Boron difluoride chelates as catalysts for curing epoxy resins

BF₂-chelates are powerful polymerisation catalysts for epoxy resins; derivatives of β-diketones and of β-ketoamides are especially interesting as ‘latent’ hardeners. Comparison of these metal halide chelates with BF₃-amine complexes in various epoxy systems has shown the chelates to be superior in several respects. Particular advantages are the ease with which reactivity can be varied by choice of chelate structure and by addition of moderators, and the reduced sensitivity to atmospheric moisture during cure. Use of BF₂-Chelates also gives cured products with better electrical properties, and in many cases better mechanical properties, than with BF₃-amine complexes.     

Preparation of silica-immobilized titanium-containing silsesquioxane catalysts and activity for the epoxidation of alkenes

Silsesquioxanes containing tetrapodal titanium species and alkenylsilyl groups were immobilized onto dimethylsilyl-functionalized silica having mesopores by chemical tethering via hydrosilylative reaction in the presence of a Pt catalyst. The immobilized catalysts showed higher activity than their corresponding homogeneous catalyst towards the epoxidation of cyclooctene by tert-butylhydroperoxide, probably because of the improvement of the micro-environment around the titanium center. The reaction was found to be truly heterogeneous, since no further reaction proceeded after the separation of the catalyst by filtration. These catalysts also showed excellent catalytic activity for the epoxidation using hydrogen peroxide as an oxidant, while the parent homogeneous catalysts did not show any activity at all.     

Polymer-supported molybdenum and vanadium catalysts for epoxidation of alkenes by alkyl hydroperoxides

Polymer-supported molybdenum and vanadium catalysts were synthesized using gel-type crosslinked copolymers with microheterogeneous structure. The supports were composed of inert ethylene–propylene rubber and crosslinked high molecular weight poly(ethylene oxide) matrices and polymeric ligands grafted or forming interpenetrating networks: poly(acrylic acid), poly(methacrylic acid), poly(4-vinylpyridine), and polyvinyl alcohol. Catalytic activity and selectivity of some of these complexes were tested in epoxidation of styrene by ethylbenzene hydroperoxide. Molybdenyl cations are strongly coordinated with pyridine-containing copolymers giving catalysts of high activity and selectivity. They provide conversion and selectivity above 70%. Because of the microheterogeneous mosaic-like structure of the supports, better accessibility of the active sites is achieved.     

Shape selectivity as a function of pore size in epoxidation of alkenes with supported titanium catalysts

Reactant shape selectivity of supported titanium catalysts for epoxidation of cyclohexene and 2-hexene has an excellent correlation with the pore diameter of the catalysts. With titanosilicate the preference to cis isomer epoxidation is small compared to TiO₂-SiO₂ probably because of the restriction of its diffusion imposed by the zeolite micropore structure.     

A high-throughput experimentation study of the epoxidation of alkenes with transition-metal-free heterogeneous catalysts

A set of transition-metal-free heterogeneous catalysts for the epoxidation of alkenes with hydrogen peroxide was studied by means of high-throughput experimentation. The catalysts were tested with a range of substrates. Gallium oxide displayed the highest epoxidation activity with all tested alkenes, followed by Ga-MCM-41. The reaction conditions were optimised by investigating the effect of the solvent in which the epoxidation takes place. Considerable improvements in the epoxide yields were obtained in the processes catalysed by Al-MCM-41, Ga-MCM-41 and zeolite USY_(2.6). This work confirms the versatility of HTE for studying catalytic systems.     

Multifunctional formaldehyde resins as curing agent for epoxy resins

Formaldehyde resins (FR) at 1/1/2 molar ratios of monomers (Cl‐phenol/amino monomers/p‐formaldehyde) were synthesized under acid catalysis. The obtained resins were characterized using elemental analysis, FTIR and RMN spectroscopic methods, being used as crosslinking agents for epoxy resin formulations. The curing of epoxy resins with FR were investigated. The glass transition temperature (T_g) and decomposition behavior of crosslinked resins were studied by differential scanning calorimetry (DSC) and thermogravimetric (TGA) techniques. All DSC scans show two exothermic peaks, which implied the occurrence of cure reactions between epoxy ring and amine or carboxylic protons, in function of chemical structures of FR. The crosslinked products showed good thermal properties, high glass transitions, and low water absorption. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dendrimeric silanes for formation of metallosilicates: new heterogeneous catalysts for the epoxidation of alkenes with tert-butylhydroperoxide

New metallosilicate catalysts were prepared by reacting a silanol capped dendrimer, Si[CH₂CH₂Si(CH₃)₂OH]₄ with MCp₂Cl₂ (M = Ti^IV, Mo^VI, W^VI and V^V). The resulting Si[CH₂CH₂>Si(CH₃)₂OMCp₂Cl]₄compounds were incorporated in a silica matrix by the sol–gel method. The catalytic activity of the metallosilicates after calcination revealed excellent activity and selectivity towards epoxidation of alkenes with tert-butylhydroperoxide. Maximum activity was observed with molybdenum-containing materials. Analysis of the catalytic activity revealed that the catalysts were truly heterogeneous.     

Co2 +-exchanged SAPO-5 and SAPO-34 as efficient heterogeneous catalysts for aerobic epoxidation of alkenes

Co-SAPO-5 and Co-SAPO-34 were prepared by a simple ion-exchange route and firstly applied in the aerobic epoxidation of alkenes. Both catalysts exhibited high activities in the epoxidation of alkenes with air to achieve 92.0–91.9 mol% conversion with the epoxide selectivity of 89.5–90.5% for styrene, 71.6–80.0 mol% conversion with 94.8–95.0% selectivity for α-pinene, and 95.3–96.8 mol% conversion with 75.2–73.6% selectivity for α-methyl styrene. Recycling studies and control experiments showed the recyclability and stability of Co-SAPO-5 and Co-SAPO-34 as heterogeneous catalysts.     

Reactive microspheres as active fillers for epoxy resins

Physical properties of epoxy resins filled with microparticles are presented and discussed. Microparticles were synthesized in the form of micron‐sized, crosslinked spherical particles, with an excess of reactive amino groups on their outer surface, and subsequently blended with EPON828‐3,3′DDS in different weight percents (10 and 20 wt %). Differential scanning calorimetry and scanning electronic microscopy were applied to investigate microsphere properties such as morphology, shape, size, and size distribution. Electron spectroscopy for chemical analysis was applied on particles to relate surface composition and reactivity of microspheres. Rheological, dynamic–mechanical, and mechanical properties of the cured blends were analyzed and related to the pure resin and to the same resin modified with PES180. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2031–2044, 2004     

Cure behavior of epoxy resins with different kinds of onium salts as latent thermal catalysts

Two latent thermal catalysts, Dimethyl phenacylsulfonium hexafluoroantimonate, (Benzyl‐S), and triphenyl benzyl phosphonuim hexafluoroantimonate, (Benzyl‐P), were synthesized. Both these synthesized catalysts fulfill requirements for a rapid cure at a moderately elevated temperature in curing the epoxy resins of neat 3,4‐epoxycyclohexylmethyl‐3,4‐epoxycyclohexane‐carboxylate, (EPC), neat 2,2‐bis(4‐glycidyloxyphenyl)propane, (EPA), and their hybrid resin. The cure behavior of these resins cured individually with the synthesized catalysts was studied through correlation of the in situ FTIR (Fourier transform infrared) spectroscopy and DSC (differential scanning calorimetry) dynamic scanning results. Catalyst Benzyl‐S is more effective than Benzyl‐P. Resin EPC is significantly more sensitive to the latent thermal catalysts than the EPA resin. Activated chain‐end (ACE) and activated monomer (AM) mechanisms are basically adopted. Isomerization occurs in the neat EPA cure system, and transesterification takes place in all systems containing EPC species in the latter curing stage. Most importantly, ester linkages C?O in the hybrid systems have been destroyed at some time during the curing process, but some reformed at the latter curing stage. It is most likely that the C?O linkage in the EPC segments was attacked by the activated chain‐end of the epoxide group of EPA species to form a five‐membered cyclic acetal. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3539–3551, 2001     

Aminosiloxane-modified epoxy resins as microelectronic encapsulants

Amine-terminated poly(dimethylsiloxanes) (ATPDMS) were used to improve the toughness of a cresol-formaldehyde novolac epoxy resin cured with a phenolic novolac resin for electronic encapsulation application. The effect of molecular weight of amine-terminated polysiloxanes on the phase separation of the resultant elastomers from epoxy matrix were investigated. Mechanical and dynamic viscoelastic properties of siloxane-modified epoxy networks were also studied. The dispersed silicone rubbers effectively improve the toughness of cured epoxy resins by reducing the coefficient of thermal expansion and flexural modulus, while the glass transition temperature was hardly depressed. Electronic devices encapsulated with the dispersed silicone rubber-modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and have resulted in an extended device use life.     

用于丙烯环氧化反应的金催化剂

以氢气和氧气混合气为氧源的丙烯环氧化反应是金催化剂应用研究的主要反应。综述了金催化剂在丙烯环氧化反应中的载体材料影响、金纳米粒子作用以及金纳米粒子与载体之间的协同作用对催化性能的影响,提出气相直接氧化丙烯生产环氧丙烷尚待解决的技术问题和相应的研究新亮点。     

Crown ethers as new curing agents for epoxy resins

Different crown ethers (4‐aminobenzo‐15‐crown‐5 (4‐aminobenzo‐15‐C5), 1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane (diaza‐18‐crown‐6), tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (H₄DOTA) and tetraazacyclododecane‐1,4,7,10‐tetraacetamide (H₂ODDA)) were used as curing agent for bisphenol A diglycidyl ether (BADGE, n = 0). The maximum enthalpy change for all systems except that formed by the epoxy resin with H₄DOTA corresponds to a stoichiometric ratio, since from this value the reaction enthalpies decrease when the proportion of epoxy increases. Heteropolymerization reaction occurs in all the crown ethers. Etherification reactions occur at temperatures much lower (30 °C less) than for the porphyrin systems studied in which a second signal appears at 300 °C. The etherification is evidenced by a slight shoulder in the thermograms for H₄DOTA and H₂ODDA. The systems BADGE (n = 0)/4‐aminobenzo‐15‐C5 and BADGE (n = 0)/diaza‐18‐crown‐6 improve the thermal stability of the epoxy resin by 30 °C approximately while the improvement for BADGE (n = 0)/H₄DOTA and BADGE (n = 0)/H₂ODDA is about 60 °C. © 2017 Society of Chemical Industry     

Hydrolytic cleavage of epoxy ring during the epoxidation of alkenes over boron modified titanium silicalites of MFI topology

Boron incorporated bifunctional microporous titanium silicalites of MFI topology, which contained both oxidizing and acidic sites, can effectively catalyse the selective epoxidation of α-olefins, followed by ring opening of the epoxide through hydrolysis reactions. Data are presented that correlate the oxidative and acidic functions of these catalysts. The rate of hydrolysis is seen to depend on the phases generated by incorporation of the boron atoms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Core-shell particles designed for toughening the epoxy resins. II. Core-shell-particle-toughened epoxy resins

The diglycidyl ether of bisphenol A–m-phenylene diamine (DGEBA–MPDA) epoxy resin was toughened with various sizes and amounts of reactive core-shell particles (CSP) with butyl acrylate (BA) as a core and methyl methacrylate (MMA) copolymerized with various concentration of glycidyl methacrylate (GMA) as a shell. Ethylene glycol dimethacrylate (EGDMA) was used to crosslink either core or shell. Among the variables of incorporated CSP indicated above, the optimal design was to obtain the maximum plastic flow of epoxy matrix surrounding the cavitated CSP during the fracture test. It could be achieved by maximizing the content of GMA in a shell-crosslinked CSP, the particle size, and the content of CSP in the epoxy resin without causing the large-scale coagulations. The incorporation of reactive CSP could also accelerate the curing reaction of epoxy resins. Besides, it was able to increase the glass transition temperature of epoxy resins if the particle size ≤0.25 μm and the dispersion was globally uniform. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2313–2322, 1998     

Evaluation of bisacrylate terminated epoxy resins as coatings

The paper describes the effect of backbone flexibility on the coating performance of vinyl ester resin. For this purpose four resins of varying flexibility were prepared. Bisacrylate terminated epoxy resin (D) was prepared by reacting 2 mol of acrylic acid with 1 mol of diglycidyl ester of hexahydrophthalic anhydride. The flexibility of the backbone was increased by chain extension of mono acryloxy derivative of diglycidyl ester of hexahydrophthalic anhydride with sebacic acid (resin G′). Partial cross-linking of resin D containing pendant hydroxyl group was also done by reacting with small amounts of isophorone diisocyanate (D₂I₁₀, D₂I₄).     

Halogenated macroporous sulfonic resins as efficient catalysts for the Biginelli reaction

A series of halogenated macroporous sulfonic resins A-15-Cl, A-15-Br and A-15-I were synthesized from the precursor Amberlyst 15 by a typical halogenation reaction, and they were evaluated for the catalytic activities of the halogenated macroporous sulfonic resins via the Biginelli reaction in detail. These modified resins possessed a larger contact angle of water droplet than the precursor and a significantly improved thermal stability, which contributed to their higher catalytic activity. In particular, the resin A-15-Br containing 31.27% bromine exhibited the best catalytic activity and excellent recyclability.