Morphology and dielectric properties of an epoxy network modified by end‐functionalized liquid polybutadiene

Epoxy resin networks modified with different functionalized liquid polybutadiene were characterized by scanning electron microscopy, atomic force microscopy (AFM), and dielectric thermal analysis techniques. Different morphologies were observed for these different systems, which were attributed to different interaction degrees between the components. Hydroxyl‐terminated polybutadiene (HTPB) and carboxyl‐ terminated polybutadiene (CTPB) resulted in epoxy networks with two‐phase morphology that differed in rubber particle size. The use of isocyanate‐terminated polybutadiene (NCOTPB) resulted in transparent thermoset material, whose rubber domains were in the nanoscale dimension, only detected by the AFM technique. The different morphological aspects in these epoxy systems also affected the dielectric properties. The epoxy–HTPB network exhibited two low temperature relaxation peaks corresponding to two different phases present in the system, whereas the epoxy–CTPB or epoxy–NCOTPB systems, whose rubber particles are well adhered to the epoxy matrix by chemical bonds, displayed only one single low temperature relaxation peak. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4053–4062, 2004     

Flame‐retardant epoxy resins with high glass‐transition temperatures from a novel trifunctional curing agent: Dopotriol

A novel phosphorus‐containing trifunctional novolac (dopotriol) was synthesized through the addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide and rosolic acid. The structure of dopotriol was confirmed with NMR spectroscopy and elemental analyses. The dopotriol was blended with phenol novolac in the ratios of 10/0, 8/2, 6/4, 4/6, 2/8, and 0/10 to serve as a curing agent for diglycidyl ether of bisphenol A. Thermal properties, such as the glass‐transition temperature, thermal decomposition temperature, and flame retardancy, moisture absorption, and dielectric properties of the cured epoxy resins were evaluated. The activity and activation energy of curing were studied with the methods of Kissinger and Ozawa by dynamic differential scanning calorimetry scans. The glass‐transition temperatures of the cured epoxy resins were 138–159 °C, increasing with the phosphorus content. This is rarely seen in the literature after the addition of a flame‐retardant element. The flame retardancy increased with the phosphorus content, and a UL‐94 V‐0 grade was achieved with a phosphorus content of 1.87%. Similar dielectric properties and moisture absorption were observed for these phosphorus‐containing epoxy resins, and this implied that the addition of phosphorus to epoxy did not affect the dielectric properties and moisture absorption. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2862–2873, 2005     

Thermomechanical properties of liquid‐crystalline epoxy networks arranged by a magnetic field

During the curing process of a liquid‐crystalline epoxy resin, a relatively strong magnetic field was applied, and the thermomechanical properties of the cured resin were investigated. The network orientation and mechanical properties of the cured system were evaluated with wide‐angle X‐ray diffraction, dynamic mechanical analysis, and fracture toughness testing. The cured system was found to have an anisotropic network structure, which arranged along the applied field, and the anisotropy was reflected in the thermomechanical properties. In particular, the fracture toughness of the system dramatically increased when the network chains were arranged across the direction of the crack propagation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 758–765, 2004     

New powder coatings with low curing temperature and enhanced mechanical properties obtained from DGEBA epoxy resins and Meldrum acid using erbium triflate as curing agent

New low curing temperature powder coatings obtained by copolymerization of epoxy resins with Meldrum acid (MA) initiated by erbium (III) trifluoromethanesulfonate have been formulated. Their mechanical and thermomechanical properties have been studied and compared with a commonly used industrial system (o-tolylbiguanide/epoxy resin) and with an already formulated epoxy powder coating homopolymerized by erbium trifluoromethanesulfonate. Systems containing low proportions of MA and initiated by erbium trifluoromethanesulfonate lead to a great reduction of curing conditions (temperature/time). Moreover, the new formulated systems present very good mechanical properties, adhesion, and impact resistance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2316–2327, 2007     

Preparation and properties of epoxy/amine hybrid resins from in situ polymerization

Homogeneous and transparent epoxy/amine hybrid resins were successfully obtained through the in situ curing of bisphenol A epoxy and hexakis(methoxymethyl)melamine with 2 wt % (3‐glycidoxypropyl)trimethoxysilane as a facial coupling agent. The hybrid resins showed good miscibility, high glass‐transition temperatures, good thermooxidative stability, and good flame retardance. The outstanding properties of the hybrid resins may lead to their use in high‐performance green electronic products. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1868–1875, 2004     

A dismantlable photoadhesion system fabricated by an anionic UV curing of epoxy resins with a base amplifier having a disulfide bond

A base amplifier (BA) that autocatalytically generates a diamine having a disulfide bond has been developed. Diamines generated from this BA are integrated into cross‐linked networks of epoxy resins that also have disulfide bonds. Anionic UV curing is performed using a photobase generator, the BA and the epoxy resins, and cured films are obtained after UV irradiation and subsequent heating at 160 °C. Furthermore, this curing system is applied successfully to adhesion of two stainless substrates, which is cancelled with gentle heating and a shear force. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 237–241     

Curing of liquid crystalline epoxy resins with a biguanide

This work extends the authors' investigations on liquid crystalline epoxy resins prepared from diglycidyl ether of 4,4′-dihydroxybiphenyl (DGE-DHBP) and aliphatic dicarboxylic compounds (ADC) or difunctional aromatic compounds. Syntheses and properties of these liquid crystalline epoxy resins are described elsewhere. In this paper a study on the curing reaction of the above mentioned liquid crystalline epoxy resins is presented. Ortho-tolylbiguanide was applied as the curing agent. The curing reactions were investigated by differential scanning calorimetry, microscopic observations and IR spectroscopy. Depending upon the temperature program of curing, it was possible to obtain polymeric networks with liquid crystalline order. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2739–2745, 1997     

Fracture toughening of epoxy matrices with blends of resins of different molecular weights and other modifiers

The microstructure and fracture behavior of epoxy mixtures containing two monomers of different molecular weights were studied. The variation of the fracture toughness by the addition of other modifiers was also investigated. Several amounts of high‐molecular‐weight diglycidyl ether of bisphenol A (DGEBA) oligomer were added to a nearly pure DGEBA monomer. The mixtures were cured with an aromatic amine, showing phase separation after curing. The curing behavior of the epoxy mixtures was investigated with thermal measurements. A significant enhancement of the fracture toughness was accompanied by slight increases in both the rigidity and strength of the mixtures that corresponded to the content of the high‐molecular‐weight epoxy resin. Dynamic mechanical and atomic force microscopy measurements indicated that the generated two‐phase morphology was a function of the content of the epoxy resin added. The influence of the addition of an oligomer or a thermoplastic on the morphologies and mechanical properties of both epoxy‐containing mixtures was also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3920–3933, 2004     

Radical induced cationic frontal polymerization as a versatile tool for epoxy curing and composite production

Radical induced cationic frontal polymerization (RICFP) is an extremely powerful and elegant alternative curing technique that allows cationic bulk curing of epoxy resins with very little energy consumption, as well as curing in compartments that are not readily accessible. We recently introduced a bisphenol‐A diglycidylether (BADGE) based system that allows the bubble‐free photocuring of this widely used epoxy resin. In this article, we describe the high storage stability and possibilities to influence the curing speed via the initiator concentrations of different formulations. These properties allow the adjustment of the frontal polymerization to ones need. We also show that the (thermo)mechanical and electrical properties of frontal cured epoxy polymers compares favorably with those of state of the art material. Finally, different strategies to overcome the challenges on producing epoxy resin based mica composites via RICFP are presented. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3751–3759     

Low dielectric thermoset. IV. Synthesis and properties of a dipentene‐containing cyanate ester and its copolymerization with bisphenol A dicyanate ester

A 2,6‐dimethylphenol‐dipentene dicyanate ester ( DPCY ) was synthesized from the reaction of 2,6‐dimethylphenol‐dipentene adduct and cyanogen bromide. The proposed structure was confirmed by Fourier transform infrared (FTIR), elemental analysis, mass, and nuclear magnetic resonance (NMR) spectra. DPCY was then cured by itself or cured with bisphenol A dicyanate ester ( BADCY ). Thermal properties of cured epoxy resins were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermogravimetric analysis (TGA). These data are compared with those of BADCY . The cured DPCY exhibits a lower dielectric constant (2.61 at 1 MHz), dissipation factor (29.3 mU at 1 MHz), thermal stability (5% degradation temperature and char yield are 429 °C and 17.64%, respectively), glass transition temperature (246 °C by TMA and 258 °C by DMA), coefficient of thermal expansion (33.6 ppm before Tg and 134.1 ppm after Tg), and moisture absorption (0.95% at 48 h) than those of BADCY , but higher moduli (5.12 GPa at 150 °C and 4.60 GPa at 150 °C) than those of the bisphenol A system. The properties of cured cocyanate esters lie between cured BADCY and DPCY , except for moduli. Moduli of some cocyanate esters are even higher than those of cured BADCY and DPCY . A positive deviation from the Fox equation was observed for cocyanate esters. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3986–3995, 2004     

Preparation and thermomechanical properties of epoxy resins modified by octafunctional cubic silsesquioxane epoxides

The thermomechanical properties of octafunctional cubic silsesquioxane‐modified epoxy resins associated with dicycloaliphatic hardener (4,4′‐dimethyldiaminodicyclo hexyl methane) were studied using thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. The structures of epoxy resin containing cubic silsesquioxane epoxides were characterized by Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering techniques. In this work, octa(dimethylsiloxybutylepoxide) octasilsesquioxane (OB), and octa(glycidyldimethyl‐siloxyepoxide) octasilsesquioxane (OG), were synthesized and used as additives to improve the properties of a commercial epoxy resin by exploring the effects of varying the ratio of OB or OG. The commercial Ciba epoxy resin (Araldite LY5210/HY2954) was used as a standard. It was found, by thermogravimetric analysis and dynamic mechanical analysis, that the highest thermal stability was observed at N = 0.5 (N = number of amine groups/number of epoxy rings). No glass transition temperature was observed by adding 20 mol % OB to the Ciba epoxy resin, indicating the reduction of chain motion in the presence of octafunctional cubic silsesquioxane epoxide. The storage modulus of the OB‐modified epoxy resin also increased, especially at higher temperatures, compared with the Ciba epoxy resin under identical curing conditions. Fourier transform infrared data elucidated the preservation of cubic silsesquioxane structure after curing at high temperature. In contrast, the OG/Araldite LY5210/HY2954 systems gave poorer thermomechanical properties. The low viscosity of OB at room temperature (～ 350 cPs) makes it suitable for composite processing and, when used in conjunction with the Ciba epoxy, lowers the viscosity of this system as well. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3490–3503, 2004     

Novel urethane/epoxy resin hybrid materials using a moisture‐curing system

Novel curing systems of a urethane/epoxy resin [diglycidyl ether of bisphenol A (DGEBA)] alloy using the moisture‐latent hardener ketimine (K‐systems) were investigated on the DGEBA‐rich side and were compared with aromatic diamine curing systems (A‐systems). Almost all the added DGEBA was separated from the polyurethane matrix and dispersed as 2–10‐μm‐diameter particles after curing in the A‐systems. Therefore, DGEBA did not act as a reinforcing agent for the polyurethane matrix. However, 50% of the added DGEBA was dispersed as particles with a diameter of 1–4 μm, and the other 50% was incorporated into the polyurethane matrix in the novel K‐systems. Therefore, the polyurethane matrix in the K‐systems should be reinforced effectively by both incorporated and finely dispersed DGEBA and should result in significant improvements in the stress–strain properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1137–1144, 2004     

Glass transition and relaxation behavior of epoxy nanocomposites

With advances in nanoscience and nanotechnology, there is increasing interest in polymer nanocomposites, both in scientific research and for engineering applications. Because of the small size of nanoparticles, the polymer–filler interface property becomes a dominant factor in determining the macroscopic material properties of the nanocomposites. The glass‐transition behaviors of several epoxy nanocomposites have been investigated with modulated differential scanning calorimetry. The effect of the filler size, filler loading, and dispersion conditions of the nanofillers on the glass‐transition temperature (T_g) have been studied. In comparison with their counterparts with micrometer‐sized fillers, the nanocomposites show a T_g depression. For the determination of the reason for the T_g depression, the thermomechanical and dielectric relaxation processes of the silica nanocomposites have been investigated with dynamic mechanical analysis and dielectric analysis. The T_g depression is related to the enhanced polymer dynamics due to the extra free volume at the resin–filler interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3849–3858, 2004     

Bio‐based epoxy vitrimers: Reprocessibility,controllable shape memory,and degradability

The research activities in the development of recyclable and reprocessable covalently crosslinked networks, and the construction of polymers from renewable resources are both stemmed from the economical and environmental problems associated with traditional thermosets. However, there is little effort in combination of these two attractive strategies in material designs. This article reported a bio‐based vitrimer constructed from isosorbide‐derived epoxy and aromatic diamines containing disulfide bonds. The resulted dynamic epoxy resins showed comparable thermomechanical properties as compared to similar epoxy networks cured by traditional curing agent. Rheological tests demonstrated the fast stress relaxation of the dynamic network due to the rapid metathesis of disulfide bonds at temperature higher than glass transition temperature. This feature permitted the recycling and reprocessing of the fragmented samples for several times by hot press. The dynamic epoxy resins also exhibited shape‐memory effect, and it is demonstrated that the shape recovery ratio could be readily adjusted by controlling the stress relaxation in the temporary state at programming temperature. Moreover, the degradability of the dynamic epoxy resins in alkaline aqueous solution was also demonstrated. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1790–1799     

High‐Tg and low‐dielectric epoxy thermosets based on a propargyl ether‐containing phosphinated benzoxazine

A propargyl ether‐containing benzoxazine (4) was prepared from a potassium carbonate‐catalyzed nucleophilic substitution of propargyl bromide and a phenolic OH‐containing benzoxazine (3) , which was prepared from 1‐(4‐hydroxyphenyl)‐1‐(4‐aminophenyl)‐1‐(6‐oxido‐6H ‐dibenz <c,e><1,2> oxaphosphorin‐6‐yl)ethane (1) by a three‐step procedure. The curing reactions of (4) were monitored by IR and DSC. A reaction mechanism was proposed based on the observation. Benzoxazines (3) and (4) were applied as epoxy curing agents. The microstructure and the structure‐property relationship of the resulting thermosets are discussed. The double‐strand structure in (4) ‐cured epoxy thermosets afforded higher crosslinking density, and led to higher thermal properties. In addition, the (4) ‐cured epoxy thermosets possess half the amount of highly polar hydroxyl groups than those of the (3) ‐cured epoxy thermosets, resulting in a lower dielectric constant, dissipation factor, and water absorption. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1359–1367     

Exploitation of introducing of catalytic centers into layer galleries of layered silicates and related epoxy nanocomposites. I. Epoxy nanocomposites derived from montmorillonite modified with catalytic surfactant‐bearing carboxyl groups

Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo‐montmorillonite (O‐MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The intercalation and exfoliation behavior of the epoxy nanocomposites were examined by X‐ray diffraction and transmission electron microscopy. The curing behavior and thermal property were investigated by in situ Fourier transform infrared spectroscopy and DSC, respectively. The results showed that MMT could be highly intercalated by acidified CAB, and O‐MMT could be easily dispersed in epoxy resin to form intercalated/exfoliated epoxy nanocomposites. When the O‐MMT loading was lower than 8 phr (relative to 100 phr resin), exfoliated nanocomposites were achieved. The glass‐transition temperatures (T_g's) of the exfoliated nanocomposite were 20 °C higher than that of the neat resin. At higher O‐MMT loading, partial exfoliation was achieved, and those samples possessed moderately higher T_g's as compared with the neat resin. O‐MMT showed an obviously catalytic nature toward the curing of epoxy resin. The curing rate of the epoxy compound increased with O‐MMT loading. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1192–1198, 2004     

Imidazole‐type thermal latent curing agents with high miscibility for one‐component epoxy thermosetting resins

Epoxy resins are important thermosetting resins widely employed in industrial fields. Although the epoxy–imidazole curing system has attracted attention because of its reactivity, solidification of a liquid epoxy resin containing imidazoles proceeds gradually even at room temperature. This makes it difficult to use them for one‐component epoxy resin materials. Though powder‐type latent curing agents have been used for one‐component epoxy resin materials, they are difficult to apply for fabrication of fine industrial products due to their poor miscibility. To overcome this situation and to improve the shelf life of epoxy–imidazole compositions, we have developed a liquid‐type thermal latent curing agent 1 , generating an imidazole with a thermal trigger via a retro‐Michael addition reaction. The latent curing agent 1 has superior miscibility toward epoxy resins; in addition, it was confirmed that the epoxy resin composition has both high reactivity at 150 °C, and long‐term storage stability at room temperature. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2680–2688     

Carbonyldiimidazole‐accelerated efficient cure of epoxidized soybean oil with dicyandiamide

This study investigates the curing of epoxidized soybean oil (ESO) using dicyandiamide (DICY) and combinations of DICY with several accelerators as curing agents. The differential scanning calorimetry (DSC) results indicated that carbonyldiimidazole (CDI) is a highly efficient accelerator for the ESO‐DICY curing system. CDI accelerated ESO‐DICY curing system can gel within a short period of 13 min at 190 °C. The activation energies of the ESO‐DICY curing systems with and without CDI are 95 and 121 kJ mol^?1, respectively. Similar acceleration effect was observed in the ESO‐diglycidyl ether of biphenyl A (DGEBA) blending formulations. When the molar part of the glycidyl epoxy groups of DGEBA was equal to the internal epoxy groups of ESO in the mixture, gelation of the DICY curing system accelerated by CDI was achieved in 3 min at 160 °C. Furthermore, the DSC results with FTIR analysis suggest that the stoichiometric curing molar ratio was 3 ESO epoxy units per 1 DICY molecule. Two epoxy units reacted with DICY to give secondary alcohols, while the other one linked to the nitrile group. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 375–382     

Using diethylphosphites as thermally latent curing agents for epoxy compounds

Diethylphosphite (DEP) and its derivative exhibited thermally latent properties for epoxy curing reactions through the formation of phosphonic acid as an active species from a reaction of ethanol elimination, which was observed with ¹H NMR and pyrolysis gas chromatography/mass spectrometry measurements. The thermally latent properties and curing reaction kinetics of the curing reaction of DEPs with diglycidyl ether of bisphenol A were studied with differential scanning calorimetry. The cured epoxy resins possessed a phosphorous element coming from the DEP derivatives, exhibiting improved flame retardancy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 432–440, 2003