Thermal resistance of cycloaliphatic epoxy hybrimer based on sol‐gel derived oligosiloxane for LED encapsulation

Cycloaliphatic epoxy hybrimer bulk was successfully fabricated by thermal curing of cycloaliphatic epoxy oligosiloxane resin synthesized by a sol‐gel condensation reaction with methylhexahydrophthalic anhydride (MHHPA) and tetrabutylphosphonium methanesulfonate (TBPM). The composition of MHHPA and TBPM in the resin was optimized to minimize yellowness of the cycloaliphatic epoxy hybrimer bulk. The sample with the optimized composition showed little discoloration upon thermal aging at 120°C for 360 h under an air atmosphere. On the basis of its high thermal stability with appropriate hardness and a high refractive index of 1.55, cycloaliphatic epoxy hybrimer bulk can be used as a LED encapsulant for white LEDs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cycloaliphatic epoxy oligosiloxane‐derived hybrid materials for a high‐refractive index LED encapsulant

Cycloaliphatic epoxy oligosiloxane resins with a high degree of condensation (>85%) were synthesized by a nonhydrolytic sol–gel reaction using 2‐(3,4‐epoxycyclohexyl)ethyltrimethoxysilane (ECTS), diphenylsilanediol (DPSD), and triphenylsilanol (TPS). Cycloaliphatic epoxy hybrimers with 2 mm thickness fabricated by thermal curing of cycloaliphatic epoxy oligosiloxane resins with a hardener and catalyst were optically transparent (～90%) with a high refractive index of up to 1.583. The fabricated hybrimers also show high thermal resistance having no yellowing during thermal aging at 120°C for 1008 h and a high decomposition temperature (>300°C). On the strengths of these characteristics, the hybrimers are expected to find application as LED encapsulants. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Comparative study of silicon‐containing cycloaliphatic epoxides between different chemical structures and curing mechanisms for potential light‐emitting diode encapsulation applications

The aim of this paper is to systematically investigate the curing behavior of three novel di‐ and trifunctional silicon‐containing cycloaliphatic epoxy resins by both anhydride and cationic ring‐opening polymerization methods as well as the viscoelasticity, thermal stability, water absorption and optical properties of the cured products. Differential scanning calorimetry curves show that, relative to anhydride curing, cationic polymerization can decrease the curing temperature to below 120 °C, and the reaction exothermic peaks become very narrow and sharp, exhibiting rapid curing characteristics at moderately low temperature. In addition, the differences between the anhydride and cationic curing methods bring about interesting variations in physical properties for the cured products which are well related to their chemical structures, polymerization mechanism, crosslinking density, segmental flexibility and inter‐segmental distance. The excellent transparency, rapid cationic curing rate, good thermal stability and high glass transition temperature of over 275 °C make this series of epoxy resins promising candidates for light‐emitting diode encapsulation applications. © 2012 Society of Chemical Industry     

Synthesis and properties of fluorinated biphenyl‐type epoxy resin

A novel fluorinated biphenyl‐type epoxy resin (FBE) was synthesized by epoxidation of a fluorinated biphenyl‐type phenolic resin, which was prepared by the condensation of 3‐trifluoromethylphenol and 4,4′‐bismethoxymethylbiphenyl catalyzed in the presence of strong Lewis acid. Resin blends mixed by FBE with phenolic resin as curing agent showed low melt viscosity (1.3–2.5 Pa s) at 120–122°C. Experimental results indicated that the cured fluorinated epoxy resins possess good thermal stability with 5% weight loss under 409–415°C, high glass‐transition temperature of 139–151°C (determined by dynamic mechanical analysis), and outstanding mechanical properties with flexural strength of 117–121 MPa as well as tensile strength of 71–72 MPa. The thermally cured fluorinated biphenyl‐type epoxy resin also showed good electrical insulation properties with volume resistivity of 0.5–0.8 × 10¹⁷ Ω cm and surface resistivity of 0.8–4.6 × 10¹⁶ Ω. The measured dielectric constants at 1 MHz were in the range of 3.8–4.1 and the measured dielectric dissipation factors (tan δ) were in the range of 3.6–3.8 × 10^?3. It was found that the fluorinated epoxy resins have improved dielectric properties, lower moisture adsorption, as well as better flame‐retardant properties compared with the corresponding commercial biphenyl‐type epoxy resins. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and mechanical characterization of epoxy resins toughened using preformed particles

Preformed, multilayer particles have been used to toughen an epoxy resin. The particles were formed by emulsion polymerization and consist of alternate glassy and rubbery layers, the outer layer having glycidyl groups to give the possibility of chemical bonding of the particles in the cured resin. Two variants of this type of particle were used, termed GM(47/15) and GM(47/37); both types have an overall diameter of 0.5 µm, but the former have a thicker rubbery layer. For comparison, acrylic toughening particles (ATP) with no surface functionality and a liquid carboxyl‐terminated butadiene–acrylonitrile (CTBN) rubber were used as toughening agents. The epoxy resin system consisted of a commercial diglycidyl ether of bisphenol A (Shell Epon 828) with diamino‐3,5‐diethyl toluene as hardener, two commercial sources of which were used, namely Ethacure‐100 (Albemarle SA) and DX6509 (Shell Chemicals). These hardeners contain a mixture of two isomers, namely 2,6‐diamino‐3,5‐diethyltoluene and 2,4‐diamino‐3,5‐diethyltoluene Thermogravimetry in nitrogen shows that the preformed toughening particles begin to degrade at 230 °C, whereas the cured resin begins to degrade rapidly at 350 °C. Thus, even though the particles are less thermally stable than the cured resin, their degradation temperature is well above the glass transition temperature of the resin, and their use does not affect the thermal stability of the toughened materials at normal use temperatures. The performance of the toughening agents was compared using Ethacure‐100 as the hardener. The GM(47/15) and GM(47/37) toughening particles gave rise to a greater toughening effect than the ATP and the CTBN. For example, the fracture energies were: 0.26 kJ m^?2 for the unmodified resin; 0.60 kJ m^?2 for the resin toughened with CTBN; and 0.69 kJ m^?2 for the resin toughened with the GM(47/15) particles. The ultimate tensile stress of the unmodified epoxy resin was 43 MPa, which increased to 55 MPa when 20 wt% of GM(47/15) toughening particles were added. The toughness of resins cured with the DX6509 hardener were superior to those obtained with the Ethacure‐100 hardener, most probably due to DX6509 producing a less‐highly‐crosslinked network. This highlights the sensitivity of the toughening process to the hardener used, even for hardeners of a similar nature. © 2001 Society of Chemical Industry     

Thermal properties of epoxy resins crosslinked by an aminated lignin

Aminated lignin possessing significant amount of reactive amino groups was studied as a curing agent of epoxy resin. Fourier transform infrared spectroscopy results proved the reactivity of the aminated lignin with the epoxy resin. Both appearance features and scanning electron microscopy images indicated that the transparent and homogeneous epoxy resin films could be formed with the aminated lignin less than 40% in the hardener mixture. In addition, thermogravimetric analysis and dynamic thermomechanical analysis results revealed that the epoxy resin cured by aminated lignin had better thermal stability compared with ones cured by a common hardener. The mass loss of the epoxy resin cured by the aminated lignin before 300°C was small around only 2.5%. The T_g (the glass transition temperature) of epoxy resin sample after cured by mixed hardener increased from 79°C to 93°C. The obvious difference (70–84°C) of T_d (the thermal deformation temperature) was also observed from the samples with and without the aminated lignin after cured at a high temperature. POLYM. ENG. SCI., 55:924–932, 2015. © 2014 Society of Plastics Engineers     

Improving the curing process and thermal stability of phthalonitrile resin via novel mixed curing agents

High curing temperature (including post‐curing temperature) and long curing time of phthalonitrile resins make them thermally stable but difficult to process. In this paper, novel mixed curing agents (CuCl/4,4′‐diaminodiphenylsulfone (DDS) and ZnCl₂/DDS) were firstly designed for solving these problems. Bisphenol‐based phthalonitrile monomer (BP‐Ph; melting point: 228–235 °C) was synthesized and used as the curing precursor. Differential scanning calorimetry results indicated that BP‐Ph cured with CuCl/DDS and ZnCl₂/DDS exhibited curing temperatures close to the melting point of BP‐Ph with curing ending temperatures of 225.4 and 287.1 °C, respectively. Rheologic investigations demonstrated obvious curing reactions of BP‐Ph occurred with the mixed curing agents at 220 °C. Thermogravimetric analysis showed that BP‐Ph cured by CuCl/DDS or ZnCl₂/DDS maintained 95% mass at 573 or 546 °C, respectively, at a post‐curing temperature of 350 °C for 2 h. Reasonable long‐term thermo‐oxidative stability was also demonstrated. When the post‐curing temperature decreased to 290 °C, char yield at 800 °C of BP‐Ph cured by CuCl/DDS was 77.0%, suggesting the curing procedure can be milder when using mixed curing agents. © 2017 Society of Chemical Industry     

High refractive index thermally stable phenoxyphenyl and phenylthiophenyl silicones for light‐emitting diode applications

Creating high refractive index (RI) thermally stable polymers for encapsulating high‐brightness light‐emitting diodes (LEDs) remains a challenge and is an opportunity for improving LED efficiencies. The best previously reported RI for a 200°C heat stable encapsulant for LEDs is 1.56. Here, we report the use of novel phenoxyphenyl and phenylthiophenyl silicone monomers to give fully formulated encapsulants with RIs above 1.60. These liquid dispensed encapsulants are highly heat stable, showing little change in optical properties after heat aging at 200°C in air for seven weeks, and were also little changed after cycling between ?10°C to 85°C over 6 months. Phenoxyphenyl(phenyl) dimethoxysilane and phenylthiophenyl(phenyl) dimethoxysilane monomers were prepared via Grignard reactions. The resulting monomers were copolymerized with commercial silicone monomers and incorporated into hydrosilation‐based thermosets designed for use as LED encapsulants. RIs for the cured polymers were 1.60 at 633 nm (1.62 at 450 nm) for the phenoxyphenyl ether system and 1.62 at 633 nm (1.65 at 450 nm) for the phenylthiophenyl ether system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39824.     

Shape‐memory property and characterization of epoxy resin‐modified Mesua ferrea L. seed oil‐based hyperbranched polyurethane

Modification of existing polymers leads to enhancement of many desirable properties. So, a hyperbranched polyurethane (HBPU) of monoglyceride of Mesua ferrea L. seed oil, poly(ε‐caprolactone)diol (M_n = 3000 g mol^?1), 2,4‐toluene diisocyanate, and glycerol with 30% hard segment (NCO/OH = 0.96) has been modified with different amounts of bisphenol‐A based epoxy resin. The system is cured by poly(amido amine) hardener at 120°C for specified period of time. Improvement of thermostability, scratch hardness, and impact strength are observed by this modification of HBPU. The differential scanning calorimetry (DSC) results show improvement of melting temperature of the modified systems. The enhancement of tensile strength is about 2.4 times compared with that of the unmodified one. The morphology and structural changes due to variation of epoxy content was studied by scanning electron microscopy (SEM) analysis and Fourier transform infrared (FTIR) spectroscopy. The rheological properties of the epoxy‐modified HBPU show the dependence on the amount of epoxy resin. Shape memory study of the crosslinked HBPUs shows 90–98% thermoresponsive shape recovery. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Adhesive Properties of Epoxy Resin with Chromic Hardener

Cohesive and adhesive properties have been compared of epoxy resins crosslinked either with chromic‐based hardener or with conventional amine‐type hardener. Higher cohesive parameters, such as yield strength, Young's modulus and impact resistance were observed for the material cured with chromic hardener. The adhesive strength of metal‐metal joints (steel‐aluminium) has been also found to be higher for chromic hardener containing epoxy compared to conventional curing systems. The time dependencies of adhesive strength after thermal treatment at 140°C of the joints showed a higher thermal resistance of the epoxy with chromic hardener when compared to the amine cured resin.     

Epoxy resin cured by bisphenol A based benzoxazine

Bisphenol A based benzoxazine was prepared from bisphenol A, formaline, and aniline. This benzoxazine was used as a hardener of the epoxy resin. Curing behavior of the epoxy resin and the properties of the cured resin were investigated. Consequently, curing reaction proceeded without a curing accelerator. The molding compound showed good thermal stability under 150°C, which corresponded to the temperature in the cylinder of injection molding. Above 150°C, the curing reaction proceeded rapidly. The cured epoxy resin showed good heat resistance, water resistance, electrical insulation, and mechanical properties compared with the epoxy resin cured by the bisphenol A type novolac. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1903–1910, 1998     

Electron beam curing of polymer composites

Electron‐beam (E‐Beam) curing of an epoxy polymer matrix and its composite (reinforced with IM7 Carbon fibers) was studied using a cationic photoinitiator. Photoinitiator concentration, dose, and process temperature were varied to understand their influence on E‐beam curing. Optimal photoinitiator concentration was found to be 5 phr. The curing was due to a primary α reaction with a strong dependence on dose, and a secondary β reaction with a weak dependence on dose and a strong dependence on initiator concentration. The extent of cure increased rapidly with dose until 100 kGy and it approached a plateau value beyond 100 kGy. This plateau value corresponded to incomplete curing by 27% for resin and 22% for composite at a process‐temperature of 22°C. The causes for incomplete curing appear to be the secondary β reaction and diffusional limitation. Increase in process temperature resulted in higher extent of cure at a dose level. The material used in this study was also found to be thermally curable and the reaction onset temperature (measured in a DSC ramp experiment) reduced from about 150°C at 0 kGy to about 50°C at 30 kGy. This indicates that simultaneous thermal curing during E‐beam curing of resin and composite is possible. After thermal post‐curing, the T_g of the E‐beam cured resin increased from 130°C at 200 kGy to a value greater than 370°C and the modulus decreased by 10%. The service temperature and the modulus of the 100% thermally cured resin and the thermally post‐cured (after E‐Beam irradiation) resin were comparable.     

Development of high Tg epoxy resin and mechanical properties of its fiber‐reinforced composites

A new epoxy resin with high glass transition temperature (T_g) (～ 180°C) and a viscosity low enough for infiltration into dry reinforcements at 40°C was developed for the vacuum‐assisted resin transfer molding process. To study the curing behavior and viscosity, several blends were formulated using multifunctional resin, aromatic hardener, and reactive diluents. Effects of these components on the viscosity and T_g were investigated by thermomechanical analysis, dynamic scanning calorimetry, and rheometer. Experimental results showed that a liquid aromatic hardener and multifunctional epoxy resin should be used to decrease the viscosity to <1 Pa·s at 40°C. Moreover, the addition of a proper reactive diluent decreased the viscosity and simultaneously minimized the deterioration of T_g. Mechanical properties of the composite produced with the optimized blend were evaluated at both room‐temperature and high‐temperature conditions. According to the results, the composite showed comparable mechanical properties with that of the current commercial resin. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Toward poly(furfuryl alcohol) applications diversification: Novel self‐healing network and toughening epoxy–novolac resin

Poly(furfuryl alcohol) bioresin (PFA) was synthesized and utilized through two distinct alloying strategies. It was crosslinked by a bismaleimide (BMI) via a Diels–Alder (DA) reaction. The novel PFA–BMI polyadduct network was spectrally, thermally, and thermo‐mechanically characterized and its thermally repeatable self‐healing behavior was visually established. The network showed a high pyrolytic thermostability (char yield ∼51% at 600 °C). PFA was also used for modification of epoxy–novolac resin (EP). EP hybrid resins containing 5, 10, and 15 wt % of PFA were cured by a polyamine hardener. Despite of different curing mechanisms of the two resins, PFA had no effect on EP curing behavior as revealed by differential scanning calorimetry, which proved homogeneous formation of the thermosets. PFA at the composition of 15 wt % improved tensile properties and toughness of EP, so that it almost doubled tensile modulus and elongation at break. However, PFA slightly deteriorated flexural properties of EP. PFA also decreased T_g of EP, with a maximum decrease of 22 °C. Besides, PFA disfavored initial thermostability of EP, but improved its pyrolytic char yield. In conclusion, PFA can be beneficial from smart materials to toughen hybrid epoxy thermosets with potential applications in composites, adhesives, and surface coatings. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45921.     

Low dielectric thermoset. I. Synthesis and properties of novel 2,6‐dimethyl phenol‐dicyclopentadiene epoxy

A 2,6‐dimethyl phenol‐dicyclopentadiene novolac was synthesized from dicyclopentadiene and 2,6‐dimethyl phenol, and the resultant 2,6‐dimethyl phenol‐dicyclopentadiene novolac was epoxidized to 2,6‐dimethyl phenol‐dicyclopentadiene epoxy. The structures of novolac and epoxy were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis, mass spectroscopy (MS), nuclear magnetic resonance spectroscopy (NMR), and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol‐dicyclopentadiene epoxy was then cured with 4,4‐diaminodiphenyl methane (DDM), phenol novolac (PN), 4,4‐diaminodiphenyl sulfone (DDS), and 4,4‐diaminodiphenyl ether (DDE). Thermal properties of cured epoxy resins were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermal gravimetric analysis (TGA). These data were compared with those of the commercial bisphenol A epoxy system. Compared with the bisphenol A epoxy system, the cured 2,6‐dimethyl phenol‐ dicyclopentadiene epoxy resins exhibited lower dielectric constants (～3.0 at 1 MHz and 2.8 at 1 GHz), dissipation factors (～0.007 at 1 MHz and 0.004 at 1 GHz), glass transition temperatures (140–188°C), thermal stability (5% degradation temperature at 382–404°C), thermal expansion coefficients [50–60 ppm/°C before glass‐transition temperature (T_g)], and moisture absorption (0.9–1.1%), but higher modulus (～2 Gpa at 60°C). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2607–2613, 2003     

Blends of poly(ethylene terephthalate) and epoxy as matrix material for continuous fibre reinforced composites

Abstract

The morphology and mechanical properties of poly(ethylene terephthalate) (PET)–epoxy blends and the application of these blends in continuous glass fibre reinforced composites have been investigated. Epoxy resin was applied as a reactive solvent for PET to obtain homogeneous solutions with a substantially decreased melt viscosity. The epoxy resin in these solutions was cured using an amine hardener according to two different schedules. In the first, high temperature curing at 260°C preceded low temperature crystallisation of the PET at 180°C. In the second, the PET was allowed to crystallise prior to low temperature curing at 180°C. After cure, all blends revealed a phase separated morphology of dispersed epoxy in a continuous PET matrix. The flexural strength and failure strain of all cured blends showed an increase with increasing epoxy content, whereas the high temperature cured blends exhibited overall lower flexural properties than those cured at the lower temperature. Microstructural analysis and flexural properties of continuous glass fibre reinforced PET–epoxy laminates showed that the composites obtained had a low void content. These PET–epoxy laminates had increased inplane shear strength in comparison with unmodified PET based laminates, indicating considerably increased fibre–matrix adhesion.     

Synthesis and properties of methyl hexahydrophthalic anhydride‐cured fluorinated epoxy resin 2,2‐bisphenol hexafluoropropane diglycidyl ether

The fluorinated epoxy resin, 2,2‐bisphenol hexafluoropropane diglycidyl ether (DGEBHF) was synthesized through a two‐step procedure, and the chemical structure was confirmed by ¹H n uclear magnetic resonance (NMR), ¹³C NMR, and Fourier transform infrared (FTIR) spectra. Moreover, DGEBHF was thermally cured with methyl hexahydrophthalic anhydride (MHHPA). The results clearly indicated that the cured DGEBHF/MHHPA exhibited higher glass transition temperature (T_g 147°C) and thermal decomposition temperature at 5% weight loss (T₅ 372°C) than those (T_g 131.2°C; T₅ 362°C) of diglycidyl ether of bisphenol A (DGEBA)/MHHPA. In addition, the incorporation of bis‐trifluoromethyl groups led to enhanced dielectric properties with lower dielectric constant (D_k 2.93) of DGEBHF/MHHPA compared with cured DGEBA resins (D_k 3.25). The cured fluorinated epoxy resin also gave lower water absorption measured in two methods relative to its nonfluorinated counterparts. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2801–2808, 2013     

Novel adamantane‐containing epoxy resin

A novel adamantane‐containing epoxy resin diglycidyl ether of bisphenol‐adamantane (DGEBAda) was successfully synthesized from 1,3‐bis(4‐hydroxyphenyl)adamantane by a one‐step method. The proposed structure of the epoxy resin was confirmed with Fourier transform infrared, ¹H‐NMR, gel permeation chromatography, and epoxy equivalent weight titration. The synthesized adamantane‐containing epoxy resin was cured with 4,4′‐diaminodiphenyl sulfone (DDS) and dicyandiamide (DICY). The thermal properties of the DDS‐cured epoxy were investigated with differential scanning calorimetry and thermogravimetric analysis (TGA). The dielectric properties of the DICY‐cured epoxy were determined from its dielectric spectrum. The obtained results were compared with those of commercially available diglycidyl ether of bisphenol A (DGEBA), a tetramethyl biphenol (TMBP)/epoxy system, and some other associated epoxy resins. According to the measured values, the glass‐transition temperature of the DGEBAda/DDS system (223°C) was higher than that of the DGEBA/DDS system and close to that of the TMBP/DDS system. TGA results showed that the DGEBAda/DDS system had a higher char yield (25.02%) and integral procedure decomposition temperature (850.7°C); however, the 5 wt % degradation temperature was lower than that of DDS‐cured DGEBA and TMBP. Moreover, DGEBAda/DDS had reduced moisture absorption and lower dielectric properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Interfacial encapsulation of bio‐based benzoxazines in epoxy shells for temperature triggered healing

Successful application of interfacial engineering for the preparation of cross‐linked epoxy microspheres containing thermally polymerizable cardanol‐based benzoxazine (Bz‐C) monomer in the core is demonstrated. Bz‐C is facilely synthesized by Mannich type condensation of cardanol (a by‐product of cashew nut industry) and aniline with formaldehyde under solventless conditions. The encapsulation process relies on the preferential reaction of polydimethylsiloxane immiscible epoxy resin and amine‐based hardener to form a cross‐linked spherical shell at the interface. The microcapsule dimensions and core content could be tailored by modulating the operating parameters, particularly stirring speed and Bz‐C: epoxy ratio. Spherical microcapsules with a core content of ～37% were obtained when the reaction was carried out at 600 rpm, while maintaining the reaction medium at 70°C with Bz‐C: epoxy ratio of 2.3 : 1. The simplicity and versatility of the present methodology are the forte of this technique, which widens the scope for large‐scale application of benzoxazines in the field of temperature triggered healing. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42832.     

Epoxy–lignin polyblends: Correlation between polymer interaction and curing temperature

A bisphenol A–polyamine hardener based epoxy adhesive (EP) was modified by polyblending with Kraft lignin (L). EP–L polyblends with an L content up to 40% by weight were cured at room temperature or above their glass transition temperature (T_g). Previous data have shown that the thermal and viscoelastic properties, as well as adhesive performance of the EP–L polyblends, are influenced by the curing temperature and by the L content in thermally cured polyblends. A reasonable explanation for the different behavior of EP–L polyblends as function of the curing temperature and their L content could be the enhanced degree of bonding between L and the EP network taking place at elevated temperature. This bonding was specifically considered to take place between L and possible unreacted amine groups of the hardener. Characterization of the EP–L polyblends was performed to search for evidence of irreversible chemical bonding between L and the EP network in thermally cured EP–L polyblends. FTIR studies, L extractibility from the crosslinked, polyblends, and quantitative data concerning the reactivity of L toward the polyamine hardener are discussed.