Synthesis and characterization of carborane-containing poly(hydroxy ethers) with excellent thermal stability

o-Carborane-containing poly(hydroxy ethers)(P1, P2 and P3) were synthesized via "advancement reaction" of o-carborane-containing bisphenol(4) and diglycidyl ether of bisphenols(DGEBA and 1). FTIR and ~(1) H-, ~(13)C-, and ~(11) B-NMR were utilized to characterize the obtained polymers. TGA test was conducted under nitrogen and air. It is found that the shielding effect of carborane moiety on its adjacent aromatic structures contributes to high initial decomposition temperatures, while oxygen in air has an adverse effect on the initial decomposition temperature. The oxygen can combine with polymer chain to form peroxide and hydroperoxide groups, which are more reactive during the degradation process. Besides, o-carborane-containing poly(hydroxy ethers) have high char yield at elevated temperatures. The boron atom combines with oxygen from the polymer structure or/and from air, thus to form a three-dimensional network linked with B―O―B and B―C bonds, and retain the polymer weight to a large extent.     

Synthesis, characterization, thermal properties and flame retardancy of a novel nonflammable phosphazene-based epoxy resin

Hexakis(4-hydroxyphenoxy)-cyclotriphosphazene (PN-OH) was synthesized through nucleophilic substitution of the chloride atoms of hexachlorocyclotriphosphazene and reduction of the aldehyde groups, and its chemical structure was characterized by elemental analysis, ¹H and ³¹P NMR, and Fourier transform infrared (FTIR) spectroscopy. A new phosphazene-based epoxy resin (PN-EP) was successfully synthesized through the reaction between diglycidyl ether of bisphenol-A (DGEBA) and PN-OH, and its chemical structure was confirmed by FTIR and gel permeation chromatography. Four PN-EP thermosets were obtained by curing with 4,4′-diaminodiphenylmethane (DDM), dicyandiamide (DICY), novolak and pyromellitic dianhydride (PMDA). The reactivity of PN-EP with the four curing agents presents an increase in the order of DDM, PMDA, novolak and DICY. An investigation on their thermal properties shows that the PN-EP thermosets achieve higher glass-transition and decomposition temperatures in comparison with the corresponding DGEBA ones while their char yields increase significantly. The PN-EP thermosets also exhibit excellent flame retardancy. The thermosets with novolak, DICY and PMDA achieve the LOI values above 30 and flammability rating of UL94 V-0, whereas the one with DDM reaches the V-1 rating. The nonflammable halogen-free epoxy resin synthesized in this study has potential applications in electric and electronic fields in consideration of the environment and human health.     

Influences of template concentration and epoxy functionality on porous epoxy systems: Characteristics of thermal stability, optical, dielectric, and mechanical properties

Two different multi-porous epoxy thermosets (MPETs), bi-functionality of DGEBA and tri-functionality of TGTPM, were prepared foremost for the interaction of template concentration and epoxy functionality under several physical properties. By performing an automated mercury porosimeter test, we found out template concentration was critical to the amount of voids/pores. Meanwhile, epoxy functionality decided the formation of porous structure through SEM. Comparing with TGTPM MPETs system, the DGEBA MPETs system with 20 wt% template displayed appreciable T_g and tan δ properties while the phenomenon exhibited higher thermal stability property. Additionally, thermal conductivity patterns show the DGEBA MPETs system is a remarkable material of thermal resistance. However, it reduces optical clarity, dielectric permittivity and mechanical strength according to the UV-visible spectroscopy, LCR meter, and DMA, normally. Therefore, we can understand that template concentration and epoxy functionality are key factors of physical degradation and stability in porous epoxy materials.     

Synthesis and thermal characterization of phosphorus containing siliconized epoxy resins

Siliconized epoxy matrix resin was developed by reacting diglycidyl ethers of bisphenol A (DGEBA) type epoxy resin with hydroxyl terminated polydimethylsiloxane (silicone) modifier, using γ-aminopropyltriethoxysilane crosslinker and dibutyltindilaurate catalyst. The siliconized epoxy resin was cured with 4, 4-diaminodiphenylmethane (DDM), 1,6-hexanediamine (HDA), and bis (4-aminophenyl) phenylphosphate (BAPP). The BAPP cured epoxy and siliconized epoxy resins exhibit better flame-retardant behaviour than DDM and HDA cured resins. The thermal stability and flame-retardant property of the cured epoxy resins were studied by thermal gravimetric analysis (TGA) and limiting oxygen index (LOI). The glass transition temperatures (T_g) were measured by differential scanning calorimetry (DSC) and the surface morphology was studied by scanning electron microscopy (SEM). The heat deflection temperature (HDT) and moisture absorption studies were carried out as per standard testing procedure. The thermal stability and flame-retardant properties of the cured epoxy resins were improved by the incorporation of both silicone and phosphorus moieties. The synergistic effect of silicone and phosphorus enhanced the limiting oxygen index values, which was observed for siliconized epoxy resins cured with phosphorus containing diamine compound.     

Effects of organo-montmorillonite dispersion on thermal stability of epoxy resin nanocomposites

Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo-montmorillonite (O-MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The dispersion state of the MMT in the matrix was investigated by X-ray diffraction and scanning electronic microscopy. The thermal stability of the epoxy nanocomposites was examined by TGA. Thermal stability of the epoxy nanocomposite is dependent upon the dispersion state of the OMMT in the epoxy matrix although all the epoxy nanocomposites had enhanced thermal stability compared with the neat epoxy resin. The thermal stability of the epoxy resin nanocomposites was correlated with the dispersion state of the MMT in the epoxy resin matrix.     

Phosphorus based epoxy terminated structural adhesive 2. Curing, adhesive strength and thermal stability

The curing behavior of phosphorus based epoxy terminated polymers was studied using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylic dianhydride and the commercial hardener of Ciba-Geigy's two-pack araldite, as curing agent. The adhesive strength of these adhesives was measured by various ASTM methods like lap-shear, peel, and cohesive tests on metal-metal, wood-wood and wood-metal interfaces. All these results were compared with the synthesized epoxy resins prepared from bisphenol-A and epichlorohydrin having the epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis.     

Effect of silica content on thermal stability of fumed silica/epoxy composites

Composites of a fumed silica industrial residue and an epoxy resin were prepared and their thermal stability and thermal degradation behaviour were studied by TGA in air. Classical thermal stability parameters, based on the initial decomposition temperature (IDT), temperature of maximum rate of mass loss (T_max) and integral procedure decomposition temperature (IPDT) were calculated before and after subtraction of the filler mass from the TGA curves. Without filler mass subtraction, the thermal stability of the epoxy resin seems to be improved and the mass loss rate was reduced by the addition of fumed silica. Nevertheless, after subtraction of the filler mass, the thermal degradation behaviour of the resin was only slightly affected by the silica content. A possible negative effect of the silica content on the cure was also found.     

Synthesis and thermal stability of a novel phosphorus-nitrogen containing intumescent flame retardant

A novel phosphorus-nitrogen containing intumescent flame retardant （P-N IFR） was prepared via the reaction of dichlor-opentate with N-methylaniline. The structure of the product was confirmed by ^1H NMR, ^31p NMR, MS and IR. TGA analysis showed it has effective thermal stability.     

Synthesis, characterization and thermal properties of novel epoxy containing silicon and phosphorus nanocomposites by sol-gel method

Organic-inorganic hybrids were prepared using diglycidyl ether of bisphenol A (DGEBA) type epoxy and tetraethoxysilane via the sol-gel process. The DGEBA type epoxy was modified by a coupling agent to improve the compatibility of the organic and inorganic phases. The sol-gel technique was used successfully to incorporate silicon and phosphorus into the network of hybrids increasing flame retardance.Fourier transform infrared spectroscopy and ²⁹Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids. In condensed siloxane species for TEOS, silicon atoms through mono-, di-, tri-, and tetra-substituted siloxane bonds are designated as Q¹, Q², Q³, Q⁴, respectively. For 3-isocyanatopropyltriethoxysilane and diethylphosphatoethyltriethoxysilane, mono-, di-, tri-, tetra-substituted siloxane bonds are designated as T¹, T², T³. Results revealed that Q⁴, Q³, T³ are the major environments forming a network structure. The morphology of the ceramer was examined by scanning electron microscopy and Si mapping. Particle sizes were below 100 nm. The hybrids were nanocomposites. The char yield of pure epoxy resin was 14.8 wt.% and that of modified epoxy nanocomposite was 31 wt.% at 800 °C. A higher char yield enhances the flame retardance. Values of limiting oxygen index of pure epoxy and modified epoxy nanocomposites are 24 and 32, respectively, indicating that modified epoxy nanocomposites possess better flame retardance than the pure epoxy resin.     

Thermal stability of microencapsulated epoxy resins with poly(urea-formaldehyde)

A series of microcapsules filled with epoxy resins with poly(urea-formaldehyde) (PUF) shell were synthesized by in situ polymerization, and they were heat-treated for 2 h at 100 °C, 120 °C, 140 °C, 160 °C, 180 °C and 200 °C. The effects of surface morphology, wall shell thickness and diameter on the thermal stability of microcapsules were investigated. The chemical structure and surface morphology of microcapsules were investigated using Fourier-transform infrared spectroscope (FTIR) and scanning electron microscope (SEM), respectively. The thermal properties of microcapsules were investigated by thermogravimetric analysis (TGA and DTA) and by differential scanning calorimetry (DSC). The thermal damage mechanisms of microcapsules at lower temperature (<251 °C) are the diffusion of the core material out of the wall shell or the breakage of the wall shell owing to the mismatch of the thermal expansion of core and shell materials of microcapsules. The thermal damage mechanisms of microcapsules at higher temperature (>251 °C) are the decomposition of shell material and core materials. Increasing the wall shell thickness and surface compactness can enhance significantly the weight loss temperatures (T_d) of microcapsules. The microcapsules with mean wall shell thickness of 30 ± 5 μm and smoother surface exhibit higher thermal stability and can maintain quite intact up to approximately 180 °C.     

Synthesis and characterization of novel multifunctional epoxy resin

A novel multifunctional epoxy resin was synthesized by polyphenol and epichlorohydrin.The structure and molecular weight ofthe multifunctional epoxy were characterized by FTIR and ESI-MS.DSC and DMTA were used to investigate the thermal propertyof multifunctional epoxy cured by DDS.The thermal resistance of the synthesized multifunctional epoxy was much better than astandard diglycidyl ether of bisphenol-A epoxy.     

Cure behavior and thermal stability of an epoxy: new bismaleimide blends for composite matrices

A new bismaleimide (BMI) resin was synthesized to formulate epoxy(tetraglycidyl diaminodiphenyl methane; TGDDM) – bismaleimide thermoset blends for composite matrix applications. 4,4′-diaminodiphenyl methane (DDM) was used as an amine curing agent for the TGDDM. A Fourier transform infrared (FTIR) spectroscopy was employed to characterize the new BMI resin. Cure behavior of the epoxy–BMI blends was studied using a differential scanning calorimeter (DSC). DSC thermograms of the thermoset blends indicated two exothermic peaks. The glass transition temperature of the thermoset blends decreased with BMI content. Thermogravimetric analysis (TGA) was carried out to investigate thermal degradation behavior of the cured epoxy–BMI thermoset blends. The new BMI resin reacted partially with the DDM and weak intercrosslinking polymer networks were formed during cure of the thermoset blends.     

Synthesis, characterization, and thermal stability of star-shaped poly(ε-caprolactone) with phosphazene core

Hexakis[p-(hydroxylmethyl)phenoxy]cyclotriphosphazene was synthesized by the reaction of hexachlorocyclotriphosphazene with the sodium salt of 4-hydroxybenzaldehyde and subsequent reduction of aldehyde groups to alcohol groups by using sodium borohydride. This compound was employed in initiating the ring-opening polymerization of ε-caprolactone. The resulting polymers were characterized using Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC). The characterization data indicated the star-shaped PCL with phosphazene core were successfully synthesized with narrow molecular weight distribution and high yields. ¹H-NMR analysis was used to calculate the number-average molecular weight. The calculated result from NMR was closer to the theoretical data than that from GPC analysis. Polarizing optical microscopy (POM) combined with differential scanning calorimetry (DSC) was used to study the crystallization behavior of the star-shaped PCL. The result indicated that the highly branched architecture of star-shaped PCL resulted in interrupted crystallization form and subsequently lower melting temperature. Thermogravimetric analysis (TGA) carried out on the star-shaped PCL suggested that introduction of phosphazene rings strengthen the thermal stability of the resulting polymers.     

Enhanced thermal stability and structural characteristics of different MMT-Clay/epoxy-nanocomposite materials

Epoxy-clay nanocomposites, HDTMA-BDGE, HDTMA-BPDG, HDTMA-BBDG, HDTMA-TGDDM and HDTPP-BDGE were synthesized using hexadecylammonium clay and hexadecylphosphonium clay, respectively. The Montmorillonite (MMT) clay was modified with quaternary ammonium salt and with triphenylphosphonium salt which was intercalated into the interlayer region of MMT-Clay. The epoxy-clay systems were cured by using diaminodiphenylsulphone as a curing agent. The X-ray diffraction patterns obtained for the systems confirmed the nanodispersion of MMT-Clay in the epoxy networks. The ammonium clay-modified systems displayed appreciable mechanical and glass-transition temperature properties while, the phosphonium clay-modified system exhibited highest thermal resistance properties compared with unmodified epoxy systems. The T_g decrease observed in all the clay-modified epoxy systems, may be compromised with their advantage of requiring the filler content very low (5wt%), when compared to the conventional epoxy systems whose filler quantity is normally required from 25 to 30 wt%.     

Thermal stability and degradation kinetics of novel organic/inorganic epoxy hybrid containing nitrogen/silicon/phosphorus by sol-gel method

Hybrids containing silicon, phosphorous and nitrogen were prepared by the sol-gel method and compared with pure epoxy. The silicon, phosphorous and nitrogen components were successfully incorporated into the networks of polymer. Thermogravimetric analysis (TGA) was used for rapid evaluation of the thermal stability of different materials. The integral procedure decomposition temperature (IPDT) has been correlated the volatile parts of polymeric materials and used for estimating the inherent thermal stability of polymeric materials. The IPDT of pure epoxy was 464 °C and the IPDTs of hybrids were higher than that of pure epoxy. The thermal stability of hybrids increased with the contents of inorganic components. The inorganic components can improve the thermal stability of pure epoxy.Two methods have been used to study the degradation of hybrids containing silicon, phosphorous and nitrogen hybrid during thermal analysis. These investigated methods are Kissenger, Ozawa's methods. The activation energies (E_a) were obtained from these methods and compared. It is found that the values of E_a for modified epoxy hybrids are higher than that of pure epoxy. The hybrids of high activation energy possess high thermal stability.     

Kinetics and thermal properties of epoxy resins based on bisphenol fluorene structure

The fluorene-containing epoxy, diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) was synthesized by a two-step reaction procedure. In order to investigate the relationship between fluorene structure and material properties, DGEBF and a commonly used diglycidyl ether of bisphenol A (DGEBA) were cured with 4,4-diaminodiphenyl methane (DDM) and 4,4-(9-fluorenylidene)-dianiline (FDA). The curing kinetics, thermal properties and decomposition kinetics of these four systems (DGEBA/DDM, DGEBF/DDM, DGEBA/FDA, and DGEBF/FDA) were studied in detail. The curing reactivity of fluorene epoxy resins was lower, but the thermal stability was higher than bisphenol A resins. The onset decomposition temperature of cured epoxy resins was not significantly affected by fluorene structure, but the char yield and T_g value were increased with that of fluorene content. Our results indicated that the addition of fluorene structure to epoxy resin is an effective method to improve the thermal properties of resins, but excess fluorene ring in the chain backbone can depress the curing efficiency of the resin.     

Cure characterization of rubber modified epoxy novolacs

A new type of toughened epoxy polymer based on epoxy cresol novolac resin (ECN) and carboxy terminated polybutadiene (CTPB) liquid functional rubber has been studied. ECN has been synthesized in the laboratory and CTPB used was also of indigenised origin. Rubber modified epoxies were characterized with the help of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) techniques.     

Thermal stability of high temperature epoxy adhesives by thermogravimetric and adhesive strength measurements

The thermal degradation of two high temperature epoxy adhesives has been measured in terms of weight loss and adhesion loss and the lifetime predictions are compared for the two independent measurements of thermal degradation. Weight loss measurements were performed at high temperature under accelerated thermal aging conditions. Adhesion loss measurements were performed at lower temperatures closer to typical continuous operating temperatures. An Arrhenius relationship is validated for the thermal degradation of the epoxy adhesives, and the extent of degradation in terms of weight loss and adhesion loss is modelled with an autocatalytic rate expression. The degradation kinetic parameters and models are compared between the two thermal degradation measurements and are found to give similar predictions for the lifetime of the adhesives. In addition, the relationship between network degradation and loss of adhesive strength is discussed.     

Synthesis, characterization and properties of a novel fluorinated polyurethane

A novel fluorinated polyurethane (FPU) was prepared by fluorinated polyether glycol (PTMG-g-HFP) as a soft segment, 1,6-hexamethylene diisocyanate (HDI) or toluene diisocyanate (TDI) as a hard segment and 1,4-butanodiol (BDO) as a chain extender. Fourier transform infrared spectroscopy (FTIR), ¹H NMR, ¹³C NMR and gel permeation chromatography (GPC) were used to characterize the structure of the fluorinated polyurethane. The thermal stabilities of the fluorinated polyurethane and the corresponding hydrogenated polyurethane were studied by thermogravimetric analysis (TGA). X-ray photoelectron spectroscopy (XPS) analysis at two different sampling depths for the fluorinated polyurethane was used to investigate the surface compositions of FPU. And the mechanical properties of the fluorinated polyurethane and the corresponding hydrogenated polyurethane were also measured. Chemical resistance of polyurethane films was estimated through spot tests with different solvents. The results showed that FPU had high thermal stability, strain-hardening property and good chemical resistance. The XPS measurements showed the fluorine enrichment on the surface of FPU.     

Studies on thermal, mechanical and morphological behaviour of caprolactam blocked methylenediphenyl diisocyanate toughened bismaleimide modified epoxy matrices

Diglycidyl ether of bisphenol A epoxy resin (DGEBA, LY 556) was toughened with 5%, 10% and 15% (by wt) of caprolactam blocked methylenediphenyl diisocyanate (CMDI) using 4,4′-diaminodiphenylmethane (DDM) as curing agent. The toughened epoxy resin was further modified with chemical modifier N,N′-bismaleimido-4,4′-diphenylmethane (BMI). Caprolactam blocked methylenediphenyl diisocyanate was synthesized by the reaction of caprolactam with methylenediphenyl diisocyanate in presence of carbon tetrachloride under nitrogen atmosphere. Thermal properties of the developed matrices were characterized by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), heat distortion temperature (HDT) and dynamic mechanical analysis (DMA). Mechanical properties like tensile strength, flexural strength and impact strength were tested as per ASTM standards. The glass transition temperature (T_g) and thermal stability were decreased with increase in the percentage incorporation of CMDI. The thermomechanical properties of caprolactam blocked methylenediphenyl diisocyanate toughened epoxy resin were increased by increasing the percentage incorporation of bismaleimide. The values of impact strength for epoxy resin were increased with increase in the percentage concentration of CMDI. The homogeneous morphology of CMDI toughened epoxy resin and bismaleimide modified CMDI toughened epoxy resin system were ascertained from scanning electron microscope (SEM).