Cure kinetics for the ultraviolet cationic polymerization of cycloliphatic and diglycidyl ether of bisphenol‐A (DGEBA) epoxy systems with sulfonium salt using an auto catalytic model

This paper investigates the cure kinetics for the ultraviolet (UV) cationic polymerization for both a cycloaliphatic and diglycidyl ether of bisphenol‐A (DGEBA) epoxy system, using the photoinitiator triarylsulfonium hexafluoroantimonate salt. Using an autocatalytic kinetic cure model, the reaction rate values for both cycloaliphatic and DGEBA epoxy systems were determined for different photoinitiator amount (wt %) added, and at different UV exposure temperatures. The value for the cycloaliphatic epoxy increased significantly with addition of the sulfonium salt, reaching a limiting maximum after 2%. The value for the DGEBA epoxy system also increased, to a limiting maximum after 3%. Addition of the sulfonium salt significantly lowered the activation energy for the cycloaliphatic epoxy at all levels of addition, with the reduction proportional to the amount of salt added. In contrast, the sulfonium salt did not have a major effect on the DEGBA until the addition of at least 3% of the salt. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1587–1591, 2002     

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.     

外电场对CER/TMPTMA IPNs形成过程的在线监测

利用自制装置研究了脂环族环氧树脂(CER)/三羟甲基丙烷三甲基丙烯酸酯(TMPTMA)互穿网络聚合物(IPNs)的固化过程.通过在线测试CER/TMPTMA体系固化过程中的交流电阻和电容,发现电阻和电容的变化反映出CER/TMPTMA体系的固化过程是一个分步IPNs的形成过程,而且电阻和电容变化趋势与体系的粘度、离子浓度以及偶极子的数量息息相关.利用自制电极和装置可以远距离在线监测热固性树脂的固化过程,在外磁场干扰下,利用CER/TMPTMA固化体系的电阻波动可以表征体系的固化反应情况.     

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     

Preparation and cured properties of novel cycloaliphatic epoxy resins

Preparation and characterization of novel cycloaliphatic epoxy resins, which are derived from octadienyl compounds, were studied. From a model peracetic acid epoxidation reaction using 2,7-octadienyl acetate-1, the structure of the liquid resins is estimated to be mainly terminal epoxides and some amount of inner epoxide depending on the epoxide content. The epoxy resins offer lower toxicity and lower vapor pressure. The reactivity of the resin with acid anhydrides is moderate but faster than that of traditional cyclohexane epoxide-type resins and slower than that of the glycidyl ester-type resins. This reactivity was also examined using model compounds. The heat deflection temperature of the hexahydro-phthalic anhydride-cured resins is shown to be directly proportional to the number of epoxy groups in the molecules. The flexural strength of the cured resins is nearly equivalent to that of the commercial resins, although the flexural elongation of the resins is larger than that of the rigid cyclohexane epoxide-type resins. The thermal stability of the cured resins is comparable to typical rigid cycloaliphatic resins; furthermore, high water resistance of the cured resins is suggested to be attributed to the hydrophobic character of the C₈ chain by cross-linking. © 1993 John Wiley & Sons, Inc.     

Morphology and thermal and dielectric behavior of cycloaliphatic epoxy/trimethacrylate interpenetrating polymer networks for vacuum‐pressure‐impregnation electrical insulation

Vacuum pressure impregnation has been known as the most advanced impregnation technology that has ever been developed for large and medium high‐voltage electric machines and apparatuses. We developed one new type of vacuum‐pressure‐impregnation resin with excellent properties by means of a novel approach based on in situ sequential interpenetrating polymer networks resulting from the curing of trimethacrylate monomer [trimethylol‐1,1,1‐propane trimethacrylate (TMPTMA)] and cycloaliphatic epoxy resin (CER). In this study, the influence of the concentrations of the components and their microstructures on their thermal and dielectric behaviors were investigated for the cured CER/TMPTMA systems via atomic force microscopy, dynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis. The investigation results show that the addition of TMPTMA to the CER–anhydride system resulted in the formation of a uniform and compact microstructure in the cured epoxy system. This led the cured CER/TMPTMA systems to show much higher moduli in comparison with the pure CER–anhydride system. The thermogravimetric analysis results show that there existed a decreasing tendency in the maximum thermal decomposition rates of the cured CER/TMPTMA systems, which implies that the thermal stability properties improved to some extent. The dielectric analysis results show that the cured CER/TMPTMA systems displayed quite different dielectric behaviors in the wide frequency range 0.01 Hz–1 MHz and in the wide temperature range 27–250°C compared with the cured CER–anhydride system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of Tertiary Amines on Reactivity of Cycloaliphatic Epoxy Resins towards Methacrylic Acid

The kinetics of the esterification of two cycloaliphatic epoxy resins containing glycidyl and epoxy cylohexane group, separately was studied using methacrylic acid in presence of triethyl-amine. The reaction was performed as a function of temperature to determine various kinetics and thermodynamic parameters such as reaction order, reaction rate constant, activation energy, frequency factor, entropy, enthalpy and free energy of the reaction. The reaction order was determined to be 2 and reaction rate constant for the resin containing epoxy cyclohexane group was found higher than that containing glycidyl epoxy group. The reaction was not found to proceed after ∼76% conversion due to the formation of adduct between nitrogen of amine and hydrogen of hydroxyl group of esterified resin. The rate of esterification reaction studied using higher homologue of triethyl-amine (tripropyl- and tributyl-) was found lower than that by triethyl-amine and conversion of acid into ester was ∼80% and ∼83% for tripropyl- and tributyl-amine, respectively due to the steric accessibility of nitrogen atom of higher amine. Based upon these kinetic data a suitable reaction mechanism is proposed for the system.     

环氧树脂/三羟甲基丙烷三甲基丙烯酸酯互穿网络聚合物的微观结构和电性能研究

采用新型脂环族环氧树脂（CER）、甲基六氢邻苯二甲酸酐（MeHHPA）和三羟甲基丙烷三甲基丙烯酸酯（TMPTMA）作为基体树脂制备了一种崭新的互穿网络聚合物。由于TMPTMA的自由基聚合反应先于CER和MeHHPA的阳离子聚合反应,得到了一种分步互穿网络聚合物,最终分步互穿网络聚合物没有出现明显微观相分离现象。着重考察了TMPTMA含量对互穿网络聚合物电性能的影响。结果表明,CER/TMPTMA互穿网络聚合物在不同温度下的交流电阻与体系的组成和微观结构有关。随着TMPTMA含量的增加,CER/TMPTMA互穿网络聚合物的击穿强度和形态参数增大,互穿网络聚合物的均匀度逐渐增加,击穿机理趋于一致。     

Synthesis and curing of new epoxycycloaliphatic polyesterimides with dianhydrides and diisocyanates as hardeners

New epoxy resins obtained from a series of bis(4,5-epoxytetrahydrophthalimides) and three different dicarboxylic diacids were prepared and characterized by spectroscopic techniques and thermal analyses. Homopolymerization of epoxy groups was observed as a parallel process to the polycondensation reaction. Using Epiclon B with a tertiary amine and hexamethylene diisocyanate as hardeners, we studied the reaction of epoxy groups and hydroxylic groups attached to the cycloaliphatic moiety in the main chain. No exotherms were clearly detected by DSC, and during the curing process, only increases in the T_g, values were observed. These cycloaliphatic epoxy polyesters have similar thermal characteristics to related aromatic epoxy polyesterimides, but have better processability. © 1996 John Wiley & Sons, Inc.     

Poly(ethyleneterephthalate) glycolysates as effective toughening agents for epoxy resin

The potential of poly(ethyleneterephthalate) glycolysates toward improving the energy absorption characteristics of cycloaliphatic epoxy resins has been explored. Microwave‐assisted glycolytic depolymerization of PET was performed in the presence of polyether diols of different molecular weights. The obtained glycolysates were blended with epoxy, and their mechanical properties were studied under both quasi‐static and dynamic conditions. Significant improvements were observed, which were found to depend both on the amount as well as nature of glycolysate. Amine functionalities were introduced at the terminal positions of glycolysates to improve the compatibility between the two phases. The amine derivatives exhibited superior performance and the Mode I fracture toughness (K_IC) of epoxy increased by ～18% in optimized compositions, which is indicative of its improved notch sensitivity. Neat epoxy specimens fractured in a brittle fashion, but all the blends exhibited ductile failure, as evidenced by surface morphological investigations. The mechanical properties of epoxy blends prepared with analogous aliphatic polyols, both before and after amine functionalization, were also studied which clearly reveal the beneficial role of aromatic groups toward improving the toughness of the base cycloaliphatic epoxy resin without compromising on the material stiffness. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39941.     

Synthesis and thermal stability of a novel cycloaliphatic epoxy resin system

A novel cycloaliphatic epoxy resin was synthesized from dicyclopentadiene, ethylene glycol, and nadic anhydride. The chemical structures of the resultant epoxy resin and its precursor were characterized with Fourier transform infrared spectroscopy, ¹H‐NMR, and mass spectrographic analyses. The thermal stability of the cured polymer was investigated with differential scanning calorimetry and thermogravimetric analysis. Compared with the thermal stability of the commercial cycloaliphatic epoxy resin 3,4‐epoxy cyclohexyl methyl‐3′,4′‐epoxy cyclohexyl carboxylate, a higher thermal stability for the cured polymer of the novel epoxy resin was observed. The results imply that the novel cycloaliphatic epoxy resin has good potential applications in electronic encapsulation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal degradation of the epoxy system BADGE n = 0/1,2‐DCH immersed in hydrochloric acid

The thermal degradation of an epoxy system consisting of diglycidyl ether of bisphenol‐A and 1,2‐diamine cyclohexane (BADGE n = 0/1,2‐DCH), immersed in hydrochloric acid for 30 days, was studied by thermogravimetric analysis, to determine the reaction mechanism of the degradation process. The results were compared with experimental data corresponding to the same epoxy system without exposure to the acid. It was found that the kinetic reaction mechanism changed with the immersion in HCl. The average activation energy of the solid‐state process was determined by using the Flynn‐Wall‐Ozawa method, resulting in 81 ± 2 kJ/mol. Different integral and differential methods and different reaction mechanisms reported in the literature were used and compared to this value. Analysis of experimental results suggests that in the conversion range studied, 5–20%, the reaction mechanism is somewhere between the different types of phase boundary controlled reaction and random nucleation with one nucleus on the individual particle. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 371–375, 2002     

Effects of the complexed moisture in metal acetylacetonate on the properties of the no‐flow underfill materials

A potential no‐flow (compression filling of encapsulant) underfill encapsulant for simultaneous solder joint reflow and underfill cure has been reported by the authors. The encapsulant is based on a cycloaliphatic epoxy/organic anhydride/Co(II) acetylacetonate system. The key of this no‐flow encapsulant is the use of a latent metal acetylacetonate catalyst that provides the solder reflow prior to the epoxy gellation and fast cure shortly after the solder reflow. However, most of the metal acetylacetonates can easily absorp moisture as their ligand. Therefore, it is of practical importance to understand the effect of the complexed water on the properties of the no‐flow material before and after cure. In this paper, differential scanning calorimetry, thermal gravimetric analysis, thermal mechanical analysis, dynamic mechanical analysis, and Fourier transform infrared spectrometry were used to validate the existence of complexed moisture in the Co(II) acetylacetonate. The effects of the complexed water on the curing profile, glass transition temperature, and storage modulus of the cured no‐flow underfill material were studied. A possible catalytic mechanism of the metal acetylacetonate in the cycloaliphatic epoxy/anhydride system was subsequently discussed and proposed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 103–111, 1999     

Cationic, thermally cured coatings using epoxidized soybean oil

Cycloaliphatic epoxy resins are used in coatings and inks because of their exceptionally low viscosity and reactivity with a variety of co-reactants, thus permitting high-solids and zero VOC coatings. The low viscosity of epoxidized soybean oil (ESBO), its reactivity, and relatively low cost make it an inexpensive candidate co-resin in cationic thermally cured coatings and inks using blocked acid catalysts. Formulations with up to 40% ESBO in the epoxy resin blend were investigated. Blending of cycloaliphatic resin with 10% ESBO gave a bake coating with the same results as the standard formulation except pencil hardness was one unit lower when cured for 12 min at 120°C with a heat de-blocked catalyst. The hardness of coatings with ESBO is adjustable by changing the epoxy/polyol ratio, using harder polyols and harder epoxy resins. Coatings Research Institute, 430 W. Forest Ave., Ypsilanti, MI 48197.     

Toughening of cycloaliphatic epoxy resins by poly(ethylene phthalate) and related copolyesters

Poly(ethylene phthalate) (PEP) and poly(ethylene phthalate–co‐ethylene terephthalate) were used to improve the brittleness of the cycloaliphatic epoxy resin 3,4‐epoxycyclohexylmethyl 3,4‐epoxycyclohexane carboxylate (Celoxide 2021?), cured with methyl hexahydrophthalic anhydride. The aromatic polyesters used were soluble in the epoxy resin without solvents and effective as modifiers for toughening the cured epoxy resin. For example, the inclusion of 20 wt % PEP (MW, 7400) led to a 130% increase in the fracture toughness (K_IC) of the cured resin with no loss of mechanical and thermal properties. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviors of the modified epoxy resin system. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 388–399, 2002; DOI 10.1002/app.10363     

On-line monitoring of cycloaliphatic epoxy/acrylate interpenetrating polymer networks formation and characterization of their mechanical properties

The novel interpenetrating polymer networks (IPNs) based on cycloaliphatic epoxy resin (CER) containing cyclohexene oxide groups and tri-functional acrylate, trimethylol-1, 1, 1-propane trimethacrylate (TMPTMA) were synthesized. The formation of the IPNs was on-line monitored by means of polarizing optical microscope, time-resolved light scattering and Fourier transform infrared spectroscopy. The morphological and mechanical properties of the resultant IPNs were investigated and evaluated with scanning electron microscopy (SEM) and dynamical thermal mechanical analysis (DTMA), respectively. The on-line monitoring results showed that during the course of the IPNs formation, the TMPTMA component was cured more quickly than the CER component, leading to the formation of the sequential IPNs. During the early curing stage, there were the phase separation phenomena in the CER/TMPTMA system. The SEM results revealed that although there were some slight phase separation phenomena in the CER/TMPTMA system in the early curing stage, the resultant IPNs displayed the homogeneous structures and did not show the apparent phase separation morphology. The DTMA results revealed that the resulting IPNs exhibited rather higher modulus and denser cross-linking network structure than the neat CER system.     

The effect of epoxy excess on the kinetics of an epoxy–anhydride system

The uncatalyzed cure of a commercial tetrafunctional epoxy monomer TGDDM (N,N,N′,N′‐tetraglycidyl‐4,4′‐diaminodiphenylmethane) with hexahydrophthalic anhydride (HHPA), using variable stoichiometric ratios is reported. The reaction was followed by differential scanning calorimetry (DSC). Two kinds of experiments were performed: (1) fresh samples were run at several heating rates, and (2) samples, precured a certain time in an oil bath at constant temperature (i.e., 80 to 120°C), were run at 10°C/min. Two peaks were observed in the case of the epoxy excess but only one for the stoichiometric formulation: the peak at low temperature was attributed to the epoxy copolymerization with the anhydride while the peak at high temperature was attributed to the epoxy homopolymerization. The catalytic effect of the OH groups present in the epoxy monomer on the copolymerization reaction was demonstrated by the decrease in the activation energy of the propagation step when increasing the epoxy excess. There is a catalytic effect of the copolymerization product on the homopolymerization reaction. Our simplest model, proposed previously for a catalyzed epoxy/anhydride system [J. Polym. Sci. Part B: Polym. Phys. Ed., 37, 2799 (1999)], can be used to fit both isothermal and dynamical kinetic data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2342–2349, 2002     

Characterization of diene monomers as healing agents for autonomic damage repair

For effective autonomic healing of damaged polymers and composites, it is essential to understand how the encapsulated healing agent behaves during and after cure. In this study, two different diene monomers [dicyclopentadiene (DCPD), 5‐ethylidene‐2‐norbornene (ENB)] and their blends were investigated as candidate self‐healing agents, using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). DSC experiments for samples showed that DCPD has a melting transition while the blends and ENB have no melting in the temperature range measured. Samples for DMA were prepared and tested by two different methods in the presence of Grubbs catalyst. In the first case (method I), monomers were mixed with the catalyst directly. In the second case (method II), the catalyst was mixed with an epoxy/amine system and cured into a film that was polished to expose the catalyst. The cure behavior of monomer samples was examined on the epoxy/catalyst film. Method II is considered to be a simulative experiment, which can occur in a real situation for damaged epoxy matrix composite. It was found that acceleration of cure reaction and reduction of catalyst concentration is possible by blending DCPD with ENB from method I. Storage modulus (G′) value after cure in method II showed that a DCPD : ENB blend ratio of 1 : 3 reached the highest G′ value at shorter cure time and lower catalyst levels than other monomer combinations. DCPD and ENB are presumably responsible for increases in rigidity and reactivity, respectively. This may improve the healing efficiency in autonomic damage repairing applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1266–1272, 2006     

Morphologies and applied properties of free radical/cationic UV‐cured CPUA/TMPTMA/CER composite films

A UV‐cured composite film was prepared by free free‐radical photopolymerization from a blend containing oligomer cycloaliphatic polyurethane acrylate (CPUA) and reactive diluent trimethylolpropane trimethaacrylate (TMPTMA) with the same weight (coded as UT) in the presence of free free‐radical photoinitiator Irgacure 754. It was proved to be a homogeneous system featuring only one phase by means of scanning electron microscopy (SEM). Cycloaliphatic epoxy resin (CER) was introduced to enhance mechanical properties of the UV‐cured UT composite film in the presence of cationic photoinitiator Irgacure 250, and a series of UV‐cured CPUA/TMPTMA/CER composite films with different component ratios were prepared by free radical/cationic hybrid UV UV‐curing technique. Results of conversion curves, SEM, and Fourier‐ transform infrared spectroscopy illustrated that UT was cured faster than CER, leading to dynamically asymmetric photopolymerization‐induced phase ‐separation behaviors. The thermal and mechanical properties were evaluated via thermal degradation analysis, dynamic mechanical analysis, and stress–strain curves. Surface properties such as pencil hardness, pendulum hardness, shrinkage rate, contact angle, flexibility, and glossiness were also studied. All these measurements revealed that component ratios, intermolecular attractions, photopolymerization velocities, and viscosities had remarkably influenced on the morphologies and applied properties of UV‐cured composite films, and interpenetrating polymer network films had better comprehensive performances than other UV‐cured composite films with different microstructures. POLYM. COMPOS., 36:1177–1185, 2015. © 2014 Society of Plastics Engineers     

单环氧基活性稀释剂对环氧酸酐体系的作用

考察添加不同量的单环氧基活性稀释剂(H8)对环氧树脂体系固化反应以及介电性能的影响,通过DSC热分析发现,稀释剂添加量越多,DSC曲线放热峰越往高温方向移动,并且峰形变钝,放热过程的△HC基本上随稀释剂用量的增大而减小;由介电损耗-温度谱实验数据显示,随着稀释剂加入量增多,介电损耗值也呈上升趋势,但总体上tanδ还是保持在较低值范围内,155℃tanδ最大值不超过0.04。同时利用DSC跟踪体系固化反应过程,根据Kissinger和Crane方程对该固化反应进行了非等温动力学分析,探讨得出环氧树脂体系的固化动力学参数:固化反应表观活化能△Ea=48.3 kJ/mol,反应级数n=0.89。