Xin Yang

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.

A new shape memory epoxy resin with excellent comprehensive properties

In this article, a new type of epoxy resin, diglycidyl ether of 9,9-bis [4-(2-hydroxyethoxy) phenyl] fluorine (DGEBEF) was successfully synthesized and characterized by 1H-NMR, FTIR, and FDMS analyses. The kinetics of DGEBEF cured with 4,4′-diamino diphenyl sulfone (DDS) was investigated by nonisothermal differential scanning calorimetry and thermal stability of the cured resin was characterized by thermogravimetric analysis. The DGEBEF/DDS system exhibits excellent processability, mechanical strength, and toughness, high thermal stability and low water absorption. Glass transition temperature (Tg) of the cured epoxy was 170xa0°C determined by DMA. The ratio of the storage modulus of the cured resin at glassy state to that at rubbery state was as large as about 400, indicating its potential applications as shape memory material. The excellent shape memory properties were confirmed by fold-deploy shape memory and tensile-shrinkage tests. The shape fixed ratio was 99xa0%. and the shape recovery ratio was nearly 100xa0% after 30-s recovery at 185xa0°C in the fold-deploy shape memory test. In the tensile-shrinkage test, the recovery stress is 2.5xa0MPa at the strain of 25xa0% and temperature of 185xa0°C, and both the shape fixed and shape recovery ratios maintained at about 99xa0% after six test cycles.

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.

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.