Effect of diluents on the curing behavior of vinyl ester resin

An acidic vinyl ester resin (～6 mg KOH per gram of solid) was prepared by reacting a bisphenol‐A‐based epoxy resin with acrylic acid in the presence of tributyl amine. The acrylated epoxy resin thus obtained was characterized by Fourier transform infrared spectroscopy. Five samples of vinyl ester resin containing styrene and methyl methacrylate (MMA) in the weight ratios 40:0, 30:10, 20:20, 10:30, and 0:40 were prepared at 30°C, and their curing behavior was studied by differential scanning calorimetry in the presence of benzoyl peroxide (2 phr). Curing behavior was dependent on the ratio of the two monomers used as reactive diluents. The kinetic parameters were determined by Ozawa's method. The energy of activation and frequency factor varied from 17 to 23 kcal mol^?1 and 8.47 × 10⁹ to 5.21 × 10¹² min^?1, respectively and were lowest for the samples containing 30:10 and 10:30 styrene/MMA weight ratios. The curing reactions followed first‐order kinetics and obeyed the Arrhenius rate expression. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1948–1951, 2003     

Curing studies on vinyl ester resin using acrylates as reactive diluents

The curing behavior of bis(methacryloxy) derivatives of diglycidyl ether of bisphenol A (vinyl ester resin) containing acrylates (methyl, ethyl and butyl acrylate) as the reactive diluents (40% w/w) were studied by DSC analysis. Data found in this study indicated that an appreciable curing rate is obtained at lower temperature with increased concentrations of initiator. The acid value, activation energy, Arrhenius factor and specific heat are discussed.     

复合引发剂对乙烯基酯树脂固化及性能的影响

采用示差扫描量热法(DSC)及力学性能测试研究了添加引发剂过氧化苯甲酸叔丁酯(TBPB)及双(4-叔丁基环己基)过氧化二碳酸酯(P16)对乙烯基酯树脂的固化反应及其拉挤复合材料性能的影响。结果表明,当乙烯基树脂,复合引发剂TBPB与P16质量比为100∶1∶0.3时,其拉挤复合材料的各项力学性能较好。     

乙烯基树脂后固化制度的优化研究

采用DSC法研究了乙烯基树脂体系的固化动力学参数,并通过对该体系树脂浇铸体的固化度、力学性能、玻璃化转变温度的测试确定了最佳后固化制度。结果表明,该体系固化反应的表观活化能为56.27 kJ/mol,频率因子为4.96×107/s,反应级数为0.9;最佳后固化制度为100℃/1 h,此时固化度可达94.7%,弯曲强度可达102.6 MPa,拉伸强度可达64.1 MPa,玻璃化转变温度可达107.8℃。     

Isothermal curing by dynamic mechanical analysis of three epoxy resin systems: Gelation and vitrification

Times to gelation (t_gel) and times to vitrification (t_vit) during isothermal curing for the epoxy systems diglycidyl ether of bisphenol A (DGEBA)/1,3‐bisaminomethylcyclohexane (1,3‐BAC), tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM)/4‐4′‐diaminodiphenylsulfone (DDS), and TGDDM/epoxy novolac (EPN)/DDS were measured at different curing temperatures. This article reports on a method to determine t_gel and t_vit by dynamic mechanical analysis (DMA). Gelation was determined at the onset of the storage modulus or by the peak of the loss factor. Vitrification was defined as the curve of the storage modulus as the curve reached a constant level (endset) in DMA tests. The experimental values obtained for t_gel and t_vit were compared with values obtained by other experimental methods and with theoretical values (t_gel's) or indirect determinations (t_vit's). From kinetic analysis by differential scanning calorimetry, conversions corresponding to gelation were obtained for the three systems; this yielded a constant value for each system that was higher than theoretical value. Values of the apparent activation energies of the DGEBA/1,3‐BAC, TGDDM/DDS, and TGDDM/EPN/DDS epoxy systems were obtained from plots of t_gel's against reciprocal temperatures. They were 53.2, 58.2, and 46.5 kJ/mol, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 78–85, 2002     

Curing kinetics and thermal properties of vinyl ester resins

The curing kinetics of dimethacrylate-based vinyl ester resins were studied by scanning and isothermal DSC, gel time studies, and by DMTA. The rate of polymerization was raised by increased methyl ethyl ketone peroxide (MEKP) concentration but the cocatalyst, cobalt octoate, retarded the reaction rate, except at very low concentrations. By contrast, the gel time was reduced for all increases in either peroxide or cobalt concentration. This contradictory behavior was explained by a kinetic scheme in which the cobalt species play a dual role of catalyzing the formation of radicals from MEKP and of destroying the primary and polymeric radicals. The scanning DSC curves exhibited multiple peaks as observed by other workers, but in the present work, these peaks were attributed to the individual influence of temperature on each of fundamental reaction steps in the free radical polymerization. Physical aging appeared to occur during the isothermal polymerization of samples cured below the “fully cured” glass transition temperature (T_g). For these undercured materials, the difference between the DSC T_g and the isothermal curing temperature was approximately 11°C. Dynamic mechanical analysis of a partially cured sample exhibited anomalous behavior caused by the reinitiation of cure of the sample during the DMTA experiment. For partially cured resins, the DSC T_g increased monotonically with the degree of cure, and this dependence was fitted to an equation related to the Couchman and DiBenedetto equations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 769–781, 1997     

Frontal polymerization of a cyanate ester

Thermal frontal polymerization is an exothermic process that uses a propagating wave to polymerize monomers via an external heat source, such as a soldering iron, to initiate front propagation. Herein, for the first time, the curing of a cyanate ester via thermal frontal polymerization is described with two different external heat sources. However, issues of bubbling due to vaporization of the amine catalyst generally resulted in incomplete frontal polymerization when a soldering iron was used as the external heat source. To counter this issue, dual‐strip polymerization systems were used, wherein the heat from the exothermic polymerization of a free‐radical system was used to initiate the frontal polymerization of a cyanate ester system with an amine catalyst. As a result, complete frontal polymerization occurred. Additionally, the effect of the width of the acrylate strip and its impact on the front temperature, initial velocity, and steady‐state velocity of the adjacent cyanate ester system were studied. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Study on the curing process of QY8911‐3 resin

The effect of t‐butyl peroxybenzoate (TBPB) on the cure reaction of QY8911‐3 resin (BMI) was studied by differential scanning calorimetry (DSC) and gel time analysis. The mechanical properties of the resin and the composite were tested and analyzed with the peroxide content. The results showed that TBPB decomposed between 117 and 191°C and the enthalpy was 1123 J/g. TBPB reduced the initial reaction temperature, prompted the reaction speed, and shortened the gel time of the BMI resin. TBPB also increased the bending strength and decreased the impacting strength of the postcured samples. So, the peroxide content should be less than 0.6%. CF/SiO₂/BMI composites were prepared from the BMI containing peroxide and their microstructure and properties were better than those of the composites free of peroxide. According to the injection‐molding experiment, the spilling problem was overcome and the forming time was reduced from 2 h to 15 min when peroxide was added. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3769–3773, 2003     

耐腐蚀性乙烯基酯树脂的研究与应用

论述了乙烯基酯树脂优异的耐腐蚀性能,耐腐蚀原理及目前国内外耐腐蚀性乙烯基酯树脂的研究进展和在一些领域的典型应用。     

成分比例不同的MEKP在乙烯基树脂固化中的应用

采用50℃等温DSC方法研究了成分比例不同的过氧化甲乙酮(MEKP)在乙烯基树脂固化中的作用并讨论了促进剂和MEKP用量对固化的影响。结果表明,成分比例不同的MEKP固化峰值时间和固化率不同,二聚体含量较高的MEKP峰值时间短,固化率高。在促进剂用量1%前提下,促进剂/MEKP质量比为1/1.5时,固化率达到最大(58.5%),是乙烯基树脂固化合适的引发剂。     

Nonisothermal curing of a solid resole phenolic resin

A commercial solid resole phenolic resin was thoroughly characterized with Fourier transform infrared spectroscopy, NMR, and gel permeation chromatography, and its nonisothermal curing reaction was studied systematically with differential scanning calorimetry at a series of heating rates (βs) of 3, 4.5, 5.7, and 10°C/min. The results show that the solid resole had a higher molecular weight than conventional liquid resoles, and its reactive hydroxymethyl (CH₂ OH) and dibenzyl ether (CH₂ O CH₂) functionalities participated in the crosslinking reaction upon heating. The nonisothermal curing reaction of the solid resole exhibited a relatively constant reaction heat, whereas the onset, peak, and end curing temperatures increased gradually with increasing βs. In addition, the reaction kinetics of the solid resole was analyzed with an nth‐order reaction model, the global activation energy was determined with the Kissinger method, and the reaction order was derived from the Crane equation. The obtained rate equation was applied to simulate the reaction time, conversion, and reaction rate, with a good fit achieved between the experimental data and the model predications. In conclusion, this study provided us with new knowledge on solid resoles at a molecular level and was also a great help for the curing procedure design, property optimization, and practical application of this commercial solid resole. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A kinetic study on the autocatalytic cure reaction of a cyanate ester resin

The cure of a novolac‐type cyanate ester monomer, which reacts to form a polycyanurate network, was investigated by using differential scanning calorimeter. The conversions and the rates of cure were determined from the exothermic curves at several isothermal temperatures (513–553 K). The experimental data, showing an autocatalytic behavior, conforms to the kinetic model proposed by Kamal, which includes two reaction orders, m and n, and two rate constants, k₁ and k₂. These kinetic parameters for each curing temperature were obtained by using Kenny's graphic‐analytical technique. The overall reaction order was about 1.99 (m = 0.99, n = 1.0) and the activation energies for the rate constants, k₁ and k₂, were 80.9 and 82.3 kJ/mol, respectively. The results show that the autocatalytic model predicted the curing kinetics very well at high curing temperatures. However, at low curing temperatures, deviation from experimental data was observed after gelation occurred. The kinetic model was, therefore, modified to predict the cure kinetics over the whole range of conversion. After modification, the overall reaction order slightly decreased to be 1.94 (m = 0.95, n = 0.99), and the activation energies for the rate constants, k₁ and k₂, were found to be 86.4 and 80.2 kJ/mol. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3067–3079, 2004     

Effect of wood on the curing behavior of commercial phenolic resin systems

Differential scanning calorimetry (DSC) was used to study the effect of wood on the curing behavior of two types of commercial oriented‐strand‐board phenolic resins. DSC analysis showed that the curing behavior of the core resin differed significantly from that of the face resin in terms of the peak shape, peak temperature, and activation energy. The addition of wood to the resins moved the two separated peaks in the DSC curves of the core resin adjacent to each other. It also accelerated the addition reactions in the curing processes of both the core and face resins. The two peaks in the DSC curves were the result of the high pH values of the resins. These two peaks became either jointed together or overlapped when the pH value of the resin was reduced. Wood also reduced the activation energies for both the core and face resins by decreasing the pH values of the curing systems. Moreover, the effects of wood on the curing behavior of the resins among the five species studied were similar. The lowest activation energy for a phenolic resin probably appeared at pH 10–11 under alkaline conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 185–192, 2005     

MFE乙烯基酯树脂的增韧研究

采用有机改性膨润土和聚乙二醇与乙烯基酯树脂复合成功制得纳米复合材料,在保持树脂拉伸、弯曲强度的同时,树脂的断裂伸长率和耐冲击性能得到了大幅度的改善。有机膨润土和聚乙二醇含质量分数为4%和15%,冲击强度为7．58 MPa,断裂伸长率为8．99%。     

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     

环氧改性氰酸酯树脂固化动力学的研究

采用示差扫描量热法(DSC)对缩水甘油醚类环氧树脂(E-51)与脂环族环氧树脂(R-122)共同改性的双酚A型氰酸酯(BADCy)树脂的固化反应历程进行了研究。由Kisserger方程求得共聚体系固化反应的表观活化能为60.5 kJ/mol,根据Crane理论求得固化反应级数为0.89,接近于1级反应。该体系起始固化温度为132.1℃,峰顶固化温度为168.7℃,终止固化温度为246.0℃。研究表明,环氧树脂可促进BADCy的固化,改性体系可在177℃以下实现较完全固化。     

Influence of the processing on the completion of curing in epoxy‐based composites

Differential scanning calorimetry analysis was used to investigate interrelationships between several thermal parameters and the processing conditions of particle‐filled thermosetting resins. On the same piece, obtained by injection molding, epoxy‐based composites exhibited sensible differences within a set of measurements of the glass‐transition temperature, the width of the transition, the difference in the heat capacity, and the conversion degree. Statistical analysis showed a strong intercorrelation between these thermal parameters, but it could not provide any explanation for the disparities. The dispersion of the measured properties could, in a second step, be directly related to a sample's position with respect to the injection point in the mold. Moreover, even the postcuring stage could not erase this topological effect. As a result, a phenomenological model is proposed that fairly describes the experimental trends. This simple polynomial approach can subsequently be used either to determine the thermal parameters of any point of a molded piece or to shed some light on phenomena responsible for the large variations of the measured quantities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1368–1376, 2005     

Process cure monitoring of unsaturated polyester resins,vinyl ester resins,and gel coats by Raman spectroscopy

The curing process of unsaturated polyester resins, vinyl ester resins, and gel coats was studied by using a process Raman spectrometer, equipped with a remote fiber‐optic probe. The resins were cured and Raman spectra were recorded during the curing reaction. The spectral changes were identified and, from the intensities, the cure process could be monitored. Gel times given by the resin suppliers correlated well with the Raman results. It could also be seen that the curing process continues for a long time, up to several weeks. Postcuring will finally complete the curing process. White and lightly colored gel coats could easily be monitored by Raman spectroscopy, but fluorescent problems were encountered with heavily colored pigments. The curing of laminates containing 50–70 wt % glass fiber mat could also be followed by Raman spectroscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1285–1292, 2004     

聚氨酯/乙烯基树脂互穿聚合物网络的研究进展

综述了聚氨酯/乙烯基树脂互穿聚合物网络（PU/VER IPNs）中两组分的聚合机理;重点讨论了分步IPNs、同步IPNs和胶乳IPNs的制备方法及其研究进展;介绍了PU/VER IPNs合成动力学的研究方法,包括化学滴定法、差示扫描量热法和傅立叶变换红外光谱法。