New type of phenolic resin: Curing reaction of phenol‐novolac based benzoxazine with bisoxazoline or epoxy resin using latent curing agent and the properties of the cured resin

In this study, we aimed to reduce the cure time, and to lower the cure temperature of the benzoxazine compound. Therefore, curing reaction of benzoxazine with bisoxazoline or epoxy resin using the latent curing agent and the properties of the cured resins were investigated. The cure behavior of benzoxazine with bisoxazoline or epoxy resin using the latent curing agent was monitored by differential scanning calorimetry and measurements for storage modulus (G′). The properties of the cured resin were estimated by mechanical properties, electrical insulation, water resistance, heat resistance, and flame resistance. As a result, it was confirmed that by using the latent curing agent, cure time of benzoxazine and bisoxazoline or epoxy resin was reduced, and cure temperature was lowered. And it was found that the curing reaction using phenol‐novolac based benzoxazine (Na) as the benzoxazine compound could proceed more rapidly than that using bisphenol‐A based benzoxazine (Ba) as the benzoxazine compound. However, the cured resins from Ba and bisoxazoline or epoxy resin using the latent curing agent showed good heat resistance, flame resistance, and mechanical properties compared with those from Na and bisoxazoline or epoxy resin using the latent curing agent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

水性环氧树脂/双氰胺体系的研究

多官能团酚醛环氧树脂F-51与适量二乙醇胺反应,制得一种分子中含环氧基和亲水基团的改性F-51环氧树脂,该树脂成盐后具有良好亲水性。以双氰胺为固化剂,对体系的反应性及固化物主要性能进行研究,结果表明固化反应起始温度显著降低,固化膜的硬度达6H,并具有很强的附着力。     

Study of the effect of BDMA catalyst in the epoxy novolac curing process by isothermal DSC

Epoxy novolac/anhydride cure kinetics has been studied by differential scanning calorimetry under isothermal conditions. The system used in this study was an epoxy novolac resin (DEN431), with nadic methyl anhydride as hardener and benzyldimethylamine as accelerator. Kinetic parameters including the reaction order, activation energy and kinetic rate constants, were investigated. The cure reaction was described with the catalyst concentration, and a normalized kinetic model developed for it. It is shown that the cure reaction is dependent on the cure temperature and catalyst concentration, and that it proceeds through an autocatalytic kinetic mechanism. The curing kinetic constants and the cure activation energies were obtained using the Arrhenius kinetic model. A suggested kinetic model with a diffusion term was successfully used to describe and predict the cure kinetics of epoxy novolac resin compositions as a function of the catalyst content and temperature. Copyright © 2003 Society of Chemical Industry     

B‐stage characterization of o‐cresol novolac epoxy resin system using raman spectroscopy and matrix‐assisted laser desorption/ionization mass spectrometry

The B‐stage of the o‐cresol novolac epoxy resin–phenol novolac hardener–triphenylphosphine (TPP) catalyst system was characterized using Raman spectroscopy and matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry. The consistent decreasing intensities of characteristic epoxy resin peaks in MALDI mass and Raman spectra according to the melt mixing time were observed, which is due to the formation of the epoxy–phenol–TPP complex and the propagation reaction between them and with another epoxy resin. Our microscopic analysis method will provide a useful tool to control the optimum condition of the melt mixing process in the B‐stage. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1940–1946, 2000     

Relationship between viscoelastic properties and gelation in the epoxy/phenol‐novolac blend system with N‐benzylpyrazinium salt as a latent thermal catalyst

A study of viscoelastic properties and gelation in epoxy/phenol‐novolac blend system initiated with 1 wt % of N‐benzylpyrazinium hexafluoroantimonate (BPH) as a latent cationic thermal initiator was performed by analysis of rheological properties using a rheometer. Latent behavior was investigated by measuring the conversion as a function of curing temperature using traditional curing agents, such as ethylene diamine (EDA) and nadic methyl anhydride (NMA) in comparison to BPH. In the relationship between viscoelastic properties and gelation of epoxy/phenol‐novolac blend system, the time of modulus crossover was dependent on high frequency and cure temperature. The activation energy (E_c) for crosslinking from rheometric analysis increased within the composition range of 20–40 wt % phenol‐novolac resin. The 40 wt % phenol‐novolac (N40) to epoxy resin showed the highest value in the blend system, due to the three‐dimensional crosslinking that can take place between hydroxyl groups within the phenol resin or epoxides within the epoxy resin involving polyaddition of the initiator with BPH. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2299–2308, 2001     

Preparation and epoxy curing of p‐nonylphenol/dicyclopentadiene adducts

Phenol/dicyclopentadiene adducts were prepared from the BF₃‐catalyzed reaction of p‐nonylphenol and dicyclopentadiene at molar ratios of 2 : 1 and 3 : 2. These dicyclopentadiene‐derived novolac products contain tricyclodecane and multiple phenol functionalities. In curing with diglycidyl ether of bisphenol A, the polymer properties were compared with those cured with formaldehyde novolac or Jeffamine D‐400 amine. When p‐nonylphenol/dicyclopentadiene adducts were mixed with other commercially available curing agents such as Jeffamine D‐400 amine, the tricyclodecane functionality was introduced into the resulting epoxy network. The flexibility of the cured resin was improved due to the presence of the tricyclodecane moiety in the polymer structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2196–2206, 1999     

Curing kinetics study of an epoxy resin system for T800 carbon fiber filament wound composites by dynamic and isothermal DSC

Curing kinetics of DGEAC/DDM/DETDA/DGEB epoxy resin system was studied using dynamic and isothermal differential scanning calorimetry (DSC) for the preparation of T800 carbon fiber filament wound composites. In dynamic experiment, four kinds of epoxy resin systems were studied. Curing characteristics, such as curing range and curing temperatures of the epoxy resin system with mixed hardeners (DGEAC/DDM/DETDA), were found lying within those of the two epoxy resin systems with a single hardener (DGEAC/DDM, DGEAC/DETDA). The addition of reactive diluter (DGEB) caused increase in curing range and exothermic heat. In addition, the activation energies calculated by the isoconversional method of all four resin systems decreased to the minimum value in the early stage due to the autocatalytic role of hydroxyl groups in the curing reaction and then increased due to the increased viscosity and crosslink of epoxy systems. The addition of reactive diluter led to the decrease in activation energies on the initial stage (conversion = 0.1–0.3). In isothermal experiment, a series of isothermal DSC runs provided information about the curing kinetics of the DGEAC/DDM/DETDA/DGEB system over a wide temperature range. The results showed that the isothermal kinetic reaction of the epoxy resin followed an autocatalytic kinetic mechanism. The autocatalytic kinetic expression chosen in this work was suitable to analyze the curing kinetics of this system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and curing kinetics of bisphenol A type novolac epoxy resins

A bisphenol A type novolac resin (Bis‐ANR) was synthesized from bisphenol A and formaldehyde; the resulting novolac was epoxidized to generate a bisphenol A type novolac epoxy resin (Bis‐ANER). The chemical structures of Bis‐ANR and Bis‐ANER were confirmed by ¹H‐NMR spectroscopy and IR spectroscopy; the molecular weights and molecular weight distributions were determined by gel permeation chromatography. In addition, the curing process of Bis‐ANER with 4,4′‐diaminodiphenyl sulfone was studied in both dynamic and isothermal modes with differential scanning calorimetry. The dynamic curing kinetic analysis was evaluated with both the Kissinger and Flynn–Wall–Ozawa methods, and the curing activation energy values were obtained. The isothermal curing reaction exhibited autocatalytic behavior, and the curing kinetics were described with the Kamal kinetics model, which accounted for both the autocatalytic and diffusion‐control effects. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 858–868, 2006     

Heterocyclic‐based epoxy‐terminated structural adhesive. II. Curing,adhesive strength,and thermal stability

We studied the curing behavior of heterocyclic‐based epoxy‐terminated resins using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylicdianhydride, and the commercial hardener of Ciba‐Geigy's two‐pack Araldite as curing agents. The adhesive strength of the adhesives was measured by various ASTM methods such as lap‐shear, peel, and cohesive tests on metal–metal, wood–wood, and wood–metal interfaces. All of these results were compared with those of an epoxy resin prepared from bisphenol‐A and epichlorohydrin resin with an epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3520–3526, 2002     

Chemical shrinkage and diffusion-controlled reaction in a cresol novolac epoxy

The reaction kinetics with a diffusion control mechanism, as well as the volumetric change upon curing, of a cresol novolac epoxy/o-cresol-formaldehyde novolac hardener system were studied. Simple equations to model the change in linear coefficients of thermal expansion with reacting thermosetting system conversion were also derived. Based on the heat of the reaction of monomeric monofunctional model compounds, the true degree of conversion of this crosslinking epoxy system can be obtained. The reaction is then modeled as a reaction of shifting order: it first reacts autocatalytically and later switches into diffusion control. The reaction in the diffusion-controlled region can be modeled by an n-th order kinetic equation with its rate constant described by a WLF-type equation. Both experimental linear coefficients of thermal expansion above and below the glass transition temperature decrease linearly with the degree of conversion, which agrees with the derived equations. The importance of chemical shrinkage upon curing is also discussed.     

环氧树脂低温快速固化剂的合成及性能研究

以苯酚、多聚甲醛、二乙烯三胺、硫脲为单体,以DMP-30为促进剂,合成了环氧树脂低温快速固化剂.分析了反应温度、反应时间以及各材料用量对环氧树脂固化剂性能的影响,并进一步考察了固化剂与环氧树脂最佳用量比.在( 110±2)℃下反应2.5 h,苯酚、多聚甲醛、二乙烯三胺、硫脲之比为1∶1.25∶1.3∶1.1,且DMP-...     

室温固化耐高温耐水胶粘剂的研制

采用酚醛环氧树脂F-51和环氧树脂CYD-128复合树脂、自制的羧基丁腈改性环氧树脂增韧剂和酚醛胺固化剂以及陶瓷耐热填充剂复配,研制出1种室温固化耐高温耐水胶粘剂。测试了不同固化剂,增韧剂,填充剂对胶粘剂粘接强度的影响并考察了胶粘剂的耐水性。结果表明,该胶A组分最佳配方为:CYD-12880g,F-5120g,羧基丁腈改性环氧树脂10g,轻质碳酸钙20g,陶瓷耐热填充剂1#40g,2#20g;B组分配方为:酚醛胺固化剂40g,轻质碳酸钙20g,陶瓷耐热填充剂1#35g,A与B质量比为2:1时,室温固化1d后的剪切强度达21.4MPa(室温),150℃剪切强度6.2MPa,水中浸泡30d后强度几乎无变化。该胶可长期在高温条件下使用,满足耐磨陶瓷粘接的技术要求。     

几种胺类固化剂对环氧树脂固化行为及固化物性能的影响

固化剂结构对环氧树脂的固化行为和固化物性能具有重要影响,本文研究了聚醚胺(D-230)、异佛尔酮二胺(IPDA)和3,3'-二甲基-4,4'-二氨基-二环己基甲烷(DMDC) 3种胺类固化剂与实验室自制的低翻度环氧树脂A进行固化反应.通过薪度分析、红外(FTIR)光谱分析、DSC分析等手段研究了环氧树脂与固化剂反应程度...     

硫脲改性胺环氧树脂固化剂的合成及性能研究

对硫脲改性胺(3,3′-二乙基4,4′-二氨基二苯基甲烷和二元脂肪胺A)固化剂固化环氧树脂进行了系统研究,分析了合成反应时间、反应温度和单体配料比对固化剂性能的影响,并进一步考察了固化剂与环氧树脂的最佳掺量比以及固化产物的热性能和力学性能。实验结果表明:反应时间为2.5 h,反应温度为130℃,3,3′-二乙基4,4′-二氨基二苯基甲烷与硫脲和二元脂肪胺A的物质的量比为1∶0.5∶0.4时,合成的固化剂以1∶3加入环氧树脂中,体系能在室温环境下1 h左右凝胶,该体系经室温固化再以100℃的温度后固化之后具有较好的耐热性能和冲击韧性。     

Dynamic mechanical analysis study of the curing of phenol‐formaldehyde novolac resins

The curing reaction of typical commercial phenol‐formaldehyde novolac resins with hexamethylentetraamine (HMTA) was followed by dynamic mechanical analysis. The evolution of the rheological parameters, such as storage modulus G′, loss modulus G″, and tanδ (G″/G′), as a function of time, for samples of the phenolic resins on cloth, was recorded. The curing reaction, leading to the formation of a crosslinked structure, is described by a third‐order phenomenological equation. This equation takes into account a self‐acceleration effect, as a consequence not only of the chemical reaction of crosslinking after the gel point but of phase segregation as well. This rheokinetic model of the curing of phenolic novolac resins permits the determination of the numerical values of the kinetic equation constants. The influence of the composition, structure, and physical treatment on the curing kinetics of the novolac resins is evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1902–1913, 2001     

Properties of epoxy resin cured by phenol novolac/4-hydroxyphenylmaleimide polymer blend hardeners

Phenol novolac/4-hydroxyphenylmaleimide (HPMI) homopolymer (PHPMI) blends or phenol novolac/HPMI-styrene copolymer (HPMI-St) blends were used as the hardener of epoxy resins. Curing behaviour of the above systems and thermal and mechanical properties of the cured epoxy resins were studied. It was not necessary to use a curing accelerator for this system because PHPMI or HPMI-St had an accelerating effect on the curing reaction. Curing behaviour was investigated by measurement of gelation time(JIS K 6910) and differential scanning calorimetry thermogram (JIS K 7122). Test pieces made from neat resins and from reinforced resins with glass fibre or fused silica were evaluated in terms of thermal and mechanical properties, respectively. It was found that the heat resistance and the mechanical properties improved with increase of PHPMI or HPMI-St content in the hardener.     

Phenol novolac/poly(4- hydroxyphenylmaleimide) blend hardeners for DGEBA-type epoxy resin

Phenol novolac/poly (4-hydroxyphenylmaleimide) (PHPMI) blends were used as an epoxy resin hardener. The curing behavior of the above system and the thermal and mechanical properties of the cured epoxy resin were studied. It was not necessary to use a curing accelerator for this system, because PHPMI caused acceleration of the curing reaction. The curing mechanism of this system was investigated by using model compounds. Test pieces from the neat resins and the glass fiber reinforced resins were evaluated in terms of thermal and mechanical properties, respectively. It was found that heat resistance and mechanical properties were improved by increasing the amount of PHPMI in the hardener.     

Conductive epoxy/amine system containing polyaniline doped with dodecylbenzenesulfonic acid

We developed a conductive epoxy/amine system containing polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA). The curing behaviors of diglycidyl ether of bisphenol A with triethylenetetramine (TETA), PAni.DBSA, and both amine compounds at different concentrations were investigated by differential scanning calorimetry (DSC). Epoxy/TETA systems containing PAni.DBSA presented two distinct exothermic peaks at 90°C due to the cure by TETA as a hardener and at 236°C related to PAni.DBSA as the curing agent. The presence of PAni.DBSA in the systems constituted by epoxy/hardener in stoichiometric proportions resulted in a decrease in the glass‐transition temperature of the epoxy matrix, as indicated by DSC and dielectric analyses. Electrical conductivity was determined in the epoxy/amine networks, with the TETA concentration kept constant and also in stoichiometric proportions of mixed hardener (TETA + PAni.DBSA) to epoxy resin. The last condition resulted in a higher electrical conductivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4059–4065, 2006     

Time–temperature–transformation cure diagrams of phenol–formaldehyde and lignin–phenol–formaldehyde novolac resins

In this study, the time–temperature– transformation (TTT) cure diagrams of the curing processes of several novolac resins were determined. Each diagram corresponded to a mixture of commercial phenol–formaldehyde novolac, lignin–phenol–formaldehyde novolac, and methylolated lignin–phenol–formaldehyde novolac resins with hexamethylenetetramine as a curing agent. Thermomechanical analysis and differential scanning calorimetry techniques were applied to study the resin gelation and the kinetics of the curing process to obtain the isoconversional curves. The temperature at which the material gelled and vitrified [the glass‐transition temperature at the gel point (_gelT_g)], the glass‐transition temperature of the uncured material (without crosslinking; T_g0), and the glass‐transition temperature with full crosslinking were also obtained. On the basis of the measured of conversion degree at gelation, the approximate glass‐transition temperature/conversion relationship, and the thermokinetic results of the curing process of the resins, TTT cure diagrams of the novolac samples were constructed. The TTT diagrams showed that the lignin–novolac and methylolated lignin–novolac resins presented lower T_g0 and _gelT_g values than the commercial resin. The TTT diagram is a suitable tool for understanding novolac resin behavior during the isothermal curing process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011