Curing reaction of o-cresol novolac epoxy resin according to hardener change

The investigations of cure kinetics and glass transition temperature (T_g) versus reaction conversion (α) of o-cresol novolac epoxy resin with the change of hardener were performed. All kinetic parameters of the curing reaction such as the reaction rate order, activation energy, and frequency factor were calculated. The curing mechanisms were classified into two types. One was an autocatalytic mechanism and the other was a nth order kinetic mechanism. The constants related to the chain mobility of polymer segments were obtained by using the DiBenedetto equation. We have tried to correlate the relationships between curing mechanism and molecular structures of hardeners from these results. © 1993 John Wiley & Sons, Inc.     

Mechanical,thermal and morphological behavior of bismaleimide modified polyurethane‐epoxy IPN matrices

An intercrosslinked network of bismaleimide modified polyurethane‐epoxy systems were prepared from the bismaleimide having ester linkages, polyurethane modified epoxy and cured in the presence of 4,4′‐diaminodiphenylmethane. Infrared spectral analysis was used to confirm the grafting of polyurethane into the epoxy skeleton. The prepared matrices were characterized by mechanical, thermal and morphological studies. The results obtained from the mechanical and thermal studies reveal that the incorporation of polyurethane into the epoxy skeleton increases the mechanical strength and decreases the glass transition temperature, thermal stability and heat distortion temperature. Whereas, the incorporation of bismaleimide having ester linkages into polyurethane modified epoxy systems increases the thermal stability, tensile and flexural properties and decreases the impact strength, glass transition temperature and heat distortion temperature. Surface morphology of polyurethane modified epoxy and bismaleimide modified polyurethane‐epoxy systems were studied using scanning electron microscopy. Copyright © 2003 John Wiley & Sons, Ltd.     

Modeling the curing kinetics for a modified bismaleimide resin

The kinetics of curing for a modified bismaleimide (BMI) has been investigated to ascertain a suitable cure model for the material. The experimental data for characterizing the curing kinetics for a modified bismaleimide resin were determined using a DSC isothermal scan method and indicated a curing mechanism involving multiple reactions. The reaction process was shown to be dominated by a different mechanism at different stages of the cure process, with an initial autocatalytic reaction shifting into an nth order reaction as the reaction proceeded. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 907–913, 2000     

Study of curing behaviour and thermal properties of elastomer-modified bismaleimide resin

Bismaleimide resin (Compimide 353) was modified with the liquid elastomer carboxyl-terminated acrylonitrile butadiene (CTBN). The prereaction synthesis and curing of the CTBN-bismaleimide resin is discussed. The structure of the modified resin was identified by IR and NMR spectroscopy. The basic curing mechanism is also discussed. DSC and TG were used to study the curing behaviour and kinetic parameters, viz. the order of reaction, energy of activation and preexponential factor. Adhesive properties such as lap shear strength and peel strength at room temperature and elevated temperature were evaluated and are discussed.     

Curing reaction characteristics and phase behaviors of biphenol type epoxy resins with phenol novolac resins

Diglycidyl ether of 4,4′-dihydroxybiphenol (BPDGE) is a liquid crystalline epoxy. The biphenyl epoxy (diglycidyl ether of 3,3′,5,5′-tetramethyl-4,4′-biphenyl, TMBPDGE) has found great applications in plastic encapsulated semiconductor packaging. Phenol novolac (PN) was used as curing agent. The reaction kinetics of BPDGE/PN and TMBPDGE/PN systems in the presence of triphenylphosphine (TPP) were characterized by an isoconversional method under dynamic conditions using differential scanning calorimetry (DSC) measurements. The results showed that the curing of epoxy resins involves different reaction stages and the values of activation energy are dependent on the degree of conversion. The effects of curing temperature on their phase structure have been investigated with polarized optical microscopy and Wide-angle X-ray diffraction. With proper curing process, BPDGE showed a nematic phase when cured with PN.     

Preparation and cryogenic mechanical properties of epoxy resins modified by poly(ethersulfone)

A thermoplastic, poly(ethersulfone) (PES) was used to modify a bisphenol‐F based epoxy resin cured with an aromatic diamine. The initial mixtures before curing, prepared by melt mixing, were homogeneous. Scanning electron microscopy (SEM) micrographs of solvent‐etched fracture surfaces of the cured blends indicated that phase separation occurred after curing. The cryogenic mechanical behaviors of the epoxy resins were studied in terms of tensile properties and Charpy impact strength at cryogenic temperature (77 K) and compared to their corresponding behaviors at room temperature (RT). The addition of PES generally improved the tensile strength, elongation at break, and impact strength at both RT and 77 K except the RT tensile strength at 25 phr PES content. It was interesting to observe that and the maximum values of the tensile strength, elongation at break, and impact strength occurred at 20 phr PES content where a co‐continuous phase formed. Young's modulus decreased slightly with the increase of the PES content. Moreover, the tensile strength and Young's modulus at 77 K were higher than those at RT at the same composition, whereas the elongation at break and impact strength showed the opposite results. Finally, the differential scanning calorimetry analysis showed that the glass transition temperature (T_g) was enhanced by the addition of PES. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 612–624, 2008     

Study on curing reaction of epoxy resin modified with prepolymers containing spiro orthocarbonate

Prepolymers were prepared by the reaction of 3,9-dihydroxyethyl-3′9′-dibenzyl-1,5,7,11-tetraoxaspiro(5,5)undecane with 4,4′-diphenylmethane diisocyanate (MDI) and 1,6-hexa-methylene diisocyanate (HDI). The number-average molecular weights of the prepolymers can be controlled by changing the mole ratios of spiro compound and diisocyanates. Kinetic studies of the cure reaction for the epoxy resin system modified with or without prepolymers were followed by a HLX-1 dynamic torsional vibration apparatus. The results indicated that gel time (t_g) and activation energy (E_a) increased as the content of prepolymers in the epoxy resin system increased. A difference with the cure reaction of the pure epoxy resin, the second-order reaction for the epoxy resin modified with the prepolymers, was obtained. Rate constants (k) of the cure reaction are 0.231 min^?1 for the epoxy resin, and 0.312 min^?1 for the modified epoxy resin. The mechanism of the cure reaction was discussed. © 1995 John Wiley & Sons, Inc.     

Preparation of epoxy-acrylic latex based on bisphenol F epoxy resin

Bisphenol F based epoxy-acrylic latex with different amount of epoxy resin was successfully prepared by semi-continuous seeded emulsion polymerization. The resulting composite latexes had a narrow size distribution of about 105 nm in diameter. The DSC result showed that the epoxy resin and polyacrylate were grafting copolymerization. The FTIR spectra showed that the epoxy group had been introduced into the epoxy acrylic latex system, and the composite latex could be crosslinked with epoxy hardener at room temperature. The crosslinked composite latex film exhibited a high Tg compared to epoxy-acrylic latexes. The surface of the films with the epoxy resin was regular, and diffused into the polyacrylate phase in the epoxy-acrylic latexes films. Since the curing reactions occurred before latex particle coalescence stage, the surfaces of the cured epoxy-acrylate latex films had a number of interface particle. Compared with the acrylic latex, the thermal stability of the epoxy-acrylate latex was increased, and the stability of the cured film increased with increasing epoxy content.     

Curing studies of epoxy resin with nadic endcapped phosphorylated amines

Polyimides have aromatic moieties in the backbone structure which are responsible for their increased thermal stability. If phosphorus is introduced in the main chain structure of polyimides, there is further improvement in the thermal stability. This has been proved by the work carried out in our group. The polyimide having amine termination can be used for crosslinking of epoxy resins.In the present study amine terminated phosphorus containing nadicimide were taken as curing agent for DGEBA resins. The curing characteristics of DGEBA resin were studied by DSC using different amounts of nadic endcapped phosphorylated amines. DSC thermogram showed the heat of polymerization was lower as compared to system cured with aromatic amines.     

Curing characteristics of carboxyl functionalized glucose resin and epoxy resin

The curing characteristics of carboxylic functionalized glucose resin (glucose maleic acid ester vinyl resin: GMAEV) and epoxy resin have been studied using DSC and FTIR methods. Exothermic reactions attributed to esterification and etherification reactions of the hydroxyl and carboxyl functionalities of GMAEV with the epoxy groups were identified. Exothermic reactions showed very different patterns according to the degree of carboxyl group substituent of GMAEV. The results showed that esterification reaction occurs in the early stage of cure and then etherification followed after completion of the esterification. A cured matrix containing epoxy resin and 50 wt.% of GMAEV was prepared and characterized. The cured matrix showed thermal stability up to 300 °C. The average glass transition temperature and storage modulus of the matrix were as high as 95 °C and 2700 MPa, respectively. The cured matrix of epoxy resin and GMAEV with higher degree of carboxyl group was found to have a lower density due to the formation of bulky groups in the crosslinks.     

Block copolymer modified novolac epoxy resin

The phase behavior of uncured and cured mixtures containing stoichiometric amounts of Epon164 novolac epoxy resin and 4,4′‐methylenedianiline combined with a nearly symmetric poly(methyl acrylate‐co‐glycidyl methacrylate‐b‐polyisoprene) diblock copolymer was investigated with small‐angle X‐ray scattering and transmission electron microscopy. A series of morphologies were documented as a function of the copolymer concentration, which ranged from pure diblock to 2.5 wt % in the thermoset resin. Ordered lamellae bordered a wide multiphase region followed by disordered wormlike micelles that transformed continuously into vesicles at the lowest compositions. The thermal curing of this pentafunctional epoxy system to complete conversion had little impact on the phase behavior of the mixtures, and this was consistent with previous experiments with difunctional epoxy and the same hardening agent. However, changing the epoxy component led to gross changes in the phase behavior that were interpreted with the concept of a wet‐to‐dry brush transition. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1994–2003, 2003     

Rheological study on structural transition in polyethersulfone‐modified bismaleimide resin during isothermal curing

The structural transition in the polyethersulfone (PES)‐modified bismaleimide resin, 4,4′‐bismaleimidodiphenylmethane (BDM), during isothermal curing was studied by using rheological technique, different scanning calorimetry (DSC), and time resolved light scattering (TRLS). Comparing with the cure of neat bismaleimide, two separate tan δ crossover points were observed because of the phase separation during curing the blends of PES/BDM. These two structural transitions stemmed from the fixing of phase structure of the system and the chemical crosslinking of bismaleimide, respectively. The effect of curing temperature and the PES content on structural transition was discussed and found that the occurrence of two structural transition exhibited the different dependency of curing temperature and PES content. The relaxation exponent n and gel strength S were also found to be temperature‐dependent and composition‐dependent. Moreover, the relaxation exponent n of the second structural transition is much lower than that of the first structural transition in the PES/bismaleimide blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3102–3108, 2006     

Curing of liquid epoxy resin in plasma discharge

Epoxy resins in the solid state, liquid state and during polymerisation were treated by microwave oxygen plasma and analysed by FTIR spectra. Curing, etching and oxidation kinetics of epoxy resin were observed. In the liquid resin and polymerising mixture the effect of structure modification was observed more intensively than in the case of solid sample due to a mixing process. A modification of bulk layers of liquid epoxy resin was observed under plasma action. The polymerisation reaction of epoxy resin with amine hardening agent can be released in plasma discharge at low pressure.     

Curing behavior of epoxy resin initiated by S‐alkylsulfonium salts of aromatic sulfides as thermal latent cationic initiators

The curing behavior of bisphenol‐A‐type epoxide oligomers (Ep) was evaluated by differential scanning calorimetry in the presence of S‐alkylsulfonium salts of dibenzothiophene, phenoxathiin, thianthrene, thioanisole, and tetrahydrothiophene as thermal latent initiators. These initiators dissolved homogeneously in Ep, except for 2,8‐dimethoxy‐5‐methyldibenzothiophenium tetrafluoroborate, and the curing reaction of the resulting mixtures occurred on heating, except for S‐methyltetrahydrothiophenium tetrafluoroborate. The initiation activity of these salts was controlled by the character of the substituents on the benzene ring, the leaving sulfide group, and the S‐alkyl group. Presumably, the electron density on the sulfide moieties and the stability of the carbocation released from the sulfonium salts affected the initiating temperature. A good correlation was obtained between the initiating temperature and the electron density of the sulfur atom of the corresponding sulfides, estimated from ab initio molecular orbital calculations in which the initiating temperature became higher as the electron density of the sulfur atom increased. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 868–871, 2001     

The effects of glass beads and silane treatments on the curing behavior of a brominated epoxy resin: DSC analyses

The curing characteristics of a brominated epoxy resin/dicyandiamide (DICY) system filled with silane-treated glass beads are studied using isothermal differential scanning calorimetry (DSC). Three different silane coupling agents, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, N-[2-(vinylbenzylamino)-ethyl]-3-aminopropyl-trimethoxysilane, and 3-glycidoxypropyl-trimethoxysilane, are applied. It is found that the reaction heats of the epoxy system are little affected by the curing temperature and the untreated glass fillers, but changed with the addition of silane-coated glass beads. The effect of glass beads on the curing reaction is more significant at the low curing temperature and conversion. The silane treatment results in changes in T_g, activation energy, reaction heat, reaction rate, and reaction order. Three silanes respond differently because of their differences in the activated reaction with the matrix system. Regardless of the various curing mechanisms involved, a simple kinetic expression can describe the curing extent at 170 and 180°C with a good accuracy for all systems studied. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2063–2071, 1997     

水性环氧树脂的研制及其固化性能研究

采用端甲氧基聚乙二醇、马来酸酐、E-44环氧树脂合成了反应型环氧树脂乳化剂MeO-PEG-Ma-E-44,以相反转乳化技术制备E-44水性环氧树脂,研究了工艺条件对其性能的影响。结果表明:酯化率达98.5%的MeO-PEG-Ma-E-44,用量为E-44的ω=16.5%-20%得到的水性环氧树脂乳液最稳定。DSC和TG分析结果表明:乳化前后的E-44环氧树脂都能室温条件2h内很好的固化,固化后热性能基本不变,分解温度约在380℃,热失重率89%,其玻璃转变温度有所降低,韧性有所提高,其它性能基本不受影响。     

Flame‐retardant epoxy resin compounds containing novolac derivatives with aromatic compounds

New flame‐retardant epoxy resin compounds containing novolac derivatives with specific aromatic compounds have been developed. After crosslinking reactions between epoxy resin and hardener, the epoxy resin compounds formed highly flame‐retardant network structures that were obtained by including biphenylene and phenylene moieties in the main chains of novolac‐type epoxy resin and phenol novolac resin hardener. The high flame retardancy is due mainly to the stable foam layers that form during combustion because of the low elasticity at high temperatures and the high pyrolysis resistance of the compounds. Furthermore, the addition of excess phenol derivative hardener not only facilitates the formation of the foam layers by decreasing the crosslink densities but also reduces the amount of flammable substances generated from the epoxy resin compounds during combustion. The use of a multifunctional epoxy resin containing four glycidyloxy groups in the compounds improved characteristics such as heat resistance and strength at high temperatures, while maintaining excellent flame retardancy. Copyright © 2001 John Wiley & Sons, Ltd.     

液晶环氧p-PEPB的合成及改性双酚-A环氧树脂的研究

本文以对羟基苯甲酸乙酯、丙烯溴、对苯二酚等为原料合成了双4-环氧丙基醚苯甲酸对苯二酚酯液晶环氧树脂(p-PEPB).用IR、1HNMR、DSC、POM和XRD的对其进行了表征,结果表明该化合物为向列型液晶,其熔点为180℃,清晰点为250 ℃.研究了 p-PEPB/双酚-A环氧(BPAER)/4,4,-二氨基二苯醚(DDE)体系的非等温固化过程,得到了固化温度参数、表观活化能Ea及p-PEPB含量对Tg的影响,结果表明p-PEPB为5%可使BPAER的Tg提高14 ℃,固化过程服从Ozawa模型.     

Synthesis and curing of liquid crystalline epoxy resin based on naphthalene mesogen

Aromatic liquid crystalline epoxy resin (LCE) based on naphthalene mesogen was synthesized and cured with aromatic diamines to prepare heat‐resistant LCE networks. Diaminodiphenylester (DDE) and diaminodiphenylsulfone (DDS) were used as curing agents. The curing reaction and liquid crystalline phase of LCE were monitored, and mechanical and thermal properties of cured LCE network were also investigated. Curing and postcuring peaks were observed in dynamic DSC thermogram. LCE network cured with DDE displayed liquid crystalline phase in the curing temperature range between 183 and 260°C, while that cured with DDS formed one between 182 and 230°C. Glass transition temperature of cured LCE network was above 240°C, and crosslinked network was thermally stable up to 330°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 419–425, 1999     

Effect of substituents on the curing of liquid crystalline epoxy resin

The synthesis of an aromatic ester based liquid crystalline epoxy resin (LCE) with a substituent in the mesogenic central group is described. Chlorine and methyl groups were introduced as substituents. The curing behaviors of three epoxy resins were investigated using diaminodiphenyl ester as the curing agent. The curing rate and heat of curing of LCE were measured with dynamic and isothermal DSC. The chlorine substituent accelerated the curing of LCE, while the methyl substituent decelerated the curing of LCE. The heat of curing of substituted LCE was diminished compared to LCE with no substituent. Glass transition temperature and elastic modulus of LCE decreased with increasing the size of the substituent. Three liquid crystalline epoxy resins based on aromatic ester mesogenic groups formed a liquid crystalline phase after curing, and the liquid crystalline phase was stable up to the decomposition temperature. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 911–917, 1998