Synthesis of a novel phosphorus‐containing dicyclopentadiene novolac hardener and its cured epoxy resin with improved thermal stability and flame retardancy

A novel phosphorus‐containing dicyclopentadiene novolac (DCPD‐DOPO) curing agent for epoxy resins, was prepared from 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and n‐butylated dicyclopentadiene phenolic resin (DCPD‐E). The chemical structure of the obtained DCPD‐DOPO was characterized with FTIR, ¹H NMR and ³¹P NMR, and its molecular weight was determined by gel permeation chromatography. The flame retardancy and thermal properties of diglycidyl ether bisphenol A (DGEBA) epoxy resin cured with DCPD‐DOPO or the mixture of DCPD‐DOPO and bisphenol A‐formaldehyde Novolac resin 720 (NPEH720) were studied by limiting oxygen index (LOI), UL 94 vertical test and cone calorimeter (CCT), and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. It is found that the DCPD‐DOPO cured epoxy resin possess a LOI value of 31.6% and achieves the UL 94 V‐0 rating, while its glass transition temperature (T_g) is a bit lower (133 °C). The T_g of epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 increases to 137 °C or above, and the UL 94 V‐0 rating can still be maintained although the LOI decreases slightly. The CCT test results demonstrated that the peak heat release rate and total heat release of the epoxy resin cured by the mixture of DCPD‐DOPO and NPEH720 decrease significantly compared with the values of the epoxy resin cured by NPEH720. Moreover, the curing reaction kinetics of the epoxy resin cured by DCPD‐DOPO, NPEH720 or their mixture was studied by DSC. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44599.     

Development of a DOPO‐containing melamine epoxy hardeners and its thermal and flame‐retardant properties of cured products

In this study, a novel Schiff base of melamine used as flame‐retardant curing agent for epoxy resins, was synthesized via condensation reaction of 4‐hydroxybenzaldehyde with melamine, followed by the addition of 9,10‐dihydro‐9‐oxa‐10‐phosphaphen‐anthrene 10‐oxide (DOPO) to the resulting imine linkage. The structure of DOPO‐containing melamine Schiff base (P‐MSB) was characterized by Fourier transformed infrared spectroscopy, ¹H‐nuclear magnetic resonance (¹H‐NMR) and ³¹P‐NMR. The compound (P‐MSB) was used as a reactive flame retardant in o‐cresol formaldehyde novolac epoxy resin (CNE) to prepare flame‐retardant epoxy resins for electronic application. The thermal and flame‐retardant properties of the epoxy resins cured by various equivalent ratios phenol formaldehyde novolac (PN) and P‐MSB were investigated by the nonisothermal differential scanning calorimetry, the thermogravimetric analysis, and limiting oxygen index test. The obtained results showed that the cured epoxy resins possessed high T_g (165°C) and good thermal stability (T_5%, 321°C). Moreover, the P‐MSB/CNE systems exhibited higher limiting oxygen index (35) and more char was maintained in P‐MSB/CNE systems than that in PN/CNE system and the effective synergism of phosphorus–nitrogen indicated their excellent flame retardancy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improving thermal and flame‐retardant properties of epoxy resins by a new imine linkage phosphorous‐containing curing agent

A new reactive phosphorus‐containing curing agent with imine linkage called 4, 4′‐[1, 3‐phenyl‐bis(9, 10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐yl)dimethyneimino)]diphenol (2) was synthesized both via two‐pot and one‐pot procedure. The chemical structure of this curing agent was confirmed by FTIR, ¹H, ¹³C, and ³¹P NMR spectra. A series of thermosetting systems were prepared by using conventional epoxy resins (E51), 4, 4′‐diaminodiphenyl methane (DDM) and (2). Resins with different phosphorus contents were obtained by changing the DDM/(2) molar ratios. Their dynamic mechanical thermal, thermal and flame‐retardant properties were evaluated by dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA), and limiting oxygen index (LOI), respectively. All samples had a single T_g, which showed that these epoxy resins were homogeneous phase. Both the two char yields under nitrogen and air atmospheres increased with increasing content of (2) and the LOI values increased from 24.5 for standard resin to 37.5 for phosphorus‐containing resin, which indicated that incorporation of (2) could impart good thermal stability and excellent flame retardancy to the conventional epoxy thermosets. POLYM. ENG. SCI., 56:441–447, 2016. © 2016 Society of Plastics Engineers     

Improving thermal and flame‐retardant properties of epoxy resins by a novel reactive phosphorous‐containing curing agent

In an attempt to improve thermal and flame‐retardant properties of epoxy resins efficiently, a new reactive phosphorus‐containing curing agent called 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐yl‐(phenylimino)‐(4‐hydroxyphenyl)me‐thane (DOPO‐PHM) was synthesized and was combined with 4,4′‐diaminodiphenyl methane (DDM) to co‐cure epoxy resins (E51), which covalently incorporated halogen‐free DOPO organ groups into the epoxy networks. The chemical structure of this curing agent was confirmed by FTIR, 1D, and 2D NMR spectra. A reaction mechanism during the preparation was proposed, and the electron effect on the stabilization of the carbocation was discussed. Various DDM/DOPO‐PHM molar ratios were used to get the materials with different phosphorus contents. Their dynamic mechanical, thermal, and flame‐retardant properties were evaluated by dynamic mechanical thermal analysis, thermogravimetric analysis, and limiting oxygen index (LOI) respectively. All samples had a single T_g, showing that these epoxy resins were homogeneous phase for long‐term use in spite of adding DOPO‐PHM. Both char yields (under nitrogen and air atmospheres) increased with the increasing of phosphorus content and the LOI values increased from 24.5 for standard resin to 33.5 for phosphorus‐containing resins, indicating the significant enhancement of thermal stability and flame retardancy. POLYM. ENG. SCI., 54:1192–1200, 2014. © 2013 Society of Plastics Engineers     

Synthesis,cationic polymerization and curing reaction with epoxy resin of 3,9‐di(p‐methoxybenzyl)‐1,5,7,11‐tetra‐oxaspiro(5,5)undecane

A new spiro ortho carbonate, 3,9‐di(p‐methoxybenzyl)‐1,5,7,11‐tetra‐oxaspiro(5,5)undecane was prepared by the reaction of 2‐methoxybenzyl‐1,3‐propanediol with di(n‐butyl)tin oxide, following with carbon disulfide. Its cationic polymerization was carried out in dichloromethane using BF₃‐OEt₂ as catalyst. The [¹H], [¹³C]NMR and IR data as well as elementary analysis of the polymers obtained indicated that it underwent double ring‐opening polymerization. The polymerization mechanism is discussed. The curing reaction of bisphenol A type epoxy resin in the presence of the monomer and a curing agent was investigated. DSC measurements were used to follow the curing process. In the case of boron trifluoride‐o‐phenylenediamine (BF₃‐OPDA) as curing agent, two peaks were found on the DSC curves, one of which was attributed to the polymerization of the epoxy group, and the other to the copolymerization of the monomer with the isolated epoxy groups or homopolymerization. However, when BF₃‐H₂NEt was used as curing agent, only one peak was present. IR measurement of the modified epoxy resin with various weight ratios of epoxy resin/monomer was performed in the presence of BF₃‐H₂NEt as curing agent. The results demonstrate that the conversion of epoxy group increases as the content of monomer increases. The curing process and the structure of the epoxy resin network are discussed. © 2000 Society of Chemical Industry     

Synthesis and properties of novel phosphorus‐containing hardener for epoxy resins

A novel phosphorus‐containing curing agent, 2‐(6‐oxid‐6H‐dibenz〈c,e〉〈1,2〉oxa‐phosphorin‐6‐yl) phenol formaldehyde novolac [OD‐PN], was prepared from phenol formaldehyde novolac resin (PN) and a reactive 2‐(6‐oxid‐6H‐dibenz〈c,e〉〈1,2〉oxa‐phosphorin‐6‐yl)chloride (ODC) while ODC was synthesized through reaction between o‐phenylphenol and phosphoryl trichloride. The compound (OD‐PN) was used as a reactive flame‐retardant in o‐cresol formaldehyde novolac epoxy resin (CNE) for electronic application. Owing to the rigid structure of ODC and pendant P group, the resulted phosphorus containing epoxy resin exhibited better flame retardancy, higher glass transition temperature, and thermal stability than the noncyclic P‐containing curing agent or the bromine containing flame‐retardant epoxy resin. UL 94‐VO rating could be achieved with a phosphorus content of as low as 1.21% (comparable to bromine content of 6%) in the cured resin, and no fumes and toxic gas emission were observed. The relationship between the structure and flammability for both phosphorus containing curing agents OD‐PN and TP‐PN (triphenyl phosphate‐phenol formaldehyde novolac reaction product) are also examined. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1636–1644, 2000     

Curing and pyrolysis of cresol novolac epoxy resins containing [2‐(6‐oxido‐6H‐dibenz(c,e)(1,2)oxaphosphorin‐6‐yl)‐1,4‐naphthalenediol]

This study investigates the curing kinetics, thermal properties and decomposition kinetics of cresol novolac epoxy (CNE) with two curing agents, 2‐(6‐oxido‐6H dibenz(c,e)(1,2) oxaphosphorin‐6‐yl)‐1,4‐benzenediol (ODOPN), and phenol novolac (PN). In comparison with the conventional PN system, introducing ODOPN, a phosphorus‐containing bulky pendant group, into CNE increases T_g by 33°C, char yield from 30% to 38%, and LOI from 22 to 31. The DSC curing study reveals that the E_a of the CNE/ODOPN epoxy can be obtained by Kissinger's method. The resulting E_a values indicate that the catalytic effect of EMI is insignificant on CNE/ODOPN but is marked on CNE/PN, whose E_a was reduced from 131.5 to 75.6 KJ/mole. This result may be caused by the fact that the symmetric diol attached to the 1 and 4 positions of the naphthalene ring in ODOPN sets up a steadily resonating structure and inhibits the catalytic action. Further investigating the conversion ratio with curing temperature yielded experimental data that agreed closely with Kaiser's model. The orders of the autocatalyzed reaction, m, and the crosslinking reaction, n, are close to 0.5 and 1.0, respectively, independently of the scan rate. Finally, the TGA decomposition study by Ozawa's method demonstrates that the mean E_a declines with the phosphorus content, because the easy decomposition of the phosphorus compound in the initiation stage facilitates the formation of an insulating layer. However, results in this study further reveal an increasing tendency for E_a with decomposition conversion for an ODOPN/PN mixture with the ODOPN content of over 50%, probably because of the retardation of gas diffusion by the insulating layer of phosphorus compound.     

Synthesis and characterization of emulsion‐type curing agent of water‐borne epoxy resin

Self‐emulsified water‐borne epoxy curing agent of nonionic type was prepared using triethylene tetramine (TETA) and derivative of epoxy resin as a capping agent, which was synthesized by liquid epoxy resin (E51) and polyethylene glycol (PEG), and the curing agent possessed emulsification and curing properties at the same time. The curing agent with good property of emulsifying liquid epoxy resin could be obtained under the condition of the molar ratio of PEG : E51 : TETA as 0.8 : 1 : 3.5 at 80°C for 5 h. The mean particle size of the emulsion liquid was about 220 nm with the prepared curing agent and epoxy resin at the mass ratio of 1 : 3. The structure of the emulsion‐type curing agent was confirmed by FTIR and ¹H NMR spectra, and the mechanism of cured film formation was also analyzed by SEM photographs. The cured film prepared by the emulsion‐type curing agent and epoxy resin under ambient cure conditions showed good properties even at high staving temperature. This study provides useful suggestions for the application of the water‐borne epoxy resins in coating industry. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2652–2659, 2013     

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.     

Preparation and epoxy curing of novel dicyclopentadiene‐derived Mannich amines

Phenol/dicyclopentadiene (DCPD) adducts were prepared from the BF₃‐catalyzed reaction of p‐nonylphenol and dicyclopentadiene at molar ratios of 2 : 1 and 3 : 2. The phenol‐terminating adducts were consequently reacted with diethylenetriamine and formaldehyde using Mannich reaction conditions. These products containing phenol, amine and tricyclodecane functionalities in the same molecule can be used as epoxy curing agents. The diethylenetriamine was add to the phenol via Mannich reaction at approximately 50% theoretical equivalent. The multiple N H groups in amines and the O H groups in phenols provide crosslinking sites for epoxy resins. The cured epoxy resins show improvement in tensile strength and elongation in comparison with those cured by the poly(oxypropylene) diamine (400 molecular weight) or diethylenetriamine. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2129–2139, 1999     

The effect of an anhydride curing agent,an accelerant,and non‐ionic surfactants on the electrical resistivity of graphene/epoxy composites

This study investigated different contents of an anhydride curing agent, an accelerant, and non‐ionic surfactants on the electrical resistivity of cured graphene/epoxy composites. The anhydride curing agent was hexahydrophthalic anhydride (HHPA), the accelerant was 2‐ethyl‐4‐methyl‐1H‐imidazole‐1‐propanenitrile (EMIP), and the non‐ionic surfactants were Triton X surfactants with different numbers of polyethylene oxide (PEO) groups (m) that influence the electrical resistivity of cured graphene/epoxy composites. During the curing process, differential scanning calorimetry (DSC) was used to determine the effects of the extent of the crosslinking for different contents of the curing agent and how different enthalpy (ΔH) on the electrical resistivity of the cured graphene/epoxy composites was then generated. The cured graphene/epoxy composite—which consisted of a 1 : 0.85 weight ratio of epoxy resin and anhydride, a 0.5 wt % accelerant, and a 13 wt % graphene powder—had a low electrical resistivity of 11.68 Ω·cm and a thermal conductivity of 1.7 W/m·K. In addition, the cured composites contained a 1.0 wt % polyethylene glycol p‐isooctylphenyl ether (X‐100) surfactant, which effectively decreased their electrical resistivity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41975     

Intercalation and exfoliation behavior of epoxy resin/curing agent/montmorillonite nanocomposite

The epoxy resin/curing agent/montmorillonite nanocomposite was prepared by a casting and curing process. The intercalation and exfoliation behaviors of epoxy resin in the presence of organophilic montmorillonite were investigated by X‐ray diffraction (XRD) and dynamic mechanical thermal analysis (DMTA). For the diethylenetriamine curing agent, the intercalated nanocomposite was obtained; and the exfoliated nanocomposite would be formed for tung oil anhydride curing agent. The curing condition does not affect the resulting kind of composite, both intercalation or exfoliation. For intercalated nanocomposite, the glass transition temperature T_g, measured by DMTA and affected by the curing temperature of matrix epoxy resin is corresponded to that of epoxy resin without a gallery. The α′ peak of the loss tangent will disappear if adding montmorillonite into the composite. It was also found that the T_g of the exfoliated nanocomposite decreases with increasing montmorillonite loading. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 842–849, 2002; DOI 10.1002/app.10354     

Poly(ester‐amine) hyperbranched polymer as toughening and co‐curing agent for epoxy/clay nanocomposites

The marriage between hardness and flexibility of epoxy resins (improved toughness) is a desired feature, which broads their application in various industrial fields, especially for high impact resistance purposes. Accordingly, this work aims to improve toughness properties of epoxy resin (Epon‐828)/Ancamine (curing agent) system using amino‐terminated hyperbranched poly(ester‐amine) [Poly(PEODA‐NPA)] (HP) as toughening and/or co‐curing agent, in presence of organo‐modified Montmorillonite clay (OMMT) as a reinforcing filler. HP was synthesized via Michael addition reaction of poly(ethylene glycol) diacrylate (PEODA) to N‐methyl‐1,3‐propanediamine (NPA). Chemical structure and molecular weight of HP were elucidated using infrared (FTIR) spectroscopy and gel permeation chromatography (GPC) techniques, respectively. Epoxy/OMMT nanocomposites toughened with HP (at different concentrations) showed remarkable improvement in their toughness without any adverse effect on the other physico‐mechanical properties. The optimum concentration of HP and OMMT was found to be 20 wt % and 1–3 wt% of the epoxy resin, respectively. The extent of exfoliation and dispersion of OMMT platelets within the epoxy cured films was assessed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. In addition, thermal gravimetric analyses (TGA‐DTA) of epoxy/OMMT nanocomposites toughened with HP showed a slight increase in their decomposition temperature, particularly at low OMMT loading. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Cure kinetics of multifunctional epoxies with 2,2′‐dichloro‐4,4′‐diaminodiphenylmethane as hardener

The curing behavior of the epoxy resin N,N,N′,N′‐tetraglycidyldiaminodiphenyl methane (TGDDM) with triglycidyl p‐aminophenol as a reactive diluent was investigated using 2,2′‐dichloro‐4,4′‐diaminodiphenylmethane (DCDDM) as the curing agent. The effect of the curing agent on the kinetics of curing, shelf‐life, and thermal stability in comparison with a TGDDM‐diaminodiphenylsulfone (DDS) system was studied. The results showed a lesser activation energy at the lower level of conversion with a broader cure exotherm for the epoxy‐DCDDM system in comparison with the epoxy‐DDS system, although the overall activation energy for the two systems was comparable. TGA studies showed more stability in the epoxy‐DCDDM system than in the epoxy‐DDS system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2097–2103, 2000     

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     

Synthesis and characterization of a novel epoxy resin containing naphthyl/dicyclopentadiene moieties and its cured polymer

A new epoxy resin containing both naphthalene and dicyclopentadiene (DCPD) groups was synthesized to produce a highly heat-resistant network, and the curing behavior was investigated using diaminodiphenylsulfone (DDS) as curing agent. The chemical structures were characterized with FTIR spectroscopy, NMR, MS, and GPC analyses. Dynamic curing behavior was investigated using differential scanning calorimetry (DSC). The physical properties of the resulting polymers were evaluated with dynamic thermal mechanical analyses (DMTA) and thermogravimetric analyses (TGA). The cured polymer showed great improvement in heat-resistant property including remarkably higher glass transition temperature (T_g) and thermal stability. Such properties make this new epoxy resin highly promising for heat-resistant applications.     

Properties and behavior of CTBN‐modified epoxy with IPN structure

CTBN‐modified epoxy resins (CMEs) with an interpenetrating‐network (IPN) structure and a nanometer‐sized morphology were prepared. Two systems of CMEs, called CNE/DDS/I‐CTBN‐B and CNE/DDS/I‐CTBN‐D, with IPN structures, were synthesized by heat‐curing a homogeneous resin, CNE/DDS/CTBN/2‐MI, obtained by mixing a carboxyl‐terminated butadiene–acrylonitrile liquid rubber (CTBN) with a solution of polyglycidyl ether of o‐cresol‐formaldehyde novolac (CNE), 4,4′‐diamino diphenyl sulfone (DDS), and 2‐methyl imidazole (2‐MI), in the presence of benzoyl peroxide and dicumyl peroxide, respectively. The IPN morphologies of the two systems of CMEs were identified by small‐angle X‐ray scattering by measuring the value of the specific interfacial surface area S_sp between the cured CNE/DDS matrix and the vulcanized CTBN. Properties such as fracture toughness, internal stress, and thermal and dynamic mechanical properties of these IPN‐structured CMEs were studied in detail, and were compared with those of a conventional CME, CNE/DDS/CTBN, obtained by dispersing CTBN particles in a crosslinked CNE/DDS matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis of poly(vinyl acetate) by degenerative transfer polymerization in the presence of iodine

A new curing agent containing maleimide and biphenyl moieties (MIBP) was synthesized by the condensation polymerization of 4,4′-bismethoxymethylbiphenyl and N-(4-hydroxyphenyl)maleimide (HPM). The chemical structure was characterized with Fourier transform infrared (FTIR) spectroscopy, and the molecular weight of the new curing agent was determined by gel permeation chromatography. Curing reactions of O-cresol formaldehyde epoxy (CNE) resin with MIBP were investigated under nonisothermal differential scanning calorimetry, and the exotherm exhibited two overlapping exothermic peaks during the curing process; this was demonstrated by FTIR traces. The Flynn–Wall–Ozawa and Friedman methods were used to examine the kinetic parameters and the kinetic models of the curing processes of the CNE/MIBP mixtures. Both reactions turned out to be nth-order curing mechanisms. Values of the reaction order (n) = 1.42 and activation energy (E_a) = 91.2 kJ/mol were obtained for the first reaction of the curing of the CNE/MIBP system, and values of n = 1.11 and E_a = 78.7 kJ/mol were obtained for the second reaction. The thermal properties of the cured resin were measured with thermogravimetric analysis, and the results show a high glass-transition temperature (T_g = 155°C), good thermal stability (temperature at 10% weight loss, under nitrogen and in air, ≈ 400 and 408°C, respectively), and high char yield (temperature = 800°C, char residue = 44.5% under nitrogen). These excellent thermal properties were due to the introduction of the maleimide and biphenyl groups of MIBP into the polymer structure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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 of 2‐ethyl‐4‐methylimidazole derivatives as latent curing agents and their application in curing epoxy resin

Three kinds of 2‐ethyl‐4‐methylimidazole (EMI) derivatives (N‐acetyl EMI, N‐benzoyl EMI, and N‐benzenesulfonyl EMI) were synthesized through the reaction of EMI with acetyl chloride, benzoyl chloride, and benzenesulfonyl chloride, respectively. And the structure was confirmed by Fourier transform infrared spectroscopy (FTIR) and ¹H‐nuclear magnetic resonance spectroscopy (¹H NMR) spectra. Furthermore, the synthesized EMI derivatives were applied in diglycidyl ether of bisphenol A epoxy resin (DGEBA) as latent curing agent. Differential scanning calorimeter (DSC) was used to analyze the curing behavior of DGEBA/EMI derivative systems, indicating DGEBA could be efficiently cured by the EMI derivatives at 110～160°C, and the corresponding curing activation energy ranged from 71 to 86 kJ/mol. Viscosity data proves that the storage life of DGEBA with N‐acetyl EMI (NAEMI), N‐benzoyl EMI (NBEMI), and N‐benzenesulfonyl EMI (NBSEMI) at room temperature was 38 d, 50 d, and 80 d, and that at 10°C was 90 d, 115 d, and 170 d, respectively. Besides, thermogravimetry (TG), izod impact strength (IIS), and tensile shear strength (TSS) were tested to characterize the thermal stability and mechanical properties of DGEBA cured by EMI derivatives. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42563.