Kinetic study of the curing of mixtures of DGEBA and five‐membered cyclic carbonates with lanthanum triflate as cationic initiator

Mixtures of diglycidylether of bisphenol A (DGEBA) with 1,3‐benzodioxolane‐2‐one (CC) or 4‐phenoxymethyl‐1,3‐dioxolane‐2‐one (PGEC) were cured in the presence of lanthanum triflate. FTIR/ATR was used to study the evolution of carbonate and epoxide groups to follow the reactive processes that take place during curing. DSC was applied to study the thermal characteristics of the curing process and to determine the glass‐transition temperatures of the cured materials. The kinetics of the curing was studied isothermally by means of FTIR and the kinetic model was selected through the isokinetic relationships. DSC experiments were used to study the kinetics in nonisothermal conditions by means of isoconversional procedures and the Coats–Redfern and Criado methodologies. By TMA we could monitor the evolution of the shrinkage during isothermal curing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2875–2884, 2007     

Copolymerization of diglycidylether of bisphenol A and bicyclic bis(γ‐lactone)s using rare earth metal triflates as initiators studied with infrared spectroscopy

The thermal cationic curing of mixtures, in various proportions, of diglycidylether of bisphenol A with two substituted condensed bis(γ‐lactone)s initiated using scandium, ytterbium and lanthanum triflates or a conventional boron trifluoride monoethylamine (BF₃·MEA) initiator was investigated. The evolution of the various reactive groups was followed by means of attenuated total reflection Fourier transform infrared spectroscopy. The formation of mono‐spiroorthoesters (monoSOE)s and bis‐spiroorthoesters (bisSOE)s is discussed. The polymerization of bisSOE structures led to the formation of ether–ester–ketone repeat units, which implied the cationic polymerization took place by a tandem reaction. The use of scandium triflate as an initiator led to the highest chemical incorporation of lactone in the network. Moreover, this initiator was the most active, incorporating a higher proportion of lactone in a shorter time. In contrast, the conventional BF₃·MEA initiator incorporated the lowest proportion of bislactone in the cured material. Copyright © 2010 Society of Chemical Industry     

Cationic curing of diglycidyl ether of bisphenol A and 2,2,5,5‐tetramethyl‐4,6‐dioxo‐1,3‐dioxane and degradation of the thermosets obtained

Ytterbium and lanthanum triflates were used as cationic initiators to cure mixtures of diglycidyl ether of bisphenol A and 2,2,5,5‐tetramethyl‐4,6‐dioxo‐1,3‐dioxane in several proportions. The evolution of the epoxy and lactone during curing and the linear ester groups in the final materials were evaluated with Fourier transform infrared in the attenuated total reflection mode. The shrinkage after curing and the thermal degradability of the materials with variations in the comonomer ratios and initiator used were evaluated and related to the chemical structure of the final network. The expandable character of 2,2,5,5‐tetramethyl‐4,6‐dioxo‐1,3‐dioxane was confirmed. The obtained materials were more degradable than conventional epoxy resins because of the tertiary ester groups incorporated into the network by copolymerization. The kinetic parameters of the curing and degradation processes were calculated with differential scanning calorimetry and thermogravimetric analysis, respectively, with isoconversional procedures applied in both cases. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Phosphorus‐containing epoxy resins: Thermal characterization

Three novel aromatic phosphorylated diamines, i.e., bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl} pyromellitamic acid (AP), 4,4′‐oxo bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AB) and 4,4′‐hexafluoroisopropylidene‐bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AF) were synthesized and characterized. These amines were prepared by solution condensation reaction of bis(3‐aminophenyl)methyl phosphine oxide (BAP) with 1,2,4,5‐benzenetetracarboxylic acid anhydride (P)/3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride (B)/4,4′‐(hexafluoroisopropylidene)diphthalic acid anhydride (F), respectively. The structural characterization of amines was done by elemental analysis, DSC, TGA, ¹H‐NMR, ¹³C‐NMR and FTIR. Amine equivalent weight was determined by the acetylation method. Curing of DGEBA in the presence of phosphorylated amines was studied by DSC and curing exotherm was in the temperature range of 195–267°C, whereas with conventional amine 4,4′‐diamino diphenyl sulphone (D) a broad exotherm in temperature range of 180–310°C was observed. Curing of DGEBA with a mixture of phosphorylated amines and D, resulted in a decrease in characteristic curing temperatures. The effect of phosphorus content on the char residue and thermal stability of epoxy resin cured isothermally in the presence of these amines was evaluated in nitrogen atmosphere. Char residue increased significantly with an increase in the phosphorus content of epoxy network. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2235–2242, 2002     

Chelation properties of poly(2‐hydroxy‐4‐acryloyloxybenzophenone) resins toward some divalent metal ions

The chelation behavior of poly(2‐hydroxy‐4‐acryloyloxybenzophenone) [poly(2H4ABP) or polymer I ] obtained through the free‐radical polymerization of 2‐hydroxy‐4‐acryloyloxybenzophenone monomer and for crosslinked polymers prepared from the monomer and known amounts of the crosslinker divinylbenzene (DVB) [4 mol % of DVB for polymer II, 8 mol % of DVB for polymer III, and 16 mol 16% of DVB for polymer IV ] toward the divalent metal ions Cu²⁺, Ni²⁺, Zn²⁺, and Pb²⁺ in aqueous solution was studied by a batch equilibration technique as a function of contact time and pH. The effect of the crosslinker, DVB, was also studied. The metal‐ion uptake of the polymers was determined with atomic absorption spectroscopy, and the highest uptake was achieved at pH 7.0 for polymers I, II, III, and IV. The selectivity and binding capacity of the resins toward the investigated divalent metal ions are discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Fracture and adhesion behaviors of epoxy resins modified with poly(amine‐quinone)

An amine‐quinone monomer, i.e. 2,5‐bis(4,4′‐methylenedianiline)‐1,4‐benzoquinone (BB), was synthesized by the Michael addition of 4,4′‐diaminodiphenyl methane with 1,4‐benzoquinone. To evaluate the effect of BB content on the glass transition temperature (T_g) and crosslinking density (ρ) of cured diglycidyl ether of bisphenol A (DGEBA)/BB systems, storage modulus and loss factor measurements were obtained using dynamic mechanical analysis. The mechanical properties of the systems were determined in terms of the fracture toughness, impact strength, and adhesion strength. As a result, the ρ values of the systems were found to decrease systematically as the BB content increased. The fracture toughness and adhesion strength of the systems increased with increasing BB content. These results indicate that the addition of BB into epoxy resins increases the free volume of the epoxy network and absorbs the deformation energy, resulting in an improvement of the mechanical properties of the DGEBA/BB systems. Copyright © 2006 Society of Chemical Industry     

New investigation of 1‐substituted imidazole derivatives as thermal latent catalysts for epoxy‐phenolic resins

Novel 1‐substituted imidazole derivatives ( 4 – 10 ) were synthesized by imidazole and the corresponding substituted reagents (chloromethylpivalate, diphenylphosphinicchloride, di‐tert‐butyldicarbonate, 1,1′‐oxalylchloride, pyrazine, phneylisocyanat, and p‐toluensulfonylchloride). Polymerization of diglycidyl ether of bisphenol A (DGEBA) with 1‐substituted imidazole derivatives, two commercial available catalysts (imidazole and 1‐cyanoethyl‐2‐ethyl‐4‐methylimidazole) and N‐benzylpyrazinium hexafluoroantimonate were investigated as model reactions of epoxy resin systems with respect to the thermal latency and storage stability of the catalysts. The catalytic activity of 1‐substituted imidazole derivatives 4 – 10 depended on the steric and withdrawing electronic effect of the substitution groups. To characterize the cure activation energy and the viscosity‐storage time, the order of thermally latent activity is 1‐tosylimidazole ( 6 ) > 1,1′‐oxalyldiimidazole ( 8 ) > N‐benzylpyrazinium hexafluoroantimonate (BPH, 3 ) > 1‐tritylimidazole ( 9 ) > N‐phenyl‐imidazole‐1‐carboxamide ( 5 ) > 3‐(diphenylphosphinoyl)imidazole ( 7 ) > tert‐butyl‐1H‐imidazole‐1‐carboxylate ( 4 ) > 1‐cyanoethyl‐2‐ethyl‐4‐methylimidazole (2E4MZ, 2 ) > 1‐[(pivalyloxy)methyl]imidazol ( 10 ) > imidazole ( 1 ). In comparison with commercially available catalysts imidazole ( 1 ) and 1‐cyanoethyl‐2‐ethyl‐4‐methylimidazole ( 2 ) and a cationic latent catalyst N‐benzylpyrazinium hexafluoroantimonate (BPH, 3 ) as the standard compounds, in addition to 1‐[(pivalyloxy)methyl]imidazole ( 10 ), the 1‐substituted imidazole derivatives ( 4 – 9 ) revealed better thermal latency. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Polymerization of epoxy resins initiated by metal complexes

BACKGROUND: Processing parameters and material properties of epoxy resins can be vastly influenced by choice of curing agent. In this work, metal complexes were investigated as initiators for anionic and cationic epoxide polymerization. Systems for thermally induced and electron beam‐induced curing are described. RESULTS: Zinc or cobalt imidazole complexes of the type [M(imidazole)₂(anion)₂] are efficient initiators for anionic polymerization of glycidyl‐based epoxy resins. The complexes can be employed to prepare tailored resin systems ranging from fast curing systems at slightly elevated temperatures to systems with very high thermal latencies curable at temperatures far above 150 °C. Silver complexes [Ag(L)_n]SbF₆ (L = crown ether or alkene) are highly efficient initiators for cationic curing and low initiator contents of around 1% are sufficient to reach high degrees of crosslinking. The complexes are excellent initiators for both thermally induced and electron beam‐induced polymerizations. CONCLUSION: Metal complexes are powerful initiators for the homopolymerization of epoxy resins and can be designed not only for anionic and cationic polymerization but also for thermal and radiation curing. Based on this study and additional work, a library can be compiled which allows retrieval of optimized metal–ligand–anion combinations and adjustment of the initiators to the respective processing and material demands. Copyright © 2009 Society of Chemical Industry     

Synthesis and application of thermal latent initiators of epoxy resins: A review

Epoxy resin, which is extensively used in civil and industrial applications, shows excellent comprehensive performance, especially as a polymer matrix used in fiber-reinforced composites. A thermal latent initiator, used as an epoxy curing agent, has high storage stability and is widely applied in the preparation of epoxy-based blends and fiber-reinforced composites. In this review, the basic properties of epoxy resins and commonly used curing agents are discussed while progress on the synthesis of thermal latent initiators is reviewed in detail. Moreover, the curing mechanisms, thermal stability, and mechanical properties of epoxy resins with thermal latent initiators are also discussed.     

Multifunctional epoxy resins: Synthesis and characterization

The tetrafunctional epoxy resins were prepared starting from diaminodiphenylmethane, diaminodiphenylether, and diaminobibenzyl. The obtained resins were characterized by IR and ¹H‐NMR spectroscopy, rheological and thermal techniques. The polymerization reaction was investigated by viscosimetry. The flow activation energy and the polymerization activation energy were evaluated from the rheological data and from the critical parameters (critical time and critical viscosity at gel point). The viscosity measurements and gel time determination showed slight differences between the synthesized resins. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2430–2436, 2000     

Polyurethane‐modified epoxy resin: Solventless preparation and properties

A polyurethane‐modified epoxy resin system with potential as an underfill material in electronic packaging and its preparation procedure were studied. The procedure enabled the practical incorporation of an aliphatic polyurethane precursor, synthesized from poly(ethylene glycol) and hexamethylene diisocyanate without a solvent, as a precrosslinking agent into a conventional epoxy resin. With a stoichiometric quantity of the polyurethane precursor added to the epoxy (ca. 5 phr), the polyurethane‐modified epoxy resin, mixed with methylene dianiline, exhibited a 36% reduction in the contact angle with the epoxy–amine surface, a 31% reduction in the cure onset temperature versus the control epoxy system, and a viscosity within the processable range. The resultant amine‐cured thermosets, meanwhile, exhibited enhanced thermal stability, flexural strength, storage modulus, and adhesion strength at the expense of a 5% increase in the coefficient of thermal expansion. Exceeding the stoichiometric quantity of the polyurethane precursor, however, reduced the thermal stability and modulus but further increased the coefficient of thermal expansion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrolytic stability of cured urea‐formaldehyde resins modified by additives

Urea‐formaldehyde (UF) resins are prone to hydrolysis that results in low‐moisture resistance and subsequent formaldehyde emission from UF resin‐bonded wood panels. This study was conducted to investigate hydrolytic stability of modified UF resins as a way of lowering the formaldehyde emission of cured UF resin. Neat UF resins with three different formaldehyde/urea (F/U) mole ratios (1.4, 1.2, and 1.0) were modified, after resin synthesis, by adding four additives such as sodium hydrosulfite, sodium bisulfite, acrylamide, and polymeric 4,4′‐diphenylmethane diisocyanate (pMDI). All additives were added to UF resins with three different F/U mole ratios before curing the resin. The hydrolytic stability of UF resins was determined by measuring the mass loss and liberated formaldehyde concentration of cured and modified UF resins after acid hydrolysis. Modified UF resins of lower F/U mole ratios of 1.0 and 1.2 showed better hydrolytic stability than the one of higher F/U mole ratio of 1.4, except the modified UF resins with pMDI. The hydrolytic stability of modified UF resins by sulfur compounds (sodium bisulfate and sodium hydrosulfite) decreased with an increase in their level. However, both acrylamide and pMDI were much more effective than two sulfur compounds in terms of hydrolytic stability of modified UF resins. These results indicated that modified UF resin of the F/U mole ratio of 1.2 by adding acrylamide was the most effective in improving the hydrolytic stability of UF resin. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Visible light polymerization of epoxy monomers using an iodonium salt with camphorquinone/ethyl‐4‐dimethyl aminobenzoate

A visible light initiator system for the photoinduced cationic polymerization of epoxy monomers is reported. The system consists of camphorquinone (CQ) in combination with ethyl‐4‐dimethyl aminobenzoate (EDMAB) and a diaryliodonium salt (Ph₂ISbF₆.) The three‐component system efficiently photoinitiates the polymerization of monomers containing an epoxycyclohexane group, 3,4‐epoxycyclohexylmethyl 3',4'‐epoxycyclohexane carboxylate (UVR) and 1,3‐bis(3,4‐epoxycyclohexyl‐2‐ethyl),1,1,3,3‐tetramethyldisiloxane (SIB), under irradiation with blue light (λ = 467 nm). Very rapid photopolymerization resulted from irradiation of SIB containing Ph₂ISbF₆ in combination with CQ and better results were obtained in the presence of EDMAB. On the other hand, no polymerization was detected after irradiation of UVR photoactivated with Ph₂ISbF₆ and CQ. However, this monomer polymerized readily and to high conversion when EDMAB was present. Moreover, almost complete conversion of UVR occurs in the absence of external heating. The polymer resulting from UVR displayed higher values of compressive and flexural properties than the polymer prepared from SIB. This is explained in terms of a higher density of crosslinking points in UVR which is accompanied by a lower content of non‐reacted monomer; this has a plasticizing effect on the hardened material. © 2013 Society of Chemical Industry     

Synthesis and properties of novel trifunctional epoxy triglycidyl of 4‐(4‐aminophenoxy)phenol with high toughness

A trifunctional epoxy containing oxyphenylene unit, triglycidyl of 4‐(4‐aminophenoxy)phenol (TGAPP) was synthesized and characterized. The chemical structure of TGAPP was confirmed with FTIR and ¹H‐NMR. DSC analysis revealed that the reactivity of TGAPP with curing agent 4, 4′‐diaminodiphenylsulfone (DDS) was significantly lower than that of triglycidyl para‐aminophenol (TGPAP). Rheological analysis showed that the processing window of TGAPP/DDS was 20°C wider compared with that of TGPAP/DDS. The thermal and mechanical properties of cured TGAPP/DDS were investigated and compared with those of the cured TGPAP/DDS. Experimental results showed that, due to the introduction of oxyphenylene unit, the heat resistance and flexural strength were slightly reduced, while the tensile strength and impact strength were enhanced. SEM also confirmed that the introduction of oxyphenylene unit could enhance the toughness of the TGAPP/DDS as evident from ridge formation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41878.     

Curing properties of high-Ortho phenol-formaldehyde resins with co-catalysis

In this study, sodium carbonate (Na₂CO₃) was used as a catalyst to prepare high-ortho phenol-formaldehyde (HOPF) resin, and ester and carbonate curing accelerators were used to increase its curing rate. The physicochemical properties of the prepared resins and the mechanism of curing acceleration were investigated. The results showed that, with the addition of Na₂CO₃, the ortho/para ratio of methylol groups increased from 7.257 to 27.800. The gel time of the cure-accelerated HOPF resins decreased from 620 to 240 s as compared with PF resin. The bonding strength of plywood bonded with the cure-accelerated HOPF resins were all above 0.70 MPa. The curing acceleration was caused by the carbonate ions rather than the metal ions, and a temporary incorporation mechanism apparently occurred for the ester accelerators. The prepared phenolic resin had fast curing rate, low curing temperature, high thermal stability, and favorable mechanical performance, which has potential for industry applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47229.     

Synthesis,characterization, and degradation investigation of water‐soluble β‐cyclodextrin‐based epoxy resins

A series of β‐cyclodextrin‐based epoxy resins were synthesized with different epoxy equivalent weights. Their chemical structures were characterized with Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR) examination. These epoxy resins were cured using L ‐arginine as a curing agent, and the degradation behavior of the cured resins was evaluated under different acidic buffer solutions at 37°C. The degradable behavior of such epoxy resins suggested potential applications as environment friendly materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Curing reaction mechanism and heat resistance properties of hexa‐(4‐carboxyl‐phenoxy)‐cyclotriphosphazene/bisphenol A aniline benzoxazine blends

A blend system of hexa‐(4‐carboxyl‐phenoxy)‐cyclotriphosphazene (HCPCP) and bisphenol A aniline benzoxazine (BA‐a) was prepared, and its curing reaction mechanism and heat resistance properties were studied. The curing reaction mechanism of the blend was explored by differential scanning calorimetry, Fourier transform infrared spectroscopy, and modeling software using model compounds Ar‐COOH and hexachlorocyclotriphosphazene (HCCP). The heat resistance properties of the cured blends were studied by thermogravimetric analysis and dynamic mechanical analysis. The polymerization of benzoxazine was catalyzed by HCPCP through phosphazene ring and acid groups, and phosphazene played a predominant role. Compared with the materials with a single functional group (Ar‐COOH and HCCP), HCPCP containing two functional groups (phosphazene ring and acid) exhibited weaker catalytic effects, mainly due to the high molecular weight of HCPCP obstructing movement and causing steric hindrance. In addition, HCPCP had a positive effect on the thermal stability of polybenzoxazine from 250 to 400 °C. When the HCPCP content reached 3%, the cured blend had the highest glass‐transition temperature (222.2 °C), which is higher by 20 °C than that of cured benzoxazine. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46389.     

Pyrolysis of epoxy resins and fire behavior of epoxy resin composites flame‐retarded with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide additives

The pyrolysis of an epoxy resin and the fire behavior of corresponding carbon fiber‐reinforced composites, both flame‐retarded with either 10‐ethyl‐9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide or 1,3,5‐tris[2‐(9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide‐10‐)ethyl]1, 3,5‐triazine‐2,4,6(1H,3H,5H)‐trione, are investigated. The different fire retardancy mechanisms are discussed, and their influence on the fire properties assessed, in particular for flammability (limiting oxygen index, UL 94) and developing fires (cone calorimeter with different external heat fluxes of 35, 50, and 70 kW m^?2). Adding the flame retardants containing 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide affects the fire behavior by both condensed phase and gas phase mechanisms. Interactions between the additives and the epoxy resin result in a change in the decomposition pathways and an increased char formation. The release of phosphorous products results in significant flame inhibition. The fire properties achieved are thus interesting with respect to industrial exploration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2260–2269, 2007     

Thermomechanical behavior of epoxy resins modified with epoxidized vegetable oils

Biobased epoxy materials were prepared from diglycidyl ether of bisphenol A (DGEBA) and epoxidized vegetable oils (EVOs) (epoxidized soybean oil and epoxidized castor oil) with a thermally latent initiator. The effects of EVO content on the thermomechanical properties of the EVO‐modified DGEBA epoxy resins were investigated using several techniques. Differential scanning calorimetry indicated that the cure reaction of the DGEBA/EVO systems proceeded via two different reaction mechanisms. Single and composition‐dependent glass transition temperature (T_g) mechanisms were observed for the systems after curing. The experimental values of T_g could be explained by the Gordon–Taylor equation [Gordon M and Taylor JS, J Appl Chem 2 :493 (1952)]. The thermal stability of the systems decreased as the EVO content increased, due to the lower crosslinking density of the DGEBA/EVO systems. The coefficient of thermal expansion of the systems was found to increase linearly with increasing EVO content. This could be attributed to the fact that the degrees of freedom available for motions of the segments of the macromolecules in the network structure were enhanced by the addition of EVO. Copyright © 2008 Society of Chemical Industry     

Volume‐expandable monomer 5,5‐dimethyl‐1,3‐dioxolan‐2‐one: Its copolymerization behavior with epoxide and its applications to shrinkage‐controlled epoxy‐curing systems

The copolymerization of epoxides and a six‐membered cyclic carbonate, 5,5‐dimethyl‐1,3‐dioxan‐2‐one (DM6CC), was carried out with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene as an initiator. In the copolymerization of glycidyl phenyl ether (GPE) and DM6CC, DM6CC remarkably accelerated the polymerization rate of GPE and also effectively suppressed chain‐transfer reactions, which occur in the homopolymerization of the epoxide. This suppression resulted in the formation of the corresponding copolymer with a higher molecular weight. Similar effects of DM6CC were also observed in a curing system with a Novolac‐type multifunctional epoxide (Novolac glycidyl ether). The curing reaction of the epoxide in the presence of DM6CC smoothly proceeded and yielded the corresponding networked polymer, showing a decrease in the volume shrinkage as the DM6CC content increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 372–378, 2005