Improvement of surface and moisture resistance of epoxy resins with fluorinated glycidyl ether

Laurylfluoro glycidyl ether (FGE) was synthesized by laurylfluoro‐1‐pentanol with epichlorohydrin, and confirmed by FTIR and ¹³C‐NMR. The surface properties, moisture absorption, and mechanical properties of the epoxy resins modified by different content of laurylfluoro glycidyl ether acted as mono functional thinner were investigated by X‐ray photoelectron spectroscopy (XPS), universal testing machine (UTM), dynamic mechanical thermal analyzer (DMTA), etc. The fluorine content at the surface of the modified resins were enriched greatly with the increase of the content of laurylfluoro glycidyl ether, and the hydrophobic property of the resins surface increased. When the FGE content was 10%, the fluorine content at the surface of the modified epoxy resin reached to 66% and the water contact angle was 102°. The equilibrium moisture content of the resin dropped by 30% when the content of FGE was 5%. The mechanical properties of the epoxy resins modified by FGE were improved while the thermal mechanical properties changed little at low content of FGE (less than 3%). Further increase of FGE content in the epoxy resins may result in decreases of the mechanical and thermal mechanical properties of the resins. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on isotactic poly(phenyl glycidyl ether)‐modified epoxy resins. II. Toughening of epoxy resins

A semicrystalline polymer, isotactic poly(phenyl glycidyl ether) (i‐PPGE) was used as a modifier for epoxy resin; 1,8‐Diamino‐p‐methane (MNDA) and 4,4′‐Diamino diphenyl sulfone (DDS) were used as curing agents. In the MNDA‐cured resins, the dispersed phase were spherical particles with diameters in the range of 0.5–1.0 μm when the resin was blended with 5 phr i‐PPGE. In the DDS‐cured resins, the particle size distribution of the dispersed phase was much wider. The difference was traced back to the reactivity of the curing agent and the different regimes used for curing. Through dynamic mechanical analysis, it was found that in the MNDA‐cured systems, i‐PPGE had a lower crystallinity than in the DDS‐cured system. In spite of the remarkable difference in the morphology and microstructure of the modified resins cured with these two curing agents, the toughening effects of i‐PPGE were similar for these resins. The critical stress intensity factor (K_IC) was increased by 54% and 53%, respectively, for the resins cured by DDS and by MNDA, blending with 5 phr of the toughner. i‐PPGE was comparable with the classical toughners carboxyl‐terminated butadiene‐acrylonitrile copolymers in effectiveness of toughening the epoxy resin. An advantage of i‐PPGE was that the modulus and the glass‐transition temperature of the resin were less affected. However, this modifier caused the flexural strength to decrease somewhat. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1223–1232, 2002; DOI 10.1002/app.10445     

Studies on isotactic poly(phenyl glycidyl ether)‐modified epoxy resins. I. Physical gels

Isotactic poly(phenyl glycidyl ether) (i‐PPGE) was prepared using a Teyssie catalyst. The polymer was dissolved in the epoxy resin at approximately 200°C and Gels were formed as the solutions cooled to room temperature. The gels were studied by rheological techniques, differential scanning calorimetry analysis, optical microscopy, and electron microscopy. The existence of a network in the gels was demonstrated by the nonlinear increase of the viscosity with i‐PPGE concentration and by the significant storage modulus. A high isotacticity of the polymer was essential for gel formation. The thermal history of the system showed a great influence on the network structure and on the performance of the gel. The yield stresses of the physical gels increased with the concentration of i‐PPGE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1214–1222, 2002; DOI 10.1002/app.10444     

Ultrasonically initiated emulsifier-free emulsion copolymerization of n-butyl acrylate and acrylamide. Part I: Polymerization mechanism

The polymerization mechanism of ultrasonically initiated emulsifier-free emulsion copolymerization of n-butyl acrylate (BA) and acrylamide (AM) was investigated. A four-step polymerization mechanism of the ultrasonically initiated emulsifier-free emulsion was put forward based on the monomer conversion and the main reaction locus. Improving the power output would increase the monomer conversion and the rate of polymerization. However, when the reaction temperature was 30 °C and the concentration of Na₂SO₄ was 0.1%, the monomer conversion and the rate of polymerization achieved maximum. The FTIR spectra showed that the sample obtained by this way was the copolymer of BA and AM, but not the blend of poly(butyl acrylate) and polyacrylamide.     

Simultaneously enhanced impact strength and dielectric properties of an epoxy resin modified with EHTPB liquid rubber

To simultaneously improve the impact strength and dielectric properties of cured epoxy (EP), herein we explore liquid rubber toughened EP based on a nonpolar epoxidized hydroxyl-terminated polybutadiene (EHTPB), where the rubber is covalently bonded to the EP. Fourier transform infrared and nuclear magnetic resonance proved the chemical reaction between EHTPB and EP, which makes the immiscible EHTPB-EP blend change to compatible one. The results indicate that both the impact strength and dielectric properties can be visibly enhanced with the addition of EHTPB and the maximum values are obtained at 10 phr of EHTPB loading. The improved mechanical toughness can be ascribed to the extensive shear yielding induced by the uniformly dispersed EHTPB domains and the enhanced interfacial compatibility between the two components. Moreover, the enhanced electrical resistivity and dielectric breakdown strength as well as the reduced dielectric constant and loss for the EHTPB-EP can be attributed to the combination of the excellent insulating properties of HTPB and dielectrically favorable interfaces. Therefore, the EHTPB-EP with a concurrent improvement in impact strength and dielectric properties can be used as promising insulating materials for high-frequency microelectronics and high-voltage electrical equipment.     

Toughening of epoxy resins by modified m-phenylene diamine having soft ether chain

A new soften curing agent for toughening epoxy resins was synthesized by m-phenylene diamine modified with epoxypropyl butyl ether. The curing processes of epoxy resin/modified m-phenylene diamine were traced by differential scanning calorimetry (DSC), then kinetic parameters, ΔE and n, were deduced. Fourier transform infrared (FTIR) analysis showed that the longer the reaction time was, the smaller the absorption peaks of epoxy group were. The results of the mechanical properties demonstrated that the impact property of the epoxy resin cured by modified m-phenylene diamine at the moderate temperature was better than that of cured by unmodified one because of the introduction of soft ether chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Simultaneous improvements in the cryogenic tensile strength,ductility and impact strength of epoxy resins by a hyperbranched polymer

Improvements in mechanical properties at low temperatures are desirable for epoxy resins such as diglycidyl ether of bisphenol A (DGEBA) that are often used in cryogenic engineering applications. In this study, a hydroxyl functionalized hyperbranched polymer (H30) is employed to improve the mechanical properties of a DGEBA epoxy resin at liquid nitrogen temperature (77 K). The results show that the tensile strength, failure strain (ductility) and impact strength at 77 K are simultaneously improved by adding a proper content of H30. The maximum tensile strength at 77 K is increased by 17.7% from 98.2 MPa of pure epoxy resin to 115.6 MPa of modified epoxy system for the 10 wt% H30 content. The failure strain at 77 K increases consistently with the increase of H30 content. The maximum impact strength at 77 K is attained by introduction of 10 wt% H30 with an improvement of 26.3% over that of pure epoxy resin. For the purpose of comparison, the mechanical properties of modified epoxy resins at room temperature (RT) are also investigated. It is interesting to note that the impact strength is not lower at 77 K than that at RT for the modified systems. Moreover, the glass transition temperature (T_g) is not reduced by the addition of H30 in appropriate amounts.     

含芳醚芴二胺/环氧树脂固化反应动力学及性能研究

以9,9-双[4-4-氨基苯氧基苯基]芴(BAOFL)作为固化剂,采用非等温DSC技术,研究了BAOFL/环氧树脂(E-51、TDE-85和芴基环氧树脂)体系的固化反应动力学,利用动态热机械分析仪(DMA)和热重分析仪(TGA)测试了固化树脂的力学性能和热稳定性。结果表明,固化反应活化能与环氧树脂和固化剂的结构密切相关,芳醚的引入提高了氨基与环氧基的反应性,固化树脂呈现出优良的热性能和力学性能,其玻璃化转变温度(T)达到206~248℃,贮能模量为2.54~2.94 GPa,初始热分解温度312~375℃,700℃g时的残炭率达到15.2%~31.7%。()     

Electrochemical and thermal properties of polymer electrolytes based on poly(epichlorohydrin-co-ethylene oxide-co-ally glycidyl ether)

A series of novel electrolytes based on the terpolymer host, poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) with lithium perchlorate and lithium bis(trifluoromethanesulfonyl)imide have been prepared and characterized by conductivity measurements, cyclic voltammetry at a gold microelectrode and thermal analysis.Electrolyte compositions, represented as p(EEO-AGE)LiX(wt%), were produced with lithium salt compositions between 0.5 and 53 wt% (where wt% indicates amount of lithium salt present in the epichlorohydrin-co-ethylene oxide-co-allyl glycidyl host matrix). The guest salt and host polymer were dissolved in tetrahydrofuran and cast to produce thin, free-standing electrolyte films.The p(EEO-AGE)LiX(wt%) (X = ClO₄ and TFSI) electrolytes showed encouraging levels of ionic conductivity and acceptable thermal stability. Electrolytes based on this host polymer were obtained as completely amorphous films with good mechanical properties.     

Reactivity, viscoelastic behaviour and mechanical performances of hybrid systems based on epoxy resins and reactive polyhedral oligosilsesquioxanes

An epoxy formulation was modified by adding various amounts of an epoxy functionalized polyhedral oligomeric silsesquioxane (POSS). The obtained networks were characterized in terms of reactivity, viscoelastic behaviour and mechanical properties. Spectroscopy measurements by FT-NIR demonstrated that the epoxy groups of POSS were almost as reactive as those of the DGEBA in the curing stage, while in the post-curing a lower reactivity of the latter was found, possibly due to steric hindrance effects. The dynamic-mechanical analysis showed an increase in the storage modulus in both glassy and rubbery regions. On the other hand, T_g and T_β decreased with POSS content. The viscoelastic analysis showed that the addition of POSS enhanced the free volume and the tendency of the network to undergo thermal expansion. In particular, the β transition was made increasingly localized by increasing the POSS content. With respect to mechanical performances, the yield process was facilitated by incorporation of the POSS nanocages within the network, possibly due to an enhancement of the chain mobility. Fracture measurements showed an improvement of the parameters K_c and G_c up to 5 wt% of POSS, after which a decrease of toughness was observed. These results were supported by a fractographic analysis.     

Waterborne polyurethane/poly(n-butyl acrylate-styrene) hybrid emulsions: Particle formation,film properties,and application

In this work, a hybrid synthesis technology has been used to fabricate waterborne polyurethane (WPU)/poly(n-butyl acrylate-styrene) (PBS) emulsions with dimethylol-propionic acid (DMPA) as chain extender. The influences of the PBS, styrene, and DMPA contents on the physical properties of the resultant emulsions and cast films have been investigated in detail using various characterization methods. The experimental results show that with an increase in the PBS or styrene content, the particle size in emulsions increases but the viscosity of the emulsions decreases and that the opposite applies for the DMPA content. For cast films, with an increase in the styrene or DMPA content, the tensile strength increases whereas the elongation decreases. The water absorption capacity of the film decreases with an increase in the styrene content or a decrease in the DMPA content. Furthermore, the emulsions synthesized have been used for paper sizing applications. The treated papers exhibit greatly improved water resistance, and the Cobb values at 30 and 60 s are only 10.23 and 11.89%, respectively, of those of unsized papers. The other paper properties, such as gloss, smoothness, folding resistance, and burst strength, are also considerably improved.     

Miscibility, morphology, thermal, and mechanical properties of a DGEBA based epoxy resin toughened with a liquid rubber

Epoxy resin based on diglycidyl ether of bisphenol A and varying content of hydroxyl terminated polybutadiene were cured using an anhydride hardener. The ultimate aim of the study was to modify the brittle epoxy matrix by liquid rubber to improve the toughness characteristics. Chemorheological analysis of the modified network was performed to understand the physical transformations taking place during the cure polymerization reaction. The delay in gel time on inclusion of rubber can be explained by lower reactivity due to dilution and viscosity effect. Tensile, flexural, and fracture toughness behaviors of neat as well as modified networks have been studied to observe the effect of rubber modification. The morphological evolution of the toughened networks was examined by scanning electron microscope, and the observations were used effectively to explain the impact properties of the network having varying content of liquid rubber. Acoustic emission studies were performed on neat and certain modified systems. Based on acoustic emission results and morphological characteristics, toughening and failure mechanisms were discussed. The behavior of the relaxation peaks were evaluated by dynamic mechanical analysis and tried to explain the composition of networks. Thermal stabilities of the toughened epoxies were studied using thermogravimetric analysis (TGA). The activation energy for decomposition of neat and modified epoxies has been estimated and compared. The reduction in cross-linking density of the thermoset upon modification has been confirmed and explained.     

Cure kinetics, morphological and dynamic mechanical analysis of diglycidyl ether of bisphenol-A epoxy resin modified with hydroxyl terminated poly(ether ether ketone) containing pendent tertiary butyl groups

Hydroxyl terminated poly(ether ether ketone) based on tert-butyl hydroquinone (PEEKTOH) was used to modify a diglycidyl ether of bisphenol-A epoxy resin. A diamine, 4,4′-diaminodiphenylsulfone was used as the curing agent. Isothermal differential scanning calorimetric measurements of the blends were carried out at 180, 165 and 150 °C. The extent of reaction was found to decrease with the addition of PEEKTOH. The phenomenological model developed by Kamal was used for kinetic analysis of curing reaction. The curing reaction followed autocatalytic mechanism regardless of the presence and amount of oligomer present in the epoxy resin. The experimental and theoretical reaction rates were in good agreement during the initial stages of the reaction. The experimental values were lower than theoretical rate during the final stages of reaction due to increase in the viscosity of the system. A semiemperical model was used to explain diffusion control during final stages of reaction. The cured blends exhibited two phase morphology at all the curing temperatures. A uniform particle size distribution was observed at all compositions. The domain size decreased slightly with increase in oligomer content and with decrease in curing temperature. Finally, the viscoelastic properties were analysed using dynamic mechanical thermal analysis. Two T_gs corresponding to epoxy rich and thermoplastic rich phases were evident from the dynamic mechanical spectrum.     

Nanostructured thermosets from epoxy and poly(2,2,2-trifluoroethyl acrylate)-block-poly(glycidyl methacrylate) diblock copolymer: Demixing of reactive blocks and thermomechanical properties

Poly(2,2,2-trifluoroethyl acrylate)-block-poly(glycidyl methacrylate) (PTFEA-b-PGMA) diblock copolymer was synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The reactive diblock copolymer was incorporated into epoxy to obtain the nanostructured thermosets. The morphology of the thermosets was investigated by means of atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). It is identified that the demixing of the reactive subchain (viz. PGMA) out of epoxy matrix occurred in the process of curing reaction, which exerted a profound impact on the glass transition temperatures of the nanostructured thermosets. The static contact angle measurements showed that the nanostructured thermosets displayed a significant enhancement in surface hydrophobicity as well as a reduction in surface free energy. The improvement in surface properties was attributed to the enrichment of the fluorine-containing block (i.e., PTFEA) of amphiphilic diblock copolymer on the surface of the thermosets, which was further evidenced by surface atomic force microscopy (AFM). The measurement of critical stress intensity factor (K_1C) showed that the fracture toughness of the materials was significantly enhanced by the inclusion of a small amount of PTFEA-b-PGMA diblock copolymer.     

Prediction of the electrochemical oligomerization of p-tert-butyl anisole by analyses of the electrolysed solution

The objective of this paper is the study of the electrochemical oxidation of p-tert-butyl anisole in acetonitrile solution and its subsequent electrodeposition on platinum anode. In dry medium, potentiostatic deposition at potential more anodic than these of the two first overlapped waves, which requires relatively high initial substrate concentration, provided an electroactive film. It is shown that whilst the formation of coated electrode at relatively low concentration is difficult in dry medium, it became possible in the presence of an excess amount of water. In the voltammetric study, we observe that the addition of water to the monomer, in the same concentrations leads to the appearance of several new consecutive redox systems, at potential region more anodic than the two overlapped waves. The number of these processes, which are attributed to oxidation of the products of the two first steps, is found to be increased with the water concentration. Combining cyclic voltammetry along with high performance liquid chromatography (HPLC), the effect of the analytical concentration of the monomer and this of the addition of water, on macroscale electrolyses is discussed. Possible reaction mechanisms as well as probable structures for oligomeric products are proposed.     

Electrosynthesis and structural characterization of a novel aryl ether trimer

The structure of a novel trimer formed by three p-tert-butyl anisole moieties via the controlled potential electrolysis of p-tert-butyl anisole was determined by X-ray diffraction method. By cyclic voltammetry, we report a multistep electron transfer, each followed by a chemical reaction, resulting in an ECECEC mechanism. Preparative scale oxidation of p-tert-butyl anisole in dry acetonitrile leads to its two first oligomers. The symmetrical dimer, 2,2′-dimethoxy-5,5′-di-tert-butylbiphenyl, shows that the favored coupling sites are those in the ortho position of the methoxy group. The title compound, namely the 1-methoxy-bis-2,3-(2′-methoxy-5′-tert-butylphenyl)-4-tert-butylbenzene crystallizes in triclinic space group P-1 with a = 10.571(3) Å, b = 11.739(1) Å, c = 12.733(2) Å, α = 74.64(1)°, β = 88.71(2)°, γ = 76.58(2)°, V = 1480.8(5) Å³, and Z = 2. The structural analysis reveals that two p-tert-butyl anisole moieties are linked in ortho position on a third p-tert-butyl anisole fragment.     

Laminar burning velocities of n-heptane, iso-octane, ethanol and their binary and tertiary mixtures

Measurements of the adiabatic laminar burning velocities of n-heptane, iso-octane, ethanol and their binary and tertiary mixtures are reported. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The Heat Flux method was used to determine burning velocities under conditions when the net heat loss from the flame to the burner is zero. Initial temperatures of the gas mixtures with air were 298 and 338 K. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be better than ±1 cm/s. These new measurements were compared with the literature data when available. Experimental results in lean ethanol + air mixtures are systematically higher than previous measurements under similar conditions. Good agreement for n-heptane + air flames and for iso-octane + air flames was found with the experiments performed in counter-flow twin flames with linear extrapolation to zero stretch.     

Mass spectra of cyclic ethers formed in the low-temperature oxidation of a series of n-alkanes

Cyclic ethers are important intermediate species formed during the low-temperature oxidation of hydrocarbons. Along with ketones and aldehydes, they could consequently represent a significant part of the heavy oxygenated pollutants observed in the exhaust gas of engines. Apart a few of them such as ethylene oxide and tetrahydrofuran, cyclic ethers have not been much studied and very few of them are available for calibration and identification.Electron impact mass spectra are available for very few of them, making their detection in the exhaust emissions of combustion processes very difficult. The main goal of this study was to complete the existing set of mass spectra for this class of molecules. Thus cyclic ethers have been analyzed in the exhaust gases of a jet-stirred reactor in which the low-temperature oxidation of a series of n-alkanes was taking place. Analyzes were performed by gas chromatography coupled to mass spectrometry and to MS/MS. The second goal of this study was to derive some rules for the fragmentation of cyclic ethers in electron impact mass spectrometry and allow the identification of these species when no mass spectrum is available.     

Physical properties of poly(n-alkyl acrylate) copolymers. Part 1. Crystalline/crystalline combinations

The physical properties of n-alkyl acrylate copolymers containing two crystallizeable monomers, including thermal characteristics, structure as determined by small angle X-ray scattering, and gas permeability as a function of temperature, were examined in detail and compared to the corresponding homopolymers. The copolymers exhibit co-crystallization and, thus, for a given average side-chain length have comparable melting temperatures as the corresponding homopolymers. For a given side-chain length, the copolymers have somewhat lower heats of fusion than the corresponding homopolymers because of a reduction in crystallite size as revealed by SAXS. This depression in crystallinity is reflected in the permeability data for the copolymers. Poly(n-alkyl acrylates) exhibit a ‘jump’ in their gas permeability at the T_m of the side-chain lengths that is mainly caused by a switch in the side-chain morphology from crystalline to amorphous upon melting. The depression in crystallinity for the copolymers results in a smaller permeation jump. The jump breadth correlates with the melting endotherms for these polymers as determined by DSC. Ultimately, the melting endotherms for these copolymer systems provide an excellent tool for predicting permeability changes across the melting region.     

Physical properties of poly(n-alkyl acrylate) copolymers. Part 2. Crystalline/non-crystalline combinations

The physical properties of n-alkyl acrylate copolymers containing one crystallizeable monomer and one non-crystallizeable or slightly crystallizeable monomer, including thermal characteristics, structure as determined by small angle X-ray scattering, and gas permeability as a function of temperature, were examined in detail and compared to the corresponding homopolymers and copolymer systems containing two crystallizeable comonomers. The current copolymers exhibit melting point depression and, for a given average side-chain length, have lower heats of fusion than the corresponding homopolymers and crystalline/crystalline copolymers. Limited SAXS experiments revealed an increase in the d-spacings, above and below the melting point, with side-chain length consistent with expectations. The crystallites predominantly exhibit end-to-end packing similar to other poly(n-alkyl acrylates) previously studied. Poly(n-alkyl acrylates) exhibit a ‘jump’ in their gas permeability at the T_m of the side-chain lengths that is mainly caused by a switch in the side-chain morphology from crystalline to amorphous upon melting. The reduced crystallinity of the crystalline/non-crystalline copolymers results in a smaller permeation jump, which in some cases were extremely broad. All jump breadths correlate with the melting endotherms for these copolymers as determined by DSC similar to that for homopolymers and crystalline/crystalline copolymers. The magnitude of the jump correlates with the heat of fusion, irrespective of the comonomer type, in all cases.