Preparation and characterization of novel ZnS/sulfur-containing polymer nanocomposite optical materials with high refractive index and high nanophase contents

A series of novel transparent bulk ZnS-polymer nanocomposites with high refractive index were successfully prepared via in-situ bulk polymerization in the presence of 2-mercaptoethanol (ME)-capped ZnS NPs. The polymerization mechanism combined the step-growth and free radical polymerization of different monomers of episulfide, m-xylylene diisocyanante (XDI), 2-hydroxyethyl methacrylate (HEMA) and N,N-dimethylacrylamide (DMAA). The high refractive index of episulfide compounds, including ESGMES, ESDGEBA and MPS, were synthesized and used as monomers in polymerization systems. The cured nanocomposites with 30 wt% nanoparticles show high refractive index and good transparency. The refractive index of the nanocomposites could be continuously regulated in the range from 1.59 to 1.65 by the content of ZnS NPs and the pencil hardness is round about 5H. The content of ME-ZnS NPs can affect the thermal stability, mechanical and optical properties of the resulting nanocomposites, and the relationship between them were studied by TGA, DMA, pencil hardness test, Charpy impact test.     

The research on syntheses and properties of novel epoxy/polymercaptan curing optical resins with high refractive indices

A novel thioether glycidyl resin bis[3-(2,3-Epoxypropylthio)phenyl]-sulfone (BEPTPhS) with high refractive index was synthesized by condensation of bis(3-mercaptophenyl)sulfone (BMPS) with epichlorohydrin. It's structure was characterized by FTIR, MS and NMR. It was the first time that trimercaptothioethylamine (TMTEA) was used as curing agent to cure epoxy resins. Optical resins possessing high refractive index were prepared by curing diglycidyl ether of bisphenol A (DGEBA) with the mixture of TMTEA and ethylendiamine (EDA) and by curing BEPTPhS/DGEBA with TMTEA. The research on the optical properties of resins of DGEBA cured by the mixtures of TMTEA and EDA indicated that these resins possess higher refractive index (n_d>1.60), lower dispersity (ν_d>34), high impact strength (IPS>30 kJ m⁻²) and higher transmittance. The n_d, ν_d and density of these resins varied linearly with the EDA content in the curing agent mixtures. The optimum ratio of the EDA content to that of TMTEA is 20:80 (molar ratio), at this ratio the cured resin has the optimum optical properties (n_d²⁰=1.61, v_d=35.4). The cured resins of BEPTPhS/TMTEA have a high refractive index (the highest is n_d=1.67). The optical, physical and thermal properties of the cured optical resins of BEPTPhS/TMTEA were discussed in this paper.     

Toughening epoxy resin with blocked isocyanate containing soft chain

A series of imidazole (MI) blocked 2,4‐toluene diisocyanate (TDI) with polyethylene glycol (PEG‐400) as soft segment (PEG‐MI‐b‐TDI) were synthesized for toughening and curing the bisphenol A type epoxy resin (E‐44). Fourier transform infrared (FTIR) spectrum indicates that the NCO groups of the isocyanate molecule are blocked with MI. For curing epoxy systems, elimination of epoxy group and the formation of urethane bonds were studied by FTIR spectroscopy. The results of mechanical property were shown that the tensile shear and impact strengths of neat MI and MI‐b‐TDI cured E‐44 are lower than those of PEG‐MI‐b‐TDI cured E‐44. Based on the scanning electron microscope studies, microstructure evolutions of the E‐44 cured by different curing agents were imaged. The mechanical, thermal, and dynamic mechanical properties were measured by universal testing machine, differential scanning calorimeter and dynamic mechanical analyzer (DMA). The toughness of E‐44 cured by PEG‐MI‐b‐TDI was effectively improved without sacrificing the tensile shear strength. Based on the DMA studies, the long soft chain of PEG brought in a noticeable lowering in the glass transition temperature (T_g). The glass transition temperature is near 165°C for the neat MI cured E‐44, which is higher than the T_gs of the other curing agents cured epoxy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41345.     

Blended hybrids based on silsesquioxane–OH and epoxy resins

Blended hybrids based on silsesquioxane cyclohexyl trisilanol [STOH; i.e., (c‐C₆H₁₁)₇Si₇O₉(OH)₃] and epoxy resin 4,5‐epoxyhexyl‐1,2‐dimethyl acid diglycidyl ester (TDE‐85) were prepared with good compatibility of STOH up to 5 wt % with TDE‐85. The blended hybrid resins, with various STOH additions, were cured by 4,4′‐diaminodiphenylsulfone, and the curing reactions were investigated with differential scanning calorimetry. The incorporation of STOH increased the curing reaction of TDE‐85 for three active hydrogens existing in the STOH molecule. The storage moduli and glass‐transition temperatures of the cured hybrid resins were studied with dynamic mechanical analysis. The cured hybrids had higher storage moduli than the pure epoxy resins at lower temperatures and increased slightly even when the temperature was above the glass‐transition temperature. Two peaks appearing in tan δ curves indicated the block copolymer structure and two different glass‐transition temperatures of the cured hybrid resins. The thermal stability and flame retardancy of the cured hybrid resins were investigated with thermogravimetric analysis and limited oxygen index values, respectively. The results showed that introducing silsesquioxane–OH units into epoxy resins could improve the thermal stability and flame retardancy of the resins. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and properties of the optical resin composed of cyclotriphosphazenes

Cyclomatrix polyphosphazenes attract more and more interest because they possess thermal stability and halogen-free flame retardant property. The hexa(Allyl 4-hydroxybenzoate)cyclotriphosphazene is synthesized using hexachlorocyclotriphosphazene (HCTP), 4-hydroxybenzoic acid and allyl alcohol, its structure is confirmed by FTIR, ¹H NMR, ¹³C NMR, ³¹P NMR and mass spectrometer. Through radical homopolymerization of itself and copolymerization with methyl methacrylate (MMA), a series of optical resins containing cyclotriphosphazene units are obtained. The refractive indices, the visible light transmittance, the density, the water absorption, the thermal and flame-retardant characteristic of the cured resins are studied. Among the tested cured resins, the cyclomatrix homopolymer has the highest refractive index (n _d = 1.596), the highest thermal stability (starting decomposed at 337 °C) and the best halogen-free flame-retardant characteristic (limited oxygen index is 34.33% via the 40.03% char yield data at 850 °C by the semi-empirical formula).     

High transmittance and environment‐friendly flame‐resistant optical resins based on poly(methyl methacrylate) and cyclotriphosphazene derivatives

Highly transparent optical resins based on poly(methyl methacrylate) (PMMA) and two cyclotriphosphazene derivatives which acting as halogen‐free flame retardants were prepared. The refractive indices, visible light transmittance, water absorption, flame‐resistant characteristic, and the mechanical properties of the resins were studied. Comparing with pure PMMA, the as‐prepared resins with the two additives exhibited higher refractive index (n_d), longer UV cutoff wavelength and better surface hardness. The water absorption of the resins was decrease with increasing of the additives. The visible light transmittance of all the samples adding Additive A was higher than 90%. When the weight ratio of additive/MMA was 20/100, the limiting oxygen index (LOI) of the samples were 26 (with Additive A) and 22 (with Additive B), respectively. The surface hardness was increased from HB to 2H with increasing the content of the additives, and the impact and the tensile strength changed little for the formulas of the additives lower than 30% by weight. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of accelerated ageing on methacrylate‐based denture resins heterogeneity as viewed by ESR‐spin‐probe method

The electron‐spin‐resonance (ESR) spin‐probe method, was used to study the heterogeneity of denture resins based on poly(methyl methacrylate). Results for three resins processed by microwave energy, conventional curing and cold curing (depending on the curing procedure and exposed to ageing in various environmental conditions) were compared. All three cured resins were stored over the same time (1200 h) in distilled water at ambient temperature and in artificial saliva at 348 K. The temperature‐dependent ESR spectra of a spin probe dispersed in the denture resins are analyzed in terms of line‐shapes and line‐widths. The appearance of two spectral components was taken as an indication of resin heterogeneity. The results reveal that the cold‐cured resin has a lower local density in comparison with microwave and conventionally cured resin. The amount of residual monomer also contributes to the local motion of polymer segments. The change of denture resins exposed to ageing is influenced both by the structure of the original resin and the ageing conditions. Restricted motion of a spin probe incorporated into the acrylic resins exposed to accelerated ageing suggests additional crosslinking of polymer chains. The differences are observed for all the investigated resins, but the highest change is observed with the cold‐cured resin. The ESR results are accompanied by T_g and T_m measurements. Copyright © 2005 Society of Chemical Industry     

Effect of cobalt on the electrical conductive property of epoxy resins

Cobalt acrylate (CoA₂) has been treated with bisphenol‐A and epichlorohydrin to modify epoxy resins. It was cured with p‐acetylbenzilidene triphenyl arsonium ylide. The properties such as epoxide equivalent weight (equiv/100 g), molecular weight, hydrolyzable chlorine content increases whereas hydroxyl content, refractive index decreases in the presence of CoA₂. The cured epoxy resins shows improve electrical conductivity due to the incorporation of CoA₂ with epoxy resins. The influence of complex formation of CoA₂ with either linkage of epoxy resins were investigated by spectroscopy. The decrease in T_g from differential scanning calorimetry support the improve in flexibility. The dispersion of cobalt in epoxy resins matrix was confirmed by scanning electron microscope. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of trifluoromethyl groups containing epoxy resins cured with amine for low Dk materials

The study synthesized a trifluoromethyl (CF₃) groups with a modified epoxy resin, diglycidyl ether of bisphenol F (DGEBF), using environmental friendly methods. The epoxy resin was cured with 4,4′‐diaminodiphenyl‐methane (DDM). For comparison, this study also investigated curing of commercially available diglycidyl ether of bisphenol A (DGEBA) with the same curing agent by varying the ratios of DGEBF. The structure and physical properties of the epoxy resins were characterized to investigate the effect of injecting fluorinated groups into epoxy resin structures. Regarding the thermal behaviors of the specimens, the glass transition temperatures (T_g) of 50–160°C and the thermal decomposition temperatures of 200–350 °C at 5% weight loss (T_d5%) in nitrogen decreased as amount of DGEBF increased. The different ratios of cured epoxy resins showed reduced dielectric constants (D_k) (2.03–3.80 at 1 MHz) that were lower than those of pure DGEBA epoxy resins. Reduced dielectric constant is related to high electrronegativity and large free volume of fluorine atoms. In the presence of hydrophobic CF₃ groups, the epoxy resins exhibited low moisture absorption and higher contact angles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Click chemistry‐assisted preparation and properties of phosphorus and nitrogen synergistic flame retardant optical resin with a high refractive index

In this study, halogen‐free flame retardant tri(acryloyloxyethyl) phosphate (TAEP) was prepared using 2‐hydroxyethyl acrylate and phosphorus oxychloride. The chemical structure of TAEP was characterized by Fourier transform infrared and proton nuclear magnetic resonance spectrometers. The mixture of TAEP, acrylamide, and pentaerythritol tetrathioglycolate with different P, N, and S content were used to prepare flame retarding optical resin via the click chemistry curing. The curing performance, thermal stability, and flame retardant performance of the optical resins were measured by differential scanning calorimeter, thermogravimetric analyzer, vertical burning tester, and limiting oxygen index test, respectively. Additionally, the morphology of the burned residual was investigated by scanning electronic microscopy, and the refractive indices of the optical resins were measured by an Abbe Refractometer. The results strongly indicated that increasing sulfur content in resins improved their refractive indices, but deteriorated their flame retardancy. Meanwhile, the nitrogen element was helpful for the flame retardancy of the optical resin. With S N, and P contents of 3.00%, 1.00%, and 6.70 wt %, respectively, the refractive index of the optical resin reached up to 1.4987, and its flame retardancy achieved the UL‐94 V‐0 level and the LOI value of 29.3%. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46648.     

Nanocomposites from phenolic resin and various organo‐modified montmorillonites: Preparation and thermal stability

Phenolic resin (PF)/montmorillonite (MMT) nanocomposites have been successfully prepared using intercalative polymerization of resole‐type phenolic resins in montmorillonites modified by octadecylamine (C18), benzyldimethylhexadecylammonium chloride (B2MH), benzyltriethylammonium chloride (B3E), and benzyldimethylphenylammonium chloride (B2MP). X‐ray diffraction measurements and transmission electron microscope observations showed that clay platelets were partially exfoliated or intercalated after complete curing of the phenolic resins. The cured nanocomposites were named as modifier‐MP (MP means montmorillonite‐phenolic resin), for example, B3E‐MP. Thermogravimetric analysis showed that thermal decomposition temperatures (T_ds) of the cured nanocomposites B2MP‐MP (826 K), B3E‐MP (794 K), and B2MH‐MP (783 K) were much higher than those of C18‐MP (768 K) and cured phenolic resin (737 K). Therefore, thermal stability of the nanocomposites depends mainly on the chemical structure of the organic modifiers. B2MP‐MP possesses the highest T_d since B2MP contains both benzyl and phenyl groups, followed with B3E‐MP and B2MH‐MP whose modifiers contain only one benzyl group. This is attributable to favorable interaction between phenolic resin and organic modifiers containing benzene rings. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5336–5343, 2006     

Preparation and analysis of a flexible curing agent for epoxy resin

A kind of novel aromatic amine bis(4‐nonyl‐2,5‐diamine‐penoxyl)alkylate (RA_n) as curing agents for epoxy resins were prepared through three steps of reactions using nonyl phenol and dibromoalkylate as materials. Dynamic mechanical analysis (DMA) indicated that the secondary relaxation for the resins cured by RA_n were generated by the nonyls in RA_n molecules when temperature was below ?50°C. Comparing with other reference resins, the enhancement for toughness of RA_n cured‐resins were at least 15%, which were contributed by such secondary relaxation. Furthermore, stiffness of the networks and thermal properties of the resins were not influent by the flexible groups (nonyl) in RA_n after curing, since the groups were located only in the branched chains of the networks. The mechanical and thermal properties of the new material have been significantly enhanced. The relevant method and procedure developed through this research have been granted Chinese patent recently (Yang and Gong, Chin. Pat. CN1978483A, 2007). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Comprehensive study of metal on the characteristic properties of epoxy resins

A series of different type of epoxy resins containing metal(s) have been prepared by the using cobalt acrylate (CoA₂), nickel acrylate(NiA₂),bismuth acrylate (BiA₃) during resinification. The values of epoxide equivalent weight, chlorine content increases whereas hydroxyl content, refractive index decreases in the presence of metal acrylate(s). The influence of complex formation of metal acrylate with ether linkage of epoxy resins were investigated by spectroscopy. Epoxy resins containing cobalt acrylate which was cured by p‐acetylbenzilidinetriphenylarsoniumylide (p‐ABTAY) shows better conducting properties in comparison to NiA₂ and BiA₃ containing epoxy resins. The dispersion of metal(s) in epoxy resins matrix was confirmed by scanning electron microscope (SEM). The glass transition temperature of epoxy resins containing CoA₂ is lower than that of blank epoxy resins and epoxy resins containing bismuth and nickel acrylate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on isotactic poly(phenyl glycidyl ether)‐modified epoxy resins. II. Toughening of epoxy resins

A semicrystalline polymer, isotactic poly(phenyl glycidyl ether) (i‐PPGE) was used as a modifier for epoxy resin; 1,8‐Diamino‐p‐methane (MNDA) and 4,4′‐Diamino diphenyl sulfone (DDS) were used as curing agents. In the MNDA‐cured resins, the dispersed phase were spherical particles with diameters in the range of 0.5–1.0 μm when the resin was blended with 5 phr i‐PPGE. In the DDS‐cured resins, the particle size distribution of the dispersed phase was much wider. The difference was traced back to the reactivity of the curing agent and the different regimes used for curing. Through dynamic mechanical analysis, it was found that in the MNDA‐cured systems, i‐PPGE had a lower crystallinity than in the DDS‐cured system. In spite of the remarkable difference in the morphology and microstructure of the modified resins cured with these two curing agents, the toughening effects of i‐PPGE were similar for these resins. The critical stress intensity factor (K_IC) was increased by 54% and 53%, respectively, for the resins cured by DDS and by MNDA, blending with 5 phr of the toughner. i‐PPGE was comparable with the classical toughners carboxyl‐terminated butadiene‐acrylonitrile copolymers in effectiveness of toughening the epoxy resin. An advantage of i‐PPGE was that the modulus and the glass‐transition temperature of the resin were less affected. However, this modifier caused the flexural strength to decrease somewhat. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1223–1232, 2002; DOI 10.1002/app.10445     

Synthesis and properties of bismaleimide resins containing ether bonds

New bismaleimides containing ether bonds were prepared. The thermal properties of the bismaleimides were investigated by differential scanning calorimetry (DSC). The effects of structure of the bismaleimides and curing conditions on the thermal and mechanical properties of the cured resins such as initial decomposition temperature (T_d), glass transition temperature (T_g), and flexural strength were studied. The introduction of ether bonds to bismaleimide resins decreased the brittleness of the resins without reductions in their heat-resistant properties.     

Development of a DOPO‐containing melamine epoxy hardeners and its thermal and flame‐retardant properties of cured products

In this study, a novel Schiff base of melamine used as flame‐retardant curing agent for epoxy resins, was synthesized via condensation reaction of 4‐hydroxybenzaldehyde with melamine, followed by the addition of 9,10‐dihydro‐9‐oxa‐10‐phosphaphen‐anthrene 10‐oxide (DOPO) to the resulting imine linkage. The structure of DOPO‐containing melamine Schiff base (P‐MSB) was characterized by Fourier transformed infrared spectroscopy, ¹H‐nuclear magnetic resonance (¹H‐NMR) and ³¹P‐NMR. The compound (P‐MSB) was used as a reactive flame retardant in o‐cresol formaldehyde novolac epoxy resin (CNE) to prepare flame‐retardant epoxy resins for electronic application. The thermal and flame‐retardant properties of the epoxy resins cured by various equivalent ratios phenol formaldehyde novolac (PN) and P‐MSB were investigated by the nonisothermal differential scanning calorimetry, the thermogravimetric analysis, and limiting oxygen index test. The obtained results showed that the cured epoxy resins possessed high T_g (165°C) and good thermal stability (T_5%, 321°C). Moreover, the P‐MSB/CNE systems exhibited higher limiting oxygen index (35) and more char was maintained in P‐MSB/CNE systems than that in PN/CNE system and the effective synergism of phosphorus–nitrogen indicated their excellent flame retardancy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Syntheses of epoxy‐bridged polyorganosiloxanes and the effects of terminated alkoxysilanes on cured thermal properties

A series of epoxy‐bridged polyorganosiloxanes have been synthesized by reacting multifunctional aminoalkoxysilanes with diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The reactions of trifunctional 3‐aminopropyltriethoxysilane (APTES), difunctional 3‐aminopropylmethyldiethoxysilane (APMDS), and monofunctional 3‐aminopropyldimethylethoxysilane (APDES) with DGEBA epoxy have been monitored and characterized by FTIR, ¹H NMR, and ²⁹Si NMR spectra in this study. The synthesized epoxy‐bridged polyorganosiloxanes precursors, with different terminated alkoxysilane groups, are thermally cured with or without the addition of curing catalysts. Organometallic dibutyltindilaurate, and alkaline tetrabutylammonium hydroxide have been used as curing catalysts to investigate the thermal curing behaviors and cured properties of epoxy‐bridged polyorganosiloxanes precursors. The maximum exothermal curing temperatures of epoxy‐bridged polyorganosiloxanes precursors are found to appear around the same region of 120°C in DSC analysis. The addition of catalysts to the epoxy/APTES precursor shows significant influence on the cured structure; however, the catalysts exhibit less influence on the cured structure of epoxy‐APMDS precursor and epoxy/APDES precursor. Curing catalysts also show significant enhancement in increasing the thermal decomposition temperature (T_d50s) of cured network of trifunctional epoxy‐bridged polyorganosiloxane (epoxy/APTES). High T_d50s of 518.8 and 613.6 in the cured hybrids of epoxy/APTES and epoxy/APMDS precursors are also observed, respectively. When trialkoxysilane‐terminated epoxy‐bridged polyorganosiloxanes precursor are cured, with or without the addition of catalyst, no obvious T_g transition can be found in the TMA analysis of cured network. The cured network of trialkoxysilane‐terminated epoxy‐bridged polyorganosiloxanes also exhibits the lowest coefficient of thermal expansion (CTE) among the three kinds of alkoxysilane‐terminated epoxy‐bridged polyorganosiloxanes investigated. The organic–inorganic hybrid, from epoxy‐bridged polyorganosiloxanes after the thermal curing process, shows better thermal stability than the cured resin network of pure epoxy‐diaminopropane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3491–3499, 2006     

Synthesis and properties of copolymer epoxy resins prepared from copolymerization of bisphenol A,epichlorohydrin, and liquefied Dendrocalamus latiflorus

Dendrocalamus latiflorus Munro (ma bamboo) was liquefied in phenol and polyhydric alcohol (polyethylene glycol/glycerol cosolvent) with H₂SO₄ as catalyst. Liquefied bamboos reacted with bisphenol A and epichlorohydrin were then employed to prepare copolymer epoxy resins. The curing property and thermal property of copolymer epoxy resins were investigated. The results showed that copolymer epoxy resins could cure at room temperature after the hardener was added, and its curing process was an exothermic reaction. Comparison showed that copolymer epoxy resins prepared with phenol‐liquefied bamboo as raw material had higher heat released than those prepared with polyhydric alcohol‐liquefied bamboo during curing. The DSC analysis showed that heat treatment could enhance the crosslinking of copolymer epoxy resins cured at room temperature. However, resins prepared with polyhydric alcohol‐liquefied bamboo had a lower glass transition temperature. The TGA analysis showed that resins prepared with phenol‐liquefied bamboo had better thermal stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study on syntheses and properties of 2,2′‐mercaptoethylsulfide dimethacrylate transparent homo‐ and copolymer resins having high refractive index

2,2′‐Mercaptoethylsulfide dimethacrylate (MESDMA) was synthesized from 2,2′‐mercaptoethylsulfide (MES) by a Phase‐Transfer Catalysis technique and, was characterized and corroborated by ¹H‐NMR and FTIR spectra. Except for the poor impact strength, the MESDMA homopolymer resin shows better comprehensive properties, such as a higher refractive index (1.625), lower dispersion (Abbe's number 36), and good heat‐resistance (T_g 150°C) and surface hardness (3H), etc. Copolymerizing with styrene (St) can modify most of the properties of the resin. The refractive index, Abbe's number, onset wavelength, density, water‐absorption ratio, and absorption intensity of peaks in NIR region, etc. all display a regular change along with the proportion of MESDMA/St. The main absorption peaks in NIR region are assigned as follows: 1680 (first overtone) and 1144 nm (second overtone) to the phenyl C—H vibration of polystyrene; 1694 nm (first overtone) to ν(CH₃); 1730 and 1750 nm (first overtone) to ν(CH₂) for ordinary CH₂ and for CH₂ connected with S or COS groups, respectively; and 1186 nm (second overtone) to aliphatic C—H vibration. The prominent advantage achieved by copolymerization is that the impact strength can be improved as much as 10‐fold at a proper composition of the monomers (75% St). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1474–1479, 2000     

Studies on UV‐stable silicone–epoxy resins

Silicone–epoxy resins were synthesized through hydrosilylation of 1,2‐epoxy‐4‐vinyl‐cyclohexane with 1,3,5,7‐tetramethycyclotetrasiloxane. The silicone–epoxy resins showed high reactivity in the presence of aluminum complex/silanol compound catalysts. Curing of the resins was effected at extremely low concentrations of the aluminum acetylacetonate/Ph₂Si(OH)₂ catalyst to give hard materials with optical clarity. For the silicone–epoxy resins containing Si? H bonds, Al(acac)₃ alone is effective for the curing. The cured silicone–epoxy resins showed excellent UV resistance. An improvement in the lifetime of UV‐LEDs was achieved using the silicone–epoxy compositions as encapsulant. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3954–3959, 2007