Epoxy/POSS organic-inorganic hybrids: ATR-FTIR and DSC studies

Organic-inorganic hybrid nanocomposites were prepared by reaction of an octaepoxy-silsesquioxane, OECh, with an epoxy-amine system. OECh was used to partially replace the thermosetting resin, diglycidyl ether of bisphenol A, DGEBA, in its reaction with an aromatic diamine, 4,4′-(1,3-phenylenediisopropylidene) bisaniline, BSA. The OECh was characterized by different techniques. The curing kinetics of ternary systems formed by DGEBA, OECh and BSA, was followed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy, ATR-FTIR. All the mixtures were prepared with a stoichiometric ratio between epoxy and amine groups. The degree of reaction of glycidyl epoxy ring along the curing cycle selected was obtained from the infrared spectra. A peak-height method based on the ratio of the height of the characteristic to reference absorbance peak was used. The curing kinetic of different blends was obtained by differential scanning calorimetry, DSC. Three different methods, the differential of Kissinger, the integral of Flynn-Wall-Ozawa and the phenomenological model of Kamal, were used in order to obtain the kinetic parameters of the cure reaction. It is observed that the presence of POSS accelerates the rate of opening of glycidyl epoxy rings from DGEBA. The behaviour of the mixture during the curing process can be explained with an autocatalytical model, corrected with the contribution of the diffusion of the molecules during the course of the reaction.     

Epoxy resins (DGEBA): The curing and physical aging process

Differential scanning calorimetry (DSC) and infrared spectroscopy (IR) were used to monitor the degree of cure of partially cured epoxy resin (Epon 828/MDA) samples. The extent of cure, as determined by residual heat of reaction, concurred with that determined by monitoring the infrared radiation absorbance of the epoxide group near 916 cm^?l. The fictive temperature T_{f, g} was found to increase with the degree of cure, increasing rapidly during cure until reaching a value near the cure temperature T_c of 130°C (approximately 80% cure) where the material vitrified. The greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification but, as revealed by infrared spectroscopy, the result of the depletion in the number of reactive epoxide groups. The endothermic peak areas and peak temperatures evident during the DSC scans were used as a measure of the extent of “physical aging” which took place during the cure of this resin, and after, fully cured samples were aged 37°C below their ultimate glass temperature for various periods of time. The rate of physical aging slowed as the temperature increment (T_t,g ? T_c) increased. Although an endothermic peak was evident after only 1 h of cure (T_{f, g} = 138.3°C), such a peak did not appear until fully cured samples were aged for 16 h or more. Enthalpy data revealed that for partially cured material, the fictive temperature T_{f, a}, reflecting physical aging, increased with curing time. In contrast, the T_{f, a}, for fully cured samples decreased with sub-T_g aging time. The characteristic jump in the heat capacity ΔC_p which occurred at the T_{f, g} decreased as curing progressed. This decrease appears to be dependent upon the rotational and vibrational degrees of freedom of the glass. Finally, a graphical method of determining the fictive temperature T_{f, a}, of partially and fully cured epoxy material from measured endothermic peak areas was developed.     

2,4,6-三(羟基苯甲基氨基)-均三嗪的合成及其与双酚A型环氧树脂的固化行为研究

合成了一种含三嗪环结构的环氧树脂固化剂2,4,6-三(羟基苯甲基氨基)-均三嗪(MFP).用动态DSC和原位红外光谱对MFP/DGEBA(双酚A型环氧树脂)体系的固化行为进行了研究.动态DSC研究表明,由于MFP分子结构中存在两种活泼氢(酚羟基氢和仲胺氢),固化反应存在明显的两个峰,相对应的表观活化能分别为70.5 kJ.mol-1和86.5 kJ.mol-1(Kissinger法),通过与另一相似化合物固化DGEBA的比较可知,在MFP固化DGEBA的过程中,酚羟基与环氧基反应相对较难.原位红外动力学结果很好地支持了上述结论.     

Curing kinetics of the synthesis of poly(2-hydroxyethyl methacrylate) (PHEMA) with ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent

An experimental study was carried out to investigate the effect of ethylene glycol dimethacrylate (EGDMA, as a crosslinking agent) content on the curing kinetics of the polymerization of 2-hydroxyethyl methacrylate (HEMA), using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). EGDMA may cause a crosslinking-facilitated gel effect which reduces the termination rate of living free radicals and enhances the overall reaction rate, but it may also induce a diffusional resistance for the reactants so that some free monomers are trapped and pendant vinyl groups are prohibited from reaction by the crosslinked structure. At higher content of EGDMA, the later effect becomes predominant, and the reaction rate and the final conversion are limited. The exothermic peak of the curing reaction tends to carry a shoulder and then split into two peaks as the amount of EGDMA is increased, possibly due to a later reaction of the trapped monomers and pendant vinyls. The heat of reaction measured by DSC in the scanning mode is 61.2 kJ/mol CC. The activation energy (E) of the curing reaction ranges from 56.5 to 78.3 kJ/mol CC depending on the EGDMA content and the type of operation. The diffusion-limited reaction rate and the different thermal history experienced in the nonisothermal and isothermal curing can result in variations of the results in the activation energy measurement. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1873–1889, 1997     

Curing kinetics of boron‐containing phenol–formaldehyde resin formed from paraformaldehyde

A boron‐containing phenol–formaldehyde resin (BPFR) was synthesized from boric acid, phenol, and paraformaldehyde. The curing reaction of BPFR was studied by Fourier‐transform infrared spectrometry and differential scanning calorimetry. According to the heat evolution behavior during the curing process, several influencing factors on isothermal curing reaction were evaluated. The results show that the isothermal kinetic reaction of BPFR follows autocatalytic kinetics mechanism, and kinetic parameters m, n, k₁, and k₂, were derived, respectively. In the latter reaction stage, the curing reaction becomes controlled mainly by diffusion. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 638–644, 2002     

Novel,environmentally friendly crosslinking system of an epoxy using an amino acid: Tryptophan‐cured diglycidyl ether of bisphenol A epoxy

Tryptophan, an amino acid, has been used as a novel, environmentally friendly curing agent instead of toxic curing agents to crosslink the diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The curing reaction of tryptophan/DGEBA mixtures of different ratios and the effect of the imidazole catalyst on the reaction have been evaluated. The optimum reaction ratio of DGEBA to tryptophan has been determined to be 3:1 with 1 wt % catalyst, and the curing mechanism of the novel reaction system has been studied and elucidated. In situ Fourier transform infrared spectra indicate that with the extraction of a hydrogen from NH₃⁺ in zwitterions from tryptophan, the formed nucleophilic primary amine and carboxylate anions of the tryptophan can readily participate in the ring‐opening reaction with epoxy. The secondary amine, formed from the primary amine, can further participate in the ring‐opening reaction with epoxy and form the crosslinked network. The crosslinked structure exhibits a reasonably high glass‐transition temperature and thermal stability. A catalyst‐initiated chain reaction mechanism is proposed for the curing reaction of the epoxy with zwitterion amino acid hardeners. The replacement of toxic curing agents with this novel, environmentally friendly curing agent is an important step toward a next‐generation green electronics industry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 181–190, 2007     

DTA studies on the thermal oxidation and crosslinking reactions of carboxyl-terminated polybutadiene

Studies on the thermal oxidation of carboxyl-terminated polybutadiene in the presence of antioxidants have been carried out by dynamic DTA. Bis-thioacetylacetonato nickel(II) compounds are found to be effective in inhibiting the air oxidation reaction in the polymer. The crosslinking reaction of the polymer through the double bonds present in the polymer molecule is desensitized by the antioxidants and the effect is more with N-phenyl-1-naphthylamine. An exothermic peak formed at 270°C in the presence of tris(2-methylaziridinyl-1) phosphine oxide has been identified as the curing reaction. The infrared spectra of CTPB in the presence of MAPO at various temperatures confirm the various stages of reaction.     

Studies on curing kinetics of a novel combined liquid crystalline epoxy containing tetramethylbiphenyl and aromatic ester‐type mesogenic group with diaminodiphenylsulfone

The curing kinetics of a novel liquid crystalline epoxy resin with combining biphenyl and aromatic ester‐type mesogenic unit, diglycidyl ether of 4,4′‐bis(4‐hydroxybenzoyloxy)‐3,3′,5,5′‐tetramethyl biphenyl (DGE‐BHBTMBP), and the curing agent diaminodiphenylsulfone (DDS) was studied using the advanced isoconvensional method (AICM). DGE‐BHBTMBP/DDS curing system was investigated the curing behavior by means of differential scanning calorimetry (DSC) during isothermal and nonisothermal processes. Only one exothermal peak appeared in isothermal DSC curves. A variation of the effective activation energy with the extent of conversion was obtained by AICM. Three different curing stages were confirmed. In the initial curing stage, the value of E_a is dramatically decreased from ～90 to ～20 kJ/mol in the conversion region 0–0.2 for the formation of LC phase. In the middle stage, the value of E_a keeps about ～80 kJ/mol for cooperative effect of reaction mechanism and diffusion control. In the final stage, a significant increase of E_a from 84 to 136 kJ/mol could be caused by the mobility of longer polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3922–3928, 2007     

Curing kinetics of epoxy resins with hyperbranched polyesters as toughening agents

The effects of hyperbranched polyesters on the cure kinetics of diglycidyl ether of bisphenol A (DGEBA) in the presence of m‐phenylene diamine were investigated with nonisothermal differential scanning calorimetry. The results showed that the addition of hyperbranched polyesters enhanced the cure reaction of DGEBA with m‐phenylene diamine, and this resulted in a reduction of the peak temperature of the curing curve and the activation energy because of the low viscosity and large number of terminal hydroxyl groups. However, when linear poly(ethylene glycol) was added, the activation energy of the blends also slightly decreased, whereas the peak temperature of the curing curve increased. The curing kinetics of the blends were calculated by the isoconversional method of Málek. The two‐parameter autocatalytic model (i.e., the ?esták–Berggren equation) was found to be the most adequate for describing the cure kinetics of the studied systems. The obtained nonisothermal differential scanning calorimetry curves showed results in agreement with those theoretically calculated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2649–2656, 2004     

Determination of pirimicarb and endosulfan in commercial pesticide formulations by Fourier transform infrared spectrometry

A routine method based on Fourier transform infrared spectrometry was developed for the simultaneous determination of pirimicarb and endosulfan in commercially available pesticide formulations. The method is based on peak area absorbance measurements between 1362 and 1352 cm(-1), corrected with a baseline fixed at 1338 cm(-1), for pirimicarb and peak area absorbance measurements between 919 and 909 cm(-1) with a baseline fixed at 931 cm(-1) for endosulfan; chloroform solutions for analysis were obtained by direct dilution of emulsifiable concentrates or by solvent extraction from solid samples. Various extraction conditions and appropriate band selection were investigated, and interference studies were performed. Under the experimental conditions selected, limits of detection of 13 microg/g for pirimicarb and 150 microg/g for endosulfan were obtained that correspond to 0.13 and 1.6% (w/w), respectively, in commercial samples. Results from analyses of commercial samples by the developed method compared well with those obtained by a liquid chromatography reference method.     

Sequence distribution of poly(ether)urethane elastomer

Poly(ether)urethane elastomers (PEUE) having different sequence distributions can be synthesized by the reaction of p-phenylene diisocyanate, poly(oxytetramethylene glycol), and hydrazine by four different routes. The degree of the sequence distribution of PEUE was determined by high-resolution NMR spectroscopy. The sequence distribution of PEUE synthesized by the prepolymer method in solvent (method 1) was found to coincide with the sequence distribution calculated from the reactivity ratio of two isocyanate groups in p-phenylene diisocyanate. On the other hand, the sequence distribution of PEUE obtained by the prepolymer method without solvent (method 2) was found to deviate from that expected from the reactivity ratio. The degree of the distribution of monomers in PEUE having the same composition ratio corresponded to the infrared absorbance ratio at 1720 and 1700 cm^?1.     

Concerted reactions of aldehyde groups during polymerization of an aldehyde‐functional benzoxazine

Polymerization reactions of a new aldehyde‐functional benzoxazine (4HBA‐a) were investigated in detail. The curing behavior of 4HBA‐a was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) methods. The results indicate that the disappearance of the aldehyde group from 4HBA‐a and the ring‐opening reaction of 4HBA‐a occur simultaneously. Gases evolved during the curing process of 4HBA‐a were analyzed by thermogravimetric analyzer interfaced with FTIR spectra. The elimination of CO₂ is attributed to the oxidation and decarboxylation of the aldehyde groups. In addition, the crosslink sites of the aldehyde groups in the polymer structure are confirmed by model reactions. A possible reactive position should be sited in ortho position of phenol rather than ortho and/or para positions of N‐phenyl ring. Finally, the crosslinked structures of polymerized 4HBA‐a have been proposed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

On Line Determination of Perphenazine Using Flow Injection Analysis

An accurate specific flow injection spectrophotometric method for the determination of perphenazine in the range 50-250 ppm is introduced. In the method, 110 μl of the drug is injected through a stream of 0.2% (w/v) potassium dichromate in 0.25 M sulfuric acid flowing on line as a carrier stream. The drug is oxidized on the flow to the red monocation radical, the peak absorbance of which is monitored at 525 nm. A throughput of up to 300 samples per hour is attained. The mechanism of the reaction is suggested and the method is compared with the United States Pharmacopeia method.     

ATR-FTIR技术用于酒精饮品中乙醇含量的快速测定

建立了快速测定酒精饮品中乙醇含量的衰减全反射-傅立叶变换红外光谱(ATR-FTIR)法.以ZnSe槽形板为ATR晶体,以水为背景采集样品的FTIR图.以1045 cm-1的C-OH伸缩振动为特征峰,用部分峰面积表示整个吸光度以消除肩峰干扰,分别建立了低浓度区(0～24%(V/V))和高浓度区(24%～84%(V/V))两条标准曲线,其线性相关系数均大于0.999,乙醇水溶液的检测限为0.20%.对啤酒、干红葡萄酒以及白酒的分析表明,该方法准确、快速、方便,适用于酒精饮品中乙醇含量的快速测定.     

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     

Preparation of cycloaliphatic epoxy hybrids with non-conventional amine-curing agents

Cycloaliphatic epoxy resin has been successfully thermally cured using a polyamino siloxane oligomer as hardener. The curing reaction was followed by infrared spectroscopy in the near range, and thermal transitions were measured by dynamic mechanical thermal analysis. The use of accelerants and a plasticizer (dodecylphenol), and different curing schedules were explored. Cured materials showed high Tg values (around 125–164 °C), and the analysis of laser scanning confocal microscopy images showed that they are homogeneous in the microscale.     

Reaction of benzoxazine-based phenolic resins with strong and weak carboxylic acids and phenols as catalysts

The reaction of 3,4-dihydro-3,6-dimethyl-2H-1,3-benzoxazine using strong and weak carboxylic acids and phenols as catalysts has been studied using Fourier transform infrared (FTIR) spectroscopy. The auto-accelerated curing using sebacic acid as catalyst is further documented using ¹H-nuclear magnetic resonance (NMR) and dielectric analysis. Termination of curing, using strong acids or no catalyst, are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1913–1921, 1999     

Cationic copolymerization of diglycidyl ether of bisphenol A with phthalide or 3,3′‐diphtalide catalyzed by lanthanide triflates

Mixtures of the diglycidylether of bisphenol A (DGEBA) and phthalide (PT) or 3,3′‐diphthalide (DPT) were cured using ytterbium or lanthanum triflate as catalyst. The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and quantify the evolution of the epoxide and lactone groups. The T_g of the crosslinked materials increased when the proportion of lactone in the curing mixture decreased. The kinetics was studied with DSC experiments and isoconversional procedures. The differences in the reactivity of the systems were related to the Lewis acidity of the lanthanide salt used as initiator. The increase in the proportion of lactone leads to an increase in the reaction rate. The shrinkage was determined from the densities before and after curing and its evolution was studied by thermomechanical analysis. The materials obtained were characterized by thermogravimetry and dynamic mechanical thermal analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1711–1721, 2006     

升温与等温法非模型动力学研究环氧树脂固化反应

基于DSC数据,采用以Vyazovkin积分法为基础的升温法非模型动力学和等温法非模型动力学对双酚A型环氧树脂E51/4,4′-二氨基二苯基砜(DDS)体系及多官能度环氧树脂AG80/DDS体系的固化过程进行了研究,并结合玻璃化转变温度的变化和原位红外测试技术,对比分析了升温与等温条件下的固化反应规律.结果表明,与传统的模型拟合法相比,非模型动力学更适合定量预测树脂固化反应过程,并能为固化过程中反应机理变化的研究提供重要依据;等温法非模型动力学能够更好地预测两种树脂体系在不同恒温条件下的固化反应历程,并且升温法与等温法非模型动力学所得到的反应活化能-固化度之间的变化关系不同,表明不同温度条件下树脂的反应机理不同,这与升温和恒温条件下玻璃化效应及环氧官能团的变化规律相吻合.     

An optimized preparation of bismaleimide–diamine co‐polymer matrices

The main aim of this study was to develop an improved method for the preparation of a bismaleimide–diamine (BMI/DDM) polymer matrix, achieving shorter curing time, longer processing time (pot life), and good thermal mechanical properties. A matrix of BMI/DDM thermoset was prepared at optimal conditions and formulation, containing BMI and DDM in a 2:1 mol ratio with 0.1 wt% of dicumyl peroxide (DCP) as the curing accelerator. An optimal temperature of 150°C was selected for both melt‐mixing and curing processes. The mechanism of matrix preparation was also investigated using differential scanning calorimetry and quantitative Fourier transformed infrared analysis. DCP at the optimal concentration was found to accelerate cross‐linking reactions between BMI and DDM without inhibiting the chain‐extension reaction of BMI. The specified formulation exhibited longer gel time (208 s/g) and shorter post‐curing time (2 h) compared to other formulations. In addition, thermomechanical behavior and thermal stability were analyzed by dynamic mechanical analysis and thermomechanical analysis, and thermogravimetric analysis, respectively. The storage modulus (E′), glass transition temperature (T_g), and decomposition temperature (T_d) of the BMI/DDM thermosets increased with the BMI content of the formulations, while the coefficient of thermal expansion and damping behavior (tan δ) decreased in a similar manner, primarily because of an increase in the degree of cross‐linking. Copyright © 2014 John Wiley & Sons, Ltd.