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     

Synthesis and properties of vinyl siloxane modified cresol novolac epoxy for electronic encapsulation

Vinyl siloxane (VS) modified cresol novolac epoxy (CNE) and cresol novolac hardener (CNH) resins are synthesized and both components are capable of further crosslinking. The reaction kinetics for both components are studied so that they can crosslink simultaneously in a designed synthesis procedure. Through careful adjustment of a triphenylphosphine dosage, the glass‐transition temperature (T_g) of CNE/CNH resins can be effectively controlled. Phenomena characteristic of the existence of a diffusion‐controlled reaction are also observed. The relationships between the T_g and crosslinking density for the CNE/CNH resin are explicitly revealed through gel content and swell ratio experiments. CNE/CNH resins with a higher T_g have lower equilibrium moisture uptake because of the higher fraction of free volume. The coefficient of diffusion also shows a similar but less apparent trend. The incorporation of VS incurs a 35% reduction in the equilibrium moisture uptake and a 20% reduction in the coefficient of diffusion for the modified resin. The VS‐modified CNE/CNH resin possesses a lower Young's modulus and a higher strain at break than its unmodified counterpart does. This modified resin can help to alleviate the popcorning problems in integrated circuit packages, which results from hygrothermal stresses. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 652–661, 2001     

Curing behavior of epoxy resin having hydroxymethyl group and different molecular weight distribution

o-Cresol novolac-type epoxy resins having hydroxymethyl group were synthesized. These epoxy resins were cured with a mixture of 4,4′-diaminodiphenylmethane and m-phenylenediamine (molar ratio, 6:4) as a hardener. Effects of molecular weight distribution of epoxy resins on curing behavior were studied. Curing behavior of epoxy resins with hardener were examined by differential scanning calorimetery (DSC), and cure reaction parameters were obtained. Viscoelastic properties of the cured epoxy resins were studied by dynamic mechanical analyzer. It was found that the lower the average molecular weight of the epoxy resin, that is, the higher the concentration of hydroxymethyl group, the shorter the onset time of exothermal reaction, the higher the rate constant (k), and the lower the activation energy (E_a) were. It was also found that glass transition temperature (T_g) of fully cured epoxy resins was higher than those of fully cured general novolac-type epoxy resins.     

Synthesis and properties of urethane elastomer-modified epoxy resin having hydroxymethyl group

Synthesis and properties of urethane elastomer-modified epoxy resins were studied. The urethane elastomer-modified epoxy resins were synthesized by the reaction of a 4-cresol type epoxy compound having hydroxymethyl groups (EPCDA) with isocyanate prepolymer. The structure was identified by IR, ¹H NMR and GPC. These epoxy resins (EPCDATDI) were mixed with a commercial epoxy resin (DGEBA) in various ratios. The mixed epoxy resins were cured with a mixture of 4,4′-diaminodiphenylmethane and 3-phenylenediamine (molar ratio 6:4) as a hardener. The curing behaviour of these epoxy resins was studied by DSC. The higher the concentration of EPCDATDI, the higher the onset temperature and the smaller the rate constant (k) of the exothermic cure reaction were. It was considered that the ratio of hydroxymethyl group to epoxide group was very small and the molecular weight of EPCDATDI was large. Therefore, the accelerating effect of the hydroxymethyl group on the epoxide–amine reaction was cancelled by the retardant effect of increased molecular weight and viscosity, and decreased molecular motion. Toughness was estimated by Izod impact strength and fracture toughness (K_1C). On addition of 10 wt% EPCDATDI with low molecular weight (M?_n 6710, estimated by GPC using polystyrene standard samples), Izod impact strength and K_1C increased by 70% and 60%, respectively, compared with unmodified epoxy resin. Glass transition temperatures (T_g) for the cured epoxy resins mixed with EPCDATDI measured by dynamic mechanical spectrometry were the same as those of unmodified epoxy resin. The storage modulus (E′) at room temperature decreased with increasing concentration of EPCDATDI. Toughness and dynamic mechnical behaviour of cured epoxy resin systems were studied based on the morphology.     

Amine-functionalized metal–organic frameworks/epoxy nanocomposites: Structure-properties relationships

Amine-functionalized MIL-101(Cr)-NH₂ metal–organic frameworks (MOF-N)/epoxy nanocomposites with Excellent cure label and high thermal stability were developed. Structure–property relationship was discussed by comparison of the cure state, thermal and viscoelastic behavior of epoxy nanocomposites containing pristine MOF or MOF-N applying differential scanning calorimetry (DSC), thermogravimetric analysis, and dynamic mechanical analysis. Epoxy containing 0.3 wt% MOF-N exhibited high glass transition temperature (T_g) of 96°C compared with 85°C observed for epoxy/MOF system. Thus, MOF-N played the role of catalyst in epoxy/amine curing reaction. Correspondingly, a lower activation energy was obtained based on cure kinetics modeling based on DSC measurements. Besides, incorporation of low amount (0.5 wt%) MOF-N induced an early-state resistance against decomposition, featured by 11°C rise in decomposition temperature at 5% weight loss. This was ascribed to the formation of porous metallic oxides during thermal decomposition of MOF-N in the epoxy system acting as a heat barrier, which increased the activation energy of decomposition. Amine-functionalization considerably prevented from further oxidation of the inner part of the matrix.     

Curing behavior of epoxy resin having hydroxymethyl group

A new type of epoxy resin having hydroxymethyl group was synthesized. This epoxy resin was mixed with commercial epoxy resin in various ratios. The mixed epoxy resins were cured with a mixture of 4,4′-diaminodiphenylmethane and m-phenylenediamine (molar ratio, 6 : 4) as a hardener. Curing behavior of the epoxy resin systems with the hardener was examined by DSC and TG-DSC, and parameters of cure reaction were obtained. Viscoelastic properties of cured resin were studied by dynamic mechanical analyzer. It was found that the higher the amount of epoxy resin having hydroxymethyl group, the lower the activation energy (Ea) and the higher the rate constant (k) were. It was also found that the higher the amount of the epoxy resin having hydroxymethyl group, the better heat resistance the fully-cured resin had. These results were explained as follows: Hydroxymethyl group accelerated an epoxideamine reaction. The crosslinking density of the cured resin was increased because in the hydroxymethyl group occurred a condensation reaction above 200°C.     

The effect of urea bond on structure and properties of toughened epoxy resins

In this article, modified poly(oxypropylene) diamines were synthesized and used as a new flexible curing agent for epoxy resins. The purpose of modification is to introduce urea group into epoxy resins. The reaction rate, mechanical properties, glass transition temperature (T_g), and fracture surface morphology of these toughened epoxy resins were investigated. Because of urea groups, the reactivity between poly(oxypropylene) diamines and epoxy resins was significantly enhanced. At the same time, the urea groups resulted in strong intersegmental hydrogen bonding between modified poly(oxypropylene) chain, which reduced the compatibility of poly(oxypropylene) with epoxy resins and resulted in higher T_g of toughened epoxy. The modified sample had tensile strength of 15.8 MPa and ultimate elongation of 118% at room temperature, whereas the unmodified sample only had 6.2 MPa and 70%. The scanning electron microscope analysis showed that the modified system displayed tough fracture feature, whereas the unmodified system showed typical brittle fracture. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

Effect of cyanate ester on the cure behavior and thermal stability of epoxy resin

Epoxy resin (diglycidyl ether of bisphenol A, DGEBA)/cyanate ester mixtures were cured with a curing agent, 4,4′-diaminodiphenylsulfone, and the effect of cyanate ester resin on the cure behavior and thermal stability in the epoxy resin was investigated with a Fourier transform infrared spectrometer, a rheometer, a dynamic mechanical analyzer, and a thermogravimetric analyzer. Cure reactions in the epoxy/cyanate ester mixture were faster than that of the neat epoxy system. The cure reaction was accelerated by increasing the cyanate ester resin component. Glass transition temperature and thermal stability in the cured resins were increased with increasing cyanate ester resin component. This may be caused by the increase of crosslinking density due to the polycyclotrimerization of the cyanate ester monomer to form triazine rings and the reaction of cyanate ester resin with the epoxy network. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 85–90, 1997     

Structure and viscoelastic properties of epoxy resins prepared from o-cresol novolacs

The relation between the structure and viscoelastic properties of the epoxy resins prepared from o-cresol novolacs was studied. Our model epoxy resins were two kinds of epoxy compounds synthesized from three-nuclei and four-nuclei o-cresol novolacs. In addition to these models, a commercially available o-cresol novolac-type epoxy resin was also studied. Each of the three epoxy compounds was cured with one of three kinds of novolacs, which were starting materials of the above-mentioned epoxy resins. Characteristic properties of the cured resins, such as glass transition temperature (T_g), average molecular weight between crosslinking points (M¯_c), and front factor (?) were obtained. It was concluded that the number of functional groups contained in the curing system almost dominated the viscoelastic properties of the cured resins.     

Thermomechanical behavior of epoxy resins modified with epoxidized vegetable oils

Biobased epoxy materials were prepared from diglycidyl ether of bisphenol A (DGEBA) and epoxidized vegetable oils (EVOs) (epoxidized soybean oil and epoxidized castor oil) with a thermally latent initiator. The effects of EVO content on the thermomechanical properties of the EVO‐modified DGEBA epoxy resins were investigated using several techniques. Differential scanning calorimetry indicated that the cure reaction of the DGEBA/EVO systems proceeded via two different reaction mechanisms. Single and composition‐dependent glass transition temperature (T_g) mechanisms were observed for the systems after curing. The experimental values of T_g could be explained by the Gordon–Taylor equation [Gordon M and Taylor JS, J Appl Chem 2 :493 (1952)]. The thermal stability of the systems decreased as the EVO content increased, due to the lower crosslinking density of the DGEBA/EVO systems. The coefficient of thermal expansion of the systems was found to increase linearly with increasing EVO content. This could be attributed to the fact that the degrees of freedom available for motions of the segments of the macromolecules in the network structure were enhanced by the addition of EVO. Copyright © 2008 Society of Chemical Industry     

Properties of networks obtained by internal plasticization of epoxy resin with aromatic and aliphatic glycidyl compounds

In order to improve the fracture properties of p, p′-diaminodiphenylmethane-cured epoxy resin, various kinds of aromatic and aliphatic glycidyl compounds were investigated as a modifier at an amount of 30 wt %. Several compounds promoted the fracture toughness. In any glycidyl compounds, however, heat resistance was decreased by the modification. The dynamic mechanical properties of the modified epoxy resins were measured. The crosslinking density ρ was calculated from the theory of rubber elasticity, and the mechanical properties of the resins were discussed in regard to the crosslinking density. Tensile strength was scarcely affected by the crosslinking density. Elongation at break and Izod impact strength increased remarkably with decrease in crosslinking density. The fracture toughness K_Ic- increased with decrease in crosslinking density except at small ρ.     

A dynamic mechanical study of the curing reaction of two epoxy resins

The curing behavior of two commercially formulated epoxy resins composed of the tetrafunctional amine dicyandiamide and with differing epoxy components, 4,4′-bisglycidylphenyl-2,2′-propane and the tetraglycidyl ether of methylene dianiline, is characterized by dynamic spring analysis. This supported viscoelastic technique is well suited to the determination of the onset of gelation under isothermal conditions but the method is not useful for monitoring later stages of reaction when the resins become more rigid. The activation energy for the curing of the two resins is about 87 kJ/mole (20.7 kcal/mole). Rate constants for the first order curing reaction are given. Additional studies of films cured below the ultimate T_g show that two relaxations can be observed upon heating. The first relaxation occurs near the original isothermal cure temperature with a low activation energy, about 250 kJ/mole, whereas the second relaxation occurs near the ultimate T_g, under the conditions used here, with an activation energy of 500–650 kJ/mole. It is believed that these activation energies provide a unique method of characterizing the molecular mobility of epoxy resins at various states of cure.     

Synthesis of Tri‐Aryl Methane Epoxy Resin Isomers and Their Cure with Aromatic Amines

In this work, two tri‐aryl and one bi‐aryl epoxy resin, bis[(glycidyloxy)phenyl)]‐m‐xylene (BGOPmX), bis[(glycidyloxy)phenyl)]‐p‐xylene (BGOPpX), and bis(glycidyloxy) biphenyl (BGOBP) are synthesized and cured with methylene dianiline and 4,4′‐diamino diphenyl sulfone. Structure, property, and processing relationships are investigated and compared against diglycidyl ether of bis‐phenol F epoxy resin to better understand the impact of rigid and flexible subunits within the network structure. The rigid BGOBP epoxy network has a higher yield strain, and displays the highest glass transition temperature and a higher coefficient of thermal expansion (CTE) regardless of amine. Conversely, the more flexible tri‐aryl epoxy resins, BGOPmX and BGOPpX, have higher moduli and lower CTE. Properties such as yield stress and thermal degradation are relatively unaffected by structure. Results where possible are discussed in terms of the likely equilibrium packing density of the network and short range and segmental motions of the polymer networks determined from sub‐ambient dynamic mechanical analysis. Differences between BGOPmX and BGOPpX highlight the effect of minor variations in structure on reactivity, glass transition temperature, and compressive properties. This work clearly illustrates how fine control of chemical structure can tune the mechanical and thermal properties and reaction kinetics of network polymers.     

Cure kinetics and thermal properties of tetramethylbiphenyl epoxy resin/phthalazinone‐containing diamine/hexa(phenoxy)cyclotriphophazene system

Inherently flame retardant epoxy resin is a kind of halogen‐free material for making high‐performance electronic materials. This work describes an inherently flame retardant epoxy system composed of 4,4′‐diglycidyl (3,3′,5,5′‐tetramethylbiphenyl) epoxy resin (TMBP), 1,2‐dihydro‐2‐(4‐aminophenyl)‐4‐(4‐(4‐aminophenoxy) phenyl) (2H) phthalazin‐1‐one (DAP), and hexa(phenoxy) cyclotriphophazene (HPCTP). The cure kinetics of TMBP/DAP in the presence or absence of HPCTP were investigated using isoconversional method by means of nonisothermal differential scanning calorimeter (DSC). Kinetic analysis results indicated that the effective activation energy (E_α) decreased with increasing the extent of conversion (α) for TMBP/DAP system because diffusion‐controlled reaction dominated the curing reaction gradually in the later cure stage. TMBP/DAP/HPCTP(10 wt %) system had higher E_α values than those of TMBP/DAP system in the early cure stage (α < 0.35), and an increase phenomenon of E_α ～ α dependence in the later cure stage (α ≥ 0.60) due to kinetic‐controlled reaction in the later cure stage. Such complex E_α ～ α dependence of TMBP/DAP/HPCTP(10 wt %) system might be associated with the change of the physical state (mainly viscosity) of the curing system due to the introduction of HPCTP. These cured epoxy resins had very high glass transition temperatures (202–235°C), excellent thermal stability with high 5 wt % decomposition temperatures (>340°C) and high char yields (>25.6 wt %). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of liquefied corn barn-based epoxy resins and their thermodynamic properties

The liquefied corn barn-based epoxy resin (LCBER) was synthesized through the glycidyl etherification reaction from liquefied corn barn (LCB), which has groups of bound phenol, and epichlorohydrin under alkali conditions. The average molecular weights of LCB and LCBER in various liquefaction conditions were examined. The thermodynamic properties of thermosetting resin cured by polyamide-650 (PA-650) were evaluated. It was found that the macromolecular chain and epoxy function of the resins would be a dominant factor for crosslinking density and properties of the cured LCBER. The cured liquefied CB-based epoxy resin (LCBER-30) using the corresponding LCB at 30 min (LCB-30) as raw materials had much macromolecular exhibited higher glass-transition and decomposition temperatures at 5% weight loss (T_d), but worse shear strength in comparison with the other LCBER ones. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of aralkyl novolac epoxy resins and their modification with polysiloxane thermoplastic polyurethane for semiconductor encapsulation

A series of phenol‐based and naphthol‐based aralkyl epoxy resins were synthesized by the condensation of p‐xylylene glycol with phenol, o‐cresol, p‐cresol, or 2‐naphthol, respectively, followed by the epoxidation of the resulting aralkyl novolacs with epichlorohydrin. The incorporation of stable dispersed polysiloxane thermoplastic polyurethane particles in the synthesized epoxy resin's matrix was achieved via epoxy ring‐opening with the isocyanate groups of urethane prepolymer to form an oxazolidone. The mechanical and dynamic viscoelastic properties of cured aralkyl novolac epoxy resins were investigated. A sea‐island structure was observed in all cured rubber‐modified epoxy networks via SEM. The results indicate that a naphthalene containing aralkyl epoxy resin has a low coefficient of thermal expansion, heat resistance, and low moisture absorption, whereas phenol aralkyl type epoxy resins are capable of imparting low elastic modulus result in a low stress matrix for encapsulation applications. Modification of the synthesized aralkyl epoxy resins with polysiloxane thermoplastic polyurethane have effectively reduced the stress of cured epoxy resins, whereas the glass transition temperature was increased because of the formation of the rigid oxazolidone structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1905–1916, 1999     

Super-crosslinked ionic liquid-intercalated montmorillonite/epoxy nanocomposites: Cure kinetics,viscoelastic behavior and thermal degradation mechanism

Super-crosslinked epoxy nanocomposites containing N-octadecyl-N′-octadecyl imidazolium iodide (IM)-functionalized montmorillonite (MMT-IM) nanoplatelets were developed and examined for cure kinetics, viscoelastic behavior and thermal degradation kinetics. The structure and morphology of MMT-IM were characterized by FTIR, XRD, TEM, and TGA. Synthesized MMT-IM revealed synergistic effects on the network formation, the glass transition temperature (T_g) and thermal stability of epoxy. Cure and viscoelastic behaviors of epoxy nanocomposites containing 0.1 wt% MMT and MMT-IM were compared based on DSC and DMA, respectively. Activation energy profile as a function of the extent of cure was obtained. DMA results indicated a strong interface between imidazole groups of MMT-IM and epoxy, which caused a significant improvement in storage modulus and the T_g of epoxy. Network degradation kinetics of epoxy containing 0.5, 2.0, and 5.0 wt% MMT and MMT-IM were compared by using Friedman, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and the modified Coats-Redfern methods. Although addition of MMT to epoxy was detrimental to the T_g value, as featured by a fall from 94.1°C to 89.7°C detected by DMA method, and from 103.3°C to 97.9°C by DSC method, respectively. By contrast, meaningful increase in such values were observed in the same order from 94.1°C to 94.7°C and from 103.3°C to 104.7°C for super-crosslinked epoxy/MMT-IM systems.     

Reaction kinetics,thermal properties of tetramethyl biphenyl epoxy resin cured with aromatic diamine

Epoxy resins, 4, 4′‐diglycidyl (3, 3′, 5, 5′‐tetramethylbiphenyl) epoxy resin (TMBP) containing rigid rod structure as a class of high performance polymers has been researched. The investigation of cure kinetics of TMBP and diglycidyl ether of bisphenol‐A epoxy resin (DGEBA) cured with p‐phenylenediamine (PDA) was performed by differential scanning calorimeter using an isoconversional method with dynamic conditions. The effect of the molar ratios of TMBP to PDA on the cure reaction kinetics was studied. The results showed that the curing of epoxy resins contains different stages. The activation energy was dependent of the degree of conversion. At the early of curing stages, the activation energy showed the activation energy took as maximum value. The effects of rigid rod groups and molar ratios of TMBP to PDA for the thermal properties were investigated by the DSC, DMA and TGA. The cured 2/1 TMBP/PDA system with rigid rod groups and high crosslink density had shown highest T_g and thermal degradation temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Preparation and epoxy curing of novel dicyclopentadiene‐derived Mannich amines

Phenol/dicyclopentadiene (DCPD) adducts were prepared from the BF₃‐catalyzed reaction of p‐nonylphenol and dicyclopentadiene at molar ratios of 2 : 1 and 3 : 2. The phenol‐terminating adducts were consequently reacted with diethylenetriamine and formaldehyde using Mannich reaction conditions. These products containing phenol, amine and tricyclodecane functionalities in the same molecule can be used as epoxy curing agents. The diethylenetriamine was add to the phenol via Mannich reaction at approximately 50% theoretical equivalent. The multiple N H groups in amines and the O H groups in phenols provide crosslinking sites for epoxy resins. The cured epoxy resins show improvement in tensile strength and elongation in comparison with those cured by the poly(oxypropylene) diamine (400 molecular weight) or diethylenetriamine. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2129–2139, 1999