Styrylpyridine-based epoxy resins: Synthesis and characterization

Polymers containing rigid aromatic structures in the chain backbone usually gave high thermal stability and good flammability resistance. Three glycidyl ethers of epoxy resins were prepared from 2,4-di(p-hydroxystyryl)pyridine (2,4-DGESP), 2,6-di-(p-hydroxystyryl)pyridine (2,6-DGESP), and 2,4,6-tri-(p-hydroxystyryl)pryidine (2,4,6-TGESP) to study the relationships of structure to polymer degradation. To prepare a highly crosslinked material, trimethoxyboroxine (TMB) was used as the curing agent. The relative char yields of the three different resins, as measured by TGA, were 2,4-DGESP ≈ 2,6-DGESP > 2,4,6-TGESP. The char yield of the cured 2,6-DGESP varied with different amounts of the TMB curing agent, and was higher than the uncured 2,6-DGESP. The oxygen index increased as a function of thermal curing time for the 2,6-DGESP epoxy resin. An intermolecular Diels–Alder reaction with 2,6-DGESP is proposed as a primary reaction during thermal curing.     

Effect of P/Si polymeric silsesquioxane and the monomer compound on thermal properties of epoxy nanocomposite

The unique polymeric silsesquioxane/4,4′-diglycidyether bisphenol A (DGEBA) epoxy nanocomposites have been prepared by sol-gel method. The structure of nanocomposites was characterized by attenuated total reflectance (ATR) and solid state ²⁹Si NMR. The characteristic intensity of trisubstituted (T) structure was higher than that of tetrasubstituted (Q) structure from solid state ²⁹Si NMR spectra of 3-isocyanatopropyltriethoxysilane (IPTS) modified epoxy. The activation energies of curing reaction of epoxy system and IPTS modified epoxy system are 28-66 kJ/mol and 57-75 kJ/mol, respectively, by Ozawa’s and Kissinger’s methods. The triethyoxysilane side chain of IPTS modified epoxy might interfere the curing reaction of epoxy/amine and increase the activation energy of curing. The thermal degradation of nanocomposites was investigated by Thermogravimetric analysis (TGA). The char yield of nanocomposites was proportional to the 2-(diphenylphosphino)ethyltriethoxysilane (DPPETES) moiety content at high temperature. A higher char content could inhibit thermal decomposition dramatically and enhance the thermal stability. Moreover, the nanocomposites possess high optical transparency.     

Synthesis and properties of novel fluorinated epoxy resins based on 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane

A novel fluorinated epoxy resin, 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane (BGTF), was synthesized through a four-step procedure, which was then cured with hexahydro-4-methylphthalic anhydride (HMPA) and 4,4′-diaminodiphenyl-methane (DDM). As comparison, a commercial available epoxy resin, bisphenol A diglycidyl ether (BADGE), cured with the same curing agents was also investigated. We found that the BGTF gave the exothermic starting temperature lower than BADGE no mater what kind of curing agents applied, implying the reactivity of the former is higher than the latter. The fully cured fluorinated BGTF epoxy resins have good thermal stability with glass transition temperature of 170-175 °C and thermal decomposition temperature at 5% weight loss of 370-382 °C in nitrogen. The fluorinated BGTF epoxy resins also showed the mechanical properties as good as the commercial BADGE epoxy resins. The cured BGTF epoxy resins exhibited improved dielectric properties as compared with the BADGE epoxy resins with the dielectric constants and the dissipation factors lower than 3.3 and dissipation 2.8 × 10⁻³, respectively, which is related to the low polarizability of the C-F bond and the large free volume of CF₃ groups in the polymer. The BGTF epoxy resins also gave low water absorption because of the existence of hydrophobic fluorine atom.     

Preparation and thermal properties of diglycidylether sulfone epoxy

A diglycidylether sulfone monomer (sulfone type epoxy monomer, SEP) was prepared from bis(4-hydroxyphenyl) sulfone (SDOL) and epichlorohydrin without any NaOH or KOH as basic catalyst. FT-IR, ¹H NMR, ¹³C NMR and mass spectroscopic instruments were utilized to determine the structure of the SEP monomer. The cured SEP epoxy material exhibited not only a higher T_g (163.81 °C) but also a higher T_g than pristine DGEBA (from 111.25 °C to 139.17 °C) when the SEP monomer moiety had been introduced into the DGEBA system. The thermal stability of cured epoxy herein was investigated by thermogravimetric analysis (TGA). The results demonstrated that the sulfone group of the cured SEP material decomposed at lower temperatures and formed thermally stable sulfate compounds, improving char yield and enhancing resistance against thermal oxidation. Additionally, the IPDT and char yield of the cured SEP epoxy (IPDT = 1455.75, char yield = 39.67%) exceeded those of conventional DGEBA epoxy (IPDT = 667.27, char yield = 16.25%).     

Synthesis and thermal decomposition of a novel hyperbranched polyphosphate ester used for flame retardant systems

A novel hyperbranched polyphosphate ester (HPPE) was synthesized via the polycondensation of bisphenol-A as an A₂ monomer and phosphoryl trichloride as a B₃ monomer at 100 °C, without gelation. The initial molar ratio of A₂ to B₃ was set to be 1.5:1. The final product was precipitated from methanol. ³¹P NMR spectroscopy was used to monitor the reaction. The formed HPPE was characterized by FTIR and ¹H NMR to confirm its end groups. Differential scanning calorimetry data revealed that the cured bisphenol-A epoxy resin with HPPE as a curing agent possessed improved glass transition temperature. Dynamic mechanical thermal analysis also showed the increase in the glass transition temperature. The thermal degradation properties and flame retardancy were investigated by thermogravimetric analysis and limiting oxygen index (LOI). The results showed that the incorporation of HPPE into bisphenol-A epoxy resin increased its thermal stability and char yield during the decomposition by raising the second stage decomposition temperature. The LOI value increased from 23 to 31 when HPPE, instead of bisphenol-A, was used as a curing agent.     

Synthesis and thermal degradation behaviors of hyperbranched polyphosphate

A novel epoxy-terminated hyperbranched polyphosphate (E-HBPP) was synthesized by employing an A₂ + B₃ polycondensation and characterized by FTIR, ¹H NMR and GPC. E-HBPP was used as a reactive-type flame retardant for diglycidyl ether of bisphenol-A/m-phenylene diamine (DGEBA/mPDA) system. A series of flame retardant resins were prepared and their flame retardancy was monitored by the limiting oxygen index (LOI). The results showed that the LOI value of the cured samples and the degree of expansion of the formed char after burning increased along with the E-HBPP content. Their thermal degradation behaviors were investigated by thermogravimetric analysis and in situ FTIR and showed that the phosphate group of E-HBPP first degraded to form poly(phosphoric acid)s at around 300 °C, which had a major contribution to form the compact char to protect the sample from further degradation. The dynamic mechanical thermal properties were studied by dynamic mechanical thermal analysis (DMTA) and the results showed a good miscibility between E-HBPP and DGEBA. The mechanical properties of the cured films were also investigated. Less than 20% E-HBPP addition improved both the tensile strength and elongation at break.     

Synthesis and thermal properties of the thermosetting resin based on cyano functionalized benzoxazine

A novel thermosetting resin based on cyano functionalized benzoxazine (BZCN) has been synthesized from 2,6-bis(4-diaminobenzoxy)benzonitrile phenol and formaldehyde by solution reaction. The structure of the monomer is supported by FTIR, ¹H NMR and ¹³C NMR spectra, which have exhibited that the reactive benzoxazine rings and cyano group exist in the molecular structure of BZCN. The curing reactions of BZCN are monitored by the disappearance of the nitrile peak and the tri-substituted benzene ring that is attached with oxazine ring peak at 2231 and 930 cm⁻¹, respectively. The complete cured materials could achieve char yields up to 70% at 800 °C in nitrogen atmosphere, above 64% at 600 °C in air (20% oxygen) environments and the glass transition temperature up to 250 °C. The thermally activated curing polymerization reaction of BZCN follows multiple polymerization mechanisms via the ring-opening polymerization of oxazine rings and the triazine ring-formation of cyano groups, which contribute to the stability of the polymer.     

Comparative studies on the curing kinetics and thermal stability of tetrafunctional epoxy resins using various amines as curing agents

The curing reactions of the epoxy resins tetraglycidyl diaminodiphenyl methane (TGDDM) and tetraglycidyl methylenebis (o-toluidine) (TGMBT) using diaminodiphenyl sulfone (DDS), diaminodiphenyl methane (DDM) and diethylenetriamine (DETA) as curing agents were studied kinetically by differential scanning calorimetry. The dynamic scans in the temperature range 20°–300°C were analyzed to estimate the activation energy and the order of reaction for the curing process using some empirical relations. The activation energy for the various epoxy systems is observed in the range 71.9–110.2 kJ·mol^–1. The cured epoxy resins were studied for kinetics of thermal degradation by thermogravimetry in a static air atmosphere at a heating rate of 10 deg·min^–1. The thermal degradation reactions were found to proceed in a single step having an activation energy in the range 27.6–51.4 kJ·mol^–1.

---

Zusammenfassung Die Vernetzungsreaktionen der Epoxidharze Tetraglycidyl-diamino-diphenyl-methan (TGDDM) und Tetraglycidyl-methylen-bis(o-toluidin) (TGMBT) unter Verwendung von Diaminodiphenylsulfon (DDS), Diaminodiphenylmethan (DDM) und Diethylentriamin (DETA) als Vernetzungsmittel wurden kinetisch mittels DSC untersucht. Die dynamischen Scans im Temperaturbereich 20°–300°C wurden analysiert, um unter Anwendung einiger empirischer Gleichungen die Aktivierungsenergie und die Reaktionsordnung des Vernetzungsprozesses zu ermitteln. Die Aktivierungsenergie der einzelnen Epoxy-Systeme liegt im Bereich 71.9–110.2 kJ·mol^–1. An der ausgehärteten Harze wurde mittels TG in einer statischen Luftatmosphäre un deiner Aufheizgeschwindigkeit von 10 Grad/min die Kinetik des termischen Abbaues untersucht. Man fand, daß die thermiscehn Abbaureaktionen in einem Schritt ablaufen und ihre Aktivierungsenergie im Intervall 27.6–51.4 kJ·mol^–1 liegt.

     

Nanocomposites based on vapor-grown carbon nanofibers and an epoxy: Functionalization, preparation and characterization

Vapor-grown carbon nanofibers (VGCNF) were functionalized with amine-containing pendants via a Friedel-Crafts acylation reaction with 4-(3-aminophenoxy)benzoic acid. The resulting H₂N-VGCNF was treated with epichlorohydrin, followed by sodium hydroxide solution to afford N,N-diglycidyl-modified VGCNF that is designated as epoxy-VGCNF. Subsequently, epoxy-VGCNF was dispersed in an epoxy resin (Epon 862) with the aid of acetone and sonication. After acetone had been removed under vacuum from the mixture, curing agent “W” was added to epoxy-VGCNF/Epon 862 mixture, which was then poured into molds and cured at 250 °F (121 °C) for 2 h and 350 °F (177 °C) for 2 h to form a series of epoxy/fVGCNF samples; fVGCNF designated for “functionalized VGCNF” was used to denote our belief that all epoxy functions have reacted in the resulting nanocomposites. The VGCNF content was increased from 0.10 to 10.0 wt%. For comparison purposes, the pristine VGCNF or pVGCNF (0.1-5.0 wt%) was also used in the in situ polymerization of Epon 862 and curing agent “W” to afford another series of epoxy/pVGCNF samples. The epoxy-VGCNF showed a better dispersion in the epoxy resin than pVGCNF according to SEM results. Both the tensile moduli and strengths of epoxy/fVGCNF nanocomposites are higher than those of epoxy/pVGCNF. The additive effect of VGCNF on glass-transition (T_g) was discussed in terms of thermal analysis results. The thermal stability of the nanocomposites was investigated by thermogravimetric analysis (TGA).     

Intrinsically flame retardant epoxy resin - Fire performance and background - Part I

The flame retardant effect of newly synthesized phosphorus-containing reactive amine, which can be used both as crosslinking agent in epoxy resins and as a flame retardant, was investigated. The effect of montmorillonite and sepiolite additives on the fire induced degradation was compared to pristine epoxy resin. The effect of combining the organophosphorous amine with clay minerals was also studied. It could be concluded that the synthesized phosphorus-containing amine, TEDAP can substitute the traditional epoxy resin curing agents providing additionally excellent flame retardancy: the epoxy resins flame retarded this way reach 960 °C GWFI value, 33 LOI value and V-0 UL-94 rating - compared to the 550 °C GWFI value, 21 LOI value and “no rate” UL-94 classification of the reference epoxy resin. The peak of heat release was reduced to 1/10 compared to non-flame retarded resin, furthermore a shift in time was observed, which increases the time to escape in case of fire. The flame retardant performance can be further improved by incorporating clay additives: the LOI and the HRR results showed that the optimum of flame retardant effect of clay additives is around 1 mass% filler level in AH-16-TEDAP system. Applying a complex method for mechanical and structural characterization of the intumescent char it was determined that the flame retarded system forms significantly more and stronger char of better uniformity with smaller average bubble size. Incorporation of clay additives (owing to their bubble nucleating activity) results in further decrease in average bubble diameter.     

Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin

A thermoplastic toughener, polyether sulphone (PES) and a number of different types of flame retardants were blended in different ratios with a commercial epoxy resin triglycidyl-p-aminophenol (TGAP) and 4,4-diamino diphenyl sulphone (DDS) a curing agent. The effect of type and levels of flame retardants (FR) and the toughening agent on the curing, thermal decomposition and char oxidation behaviour of the epoxy resin was studied by the simultaneous differential thermal analysis and thermogravimetric techniques. It was observed that the toughener slightly increases the curing temperature (by up to 20 °C) but had minimal effect on the decomposition temperature of the resin. Flame retardants, however affected all stages depending upon the type of flame retardant used. The curing peak for samples containing tougher and flame retardants although slightly changed depending upon the type of FR, was not more than ± 20 °C compared to that of samples containing toughener only. All flame retardants lowered the decomposition temperature of the epoxy resin. Phosphorus- and nitrogen-containing flame retardants reduced the char oxidation leading to more residual char, whereas halogen- containing flame retardants had less effect on this stage.     

Modified epoxy coatings on mild steel: Tribology and surface energy

A commercial epoxy diglycidylether of bisphenol-A (DGEBA) was modified by adding fluorinated poly(aryl ether ketone) fluoropolymer and in turn metal micro powders (Ni, Al, Zn, and Ag) and coated on mild steel. Two curing agents were used; triethylenetetramine (a low temperature curing agent) and hexamethylenediamine (a high temperature curing agent) for understanding the curing temperature effect on the properties. Variations in tribological properties (dynamic friction and wear) and surface energies with varying amounts of metal powders and curing agents were evaluated. When cured at 30 °C, dynamic friction and wear decrease significantly due to phase separation reaction being favored between the fluoropolymer and the epoxy. However, when cured at 80 °C, friction and wear increase; this can be explained in terms of a crosslinking reaction favored at that temperature. There is a significant decrease in surface energies with the addition of modifiers.     

Polyethylene thermal oxidative stabilisation in carbon nanotubes based nanocomposites

Multiwall carbon nanotubes (MWNT)/linear low density polyethylene (LLDPE) nanocomposites were studied in order to understand the stabilisation mechanism for their thermal and oxidative degradation. Thermogravimetry coupled with infrared evolved gas analysis and pyrolysis gas chromatography-mass spectrometry demonstrate that MWNT presence slightly delays thermal volatilisation (15-20 °C) without modification of thermal degradation mechanism. Whereas thermal oxidative degradation in air is delayed by about 100 °C independently from MWNT concentration in the range used here (0.5-3.0 wt.%). The stabilisation is due to formation of a thin protective film of MWNT/carbon char composite generated on the surface of the nanocomposites is shown by SEM and ATR FTIR of degradation residues. The film formation mechanism is discussed.     

Thermo-oxidative degradation of novel epoxy containing silicon and phosphorous nanocomposites

Modified epoxy nanocomposites containing silicon and phosphorous was prepared and compared with pure epoxy. The study of thermo-oxidative degradation of modified epoxy nanocomposites and pure epoxy has been utilized by thermal analysis. The thermal stability of modified epoxy nanocomposites is not superior to that of the pure epoxy at low temperature, however, the char yield of modified epoxy nanocomposites is higher than that of the pure epoxy at 800 °C in air atmosphere. The modified epoxy nanocomposites possess better thermal stability at high temperature range. The values of the limiting oxygen index of pure epoxy and modified epoxy nanocomposites are 24 and 32, respectively. This indicates that modified epoxy nanocomposites possesses better flame retardance.By the Kissinger’s method, the activation energies of thermo-oxidative degradation for epoxy nanocomposites are less than those of thermo-oxidative degradation for pure epoxy in first stage of thermo-oxidative degradation. However, the activation energies of thermo-oxidative degradation for epoxy nanocomposites are more than those of thermo-oxidative degradation for pure epoxy in second stage of thermo-oxidative degradation.     

Photopolymerization and thermal behaviors of acrylated benzenephosphonates/epoxy acrylate as flame retardant resins

Di(acryloyloxyethyl) benzenephosphonate (DABP) and acryloyloxyethyl phenyl benzenephosphonate (APBP) were synthesized starting from phenylphosphonic dichloride, and characterized by FT-IR and ¹H NMR. DABP and APBP were blended in the ratios of 10-50 wt.% with a commercial epoxy acrylate oligomer (EB600) to obtain a series of flame retardant UV-curable formulations. The viscosity of the formulations greatly reduced by the addition of the reactive monomers, whereas the photopolymerization rate according to the photo-DSC analysis increased. The thermal degradation behavior and flame retardancy of the UV-cured films were investigated by thermogravimetric analysis and the limiting oxygen index (LOI). The results revealed that the blended epoxy acrylates with DABP or APBP possess improved thermal stability at elevated temperature and have higher char yields, together with higher LOI values. The data from dynamic mechanical thermal analysis showed that DABP and APBP have good miscibility with EB600. The crosslink density increased along with the content of DABP or APBP in the blend, whereas the glass-transition temperatures of the blended resins decreased compared to pure cured EB600.     

Thermal characterization and thermal degradation of poly(norbornene-2,3-dicarboxylic acid dialkyl esters) synthesized by vinyl addition polymerization

The thermal properties and degradation behaviors of poly(norbornene-2,3-dicarboxylic acid dialkyl esters) (PNB-dialkyl esters) (alkyl = Me (PNB-Me), Et (PNB-Et), Pr (PNB-Pr), and Bu (PNB-Bu)) were investigated by thermogravimetric analysis (TGA) in dynamic conditions and by infrared (IR) spectroscopy. The PNB-dialkyl esters show good thermal stability up to 350 °C, and the thermal stability decreases in the order Me > Et > Pr > Bu with the increase in size of side chain. The effect of side-chain size on the thermal degradation behaviors of PNB-dialkyl esters is evidenced by one-step thermal degradation profile for PNB-Me while two-step thermal degradation profile for PNB-Et, PNB-Pr, and PNB-Bu. Transformation is deduced to undergo β-hydrogen elimination and formation of anhydride group in the first stage of thermal degradation reaction according to TGA and IR results for PNB-Et, PNB-Pr, and PNB-Bu. The apparent activation energy and thermal degradation model of PNB-dialkyl esters are estimated by means of Ozawa-Flynn-wall method and Phadnis-Deshpande method, respectively.     

Synthesis and characterization of P/Si flame retardant and its application in epoxy systems

In this report, a novel phosphorus/silicon‐containing reactive flame retardant, hexa(3‐triglycidyloxysilylpropyl)triphosphazene (HGPP), was synthesized and characterized by Fourier transform infrared spectrometry and nuclear magnetic resonance spectra (¹H, ³¹P, and ²⁹Si), respectively. To prepare cured epoxy, HGPP had been co‐cured with diglycidyl ether of bisphenol‐A (DGEBA) via 4,4‐diaminodiphenylsulfone as a curing agent. The mechanical, thermal, and flame retardant properties of the cured epoxy were evaluated by dynamic mechanical analysis, thermogravimetric analysis, and limiting oxygen index (LOI). According to these results, it could be found that incorporation of HGPP in the cured epoxy system showed good thermal stability, high LOI values, and high char yield at high temperature. As moderate loading of HGPP in the epoxy system, its storage modulus and glass transition temperature were higher than those of neat DGEBA. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of a novel charring-foaming agent on flame retardancy and thermal degradation of intumescent flame retardant polypropylene

A new triazine polymer was synthesized by using cyanuric chloride, ethanolamine and ethylenediamine as raw materials. It is used both as a charring agent and as a foaming agent in intumescent flame retardants, designated as charring-foaming agent (CFA). Effect of CFA on flame retardancy, thermal degradation and mechanical properties of intumescent flame retardant polypropylene (PP) system (IFR-PP system) has been investigated. The results demonstrated that the intumescent flame retardant (IFR) consisting of CFA, APP and Zeolite 4A is very effective in flame retardancy of PP. It was found that when the weight ratio of CFA to APP is 1:2, that is, the components of the IFR are 64 wt% APP, 32 wt% CFA and 4 wt% Zeolite 4A, the IFR presents the most effective flame retardancy in PP systems. LOI value of IFR-PP reaches 37.0, when the IFR loading is 25 wt% in PP. It was also found that when the IFR loading is only 18 wt% in PP, the flame retardancy of IFR-PP can still pass V-0 rating, and its LOI value reaches 30.2. TGA data obtained in pure nitrogen demonstrated that CFA has a good ability of char formation itself, and CFA shows a high initial temperature of the thermal degradation. The char residue of CFA can reach 35.7 wt% at 700 °C. APP could effectively promote the char formation of the APP-CFA system. The char residue reaches 39.7 wt% at 700 °C, while it is 19.5% based on calculation. The IFR can change the thermal degradation behaviour of PP, enhance T_max of the decomposition peak of PP, and promote PP to form char, based upon the results of the calculation and the experiment. This is attributed to the fact that endothermic reactions took place in IFR charring process and the char layer formed by IFR prevented heat from transferring into inside of IFR-PP system. TGA results further explained the effective flame retardancy of the IFR containing CFA.     

Curing conditions of polyarylacetylene prepolymers to obtain thermally resistant materials

Prepolymers of polyarylacetylene (PAA) were synthesized from 1,4-diethynylbenzene using nickel catalyst (C20, C25, and C30) or by direct thermal polymerization (T48). Their curing behaviors were investigated in detail to determine the proper curing conditions that lead to high char yields in cured PAA resins. Dynamic and isothermal differential scanning calorimetry (DSC) measurements were employed to investigate the curing conditions of the prepolymers. Dynamic DSC study reveals that exothermic heat starts at about 120 °C, reaches to a maximum at 210 °C, and ends around 300 °C. Moreover, step isothermal DSC investigation (at 120, 160, 200, 250, and 300 °C; 1 h for each temperature) shows that the major curing occurs at 160 °C, 200 °C and 250 °C, with more than 85% of the acetylene groups reacted. Using this step-curing conditions, very high thermal resistance is realized on C30, with thermal decomposition temperature (at 10% weight loss) and char yield (at 800 °C) being 686 °C and 86%, respectively. Current results indicate that highly thermal resistant PAA resins are obtainable using step curing of PAA prepolymers synthesized by Ni-catalyzed reaction.     

Flame retarding mechanism of polycarbonate containing methylphenyl-silicone

The thermal degradation of polycarbonate (PC) containing methylphenyl-silicone with a branched structure (SFR-PC) was investigated by the thermogravimetric analysis (TGA). The decomposition activation energies were determined using the Ozawa method. It was found that the decomposition activation energy and the degradation residue of the SFR-PC at 800 °C in air atmosphere were much higher than those of the PC. The addition of methylphenyl-silicone enhanced the thermal stability of PC and promoted the formation of char. The silicone was found effective in retarding the combustion of the PC. The limited oxygen index of the PC containing 5 wt.% of methylphenyl-silicone was 34%. Surfaces of the SFR-PC before and after combustion were analyzed by energy dispersive X-ray analysis (EDX) and infrared (IR) spectroscopy. Based on these results obtained, the flame retarding mechanism of the SFR-PC was discussed.