Study of cure kinetics of epoxy-silica organic-inorganic hybrid materials

Cure kinetics of organic-inorganic hybrids based on epoxy resin was investigated, using differential scanning calorimetry (DSC). Thermoset hybrid materials were prepared from diglycidyl ether of bisphenol A (DGEBA) as organic precursor, and 3-glycidyloxypropyltrimethoxysilane (GLYMO) as inorganic precursor. Precursors were polymerised simultaneously using poly(oxypropylene)diamine (Jeffamine D230) as a curing agent. Isothermal DSC characterisation of DGEBA/Jeffamine system and two hybrid DGEBA/GLYMO/Jeffamine systems, with DGEBA and GLYMO mixed in mass ratios of 2:1 and 1:1, respectively, was performed at different temperatures. Applicability of empirical models, commonly used to describe the curing kinetics of thermosets, to hybrid systems was investigated, and the resulting parameters were tested on dynamic DSC scans. Additionally, prepared materials were studied by FTIR and the extraction in tetrahydrofuran. The presence of inorganic phase was found to hinder complete cross-linking of organic phase and influence the kinetics of cure.     

Thermal degradation of epoxy-silica organic-inorganic hybrid materials

Degradation kinetics of organic-inorganic hybrid materials based on epoxy resin were investigated by thermogravimetric analysis (TGA). The hybrid materials were prepared from diglycidyl ether of bisphenol A (DGEBA) and 3-glycidyloxypropyltrimethoxysilane (GLYMO) polymerised simultaneously by poly(oxypropylene)diamine (Jeffamine D230). Nanometric level of homogeneity in the hybrids was verified by electron microscopy. Energy of activation of degradation for the hybrids with varying inorganic content, as well as for the unmodified epoxy-amine system, was determined by the isoconversional Kissinger-Akahira-Sunose method, and was found to be significantly higher for the hybrid materials than for the unmodified epoxy-amine system. The degradation process was described by empirical kinetic models. The results indicated that presence of the inorganic network influences the mechanism of degradation of organic phase. Greater thermal stability of hybrid materials was confirmed by other parameters obtained from TGA curves.     

Layered silicate/epoxy nanocomposites: synthesis,characterization and properties

Novel epoxy‐clay nanocomposites have been prepared by epoxy and organoclays. Polyoxypropylene triamine (Jeffamine T‐403), primary polyethertriamine (Jeffamine T‐5000) and three types of polyoxypropylene diamine (Jeffamine D‐230, D‐400, D‐2000) with different molecular weight were used to treat Na‐montmorillonite (MMT) to form organoclays. The preparation involves the ion exchange of Na⁺ in MMT with the organic ammonium group in Jeffamine compounds. X‐ray diffraction (XRD) confirms the intercalation of these organic moieties to form Jeffamine‐MMT intercalates. Jeffamine D‐230 was used as a swelling agent for the organoclay and curing agent. It was established that the d₀₀₁ spacing of MMT in epoxy‐clay nanocomposites depends on the silicate modification. Although XRD data did not show any apparent order of the clay layers in the T5000‐MMT/epoxy nanocomposite, transmission electron microscopy (TEM) revealed the presence of multiplets with an average size of 5 nm and the average spacing between multiplets falls in the range of 100 Å. The multiplets clustered into mineral rich domains with an average size of 140 nm. Scanning electron microscopy (SEM) reveals the absence of mineral aggregate. Nanocomposites exhibit significant increase in thermal stability in comparison to the original epoxy. The effect of the organoclay on the hardness and toughness properties of crosslinked polymer matrix was studied. The hardness of all the resulting materials was enhanced with the inclusion of organoclay. A three‐fold increase in the energy required for breaking the test specimen was found for T5000‐MMT/epoxy containing 7 wt% of organoclay as compared to that of pure epoxy. Copyright © 2004 John Wiley & Sons, Ltd.     

DSC study of cure kinetics of DGEBA-based epoxy resin with poly(oxypropylene) diamine

Summary A kinetic study of cure kinetics of epoxy resin based on a diglycidyl ether of bisphenol A (DGEBA), with poly(oxypropylene) diamine (Jeffamine D230) as a curing agent, was performed by means of differential scanning calorimetry (DSC). Isothermal and dynamic DSC characterizations of stoichiometric and sub-stoichiometric mixtures were performed. The kinetics of cure was described successfully by empirical models in wide temperature range. System with sub-stoichiometric content of amine showed evidence of two separate reactions, second of which was presumed to be etherification reaction. Catalytic influence of hydroxyl groups formed by epoxy-amine addition was determined.     

Synthesis and characterization of an epoxy based thermoset containing a fluorinated thermoplastic

A novel fluorinated thermoplastic (FT) was synthesized from diglycidyl ether of bisphenol A (DGEBA), and 3‐(trifluoromethyl)aniline. FT was found to be miscible with DGEBA as shown by the existence of a single glass transition temperature (T_g) within the whole composition range. On the basis of several experimental techniques, it was found that upon heating etherification reaction takes place between FT and DGEBA. A DGEBA‐aromatic diamine (4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) formulation was modified with the FT. The influence of FT on the epoxy‐amine kinetics was investigated. Both structural parameters, gelation, and vitrification, were found to be affected by etherification reaction between epoxy and hydroxyls groups belonging to FT. The presence of ether linkages induced system stoichiometry modification. In addition, the curing conditions influence on FT migration towards the surface was studied on samples prepared with 20 wt % of modifier. SEM–EDX analysis confirmed that modified systems exhibits notable fluorine enrichment within the uppermost 200 μm. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2781–2792, 2007     

Kinetic studies of the polymerization of an epoxy resin modified with rhodamine B

Novel fluorescent materials were satisfactorily synthesized. With this aim, an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) was reacted with a laser dye, rhodamine B (RB), to achieve an epoxy-based prepolymer. Then, a diamine, m-xylylenediamine (MXDA), was used as hardener with the purpose of obtaining a crosslinked polymer. The curing conditions strongly influence the intended final properties and the optimization of the curing requires a reliable kinetic model. For that reason, this work presents the kinetic study of the polymerization of the epoxy resin by differential scanning calorimetry (DSC) in isothermal mode as well as by Fourier transform infrared spectroscopy (FTIR). DSC data were fitted using a Kamal autocatalytic equation. Conversion as a function of reaction time curves obtained by means of both techniques agreed well. In addition, the synthesized epoxy-based materials were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR) and their fluorescent properties were also analysed.     

Conductivity of crosslinked low surface energy epoxy coatings

A new and straightforward method has been studied to prepare crosslinked low surface energy semiconductive epoxy coatings. The low surface energy is obtained by adding a small amount of partially fluorinated bifunctional primary amine Jeffamine D230 crosslinker and the conductivity is achieved by adding a small amount of semiconductive nanosized Cobalt(III) phthalocyanine particles. The use of partially fluorinated crosslinker strongly influences the conductivity, the conductive particle network structure, and the network distribution in the coatings. Compared to coatings that are free of fluorine, variations in fractal dimension, percolation threshold, particle‐containing layer thickness, and conductivity level are observed as the amount of fluorinated species is varied. These differences can be explained by (local) differences in effective Hamaker constant, viscosity, curing rate, evaporation of the solvent, and presence or absence of polymer matrix between the particles in the network. Our results suggest that other crosslinked semiconductive low surface energy epoxy coatings can be realized in a similar manner, but careful optimization of processing conditions is required to obtain the desired conductivity levels at low filler concentration. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Chem 47: 366–380, 2009     

含亚胺结构新型磷-氮协效阻燃化合物的合成及对环氧树脂的阻燃作用

采用醛胺缩合反应,以4-(5,5-二甲基-1,3-二氧杂环己内磷酰基)苯甲醛(PCHO)分别与对苯二胺、乙二胺反应合成两种磷酸酯-亚胺双官能化合物阻燃剂(FR:N¹,N⁴-二[4-(5,5-二甲基-1,3-二氧杂环己内磷酰氧基)苯基亚甲基]-1,4-苯二胺(PNB)和N¹,N²-二[4-(5,5-二甲基-1,3-二氧杂环己内磷酰氧基)苯基亚甲基]-1,2-乙二胺(PNE)),研究了FR对4,4'-二氨基二苯砜(DDS)固化双酚A二缩水甘油醚型环氧树脂(DGEBA)体系的阻燃作用及阻燃机理。 研究发现FR的引入显著提高了DGEBA/DDS在700 ℃时的残炭率(R_c),同时提升了材料的阻燃性能,其中以乙二胺合成的PNE阻燃性能显著优于以苯二胺合成的PNB。 当磷添加质量分数为1.5%时,PNE-1.5/DGEBA/DDS在N₂气下的R_c为35.1%,在空气下的R_c为14.4%,极限氧指数(LOI)为33.2%,并可达阻燃等级UL-94最高阻燃级别V-0级。 同时,PNE-1.5/DGEBA/DDS相较于DGEBA/DDS保持了弯曲强度和76%以上的冲击强度,机械性能显著优于PNB-1.5/DGEBA/DDS。 通过阻燃机理分析FR在DGEBA/DDS体系中具有凝聚相、气相及磷-氮协效共同作用的阻燃特点。 磷酸酯-亚胺双官能团化合物FR对环氧树脂体系具有良好的阻燃作用,其中PNE阻燃效率高、机械性能负面影响小,具有潜在应用价值。     

DGEBA monomer as a solvent for syndiotactic polystyrene

Syndiotactic polystyrene (sPS) has to be processed at high temperatures (i.e. >290°C due to its melting point of 270°C), which approaches its degradation temperature. We aim to facilitate the processing of sPS by lowering its melt temperature and viscosity with a curable epoxy/amine model system as reactive solvent, which will result in a thermoplastic-thermoset polymer blend. As a first step we therefore investigated the melting behaviour of sPS in epoxy monomer, established its phase diagram, and investigated the crystalline form of sPS in these mixtures. DGEBA epoxy monomer is found to be a solvent for syndiotactic polystyrene at temperatures above 220°C. The DGEBA-sPS phase diagram was established by means of DSC, on the basis of crystallization and melting peaks. The form of the curve in the phase diagram indicates that DGEBA is a poor solvent for sPS. In WAXS studies of blends only the β crystalline form was detected, not the δ form, thus no sPS-DGEBA polymer-solvent compounds (clathrates) were detected. However, DGEBA can still serve as a monomer for improved processing as it depresses the crystallization temperature by 20 to 60 K upon addition of 20 to 90 wt% DGEBA respectively, while a 16 to 45 K melting peak depression can be observed by adding 20 to 90 wt% DGEBA.     

Evaluation of furfurylamines as curing agents for epoxy resins

Epoxy resin adhesives are widely used because of their strength, versatility, and ability to bond a variety of substrates. Furfurylamines represent a potential, new class of epoxy curing agents. Furfuryl amine (FA), tetrahydrofurfuryl amine (THFA), and 5,5′-methylenebis-2-furanmethanamine (DFA) were studied as possible epoxy curing agents. The utility of FA and THFA are limited by their volatility at the temperatures needed to effect cure of diglycidyl-ether of bisphenol A (DGEBA) based epoxy resins. DFA is a very effective epoxy curing agent with the ability to cure DGEBA at rates similar to that of standard epoxy curing agents such as liethylenetriamine.     

Synthesis and characterization of novel fluorinated polyimides derived from 4-phenyl-2,6-bis[4-(4′-amino-2′-trifluoromethyl-phenoxy)phenyl]pyridine and dianhydrides

A series of organo-soluble polyimides were prepared from a novel fluorinated diamine monomer, 4-phenyl-2,6-bis[4-(4′-amino-2′-trifluoromethylphenoxy)phenyl]pyridine and various commercial aromatic dianhydrides. These polyimides had good solubility in common organic solvents. The obtained strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 561 °C and the glass transition temperature in the range of 258-312 °C. Moreover, the polymer films showed good electrical insulating property, low dielectric constant and low water uptake due to the introduction of fluorinated substitutes in the polymer backbone. The remarkable combined features ensure these polymers to be ideal candidate materials for advanced microelectronic industry and other related applications.     

Cure behavior and thermal degradation mechanisms of epoxy and epoxy–cyanate resins

The cure reactions of tetraglycidyl methylene diamine (TGMDA) epoxy cured with tetrasubstituted aromatic diamine on one hand and diglycidyl ether of bisphenol A and diglycicyl ether tetrabromobisphenol A epoxies cured with methylene bis (phenyl‐4‐cyanate) on the other hand are reported. Systematic Fourier transform infrared (FTIR) spectroscopy studies of the cure reaction of epoxy and epoxy–cyanate during thermal cycles are presented. FTIR studies indicate that the reaction of TGMDA monomer is total but the network contains a large amount of primary amine. The cyanate monomer reacts rapidly to form triazine structures. Then the epoxy monomers homopolymerize and crosslink with free cyanate groups. The gas chromatography/mass spectrometry study of volatile products evolved during the polymer thermal degradation shows the dehydration of the epoxy network and the decomposition of the amine structure. The FTIR and solid‐phase ¹³C nuclear magnetic resonance analysis revealed that the ether functions and the amine groups are temperature sensitive but the triazine structure is not. Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesis and characterization of liquid‐crystalline epoxy and its blend with conventional epoxy

Terephthaloyl chloride was reacted with 4‐hydroxy benzoic acid to get terephthaloylbis(4‐oxybenzoic) acid, which was characterized and further reacted with epoxy resin [diglycidyl ether of bisphenol A (DGEBA)] to get a liquid‐crystalline epoxy resin (LCEP). This LCEP was characterized by Fourier transform infrared spectrometry, ¹H and ¹³C NMR spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). LCEP was then blended in various compositions with DGEBA and cured with a room temperature curing hardener. The cured blends were characterized by DSC and dynamic mechanical analysis (DMA) for their thermal and viscoelastic properties. The cured blends exhibited higher storage moduli and lower glass‐transition temperatures (tan δ_max, from DMA) as compared with that of the pure DGEBA network. The formation of a smectic liquid‐crystalline phase was observed by POM during the curing of LCEP and DGEBA/LCEP blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3375–3383, 2003     

A modifier that enables the easy dispersion of alkyl-coated nanoparticles in an epoxy network

Nanoparticles (NPs) coated with alkyl chains cannot be dissolved in diglycidylether of bisphenol A (DGEBA), which is a typical monomer used in the synthesis of epoxy networks. We show that adding small amounts of the linear amphiphilic polymer obtained by reaction of DGEBA with dodecylamine, produced a stable dispersion of dodecanethiol-coated gold NPs in DGEBA. The anionic homopolymerization of this blend initiated by a tertiary amine led to a nanocomposite with a uniform dispersion of gold NPs. The selected crosslinking chemistry allowed covalent bonding of the modifier to the matrix, avoiding phase separation and enabling easy tuning of the thermal properties of the matrix.     

Facile fabrication of fast recyclable and multiple self‐healing epoxy materials through diels‐alder adduct cross‐linker

A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2094–2103     

Influence of chromophore concentration and network structure on the photo‐orientation properties of crosslinked epoxy‐based azopolymers

An azo prepolymer (TAZ) was synthesized by reaction between Disperse Orange‐3 (DO3) and diglycidyl ether of bisphenol A (DGEBA). Selected amounts of TAZ were blended with DGEBA and cured with an aliphatic diamine, either meta‐xilylenediamine (MXDA) or polyetheramines (Jeffamine D series). The photoinduced anisotropy and optical storage properties in two series of crosslinked epoxy‐based azo polymers with different architectures and chromophore contents (from 3 to 24 in weight) have been investigated. Measurements of the birefringence (Δn) induced with linearly polarized 488 nm light show that the Δn values increases with DO3 weight fraction. Networks with the same chromophore concentration but different backbones exhibit similar levels of induced anisotropy under the same irradiation conditions. The remaining birefringence and relaxation times are influenced by the molecular weight between crosslinks of networks. Higher is reflected in shorter relaxation times and lower remaining birefringence. In terms of the level of induced dichroism measured on relaxed films, it was found an agreement with the remaining anisotropy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1004–1014, 2009     

Polymers from siloxane-containing epoxides

The synthesis and polymerization of seven epoxy polymer precursors which contained the siloxane linkage in varying structural arrangements was carried out. The polymers prepared from such precursors have utility as embedding compounds for electrical circuits. Polymerization of these epoxy intermediates with siloxane-containing diamines resulted in solid, thermosetting materials for which dielectric data were obtained. Dielectric constants of 3.1 were measured at 1 keps for polymers prepared by polymerization of 1,9-bis[p-(2,3-epoxypropyl)phenyl]decamethylpentasiloxane with 1,3-bis(p-am-inophenoxy)tetramethyldisiloxane, whereas polymers derived from 1,4-bis{[p-(2,3-epoxypropyl)phenyldimethylsiloxy]dimethylsilyl}benzene and the same diamine were characterized by slightly higher dielectric constants and a high degree of toughness, being nonbrittle at ?50°C.     

Morphology, flexural, and thermal properties of sepiolite modified epoxy resins with different curing agents

A bisphenol A-based epoxy resin was modified with 5 wt% organically modified sepiolite (Pangel B40) and thermally cured using two different curing agents: an aliphatic diamine (Jeffamine D230, D230) and a cycloaliphatic diamine (3DCM). The morphology of the cured materials was established by scanning and transmission electron microscopy analysis. The thermal stability, thermo-mechanical properties, and flexural behaviour of the sepiolite-modified matrices were evaluated and compared with the corresponding neat matrix. The initial thermal decomposition temperature did not change with the addition of sepiolite. The flexural modulus of the epoxy matrix slightly increases by the incorporation of the organophilic sepiolite. The flexural strength of the sepiolite modified resin cured with D230 increased by a 10% while the sepiolite modified resin cured with 3DCM resulted in a lower flexural strength compared with the unmodified resin. The reduced flexural strength was attributed to the stress concentrations caused by the sepiolite modifier, which rendered the resins more brittle.     

Epoxy as a reactive plasticizer for improving polycarbonate processibility

An oligomer of a diepoxy (diglycidyl ether of bisphenol-A, DGEBA) and an aromatic diamine (MCDEA) have been used as reactive plasticizers for polycarbonate (PC). A small amount of PC chain scission occurred during this blending process, probably due to transesterification of the PC carbonate group by the hydroxyl group of the DGEBA oligomer. Addition of DGEBA to PC was found to greatly reduce the T_g and processing temperature. Dynamic rheology measurements showed that the added epoxy can very effectively reduce the viscosity, but that the addition of epoxy also accelerated the crystallisation rate of the PC, which was confirmed by XRD, optical transmission microscopy and DMTA. The DMTA results of cured blends also showed that this crystallization of the PC enhanced their heat resistance properties. Sol–gel studies of the cured samples showed that some of the PC was grafted to the crosslinked epoxy network. Studies of the rubbery behaviour, solvent resistance of the cured blend and SEM images suggest that PC is the main continuous phase in the matrix and that the epoxy phase is mainly dispersed as sub-micron particles in the matrix.     

Curing and thermal behaviour of diamide–diimide–diamines based on l-phenylalanine with epoxy blends containing phosphorus/silicon

A series of diamide?Cdiimide?Cdiamines (DADIDAs) were synthesized by reacting diacid N,N??-(3,3??,4,4??-benzophenone tetracarboxylic)-3,3??4,4?? diimido-bis-l-phenylalanine (I) with different aromatic diamines viz. 1,4-phenylene diamine (PD), 1,5-diamino naphthalene (N), 4,4??-(9-fluorenyllidene)-dianiline (F), 4,4??-diaminodiphenyl sulphide (DS) and 3,4??-oxydianiline (O). The diacid (I) was synthesized by the condensation of 3,3??,4,4??-benzophenone tetracarboxylic dianhydride (BTDA) with l-phenylalanine (PA) in a solution of glacial acetic acid and pyridine (3:2 v/v) at refluxing temperature. The resulting DADIDAs so synthesized were characterized with the help of elemental analysis (EA) and spectroscopic techniques, and were used as epoxy curing agents. Two epoxy blends (EP and ES) were prepared, each by mixing in an equivalent ratio of 2:3 of tris(glycidyloxy)phosphine oxide (TGPO) with diglycidyl ether of bisphenol-A (DGEBA) and 1,3-bis(3-glycidyloxypropyl)tetramethyl disiloxane (BGPTMSO) with diglycidyl ether of bisphenol-A (DGEBA), respectively. A series of new epoxy thermosets with good thermal stability were prepared by reacting EP/ES with synthesized DADIDAs stoichiometrically. Thermal properties of these epoxy resins were observed using the techniques viz. Differential scanning calorimeter (DSC) for curing behaviour and Thermogravimetric analysis (TGA) to study the thermal stability and mass loss behaviour. All the samples showed good thermal stabilities in terms of char yield (24.8?C52.7) and calculated LOI (27.4?C38.6), thereby demonstrate their effective use as flame retardant systems.