Improvement of Bonding Strength of AZ31B Magnesium Alloy by Anodizing and Chromium-free Conversion Treatments

The influences of chromium-free chemical conversion treatment and anodizing treatment on bonding strength of AZ31 magnesium alloy were studied by lap-shear test, SEM and electrochemical methods. Both chemical conversion treatment and anodizing can increase the bonding strength. The anodizing treatment gives higher bonding strength and better corrosion resistance than chemical conversion treatment. The increase of bonding strength by the treatmetlts may be attributed to the uneven surface structures with micro-pores, resulting in increased bonding areas and the embedding effect.

Preparation of Titanium-silphenylene-siloxane Hybrid Polymers with High Refractive Index,Transmittance,and Thermal Stability

Vinyl-containingtitanium-silphenylene-sioxane oligomers(O1,O2,O3,andO4)withdifferent molar ratios of titanium to silicon were successfully synthesized in high yields by nonhydrolytic sol-gel reaction,and the obtained four oligomers were further crosslinked with methylphenyl hydro-silicone oil(4)to form corresponding polymers(P1,P2,P3,and P4)by hydrosilylation reaction.Their structures were characterized with spectroscopic characterization techniques including FTIR,1H-NMR,and Raman spectroscopy.The effect of titanium element on crosslinking behavior,thermal resistance,refractive index,transparency,thermal aging stability,glass transition temperature,and surface properties of the polymers were studied.Compared with titanium-free polymer P1,the thermal resistance,refractive index,and thermal aging stability of titanium-silphenylene-siloxane polymers(P2,P3,and P4)were significantly improved.The titanium-silphenylene-siloxane polymers achieved a high refractive index(n=1.580-1.584)and thermostability(Tsd>500℃).In thermal aging,the polymers exhibited superior performances with high optical transparency(~90%at 450 nm)and exhibited high thermal stability(~84%at 450 nm after thermal aging at 150℃for 120 h).These data indicate that the polymers have potential application in optical materials such as LED encapsulants.

Synthesis, Characterization and Thermal Stability of Novel Carborane- Containing Epoxy Novolacs

Carborane bisphenol novolacs （3 and 4） were synthesized in the presence of acid catalyst from carborane bisphenols （5 and 6） and formaldehyde. Further epoxidization of carborane bisphenol novolacs with epichlorohydrin gave carborane bisphenol epoxy novolacs （1 and 2）. The molecular weight and epoxy value of obtained resins were determined using the molecular weight of their precursors. The epoxy values of 1 and 2 were 0.48 and 0.52 respectively, higher than the maximum theoretical epoxy value （0.45） of difunctional carborane bisphenol epoxy resins. FTIR and NMR were utilized to characterize 1 and 2. The curing behaviors were also studied by DSC and the optimized curing conditions were obtained. TGA analysis indicated that carborane moiety could shield its adjacent organic structures against initial decomposition. On the other hand, B--H on carborane cage could react with oxygen to form a three-dimensional network linked by B--O--B and B--C bonds, which further blocked the movement of formed radicals and thus the degradation process was inhibited.

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 and Characterization of Carborane Bisphenol Resol Phenolic Resins with Ultrahigh Char Yield

Two carborane-containing resol phenolic resins（P1 and P2） with high boron content were synthesized via the reaction of carborane bisphenols（1 and 2） with formaldehyde in the presence of alkaline. HRMS results indicate that P1 is mainly composed of hydroxymethylated o-carborane bisphenols, the Mw of which was restrained around 500 due to the strong steric hindrance of o-carborane bisphenol. In contrast, the molecular weight of P2 was well regulated under various reaction conditions. The obtained resins were characterized with spectroscopic techniques including FTIR, 1H-NMR, ^13C-NMR, and 11B-NMR, which gave satisfactory results. TGA studies show that P2 shows char yield of 88.9% and 92.9% at 900 ℃ under nitrogen and air respectively. The imported carborane cage endows phenolic resin with ultrahigh char yield. Particularly, the char yield of the obtained carborane-containing phenolic resin under air is higher than that under nitrogen. FTIR and XRD confirm that the carborane cage could react with oxygen to form B2O3 at elevated temperatures, which postpones the thermal decomposition of phenolic resin and accounts for the high char yield.

Surface Modification of Polyamide66 Fabric by Grafting with Vinyltrimethoxysilane

Melt-dripping is always a big chanllenge in flame retardant finishing of synthetic fabrics. In this work, vinyltrimethoxysilane（VTMS） was introduced onto the polyamide66（PA66） surface by microwave grafting to improve the fire performance. The chemical structure of the grafted fabric was characterized by attenuated total reflection Fourier transformation infrared spectroscopy（ATR-FTIR） and X-ray photoelectron spectroscopy（XPS）. The thermal stability analysis and flammability evaluation of the grafted samples by thermogravimetric analysis（TGA）, cone calorimetry, vertical burning tests and limiting oxygen index（LOI） demonstrate that the presence of grafting chains significantly reduces the dripping tendency and decreases the heat release rate of polyamide66（PA66） fabric. The surface morphology observed by scanning electron microscope（SEM） indicates that VTMS can not only promote the formation of protective layers, which prevent the substrate from further thermal degradation, but also promote the char formation ofPA66 substrate during combustion.

Self-healing Supramolecular Polymer Composites by Hydrogen Bonding Interactions between Hyperbranched Polymer and Graphene Oxide

A self-healing supramolecular polymer composite（HSP-GO） was designed and prepared via incorporation of modified graphene oxide to hyperbranched polymer by hydrogen-bonding interactions. The polymer matrix based on amino-terminated hyperbranched polymer（HSP-NH_2） was synthesized by carboxylation, Curtius rearrangement, and amination of hydroxyl-terminated hyperbranched polyester（HP-OH）, while the modified graphene oxide was prepared by transformation of hydroxyl to isocyanate and further to carbamate ester. Spectroscopic methods were utilized to characterize the obtained polymer composites. Stress-strain test was selected to carefully study the self-healing property of HSP-GO. It is found that a small amount of modified graphene oxide（up to 2 wt%） improves the glass transition temperature（T_g）, tensile strength, Young＇s modulus, and self-healing efficiency of the polymer composites. After healed at room temperature for 10 min, the addition of modified graphene oxide improves the self-healing efficiency to 37% of its original tensile strength. The experiment result shows that the self-healing efficiency is related to the density of hydrogen bonding site and the molecular movement.