Synthesis, characterization and thermal properties of novel PMDA-PAPD/silica hybrid network polymers

Novel PMDA-PAPD/silica hybrid polymers were synthesized by the sol-gel process. Fourier transform infrared spectroscopy and ²⁹Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids, (condensed siloxane bonds designated as Q¹, Q², Q³, Q⁴, wth 3-aminopropyltriethoxysilane having mono-, di-, tri-, tetra-substituted siloxane bonds is designated as T¹, T² and T³). The results revealed that Q³, Q⁴ and T³ are the major microstructure elements in forming a network structure. The surface morphology, particle size, crystallinity and the thermal stability of the hybrids were investigated using Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). SEM and TEM revealed that the hybrids were nanocomposites. The XRD indicated that covalent bonding (Si-O-Si) between the organic and inorganic components enhanced miscibility. DSC and TGA results showed that these hybrid materials had excellent thermal stability. The heat capacities of some materials were reported for the temperature range 273 K and 363 K as no thermal anomaly was found in this temperature range.     

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.     

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.     

The non-halogen flame retardant epoxy resin based on a novel compound with phosphaphenanthrene and cyclotriphosphazene double functional groups

A novel flame retardant additive hexa-(phosphaphenanthrene -hydroxyl-methyl-phenoxyl)-cyclotriphosphazene (HAP-DOPO) with phosphazene and phosphaphenanthrene double functional groups has been synthesized from hexa-chloro-cyclotriphosphazene, 4-hydroxy-benzaldehyde and 9,10-dihydro-9-oxa-10- phosphaphenanthrene 10-oxide(DOPO). The structure of HAP-DOPO was characterized by Fourier transformed infrared (FT-IR) spectroscopy and ¹H nuclear magnetic resonance (¹H NMR) and ³¹P nuclear magnetic resonance (³¹P NMR). The additive HAP-DOPO was blended into diglycidyl ether of bisphenol-A (DGEBA) to prepare flame retardant epoxy resins. The flame retardant properties and thermal properties of the epoxy resins cured by 4, 4′-Diamino-diphenyl sulfone (DDS) were investigated from the differential scanning calorimeter (DSC), the thermogravimetric analysis (TGA), UL94 test, the limiting oxygen index (LOI) test and Cone calorimeter. Compared to traditional DOPO-DGEBA and ODOPB-DGEBA thermosets, the HAP-DOPO/DGEBA thermosets have higher T_gs at the same UL94 V-0 flammability rating for their higher crosslinking density and have higher char yield and lower pk-HRR at same 1.2 wt.% phosphorus content which confirm that HAP-DOPO has higher flame retardant efficiency on thermosets. The scanning electron microscopy (SEM) results shows that HAP-DOPO in DGEBA/DDS system obviously accelerate formation of the sealing, stronger and phosphorus-rich char layer to improve flame retardant properties of matrix during combustion.     

Effect of dendrimer modified montmorillonite on structure and properties of EPDM nanocomposites

The purpose of this work was to study the effect of dendrimer modified clay minerals on the structure and properties of ethylene-propylene-diene monomer (EPDM) nanocomposites.Flame-retardant and dendrimer modified organic montmorillonite (FR-DOMt) was successfully prepared by Na⁺-montmorillonite, tetrahydroxymethyl phosphonium chloride (THPC), N, N-dihydroxyl-3-aminomethyl propionate, and boric acid. This dendritic type of organoclay (OC) was used in preparation of EPDM/FR-DOMt nanocomposites. The properties of these nanocomposites were studied. The dispersion status of the layered silicates in EPDM was revealed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD and TEM results showed that FR-DOMt was exfoliated in the EPDM matrix when 10 phr of FR-DOMt was incorporated. The mechanical behavior, thermal stability, and flame retardance of the samples were examined. The experimental data demonstrated that the EPDM hybrids owned an improved tensile strength and elongation at break. In addition, the nanocomposites exhibited higher thermal stability and flame retardance than that of unfilled EPDM matrix.     

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%).     

Thermal degradation of a reactive flame retardant based on cyclotriphosphazene and its blend with DGEBA epoxy resin

Hexaglycidyl cyclotriphosphazene (HGCP) was synthesized, and characterized by FTIR, ³¹P, ¹H, and ¹³C-NMR. This compound was used as a reactive flame retardant to blend with commercial epoxy resin DGEBA (Diglycidyl ether of bisphenol A). Its effect on the DGEBA decomposition pathways was characterized by studying both gas and solid phases produced during thermogravimetric analysis (TGA). The gases evolved during TGA in air were studied by means of thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), while the solid residues were analysed by FTIR and scanning electron microscopy (SEM). The results showed that HGCP presents a good dispersion in DGEBA, and the blend thermoset with 4,4′-methylene-dianiline (MDA) curing agent leads to a significant improvement of the thermal stability at elevated temperature with higher char yields compared with pure DGEBA thermoset with the same curing agent. Improvement has also been observed in the fire behaviour of blend sample.     

Synergistic effects of novolac-based char former with a phosphorus/nitrogen-containing flame retardant in polyamide 6

The synergistic effect of phosphorus oxynitride（PON） with a novolac-based char former modified by salification （NA-metal salt） on the flame retardance of polyamide 6（PA6） was investigated.For this purpose,various flame-retardant PA6 systems were melt-compounded with PON,PON/NA,PON/NA-V₂O₅ and PON/NA-Fe₂O₃,and their flame retardance was evaluated by measuring the limiting oxygen index（LOI） values and UL-94 vertical burning ratings.The results showed that,compared with the PA6/PON/NA system,the combination of two char formers（NA-V₂O₅,NA-Fe₂O₃） with PON could obviously improve the char formation and flame retardance of PA6.The flame retardance and cone calorimetric analyses showed the stronger synergism as well as the better flame retardant performance of PON/NA-Fe₂O₃ flame retardant system. The effects of different char formers on the flame retardance and thermal stability of this system were also discussed.     

Dilactams. Synthesis of nonsymmetrical dibenzodiazocinediones

We report the first examples of nonsymmetrical dibenzodiazocinediones, mono-, di-, tri- and tetra-substituted in the aromatic rings including a benzo pyridino diazocine, by a new short method without the requirement of protection. The procedure involves conversion of an anthranilic acid to its sulfinamide lactone followed by direct heating with a different N-alkylanthranilic acid.     

Synthesis of water-soluble N-Acetyl-L-cysteine conjugates of naphtazarin (5,8-Dihydroxy-1,4-naphthoquinone) derivatives

Base-catalytic condensation of N-acetyl-L-cysteine with substituted naphthazarins was first obtained a series of mono-, di-, tri- and tetra-substituted S-aminoacid naphthazarin conjugates bearing alkyl (hydroxy) groups. It was shown that three- and tetra-N-acetyl-L-cysteine naphthazarin derivatives are readily soluble in water.     

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.     

Molecular motion,morphology, and thermal properties of multiwall carbon nanotube/polysilsesquioxane composite

Diglycidyl ether of bisphenol A (DGEBA)‐bridged polyorganosiloxane precursors have been prepared successfully by reacting diglycidyl ether of bisphenol A epoxy resin with 3‐aminopropyltriethoxysilane. Acid‐modified and unmodified multiwalled carbon nanotube (MWCNT) were dispersed in the diglycidyl ether of bisphenol A‐bridged polyorganosiloxane precursors and cured to prepare the carbon nanotube/diglycidyl ether of bisphenol A‐bridged polysilsesquioxane (MWCNT/DGEBA‐PSSQ) composites. The molecular motion of MWCNT/DGEBA‐PSSQ nanocomposites was studied by high‐resolution solid‐state ¹³C NMR. Acid‐modification can improve the affinity between MWCNT and the polymer matrix. The molecular motion of the DGEBA‐PSSQ decreased with acid‐modified MWCNT content. However, when unmodified MWCNT was used, the molecular motion of the DGEBA‐PSSQ was increased. SEM and TEM microphotographs confirm that acid‐modified MWCNT exhibits better dispersion than unmodified MWCNT in DGBEA‐PSSQ. The dynamic mechanical properties of acid‐modified MWCNT/DGBEA‐PSSQ composites are more favorable than those of unmodified MWCNT. T_g of the DGEBA‐PSSQ decreased from 174.0 °C (neat DGEBA‐PSSQ) to 159.0 °C (1 wt % unmodified MWCNT) and 156.0 °C (1 wt % acid‐modified MWCNT). The storage modulus (at 30 °C) of the DGEBA‐PSSQ increased from 1.23 × 10⁹ Pa (neat DGEBA‐PSSQ) to 1.65 × 10⁹ Pa (1 wt % acid‐modified MWCNT). However, when unmodified MWCNT was used, the storage modulus of the DGEBA‐PSSQ decreased to 6.88 × 10⁸ Pa (1 wt % unmodified MWCNT). At high temperature, above 150 °C, storage modulus of nanocomposites was higher than that of neat polymer system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 472–482, 2008     

Synthesis and properties of phosphorus-containing bio-based epoxy resin from itaconic acid

A phosphorus-containing bio-based epoxy resin (EADI) was synthesized from itaconic acid (IA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO). As a matrix, its cured epoxy network with methyl hexahydrophthalic anhydride (MHHPA) as the curing agent showed comparable glass-transition temperature and mechanical properties to diglycidyl ether in a bisphenol A (DGEBA) system as well as good flame retardancy with UL94 V-0 grade during a vertical burning test. As a reactive flame retardant, its flame-resistant effect on DGEBA/MHHPA system as well as its influence on the curing behavior and the thermal and mechanical properties of the modified epoxy resin were investigated. Results showed that after the introduction of EADI, not only were the flame retardancy determined by vertical burning test, LOI measurement, and thermogravimetric analysis significantly improved, but also the curing reactivity, glass transition temperature (T _g), initial degradation temperature for 5% weight loss (T _d(5%)), and flexural modulus of the cured system improved as well. EADI has great potential to be used as a green flame retardant in epoxy resin systems.     

Silicon-containing flame retardant epoxy resins: Synthesis, characterization and properties

Epoxy resins with different silicon contents were prepared from silicon-containing epoxides or silicon-containing prepolymers by curing with 4,4′-diaminodiphenylmethane. The reactivity of the silicon-based compounds toward amine curing agents was higher than that of the conventional epoxy resins. The T_g of the resulting thermosets was moderate and decreased when the silicon content increased. The onset decomposition temperatures decreased and the char yields increased when the silicon content increased. Epoxy resins had a high LOI value, according to the efficiency of silicon in improving flame retardance.     

Preparation, characterization and curing properties of epoxy-terminated poly(alkyl-phenylene oxide)s

A series of dihydroxyl telechelic poly(alkyl-phenylene oxide)s (1) have been synthesized by oxidative polymerization of alkylphenols with various aromatic diols using manganese or copper amine catalysts. The novel telechelic derivatives (1) were epoxidized with epichlorohydrin yielding a series of new epoxidized poly(alkyl-phenylene oxide)s (EPPO, 2) and the structures, properties were studied by nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and gel permeation chromatography (GPC). The 1:1 blends of diglycidyl ether of bisphenol-A (DGEBA) with EPPO resins were cured with three curing agents and the effects of chemical structure change on thermal property of the curing matrixes were discussed. Incorporation of EPPOs to DGEBA epoxy system resulted in a significant increase in its glass transition temperature (T_g), thermal stability and flame resistance. The T_g values and char yields arising from a DDM-cured epoxy resin are usually higher than those of dicyandiamide (DICY) or 2-methylimidazole (2-MI) analogues and the reactivity of epoxy blends with three curing agents presents an increase in the order of 2-MI, DDM and DICY. In general, the tetramethylbisphenol-A (TMBPA)-derived polymer exhibits the lowest T_g, char yield and dielectric constant among PPO derivatives whereas the biphenol polymers usually results in higher T_g and char yield due to its rigid rod structure.     

Synthesis of CeO2‐loaded titania nanotubes and its effect on the flame retardant property of epoxy resin

A series of CeO₂‐loaded titania nanotubes (CeO₂‐TNTs) hybrid materials with different CeO₂ loadings were synthesized by co‐precipitation method and then incorporated into epoxy resin (EP) to prepare CeO₂‐TNTs flame‐retardant epoxy nanocomposites. Structure and morphology characterization indicated the successful synthesis of CeO₂‐TNTs. The effect of CeO₂‐TNTs with different CeO₂ loading capacity on the flame retardance of EP was compared and analyzed by the thermogravimetric analysis, Cone and Raman. The results showed that CeO₂ loading could increase the carbon residue of nanocomposites, reduce the peak heat release rate (PHRR) and total heat release (THR), and improve the fire safety of EP. The residual carbon content of EP/0.1CeO₂‐TNTs sample at 700°C reached 19.8% with the lowest degradation rate, and the PHRR and THR were reduced to 680 kW/m² and 32.9 MJ/m², respectively. Such a significant improvement in flame‐retardant properties for EP could be attributed to the protective effect of CeO₂‐TNTs.     

Thermal decomposition of fire retardant brominated epoxy resins cured with different nitrogen containing hardeners

Epoxy resins frequently have to meet a flame retardancy grade which can be accomplished by incorporating brominated reactive compounds, like tetrabromobisphenol A (TBBA) cured by a number of hardeners. A few brominated epoxy resins (BERs) have been prepared by curing a mixture of diglycidyl ethers of bisphenol A (DGEBA)/diglycidyl ethers of tertabromobisphenol A (DGETBBA) and different hardeners: dicyandiamide (DICY), 4,4′-diaminodiphenyl sulphone (DDS) and polyethylene polyamine (PEPA). The use of different hardeners strongly affects the thermal degradation behaviour of the BER.The main volatile products of pyrolysis, characterized by Pyrolysis-Gas Chromatography-Mass Spectroscopy (PY-GC-MS) at 423 °C were phenol, isopropyl- and isopropenylphenol, mono- and di-brominated phenols, bisphenol A, mono-, di-, tri- and tetra-brominated bisphenol A. No nitrogen containing volatile products or HBr were evolved whereas SO₂ is formed from BER cured with DDS (BER-DDS) and bromoethylene from BER cured with PEPA (BER-PEPA). Differences of 30-60 °C in thermal stability of epoxy network have been found, depending on the hardener. The experimental evidence suggests a cooperative action of bromine and nitrogen in chain scission of epoxy resins. In particular the ability of the hardener in fixing HBr, evolved from TBBA units, seems to depend on the basicity of the N atom of the hardener: the lower the basicity, the lower the scavenging effectiveness and consequently the higher the thermal stability.     

Benzoxazine modified diglycidyl ether of bisphenol-a/silicon/siliconized epoxy hybrid polymer matrices: Mechanical,thermal, electrical and morphological properties

Benzoxazines modified epoxy hybrid polymer matrices were developed using benzoxazines (CB_DDM and BMPB_DDM) and epoxy resins (DGEBA, SE and EP-HTPDMS) to make them suitable for high performance applications. The benzoxazine-epoxy hybrid polymer matrices were prepared via in-situ polymerization and were investigated for their thermal, thermo-mechanical, mechanical, electrical and morphological properties. Two types of skeletal modified benzoxazines namely 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane benzoxazine (CB_DDM) and bis(4-maleimidophenyl) benzoxazine (BMPB_DDM) were synthesized by reacting paraformaldehyde and 4,4′-diaminodiphenylmethane with 1,1-bis (3-methyl-4-hydroxyphenyl)cyclohexane and N-(4-hydroxyphenyl)maleimide respectively. Epoxy resins viz., diglycidyl ether of bisphenol-A (DGEBA), silicon incorporated epoxy (SE) and siliconized epoxy resin (EP-HTPDMS) were modified with 5, 10 and 15 wt% of benzoxazines using 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of benzoxazines with the epoxy resin was carried out thermally and the resulting product was analyzed by FT-IR spectra. The glass transition temperature, curing behavior, thermal stability, char yield and flame resistance of the hybrid polymers were analysed by means of DSC, TGA and DMA. Mechanical properties were studied as per ASTM standards. The benzoxazines modified epoxy resin systems exhibited lower values of dielectric constant and dielectric loss with an enhanced values of of arc resistance, glass transition temperatures, degradation temperatures, thermal stability, char yield, storage modulus, tensile strength, flexural strength and impact strength.     

A Well-Defined Cyclotriphosphazene-Based Epoxy Monomer and Its Application as A Novel Epoxy Resin: Synthesis,Curing Behaviors,and Flame Retardancy

Abstract

A novel cyclotriphosphazene-based epoxy monomer, hexa-[4-(glycidyloxycarbonyl) phenoxy]cyclotriphosphazene (HGCP), was synthesized via a four-step synthetic route, and fully characterized by ¹H, ¹³C, and ³¹P NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. Thermosetting systems based on HGCP with three curing agents, for example, 4,4′-diaminodiphenylsulfone (DDS), 4,4′-diaminodiphenylmethane (DDM), and dicyandiamide (DICY), were used for making a comparison of their thermal curing behaviors. The curing behaviors were measured by differential scanning calorimetry. Moreover, flame retardancy of HGCP thermosetting systems was estimated by Limiting Oxygen Index (LOI) and Vertical Burning Test (UL-94). The resulting HGCP thermosetting systems exhibited better flame retardancy than the common epoxy resins diglycidyl ether of bisphenol A (DGEBA) and the regular brominated bisphenol A epoxy resin (TBBA) cured by DDS, respectively. When HGCP was cured by DDS, its thermosetting system gave the most char residues, met the UL-94 V-0 classification, and had a limiting oxygen index value greater than 35.     

Thermal degradation of wood treated with flame retardants

Wood, one of the most flammable materials, was treated with various compounds containing nitrogen, phosphorus, halogens, and boron. For a study of flame retardance from the standpoint of thermal degradation, the samples were subjected to thermogravimetry (TG), differential thermal analysis (DTA) and differential thermogravimetry (DTG) in nitrogen to determine if there were any characteristic correlations between thermal degradation behaviors and the level of flame retardance. From the resulting data, kinetic parameters for different stages of thermal degradation are obtained using the method of Broido. The energies of activation for the decomposition of samples are found to be from 72 to 109 kJ mol^–1. For wood and modified wood, the char yields are found to increase from 10.2 to 30.2%, LOI from 18 to 36.5, which indicates that the flame retardance of wood treated with compounds is improved. The flame retardant mechanism of different compounds has also been proposed.