolysis of acetylsalicylic acid in AOT/near-critical propane microemulsion.

A significant acceleration of the hydrolysis of acetylsalicylic acid was accomplished by the introduction of an AOT/near-critical propane microemulsion at lower W0 values; the rate constant at W0 = 1 was found to be 54 times that in aqueous buffer medium in the presence of imidazole catalyst.

Effect of reactivity of different types of hydroxyl groups of HTPB on mechanical properties of the cured product

The amount of three types of hydroxyl functional groups (GOH, HOH, and VOH) in hydroxyl terminated polybutadiene (HTPB), remaining in samples acetylated to the same extent under two different conditions, viz., fast acetylation using acetyl chloride in presence of N-methyl imidazole catalyst and slow acetylation by acetic anhydride, differed significantly. For the fast acetylation there is a uniform reduction in all the three types of hydroxyls, probably because the reaction becomes random at rapid rates and the reactivity of the different types of hydroxyls does not play a major role. However, in the slow reaction, the reduction of G-type hydroxyls was 30% more than the expected value and there was a corresponding increase in the amount of V-type hydroxyls remaining in the acetylated product, showing reactivity of OH in the order of G > H > V. When the reaction is slow, it becomes selective and the change in reactivity of the three types of OH groups is reflected in the extent of conversion. The mechanical properties and the crosslink density data show a reduction in the samples containing lesser amounts of GOH, confirming the branching nature of GOH, which is involved in the crosslinking reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1313–1320, 1997

Effect of reactivity of different types of hydroxyl groups of HTPB on mechanical properties of the cured product

The amount of three types of hydroxyl functional groups (GOH, HOH, and VOH) in hydroxyl terminated polybutadiene (HTPB), remaining in samples acetylated to the same extent under two different conditions, viz., fast acetylation using acetyl chloride in presence of N-methyl imidazole catalyst and slow acetylation by acetic anhydride, differed significantly. For the fast acetylation there is a uniform reduction in all the three types of hydroxyls, probably because the reaction becomes random at rapid rates and the reactivity of the different types of hydroxyls does not play a major role. However, in the slow reaction, the reduction of G-type hydroxyls was 30% more than the expected value and there was a corresponding increase in the amount of V-type hydroxyls remaining in the acetylated product, showing reactivity of OH in the order of G > H > V. When the reaction is slow, it becomes selective and the change in reactivity of the three types of OH groups is reflected in the extent of conversion. The mechanical properties and the crosslink density data show a reduction in the samples containing lesser amounts of GOH, confirming the branching nature of GOH, which is involved in the crosslinking reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1313–1320, 1997

Spectrophotometric study of coproporphyrin-I complexes of copper(II) and cobalt(II)

The reagent 3,8,13,18-tetramethyl-21 H,23 H-porphine-2,7,12,17-tetrapropionic acid or coproporphyrin-I (CPI) was used for the spectrophotometric determination of copper(II) and cobalt(II) in the presence of pyridine and imidazole catalysts. Optimum conditions were investigated and the methods were applied to the determination of parts per billion levels of copper(II) and cobalt(II). The Sandell sensitivities of the recommended procedures were 0.568 μm cm −2 and 0.464 μg cm −2 (for A = 0.001) for copper and cobalt, respectively. The relative standard deviations were 2.0% for copper and 1.0% for cobalt. The kinetics of the reaction of CPI with copper(II) and cobalt(II) in the presence of the catalysts and the influence of the temperature were studied, and their kinetic constants determined. The influence of light on the photodecomposition of CPI was also studied.

Effects of catalysts on the model reactions of several maleimide resin systems (III): allyl-modified maleimniide

A detailed investigation on the effects of catalysts on the curing reactions of the allyl-modified maleimide resin system was carried out by using model reactions. Various products and various degrees of polymerization of N-phenylmaleimide are obtained by changing catalysts (no catalyst, imidazole catalyst, radical catalyst and triphenyl phosphine). The products are identified by NMR spectroscopy. These results suggest that the choice of catalyst could control the crosslinking densities and structures of various maleimnide resins; those factors also relate to the physical and mechanical properties. These results would be useful in maleimide chemistry and its application.

Characterization of epoxy resins cured with dicyandiamide in the presence of imidazole catalysts by high-resolution pyrolysis—gas chromatography

Epoxy resins cured with dicyandiamide (DCDA) in the presence of various imidazole catalysts were characterized by high-resolution pyrolysis-gas chromatography (HR-Py—GC) with simultaneous detection by a nitrogen phosphorus detector (NPD) and a flame ionization detector (FID). Sharp peaks of the nitrogen-containing degradation products characteristic of the various imidazole catalysts were observed, along with those of DCDA in the pyrograms obtained, by use of NPD. The observed characteristic peaks of the imidazole catalysts in the pyrograms obtained by use of both NPD and FID were successfully correlated to the contents of the imidazole catalysts in the epoxy resins.

Single‐step dyeing and finishing treatment of cotton with 1,2,3,4‐butanetetracarboxylic acid

AbstractA single‐step dyeing and finishing (SDF) process was developed to eliminate dyeing problems associated with cotton crosslinked by polycarboxylic acid such as 1,2,3,4‐butanetetracarboxylic acid (BTCA). This process consisted of several steps: (a) impregnation of the fabric by the bath containing BTCA, dye, and catalyst; (b) drying; and (c) curing at high temperature. Color strength (K/S) and dye fixation of cotton treated by the SDF process were excellent, especially with reactive dyes containing mono‐ or dichlorotriazinyl compounds and, in some cases, were higher than those of the sample dyed by a conventional batch process without finishing treatment. The presence of dye in the SDF process did not interfere with crosslinking of cotton. We believed that the reaction occurred between carboxyl groups of BTCA and s‐triazinyl groups in reactive dyes in the presence of imidazole and other catalyst. FTIR, Raman, and X‐ray fluorescence spectroscopies were used to confirm the mechanism of dye fixation. Elemental analysis also supported this mechanism. The SDF process can be an excellent way to dye fabric that also requires crosslinking treatment for smooth drying appearance. © 1994 John Wiley & Sons, Inc.

Effects of catalysts on the model reactions of several maleimide resin systems—(I) Amine-modified maleimide

A detailed investigation on the effects of catalysts on'the curing reactions of maleimide, amine-modified maleimide systems was carried out using model reactions. N-phenylmaleimide (PMI) and N,N'-diphenylaspartimide (API) were selected as model compounds. The degree of polymerization of PMT is controlled by changing catalysts (imidazole catalyst and radical catalyst). The radical catalytic effect is hindered by API. As the polymerization degree of PMI in the model reaction corresponds to the crosslinking density of the maleimide resin system, the choice of catalyst could control the crosslinking density and structure of the maleimide resin system, which could also affect the physical and mechanical properties.

Synthesis of polyphenylacetylene free‐standing films in the presence of rhodium–imidazole catalysts

AbstractA new dinuclear rhodium(I) complex [Rh2(cod)2(imH)2im]PF6 (I) has been synthesized and characterized. The complex is unstable in solution where it undergoes modifications leading to insoluble oligomers. However, it exhibits high catalytic activity towards polymerization of phenylacetylene (PPA) films can be obtained under mild reaction conditions. As‐grown PPA films are stable and soluble. Two different types of morphologies were found: one exhbits a cell‐like structure with microfibrils inside the cell and the other a dense enamel‐like smooth surface.

Influence of different imidazole catalysts on epoxy‐anhydride copolymerization and on their network properties

AbstractThe copolymerization of naidc and methyltetrahydrophthalic anhydrides and diglycidyl ether of bisphenol A (DGEBA) with various stoichiometric ratios [r = 2[anhydride]/DGEBA] and with different concentrations of several imidazoles has been studied. These results are compared with those obtained with a tertiary amine such as benzyldimethylamine, a well‐known efficient catalyst of epoxy‐anhydride copolymerization. Thermal and hydrothermal behaviors of these networks also have been examined.

Fracture toughness and molecular structure of unfilled epoxy adhesives

The cohesive, mode I (tensile cleavage) fracture energy (or fracture toughness), GIc, of bulk tapered double cantilevered beam (TDCB) samples of a series of three epoxy thermoset networks was determined using a linear elastic fracture mechanics (LEFM) analysis. Networks of different crosslink density were obtained by mixing various amounts of an aromatic epoxy novolac and an aliphatic epoxy and crosslinking with an imidazole catalyst. Brittle, stick-slip fracture was observed for all formulations, with GIc increasing as the amount of aliphatic epoxy increased. However, fracture surface morphologies exhibited evidence of increasing plastic deformation as GIc increased. In the investigation of structure-property relationships for this series of thermoset networks, GIc was found to be inversely related to both network crosslink density and glass transition temperature (Tg). It was also found that the room temperature frequency of the glassy state transition (β-transition) increased as fracture toughness increased.