Epoxy curing reaction studied by using two‐dimensional correlation infrared and near‐infrared spectroscopy

The isothermal curing process of bisphenol A epoxy resin with polyamine reagent (1,6‐diaminohexane) was monitored in situ by using temperature‐controlled Fourier‐transform infrared (FTIR) and Fourier‐transform near infrared (FTNIR) spectroscopy to elucidate the relative changes in functional groups during the curing reaction. It was shown that generalized two‐dimensional correlation spectroscopy can provide new information about the mechanisms and kinetics of the curing process, and the band assignments for complex NIR spectrum associated with this system. The sequential order of relative changes in functional groups during the curing process was examined by generalized 2D correlation spectroscopy and NIR‐IR hetero‐correlation spectroscopy, and the details of the complex epoxy curing reaction involving both primary and secondary amino group were revealed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of a self‐emulsifiable waterborne epoxy curing agent based on glycidyl tertiary carboxylic ester and its cure characteristics

A novel self‐emulsifiable waterborne amine‐terminated curing agent for epoxy resin based on glycidyl tertiary carboxylic ester (GTCE) was synthesized through three steps of addition reaction, capping reaction, and salification reaction of triethylene tetramine (TETA) and liquid epoxy resin (E‐44). The curing agent with good emulsifying and curing properties was gradually obtained under condition of the molar ratio of TETA: E‐44 as 2.2: 1 at 65 °C for 4 h, 100% primary amine capped with GTCE at 70 °C for 3 h, and 20% salifiable rate with glacial acetic acid. The curing agent was characterized by Fourier transform‐infrared spectroscopy (FT‐IR). The curing behavior of the E‐44/GTCE‐TETA‐E‐44 system was studied with differential scanning calorimetry (DSC) and FT‐IR. Results showed that the optimal mass ratio for E‐44/GTCE‐TETA‐E‐44 system was 3 to 1, and the curing agent showed a relatively lower curing temperature. The cured film prepared by the self‐emulsifiable curing agent and epoxy resin under the optimal mass ratio displayed good thermal property, hardness, toughness, adhesion, and corrosion resistance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44246.     

Ultraviolet‐curing behavior of an epoxy acrylate resin system

Ultraviolet (UV)‐curing behavior of an epoxy acrylate resin system comprising an epoxy acrylate oligomer, a reactive diluent, and a photoinitiator was investigated by Fourier transform infrared (FTIR) spectroscopy. The conversion changes of the resin system containing 20 phr of 1,6‐hexanediol diacrylate as a reactive diluent and 2‐hydroxy‐2‐methyl‐1‐phenyl‐propan‐1‐one as a photoinitiator were measured under different UV‐curing conditions. The fractional conversion was calculated from the area of the absorption peak for the vinyl group vibration occurring at 810 cm^?1. The effects of photoinitiator concentration, total UV dosage, one‐step or stepwise UV irradiation, UV intensity, atmosphere, and temperature on the curing behavior of the resin system were investigated. The conversion of the resin system increased rapidly at the initial stage of the UV‐curing process but increased very slowly after that. The final conversion of the resin system was mainly affected by total UV dosage. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1180–1185, 2005     

Thermal curing of glass‐epoxy prepregs by luminescence spectroscopy

In this study, we investigated the application of the luminescence spectroscopy technique in steady‐state conditions to study glass fiber‐epoxy F161 prepregs. We conducted this study by comparing the results obtained from the intrinsic fluorescence with Fourier transform near infrared spectroscopy. The extrinsic fluorescence of 9‐anthroic acid (9‐AA) was also used. Fourier transform infrared spectroscopy was also used to characterize the epoxide resin. The prepregs containing 9‐AA and those that did not were heat‐treated at 177°C (F161) for 1100 min at a 2°C/min heating rate. The results obtained by both methods indicated that the crosslinking reaction could be monitored by analysis of the spectral changes of the emission bands of the prepreg and 9‐AA. The intrinsic emission at 320 nm was attributed to the fluorophore group containing the epoxy ring and was used to calculate the conversion degree. The photophysical behavior of the 9‐AA probe indicated a reduction of free volume of the polymeric matrix with curing process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of rosin‐based flexible anhydride‐type curing agents and properties of the cured epoxy

BACKGROUND: Although rosin acid derivatives have received attention in polymer synthesis in recent years, to the best of our knowledge, they have rarely been employed as epoxy curing agents. The objective of the study reported here was to synthesize rosin‐based flexible anhydride‐type curing agents and demonstrate that the flexibility of a cured epoxy resin can be manipulated by selection of rosin‐based anhydride‐type curing agents with appropriate molecular rigidity/flexibility. RESULTS: Maleopimarate‐terminated low molecular weight polycaprolactones (PCLs) were synthesized and studied as anhydride‐type curing agents for epoxy curing. The chemical structures of the products were confirmed using ¹H NMR spectroscopy and Fourier transform infrared spectroscopy. Mechanical and thermal properties of the cured epoxy resins were studied. The results indicate that both the epoxy/anhydride equivalent ratio and the molecular weight of PCL diol play important roles in the properties of cured resins. CONCLUSION: Rosin‐based anhydride‐terminated polyesters could be used as bio‐based epoxy curing agents. A broad spectrum of mechanical and thermal properties of the cured epoxy resins can be obtained by varying the molecular length of the polyester segment and the epoxy/curing agent ratio. Copyright © 2009 Society of Chemical Industry     

Preparation and properties of halogen‐free flame‐retarded phthalonitrile–epoxy blends

Halogen‐free flame‐retarded blends composed of 2,2‐bis[4‐(3,4‐dicyanophenoxy) phenyl] propane (BAPh) and epoxy resin E‐44 (EP) were successfully prepared with 4,4′‐diaminodiphenyl sulfone as a curing additive. The structure of the copolymers was characterized by Fourier transform infrared spectroscopy, which showed that epoxy groups, a phthalocyanine ring, and a triazine ring existed. The limiting oxygen index values were over 30, and the UL‐94 rating reached V‐0 for the 20 : 80 (w/w) BAPh/EP copolymers. Differential scanning calorimetry and dynamic rheological analysis were employed to study the curing reaction behaviors of the phthalonitrile/epoxy blends. Also, the gelation time was shortened to 3 min when the prepolymerization temperature was 190°C. Thermogravimetric analysis showed that the thermal decomposition of the phthalonitrile/epoxy copolymers significantly improved with increasing BAPh content. The flexible strength of the 20:80 copolymers reached 149.5 MPa, which enhanced by 40 MPa compared to pure EP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

New epoxy/silica‐titania hybrid materials prepared by the sol–gel process

A new type of inorganic‐polymer hybrid materials of epoxy/silica‐titania had been prepared by incorporating grafted epoxy, which had been synthesized by epoxy and tetraethoxysilane (TEOS), with highly reactive TEOS and tetrabutyltitanate (TBT) by using the in situ sol–gel process. The grafted epoxy was confirmed by Fourier transform infrared spectroscopy (FT‐IR) and ¹H‐NMR spectroscopic technique. Results of FT‐IR spectroscopy and atomic force microscopy (AFM) demonstrated that epoxy chains have been covalently bonded to the surface of the SiO₂‐TiO₂ particles. The particles size of SiO₂‐TiO₂ are about 20–50 nm, as characterized by AFM. The experimental results showed that the glass‐transition temperatures and the modulus of the modified systems were higher than that of the unmodified system, and the impact strength was enhanced by two to three times compared with that of the neat epoxy. The morphological structure of impact fracture surface and the surface of the hybrid materials were observed by scanning electron microscopy and AFM, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1075–1081, 2006     

Novel polymer composites based on a mixture of preformed nanosilica‐filled poly(methyl methacrylate) particles and a diepoxy/diamine thermoset system

In this work, a new material based on an epoxy thermoset modified with a thermoplastic filled with silica nanoparticles was investigated. When thermoplastic particles are filled with nanoparticles with unique properties such as high efficiency for absorbing ultraviolet light, electric or magnetic shielding, high electrical conductivity, and high dielectric constants, more than an enhancement of the mechanical properties is expected to be achieved for modified epoxy‐based thermosets. Particles of poly(methyl methacrylate) (PMMA) filled with silica nanoparticles were used to modify a thermoset based on a full reaction between diglycidyl ether of bisphenol A and 3‐(aminomethyl)benzylamine. When the preformed thermoplastic particles were mixed with the reactive constituents of the epoxy system under certain curing conditions in which total miscibility was avoided, uniform particle dispersions could be obtained. The relationships between the composition, morphology (nanoscale and microscale), glass‐transition temperature, mechanical properties, and fracture toughness were considered. Four main results were obtained for consideration of the potential of silica‐filled PMMA as an important modifier of brittle epoxy thermoset systems: (1) a good dispersion of the silica nanoparticles in the PMMA domains, (2) a good dispersion of the silica‐filled PMMA microparticles in the epoxy matrix, (3) the possibility of partial dissolution of the PMMA‐rich domains into the epoxy system, and (4) a slight increase in properties such as the hardness, indentation modulus, and fracture toughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Kinetics modeling of carbon‐fiber‐reinforced bismaleimide composites under microwave and thermal curing

This article focuses on the analysis of the curing kinetics of carbon‐fiber‐reinforced bismaleimide (BMI) composites during microwave (MW) curing. A nonisothermal differential scanning calorimetry (DSC) method was used to obtain an accurate kinetic model. The degree of curing, chemical characterization, and glass‐transition temperature of the resin and composites cured by thermal and MW heating were analyzed with DSC, Fourier transform infrared spectroscopy, and dynamic mechanical analysis. The experimental results indicate that MW accelerated the crosslinking reaction of the BMI resin and had different effects on the reaction processes, especially for the glass‐transition temperature and chemical bonds. However, the curing reaction rate of the BMI resin decreased when the carbon fibers were added to the BMI resin during thermal and MW curing. According to the experimental results, the curing kinetic model of the BMI composite was used to provide a theoretical foundation for MW curing analysis. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43770.     

High‐performance biobased epoxy derived from rosin

Great achievements have been made in the research of biobased thermoplastic polymers, but the progress concerning thermosetting resins has been minor. In particular, research on high‐performance thermosetting polymers from renewable feedstock has not been reported elsewhere. A novel biobased epoxy was synthesized from a rosin acid. Its chemical structure was confirmed using ¹H NMR, ¹³C NMR and Fourier transform infrared spectroscopy. The results indicated that the rosin‐based epoxy possessed high glass transition temperature (T_g = 153.8 °C), high storage modulus at room temperature (G′ = 2.4 GPa) and good thermal stability. A rosin‐based epoxy with excellent properties was achieved. The results suggest it is possible to develop high‐performance thermosetting resins from renewable resources. Copyright © 2010 Society of Chemical Industry     

Study of the isothermal curing of an epoxy prepreg by near‐infrared spectroscopy

The commercial epoxy prepreg SPX 8800, containing diglycidyl ether of bisphenol A, dicyanodiamide, diuron, and reinforcing glass fibers, was isothermally cured at different temperatures from 75 to 110°C and monitored via in situ near‐infrared Fourier transform spectroscopy. Two cure conditions were investigated: curing the epoxy prepreg directly (condition 1) and curing the epoxy prepreg between two glass plates (condition 2). Under both curing conditions, the epoxy group could not reach 100% conversion with curing at low temperatures (75–80°C) for 24 h. A comparison of the changes in the epoxy, primary amine, and hydroxyl groups during the curing showed that the samples cured under condition 2 had lower initial epoxy conversion rates than those cured under condition 1 and that more primary amine–epoxy addition occurred under condition 2. In addition, the activation energy under cure condition 2 (104–97 kJ/mol) was higher than that under condition 1 (93–86 kJ/mol), but a lower glass‐transition temperature of the cured samples was observed via differential scanning calorimetry. The moisture in the prepreg was assumed to account for the different reaction kinetics observed and to have led to different reaction mechanisms. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2295–2305, 2003     

氯甲基笼型倍半硅氧烷改性双酚A环氧树脂性能

引言双酚A环氧树脂是目前应用最广、用量最大的环氧树脂,具有良好的化学稳定性、电气绝缘性被广泛应用于涂料和电子电器等领域;然而,双酚A环氧树脂存在耐热性较差和固化后脆性大等缺点,因此如何提高环氧树脂的耐热性及力学性能等是目前改性研究的热点之一[1-5]。而笼型多面体倍半硅氧烷(POSS)是一类具有(RSiO1.5)n通式的纳米材料,因其特殊的分子组成结构使得POSS具     

Tailored thermal and mechanical properties of epoxy resins prepared using multiply hydrogen‐bonding reactive modifiers

In this study, we synthesized a phosphorus‐containing triply functionalized reactive modifier, DOPO‐tris(azetidine‐2,4‐dione), and a phosphorus‐free doubly functionalized reactive modifier, bis(azetidine‐2,4‐dione), and embedded them into epoxy resin systems. We characterized these synthesized reactive modifiers using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis, and mass spectrometry. During the thermosetting processes, we reacted the epoxy curing agents 4,4‐diaminodiphenylmethane and tris(4‐aminophenyl)amine with the multiply hydrogen‐bonding reactive modifiers and epoxy monomers. The introduction of the DOPO segment, strongly hydrogen bonding malonamide linkages, and hard aromatic groups into the backbones of the synthesized reactive modifiers resulted in epoxy networks exhibiting tailorable crosslinking densities, flexibilities, glass transition temperatures, thermal decomposition temperatures, and flame retardancies. Furthermore, dynamic mechanical analyses indicated that intermolecular hydrogen bonding of these reactive modifiers enhanced the thermal and physical properties of their epoxy resins through the formation of unique pseudocrosslinked polymer networks. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of rosin‐based imidoamine‐type curing agents and curing behavior with epoxy resin

Rosin is an abundantly available natural product. The characteristic fused ring structure of rosin acids is analogous to that of some aromatic compounds in rigidity, and makes rosin and its derivatives potential substitutes for those aromatic compounds. In the study reported, the synthesis of biobased curing agents containing imide structure using rosin and the cure reaction were investigated. Rosin‐based imidoamine‐type curing agents were synthesized, and the chemical structure was confirmed using ¹H NMR, Fourier transform infrared and electrospray ionization spectroscopy. The curing behavior with diglycidyl ether of bisphenol A epoxy was studied using differential scanning calorimetry. The thermal mechanical properties and thermal stability of the cured epoxy resins were evaluated using dynamic mechanical analysis and thermogravimetry, respectively. The results indicate that the curing behavior of the rosin‐based curing agents is similar to that of curing agents with analogous structures. Cured products have good thermal stability due to the presence of the imide group and the bulky hydrogenated phenanthrene ring structure. Rosin acids have a great potential in the synthesis of epoxy curing agents as replacements for some of the current commercial aromatic or cycloaliphatic analogues. Copyright © 2010 Society of Chemical Industry     

An epoxy‐ended hyperbranched polymer as a new modifier for toughening and reinforcing in epoxy resin

A new epoxy‐ended hyperbranched polyether (HBPEE) with aromatic skeletons was synthesized through one‐step proton transfer polymerization. The structure of HBPEE was confirmed by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR) measurements. It was proved to be one high efficient modifier in toughening and reinforcing epoxy matrix. In particular, unlike most other hyperbranched modifiers, the glass transition temperature (T_g) was also increased. Compared with the neat DGEBA, the hybrid curing systems showed excellent balanced mechanical properties at 5 wt % HBPEE loading. The great improvements were attributed to the increased cross‐linking density, rigid skeletons, and the molecule‐scale cavities brought by the reactive HBPEE, which were confirmed by dynamical mechanical analysis (DMA) and thermal mechanical analysis (TMA). Furthermore, because of the reactivity of HBPEE, the hybrids inclined to form a homogenous system after the curing. DMA and scanning electron microscopy (SEM) results revealed that no phase separation occurred in the DGEBA/HBPEE hybrids after the introduction of reactive HBPEE. SEM also confirmed that the addition of HBPEE could enhance the toughness of epoxy materials as evident from fibril formation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1064‐1073, 2013     

双(4-胺基苯基)-苯基磷酸酯的合成及其性能研究

以对硝基苯酚和苯基二氯磷酸酯为原料,采用两步法合成了双(4-胺基苯基)-苯基磷酸酯(BAPP)含磷二胺固化剂,用红外光谱法对合成产物进行了分析和表征。固化反应动力学分析表明,BAPP与环氧树脂的反应活性较DDM的反应活性略高。BAPP与环氧树脂的固化产物热失重分析表明,在低温区主要是有机磷化合物的分解,在高温区主要是基体主链的断裂;与DDM的环氧固化产物相比较,BAPP与环氧树脂的固化产物有较高的成炭率,极限氧指数(LOI)为34,BAPP对固化产物的玻璃化温度影响不大。     

Preparation,curing properties,and phase morphology of epoxy‐novolac resin/multiepoxy‐terminated low‐molecular‐weight poly(phenylene oxide) blend

The multiepoxy‐terminated low‐molecular‐weight poly (phenylene oxide) (PPOE) was synthesized by modifying the terminal hydroxyl group of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) with epoxy‐novolac resin (EPN). The curing kinetics, phase morphology, and thermal stability of the cured EPN/PPOE blends were investigated and compared to the unmodified EPN/PPO and EPN/EPPO (epichlorohydrin‐modified PPO) blends. As revealed by the Fourier transform infrared and differential scanning calorimetry analyses, PPOE took part in the curing reaction and formed a crosslinked structure with EPN. The curing rate of EPN/PPOE blends first increased and then decreased with the increase of PPOE fraction. PPOE had both catalytic and steric hindrance effects on the curing reaction. EPN/PPOE blends showed faster curing rate and higher degree of curing than the corresponding EPN/PPO and EPN/EPPO blends. The reactive blending improved the dispersion of PPOE in EPN matrix and the thermal stability of the blend. POLYM. ENG. SCI., 54:2595–2604, 2014. © 2013 Society of Plastics Engineers     

FT‐IR studies on the curing behavior of polycardanol from naturally renewable resources

In the present study, the curing behavior of polycardanol prepared by enzymatic oxidative polymerization of thermally treated cashew nut shell liquid, which can be available from naturally renewable resources, was explored in the presence of methyl ethyl ketone peroxide (MEKP) and cobalt naphthenate (Co‐Naph). The curing behavior was monitored varying Co‐Naph concentration and curing temperature by means of Fourier transform infrared (FT‐IR) spectroscopy. The result revealed that the characteristic absorption bands were significantly affected by the given curing condition, resulting mainly from the unsaturated moiety in the polycardanol molecule. The extent of curing of polycardanol strongly depended on curing temperature, showing a typically sigmoidal curve reaching almost 1.0 upon processing at 200°C for 120 min. The thermal curing conditions for preparing polycardanol with an optimal state of cure were provided in the work. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Miscibility and mechanical properties of an amine‐cured epoxy resin blended with poly(ethylene oxide)

Blends composed of diaminodiphenylmethane bisphenol‐A epoxy resin and poly(ethylene oxide) (PEO) were prepared via in situ curing reaction of epoxy in the presence of PEO. The miscibility of the blends before and after curing was established by thermal (differential scanning calorimetry, DSC), microstructural (atomic force microscopy) and dynamic mechanical analysis. Fourier transform infrared spectroscopy indicated that the OH groups developed through cure reactions interact by hydrogen bonding with PEO. After crystallinity analysis by DSC, the interaction parameter was determined through the depression of the equilibrium melting temperature. Mechanical properties of the miscible blends do not show any significant change, although improvement of fracture toughness has been observed with respect to the matrix properties. Copyright © 2006 Society of Chemical Industry     

Synthesis and curing properties of a novel curing agent based on N‐(4‐hydroxyphenyl) maleimide and dicyclopentadiene moieties

A new type of epoxy resin curing agent, containing pendant phenol functions, was synthesized by the free‐radical copolymerization of N‐(4‐hydroxyphenyl) maleimide with dicyclopentadiene (DCPD) monomer in the presence of a radical initiator. The chemical structure was characterized with Fourier transform infrared spectroscopy and nuclear magnetic resonance. The molecular weight of the new curing agent was determined by gel permeation chromatography. The activity and activation energy of this new curing agent with o‐cresol formaldehyde novolac epoxy (CNE) was investigated with a nonisothermal differential scanning calorimetry technique at different heating rates. The thermal properties of the cured polymers were evaluated with thermogravimetric analysis, and the results exhibit good thermal stability. In addition, this new curing agent with CNE showed low moisture absorption because of the hydrophobic nature of the DCPD structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011