Xiaojuan Zhao

Morphology and properties of TGDDM/DDS epoxy systems toughened by amino-bearing phenyl silicone resins

A series of amino-bearing phenyl silicone resins (APSR) were synthesized for toughening the tetraglycidyl 4,4′-diaminodiphenyl-methane (TGDDM) epoxy resin cured with 4,4′-diamino diphenyl sulfone. The microstructure of the TGDDM/APSR resins was highly dependent on the amino content of APSR and the loading level of the modifier. Based on the SEM and TEM studies, microstructure evolution of the TGDDM/APSR resins in the curing process was imaged. The toughness of the TGDDM resin was effectively improved without sacrificing the tensile strength, the flexural strength, and the modulus. The thermal stability and water resistance were improved as well. However, the modifier brought in a noticeable lowering in the glass transition temperature.

Three-Dimensional Printing of Shape Memory Composites with Epoxy-Acrylate Hybrid Photopolymer

Four-dimensional printing, a new process to fabricate active materials through three-dimensional (3D) printing developed by MITs Self-Assembly Lab in 2014, has attracted more and more research and development interests recently. In this paper, a type of epoxy-acrylate hybrid photopolymer was synthesized and applied to fabricate shape memory polymers through a stereolithography 3D printing technique. The glass-to-rubbery modulus ratio of the printed sample determined by dynamic mechanical analysis is as high as 600, indicating that it may possess good shape memory properties. Fold-deploy and shape memory cycle tests were applied to evaluate its shape memory performance. The shape fixity ratio and the shape recovery ratio in ten cycles of fold-deploy tests are about 99 and 100%, respectively. The shape recovery process takes less than 20 s, indicating its rapid shape recovery rate. The shape fixity ratio and shape recovery ratio during 18 consecutive shape memory cycles are 97.44 ± 0.08 and 100.02 ± 0.05%, respectively, showing that the printed sample has high shape fixity ratio, shape recovery ratio, and excellent cycling stability. A tensile test at 62 °C demonstrates that the printed samples combine a relatively large break strain of 38% with a large recovery stress of 4.7 MPa. Besides, mechanical and thermal stability tests prove that the printed sample has good thermal stability and mechanical properties, including high strength and good toughness.

Organo-Soluble Fluorinated Polyimides Derived from Bis-Trifluoromethyl-Substituted Aromatic Diamines and Various Aromatic Dianhydrides:

A new diamine monomer with bis-trifluoromethyl-substituted phenyl in the side chain, α,α-bis (4-amino-3,5-dimethylphenyl)-3′,5′-bis(trifluoromethyl)phenyl methane (6FMA) was successfully synthesized. A series of fluorinated polyimides (PI-IIa-d) were prepared by reacting the diamine with various aromatic dianhydrides. For comparison, another series of polyimides (PI-Ia-d) derived from another diamine with single-trifluoromethyl-substituted phenyl in the side chain, α,α-bis(4-amino-3,5-dimethylphenyl)-3′-trifluoromethyl phenyl methane and the same dianhydrides were also synthesized. The polymers were characterized by inherent viscosity, elemental analysis, Fourier transform-infrared, X-ray, ultraviolet-visible analysis, moisture absorption, thermogravimetric analysis, and differential scanning calorimetry measurements. It was shown that PI-II polyimides exhibited good film formability, enhanced solubility, good thermal stability, superior optical transparency, and acceptable mechanical properties. In addition, the polyimides derived from 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and 6FMA showed high sensitivity to i-line (365 nm) of a high-pressure mercury lamp. The combined properties of the polyimides make them good candidates for microelectronic fabrications.

Organo-Soluble Fluorinated Polyimides Derived from 4,4′-Bis (3-amino-5-tri uoromethylphenoxy)-3,3′,5,5′-tetramethyl biphenyl (TFMDA) and Aromatic Dianhydrides

A series of organo-soluble polyimides based on a new fluorinated diamine, 4,4′-bis(3-amino-5-trifluoromethylphenoxy)-3,3′,5,5′-tetramethyl biphenyl (3,5-TFMDA) and various aromatic dianhydrides, were synthesized and characterized. The structures of the obtained polyimides were affirmed by Fourier transform infrared measurement and the properties were evaluated by wide-angle X-ray diffraction measurement, ultraviolet-visible analysis, thermogravimetry (TG), differential scanning calorimetry (DSC), tensile and electrical tests, and solubility tests. It was shown that the polyimides have good solubility not only in polar aprotic solvents, but in many common solvents, such as cyclopentanone, chloroform, and even in toluene for PI-4, derived from TFMDA and 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The polyimide solutions could be cast into flexible and tough films, which exhibited good thermal stability up to 500° C and showed glass transition temperatures in the range of 250–280° C. The films also showed acceptable tensile properties and good electrical insulating properties. Furthermore, the polyimide films exhibited good transparency in the visible light region with transmittance higher than 80% at 450 nm and a cut-off wavelength lower than 360 nm.

Poly(aryl ether ketone/sulfone)s containing ortho-methyl and pendant trifluoromethyl-substituted phenyl groups: Synthesis and properties

Two novel bisphenols, 1,1-bis(4′-hydroxy-3′,5′-dimethylphenyl)-1-(3′′-trifluoromethylphenyl)-2,2,2-trifluoroethane (4M6FDO) and 1,1-bis(4′-hydroxy-3′,5′-dimethylphenyl)-1-[3′′,5′′-bis(trifluoromethyl)phenyl]-2,2,2-trifluoroethane (4M9FDO), with methyl groups ortho-substituted to the phenol groups, bulky trifluoromethyl-substituted phenyl groups and trifluoromethyl groups in the structure, were synthesized and characterized. The bisphenols were polymerized with 4,4′-difluorobenzophenone and bis(4-fluorophenyl) sulfone, respectively, via a aromatic nucleophilic substitution polycondensation to afford four poly(aryl ether ketone/sulfone)s (PAEKs/PAESs) with the inherent viscosities of 0.32–0.52 dL g−1. The ortho-methyl and pendant trifluoromethyl-substituted phenyl groups endow the polymers with good solubility, the rigidity of the polymer chains increase the glass transition (Tg) of the polymers to 197–235 °C. Flexible and tough films cast from N,N-dimethylacetamide showed good thermal stability, low dielectric constants of 2.67–2.73 and low water uptakes of 0.21–0.40%. Moreover, the polymers showed good transparency with light transmittance at 450 nm as high as 96% and cutoff wavelength as low as 285 nm. The PAEKs also exhibited low light-absorption at the optocommunication wavelengths of 1310 and 1550 nm.

Epoxy resin containing trifluoromethyl and pendant polyfluorinated phenyl groups: Synthesis and properties

A novel epoxy resin containing trifluoromethyl and pendant polyfluorinted phenyl groups, 1,1-bis[4-(2,3-epoxypropoxy)phenyl]-1-(3,4,5-trifluorophenyl) -2,2,2-trifluoroethane (6FEP) was synthesized and characterized. The reactivtiy of 6FEP with two aromatic diamines, 4,4′-diaminodiphenyl methane (DDM) and 1,4-bis(4-amino-2-trifluoromethylphenoxy) benzene (6FAPB), and the properties of the cured 6FEP were investigated and compared with those of the commonly used epoxy resin diglycidyl ether of bisphenol A (DGEBA). The experimental results indicated that 6FEP showed lower reactivity than DGEBA. The cured 6FEP exhibited good thermal stabilities with decomposition temperature at 5% weight loss of 374–397°C, high glass transition temperature of 159–177°C and good mechanical properties. The cured 6FEP epoxy resin also showed low dielectric constants at 1 MHz in the range of 3.2–3.4 and dielectric dissipation factors (tan δ) in the range of 2.10–2.48 × 10−3. Moreover, the cured 6FEP epoxy resins exhibited higher surface hydrophobicity and lower moisture absorption compared with DGEBA. The improved dielectric properties and hydrophobic properties of the cured 6FEP epoxy resin could be attributed to the introduction of trifluoromethyl and pendant polyfluorinated phenyl groups into the molecular structure of the epoxy resin.

Synthesis and Properties of Silphenylene-containing Epoxy Resins with High UV-stability

Two novel silphenylene-containing cycloaliphatic epoxy resins, 1,4-di [2-(3, 4-epoxycyclohexylethyl) dimethylsilyl] benzene (DEDSB) and 1,3,5-tri [2-(3, 4-epoxycyclohexylethyl) dimethylsilyl] benzene (TEDSB) were synthesized through in situ Grignard reaction and hydrosilylation, and characterized by FT-IR and 1H-NMR. They were colorless transparent viscous liquids. Methyhexahydrophthalic anhydride (MeHHPA) was used to cure the epoxy resins to give glassy solids with high optical clarity. Differential scanning calorimetry (DSC) results indicated that DEDSB and TEDSB showed similar curing reactivity. The cured TEDSB had a higher glass transition temperature, a higher storage modulus and a lower coefficient of linear thermal expansion than the cured DEDSB due to a higher crosslink density. The cured silphenylene-containing epoxy resins exhibited a much higher resistance to discoloration under UV irradiation than the commonly used epoxy resins diglycidyl ether of bisphenol-A (DGEBA). XPS analysis revealed that they were much less susceptible to photo-oxidation than DGEBA.

Synthesis and characterization of thianthrene-based epoxy with high refractive index over 1.7

GRAPHICAL ABSTRACT ABSTRACT A novel glycidyl resin 2,7-bis(β-epoxypropylthio)thianthrene (4SEP) with high refractive index was synthesized and characterized by 1H NMR, FT IR and FD-MS analyses. The kinetics of 4SEP cured with methylhexahydrophthalic anhydride (MeHHPA) was investigated by nonisothermal differential scanning calorimetry. The results revealed that the reactivity of 4SEP was higher compared with that of diglycidyl ether of bisphenol A (DGEBA) due to the weakened electron-withdrawing effect of thioether on the epoxy group. The thermal properties and refractive index of 4SEP/MeHHPA were investigated with differential scanning calorimetry, thermogravimetric analyses, Abbe refractometer, prism coupler, and compared with those of the DGEBA/MeHHPA. Experimental results showed that, due to the introduction of thianthrene and thioether units, the glass transition temperature (Tg) was slightly enhanced, while the thermal stability was reduced. The refractive index of 4SEP was over 1.7000, and the refractive index of 4SEP/MeHHPA was up to 1.6808.

A facile access to stiff epoxy vitrimers with excellent mechanical properties via siloxane equilibration

A new high performance stiff epoxy vitrimer based on siloxane equilibration has been fabricated in a simple way in which a polysiloxane oligomer containing aminopropyl side groups and catalytic potassium silanolate end groups was synthesized and used as a curing agent. The viscoelastic properties of the cured epoxy can be controlled by varying the concentration of potassium silanolate groups and the vitrimer possessing a complete stress relaxation behavior can be prepared, with relaxation times ranging from 376.8 s at 90 °C to 40.2 s at 170 °C. Due to the dynamic siloxane equilibration of polysiloxane catalyzed by potassium silanolate groups, this epoxy vitrimer exhibits excellent self-healing and recycling abilities. It can self-repair with a high healing efficiency, and be recycled at 130 °C within 40 min, retaining its original mechanical and thermal properties after at least four recycling cycles. Furthermore, such a material exhibits simultaneously a high service temperature (a glass transition temperature of 83 °C and an initial degradation temperature of 358 °C) and a strong (a stress at break of 46.6 MPa) and stiff (Youngs modulus of 2.2 GPa) nature.