Curing and Morphology of BPA Epoxy Resin/LC Epoxy Resin PEPEB Composites

Liquid crystalline epoxy resin (LC epoxy resin) – p-phenylene di{4-[2-(2,3-epoxypropyl)ethoxy]benzoate} (PEPEB) was synthesized. The mixture of PEPEB with bisphenol-A epoxy resin (BPAER) was cured with a curing agent 4,4-diamino-diphenylmethane (DDM). The curing process and thermal behavior of this system were investigated by differential scanning calorimeter (DSC) and torsional braid analysis (TBA). The morphological structure was measured by polarizing optical microscope (POM) and scanning electron microscope (SEM). The results show that the initial curing temperature Ticu (gel point) of this system is 68.1°C, curing peak temperature T _pcu is 102.5°C, and the disposal temperature T _fcu is 177.6°C. LC structure was fixed in the cured epoxy resin system. The curing kinetics was investigated by dynamic DSC. Results showed that the curing reaction activation energy of BEPEB/BPAER/DDM system is 22.413 kJ/mol. The impact strength is increased 2.3 times, and temperature of mechanical loss peak is increased to 23°C than the common bisphenol-A epoxy resin, when the weight ratio of BEPEB with BPAER is 6 100.     

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     

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     

Novel flame retardant thermosets from nitrogen‐containing and phosphorus‐containing epoxy resins cured with dicyandiamide

A novel phosphorus‐containing epoxy resin (EPN‐D) was prepared by addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO) and epoxy phenol‐ formaldehyde novolac resin (EPN). The reaction was monitored by epoxide equivalent weight (EEW) titration, and its structure was confirmed by FTIR and NMR spectra. Halogen‐free epoxy resins containing EPN‐D resin and a nitrogen‐containing epoxy resin (XT resin) were cured with dicyandiamide (DICY) to give new halogen‐free epoxy thermosets. Thermal properties of these thermosets were studied by differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), thermal mechanical analyzer (TMA) and thermal‐gravimetric analysis (TGA). They exhibited very high glass transition temperatures (T_gs, 139–175°C from DSC, 138–155°C from TMA and 159–193°C from DMA), high thermal stability with T_{d,5 wt %} over 300°C when the weight ratio of XT/EPN‐D is ≥1. The flame‐retardancy of these thermosets was evaluated by limiting oxygen index (LOI) and UL‐94 vertical test. The thermosets containing isocyanurate and DOPO moieties showed high LOI (32.7–43.7) and could achieve UL‐94 V‐0/V‐1 grade. Isocyanurate and DOPO moieties had an obvious synergistic effect on the improvement of the flame retardancy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The boron trifluoride monoethyl amine complex cured epoxy resins

The curing exotherm pattern is affected by the equivalent ratio of curing agent, boron trifluoride monoethylamine complex (BF₃ · MEA), to epoxy resin. The diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) cures more slowly than the diglycidyl ether of bisphenol A (Epon 828). The glass transition temperatures (T_g's) of BF₃ · MEA cured Epon 828 are increased with inceasing concentration of curing agent (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF₃ · MEA (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF₃ · MEA (0.0450 eq./epoxy eq.) cured Epon 828 and DGEBF are almost equivalent 43 and 44 kcal/mol, respectively. DGEBF when added to DGEBA improves the T_g and char yield with the BF₃ · MEA curing system. The T_g of both resin systems can be increased by longer post cure, whereas the char yield does not appear to change significantly. No ester group formation is found for the BF₃ · MEA-cured DGEBF, although this has been previously reported for the DGEBA system. The BF₃ · MEA cure at 120°C is better than at 140°C because of vaporization and degradation of the curing agent at the higher temperature. The rapid gelation of the epoxy resin may be another reason for the lower degree of cure at high temperature.     

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     

Novel cycloaliphatic epoxy resins. II. Curing reaction with BF3MEA and its cured properties

The BF₃MEA curing reaction and the cured properties of novel cycloaliphatic epoxy resins (CE-resins), which were derived from an octadienyl compound, were studied. Gelation time and the DSC scan of the CE resins, with BF₃MEA hardener, proved that the reactivity of the CE resins is intermediate among the reactivities of the conventional resins; it was found that the CE resins react faster than DGEBA, but slower than the conventional cycloaliphatic epoxy resins. The pot life of the CE- (III) resin with BF₃MEA hardener proved to be over 30 days at a temperature of 20°C. The thermal properties are affected by the amount of BF₃MEA used and the curing conditions. CE-(III) showed the highest HDT of over 200°C with 2–3 phr of BF₃MEA. The flexural properties of CE-(I) proved to be flexible and tough. CE-(II) exhibited the highest strength and elongation, while CE-(III) had the same flexural properties as DGEBA. Furthermore, the blending of CE-(II) with DGEBA produced greater flexural strength and greater elongation than each original resin had. The thermal stability at elevated temperature and the water resistance of the cured CE resins proved to be inferior to those of DGEBA and novolac epoxy resin, probably due to the use of BF₃MEA. These results suggest the CE resin will provide a new application for a one-component curing system for composites. © 1993 John Wiley & Sons, Inc.     

Synthesis of a novel lignin-based epoxy resin curing agent and study of cure kinetics,thermal, and mechanical properties

In this contribution, first of all, the methoxy groups of organic solvent lignin (OSL) was converted to phenolic hydroxyl groups through demethylation reaction for the purpose of fabricating demethylated organic solvent lignin (DOSL). In addition, the resulting DOSL was utilized as a renewable material to synthesize a novel esterified lignin (EDOSL) by reacting with isobutyryl chloride for curing of epoxy resin. Finally, commercial liquid diglycidyl ether of bisphenol A was cured by EDOSL in the presence of 4-dimethylaminopyridine (DMAP) used as a catalyst based on dual-curing mechanism. Dual curing is a processing methodology based upon the alliance of two diverse and compatible polymerization reactions occurring sequentially or simultaneously. According to the FTIR spectra and ¹H-NMR analyses, the demethylation of OSL, esterification of DOSL, and the curing reaction of epoxy resin with EDOSL were successfully conducted. The value of the phenolic hydrogen in the DOSL was approximately 4.89 mmol/g, which increased by 12.64% after demethylation. The thermal and mechanical performances of these cured epoxy samples were measured by DSC, DMA, TGA, and tensile testing. The epoxy system cured by 10%wt esterified lignin with 1%wt DMAP possessed the tensile strength of 71.54 ± 7.50 MPa and the initial degradation temperature (T_5%) of 370°C, which can compete fairly with commercial aromatic curing agents or other lignin-based agents studied currently for the curing of epoxy systems.     

The effects of polyamic acid on curing behavior,thermal stability,and mechanical properties of epoxy/DDS system

A thermoplastic modification method was studied for the purpose of improving the toughness and heat resistance and decreasing the curing temperature of the cured epoxy/4, 4′‐diaminodiphenyl sulfone resin system. A polyimide precursor‐polyamic acid (PAA) was used as the modifier which can react with epoxy. The effects of PAA on curing temperature, thermal stability and mechanical properties were investigated. The initial curing temperature (T_i) of the resin with 5 wt % PAA decreased about 50°C. The onset temperature of thermal decomposition and 10 wt %‐weight‐loss temperature for the resin system containing 2 wt % PAA increased about 60°C and 15°C respectively. Besides, the value of impact toughness and plain strain fracture toughness for the modified epoxy resin increased ～ 190% and 55%, respectively. Those changes were attributed to the outstanding thermal and mechanical properties of polyimide, and more importantly to formation of semi‐interpenetrating polymer networks composed by the epoxy network and linear PAA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

Elaboration and dielectric property of modified PZT/epoxy nanocomposites

Composites of lead zirconate titanate (PZT) 50 nm nanoparticles and epoxy resins have been produced with various PZT contents from 0 to 20 wt%. The morphology and thermal properties of prepared composites were characterized using scanning electron microscopy and differential scanning calorimetry. The PZT nanoparticles were found to be well dispersed in the epoxy resin matrix. The glass transition temperature (T_g) value of the nanocomposites increases from 164 to 178°C with increasing the PZT weight fraction. The dielectric composites properties dependences were studied via a wide range of frequency from 10 Hz to 100 kHz. The dielectric constant of PZT/epoxy composite was increased from 5.56 to 6.29 (at f = 1 kHz, T = 30°C), respectively to the incorporated PZT amount, and these values are higher than that the dielectric constant of pure cured epoxy resin, ε = 4.86. POLYM. COMPOS., 37:455–461, 2016. © 2014 Society of Plastics Engineers     

Change of viscoelastic properties of epoxy resin in the curing process

This paper is concerned with the relation between the time and temperature dependences of the flexural properties and the curing conditions for the bisphenol A-type epoxy resin with acid anhydride hardener. Relaxation moduli of epoxy resin, prepared at several curing temperatures and times, were measured in the temperature range from T_g ?70°C to T_g. The master curves of relaxation modulus for the epoxy resin could be constructed, using their thermorheological simple properties. The time–temperature shift factors of the epoxy resin could be approximately expressed by the Arrhenius equation with the activation energy 59.4 kcal/mole. independent of its curing conditions. The curing time and temperature were equivalent, that is, the short curing time at high temperature corresponded to the long curing time at low temperature. The curing time–temperature shift factor could be approximately expressed by the Arrhenius equation with the activation energy 21.3 kcal/mole, which was higher than the activation energy 14.2 kcal/mole obtained in the measurements of gel times. The increase in the values shows that the temperature dependences of reaction rates increase with progressing gelation.     

Thermophysical properties of anhydride‐cured epoxy/nano‐clay composites

Polymer nano‐composites made with a matrix of anhydride‐cured diglycidyl ether of bisphenol A (DGEBA) and reinforced with organo‐montmorillonite clay were investigated. A sonication technique was used to process the epoxy/clay nano‐composites. The thermal properties of the nano‐composites were measured with dynamic mechanical analysis (DMA). The glass transition temperature T_g of the anhydride‐cured epoxy was higher than the room temperature (RT). For samples with 6.25 wt% (4.0 vol%) of clay, the storage modulus at 30°C and at (T_g + 15)°C was observed to increase 43% and 230%, respectively, relative to the value of unfilled epoxy. The clay reinforcing effect was evaluated using the Tandon‐Weng model for randomly oriented particulate filled composites. Transmission electron microscopy (TEM) examination of the nano‐composites prepared by sonication of clays in acetone showed well‐dispersed platelets in the nano‐composites. The clay nano‐platelets were observed to be well‐intercalated/expanded in the anhydride‐cured epoxy resin system. POLYM. COMPOS., 26:42–51, 2005. © 2004 Society of Plastics Engineers.     

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     

Effect of oxirane groups on curing behavior and thermal stability of vinyl ester resins

The effects of oxirane groups in vinyl ester (VE) resin and reactive diluent on curing characteristics and thermal behavior of cured resins are described. Stoichiometric (0.5:1, sample A) as well as nonstoichiometric (0.5:0.85, sample B) ratios of the diglycidyl ether of bisphenol-A (DGEBA) and methacrylic acid (MA) were used for the synthesis of VE resins. Resin sample B had more residual epoxy groups because of the stoichiometric imbalance of the reactants. VE resins thus obtained were diluted with methyl methacrylate (MMA; 1:1, w/w), and controlled quantities of epoxy groups were introduced by partial replacement of MMA with glycidyl methacrylate (GMA), keeping the overall ratio of resin and reactive diluent constant. Increase of GMA content in resin A or B resulted in a decrease in gel time, indicating that the curing reaction is facilitated by the presence of epoxy groups. An increase in initiator content also reduced the gel time. In the differential scanning calorimetry (DSC) scans, a sharp curing exotherm was observed in the temperature range 107 ± 3–150 ± 1 °C. The onset temperature (T_onset) and peak exotherm temperature (T_exo) decreased with increase in GMA content. Heat of curing (ΔH) also increased with increase in GMA content. A broad exotherm was observed after the initial sharp exotherm that was attributed to the etherification reaction. Cured VE resins were stable up to 250–260 °C, and started losing weight above this temperature. Rapid decomposition was observed in the temperature range 400–500 °C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 416–423, 2001     

Synthesis of a novel phosphorus‐containing dicyclopentadiene novolac hardener and its cured epoxy resin with improved thermal stability and flame retardancy

A novel phosphorus‐containing dicyclopentadiene novolac (DCPD‐DOPO) curing agent for epoxy resins, was prepared from 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and n‐butylated dicyclopentadiene phenolic resin (DCPD‐E). The chemical structure of the obtained DCPD‐DOPO was characterized with FTIR, ¹H NMR and ³¹P NMR, and its molecular weight was determined by gel permeation chromatography. The flame retardancy and thermal properties of diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with DCPD‐DOPO or the mixture of DCPD‐DOPO and bisphenol A‐formaldehyde Novolac resin 720 (NPEH720) were studied by limiting oxygen index (LOI), UL 94 vertical test and cone calorimeter (CCT), and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. It is found that the DCPD‐DOPO cured epoxy resin possess a LOI value of 31.6% and achieves the UL 94 V‐0 rating, while its glass transition temperature (T_g) is a bit lower (133 °C). The T_g of epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 increases to 137 °C or above, and the UL 94 V‐0 rating can still be maintained although the LOI decreases slightly. The CCT test results demonstrated that the peak heat release rate and total heat release of the epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 decrease significantly compared with the values of the epoxy resin cured by NPEH720. Moreover, the curing reaction kinetics of the epoxy resin cured by DCPD‐DOPO, NPEH720 or their mixture was studied by DSC. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44599.     

Thermal and mechanical properties of tetra‐functional mesogenic type epoxy resin cured with aromatic amine

A novel tetra‐functional epoxy monomer with mesogenic groups was synthesized and characterized by ¹H‐NMR and FTIR. The synthesized epoxy monomer was cured with aromatic amine to improve the thermal property of epoxy/amine cured system. The glass transition temperature (T_g) and coefficient of thermal expansion (CTE) of the cured system were investigated by dynamic mechanical analysis and thermal mechanical analysis. The properties of the cured system were compared with the conventional bisphenol‐A type epoxy and mesogenic type epoxy system. The storage modulus of the tetra‐functional mesogenic epoxy cured systems showed the value of 0.96 GPa at 250 °C, and T_g‐less behavior was clearly observed. The cured system also showed a low CTE at temperatures above 150 °C without incorporation of inorganic components. These phenomena were achieved by suppression of the thermal motion of network chains by introduction of both mesogenic groups and branched structure to increase the cross linking density. The temperature dependency of the tensile property and thermal conductivity of the cured system was also investigated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46181.     

Effect of cure history on dynamic mechanical properties of an epoxy resin

The effect of cure history on the dynamic thermomechanical properties of a high temperature curing epoxy resin has been studied using torsional braid analysis. In isothermal cures “full cure” is not possible except at temperatures above the maximum glass transition temperature (T_g) of the cured resin, hence the necessity of a “post-cure” after lower temperature isothermal cures. The highest T_g and maximum cross-linking in the cured resin was for a linear heating rate of 0.05°C/min from 30 to 200°C; higher heating rates lead to lower glass transition temperatures.     

Structure and viscoelastic properties of epoxy resins prepared from four-nuclei novolacs

The relation between the structure and the viscoelastic properties of seven kinds of epoxy resins was studied. Seven tetraglycidylethers were synthesized from four-nuclei novolacs in which the positions of methylene linkage or number of kind of substituents were different. These epoxy compounds were cured with diaminodiphenylmethane as a hardener. From the viscoelastic properties of the fully cured resins with the hardener, characteristic properties such as glass transition temperature (T_g), average molecular weight between crosslinking points (M̄_c), and front factor (ϕ) were obtained. It was concluded that higher linearity in the main chain of epoxy resins gave a cured resin with a higher T_g, a smaller M̄_c, and a larger ϕ.     

Low temperature curable epoxy siloxane hybrid materials for LED encapsulant

A thermally cured epoxy‐siloxane hybrid material that is curable at low temperature (L‐expoxy hybrimer) was investigated for use as an LED encapsulant. This new hybrimer was fabricated using thermally initiated, cationic polymerization of cycloaliphatic epoxy oligosiloxane (CAEO) resin, derived from non‐hydrolytic sol – gel, mixed with oxetane hardener in the presence of a hexafluoroantimonate‐type thermo‐cationic initiator. The L‐epoxy hybrimer was cured at a lower temperature (below 120 ° C) than previously reported for an epoxy hybrimer with anhydride hardener (above 180 ° C). The L‐epoxy hybrimer showed high thermal resistance to yellowing under long‐term high temperature condition, and maintained good optical transmittance. Also, it had a high refractive index (up to 1.57), as well as the hardness (Shore D 80), and low water‐vapor permeability, w hen the new hybrimer was used to encapsulate an LED, it showed good adhesion without cracks or delamination and maintained their initial performance after the long‐term aging tests (120 and 85 ° C at 85% humidity). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39968.