Characterization of mechanical properties of γAl2O3 dispersed epoxy resin cured by γ‐ray radiation

Epoxy resins are widely utilized as high performance thermosetting resins for many industrial applications, but they are characterized by relatively low toughness. Incorporation of rigid inorganics is suggested to improve the mechanical properties of epoxy resins. An attempt is made to disperse nanosized γ‐Al₂O₃ particles into diglycidyl ether of bisphenol A epoxy resins for the improvement of the mechanical properties. These hybrid epoxy–alumina composites are prepared using by the γ‐ray curing technique conducted at 100 kGy under nitrogen at room temperature. The composites are characterized by determining the gel content, flexural strength, Youngis modulus, and toughness at room temperature using scanning electron microscopy and FTIR studies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1898–1903, 2004     

Water uptake of epoxy coatings modified with γ-APS silane monomer

Epoxy resin was modified by a silane monomer, γ-aminopropyltrimethoxy silane (γ-APS), and was used as the protective coatings for LY12 aluminum alloys. The aim of the modification is to reduce the water uptake of polymeric coatings. The water absorption of coatings was measured by coating capacitance method in 3.5 wt.% NaCl aqueous solution. The result indicates that water uptake of epoxy coatings modified with 1.0 wt.% γ-APS decreases compared with pure epoxy coatings, whereas larger amounts of sliane result in the deterioration in performance against water permeation, due to the excessive consumption of epoxide group in epoxy resin by amino-group in silane agent, thus reduce the cross-linking of epxoy coating as a result of presence of excessive curing agent (polyamide). T_g of silane-modified coatings increases slightly after immersion, extremely contrasting with that of pure epoxy coating, which was observed to decrease significantly after water permeation. The formation of Si–O–Si structure resulting from the hydrolysis and condensation of silane components during the immersion in aqueous media may be a reasonable explanation for the abnormal change in T_g of silane-modified coatings. In addition, all silane-modified coatings display better protection performance, which is characterized by higher charge transfer resistances (R_ct) and lower double layer capacitance (C_dl) at substrate/electrolyte interface.     

Synthesis,characterization, and degradation investigation of water‐soluble β‐cyclodextrin‐based epoxy resins

A series of β‐cyclodextrin‐based epoxy resins were synthesized with different epoxy equivalent weights. Their chemical structures were characterized with Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR) examination. These epoxy resins were cured using L ‐arginine as a curing agent, and the degradation behavior of the cured resins was evaluated under different acidic buffer solutions at 37°C. The degradable behavior of such epoxy resins suggested potential applications as environment friendly materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

有机硅改性双酚F环氧树脂热性能研究

以TMA和TGA研究了含酚羟基的有机烷氧基硅烷及3,3′,3″-三羟基苯氧基硅烷三缩水甘油醚等多种自行设计、合成的有机硅改性剂改性双酚F环氧树脂的热性能。研究结果表明,有机硅可降低改性树脂的线胀系数,但端环氧基脂肪族聚硅氧烷及含酚羟基的二官能度有机硅的加入均使固化物玻璃化温度降低10℃以上;含环氧基的多官能度有机硅改性剂3,3′,3″-三羟基苯氧基硅烷三缩水甘油醚的加入可使线胀系数降低约20%,内应力指数降低约20%,抗开裂指数提高50%以上,固化物玻璃化温度基本不变,热分解温度有较大幅度的提高,是一种理想的环氧树脂增韧改性剂,可用于电子封装等行业用环氧树脂的改性。     

Synthesis and characterization of ethoxyethyl α‐cyanoacrylate and reaction intermediates

Ethoxyethyl α‐cyanoacrylate was synthesized by first making oligo(ethoxyethyl α‐cyanoacrylate) through a condensation reaction of ethoxyethyl cyanoacetate with paraformaldehyde, followed by a depolymerization of the oligomer at an elevated temperature in an acidic atmosphere with a high vacuum. The ethoxyethyl cyanoacetate was in turn synthesized from an esterification of ethoxyethanol and cyanoacetic acid. The molecular structure of the target monomer and the corresponding intermediates were corroborated by IR and ¹H‐NMR. Solvents having a lower polarity led to the formation of oligomers having higher molecular weights. The molecular weight distribution of the oligomer revealed that the reaction of ethoxyethyl cyanoacetate with formaldehyde followed a mechanism comprising monomer activations, anionic reactions, and chain scissions. DSC thermograms demonstrated the cured ethoxyethyl α‐cyanoacrylate was nearly amorphous, containing little or low crystallinity. Mechanical testing data indicated that the cured ethoxyethyl α‐cyanoacrylate was a hard adhesive with higher toughness than the conventional ethyl α‐cyanoacrylate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1758–1773, 2003     

Synthesis and characterization of grafting β‐cyclodextrin with chitosan

Two new adsorbents [β‐cyclodextrin–chitosan (β‐CD–CTS) and β‐cyclodextrin‐6–chitosan (β‐CD‐6‐CTS)] were synthesized by the reaction of β‐cyclodextrin (β‐CD) with epoxy‐activated chitosan (CTS) and the sulfonation of the C‐6 hydroxyl group of β‐cyclodextrin with CTS, respectively. Their structures were confirmed by IR spectral analysis and X‐ray diffraction analysis, and their apparent amount of grafting was determined by ultraviolet spectroscopy. The adsorption properties of β‐CD‐CTS and β‐CD‐6‐CTS for p‐dihydroxybenzene were studied. The experimental results showed that the two new adsorbents exerted adsorption on the carefully chosen target. The highest saturated capacity of p‐dihydroxybenzene of β‐CD‐CTS and β‐CD‐6‐CTS were 51.68 and 46.41 mg/g, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 860–864, 2004     

硅烷偶联剂改性环氧丙烯酸酯的合成与应用

针对环氧丙烯酸酯附着力和柔韧性差的缺点,通过在环氧丙烯酸酯中引入硅烷基团,合成硅烷改性的环氧丙烯酸酯。考察了各工艺参数对反应产品的影响,通过滴定和红外光谱分析跟踪反应进程和确定产物结构。合成产物通过和光固化单体、光引发剂混配成紫外光固化胶粘剂,并与改性之前的环氧丙烯酸酯作为主体树脂时的紫外光固化胶粘剂的性能进行了对比。研究发现,合成产物通过硅烷基团的引入,改善了环氧丙烯酸酯的柔韧性。同时,由于硅烷偶联剂基团在固化过程中水解露出的硅羟基增强了对无机底材的附着力,使得紫外光固化胶粘剂的综合性能得到了优化和改善。     

Cationic copolymers of α,β‐poly‐(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy): synthesis and characterization

In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry     

Transesterification in homogeneous poly(ε‐caprolactone)–epoxy blends

Transesterification has been investigated in poly(ε‐caprolactone) (PCL)–epoxy blends. In the hot melt process, the hydroxyl on diglycidyl ether of bisphenol‐A (DGEBA) monomers is too low to give a noticeable transesterification reaction. In the postcure process, model reactions reveal that the hydroxyls from a ring‐opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular weight decrease and its distribution becomes broader. Nuclear magnetic resonance spectra reveal that fraction of the tertiary hydroxyls converts to secondary hydroxyls. In the cured DGEBA–3,3′‐dimethylmethylene‐di(cyclohexylamine)–PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and result in the lower T_g observed in the differential scanning calorimetry thermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 75–82, 1999     

Synthesis and characterization of diphenylsilanediol modified epoxy resin and curing agent

A series of diphenylsilanediol modified epoxy resins and novel curing agents were synthesized. The modified epoxy resins were cured with regular curing agent diethylenetriamine (DETA); the curing agents were applied to cure unmodified diglycidyl ether of bisphenol A epoxy resin (DGEBA). The heat resistance, mechanical property, and toughness of all the curing products were investigated. The results showed that the application of modified resin and newly synthesized curing agents leads to curing products with lower thermal decomposition rate and only slightly decreased glass transition temperature (T_g), as well as improved tensile modulus and tensile strength. In particular, products cured with newly synthesized curing agents showed higher corresponding temperature to the maximum thermal decomposition rate, comparing with products of DGEBA cured by DETA. Scanning electron microscopy micro images proved that a ductile fracture happened on the cross sections of curing products obtained from modified epoxy resins and newly synthesized curing agents, indicating an effective toughening effect of silicon–oxygen bond.     

噁唑烷酮改性环氧树脂的性能

采用4,4-二苯基甲烷二异氰酸酯(MDI)对双酚A环氧树脂和脂肪族环氧树脂进行噁唑烷酮化共改性,研究了MDI及作为活性稀释剂的脂肪族环氧用量对改性产物黏度及树脂固化物力学性能、耐热性的影响。结果表明,低改性比和稀释剂可以有效降低唑烷酮改性环氧树脂黏度,当改性比为4∶1时,树脂固化物拉伸强度、弯曲强度达到75.4 MPa和158.2 MPa,分别比环氧树脂固化物提高了64%和57%,断裂延伸率和冲击强度有较大提高,具有高强高韧的特点。稀释剂含量对Tg影响较小,各改性树脂Tg在108～118℃之间,与纯环氧树脂的耐热性相当。     

The Synthesis of trans‐Perhydroindolic Acids and their Application in Asymmetric Domino Reactions of Aldehyde Esters with β,γ‐Unsaturated α‐Keto Esters

(2S,3aR,7aS)‐Perhydroindolic acid, the key intermediate in the synthesis of trandolapril, and its trans‐isomers, were readily prepared. These proline‐like molecules are unique in that they contain a rigid bicyclic structure, with two hydrogen atoms trans to each other at the bridgehead carbon atoms. These molecules were used successfully as chiral organocatalysts in asymmetric domino Michael addition/cyclization reactions of aldehyde esters with β,γ‐unsaturated α‐keto esters. They proved to have excellent catalytic behavior, allowing for the synthesis of multi‐substituted, enantiomerically enriched hemiacetal esters. Under optimal conditions (using 10 mol% catalyst loading), a series of β,γ‐unsaturated α‐keto esters was examined with up to 99% de, ee and yield, respectively. Additionally, the enantiomerically enriched hemiacetal esters could be readily transformed into their corresponding bioactive pyrano[2,3‐b]pyrans (possessing a multi‐substituted bicyclic backbone).     

Synthesis and characterization of polyimide‐γ‐Fe2O3 nanocomposites

Novel polyimide‐γ‐Fe₂O₃ hybrid nanocomposite films (PI/γ‐Fe₂O₃) has been developed from the poly(amic acid) salt of oxydianiline with different weight percentages (5, 10, 15 wt %) of γ‐Fe₂O₃ using tetrahydrofuran (THF) and N,N‐dimethylacetamide (DMAc) as aprotic solvents. The prepared polyimide‐γ‐Fe₂O₃ nanocomposite films were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy (FTIR), scanning electron micrograph (SEM), transmission electron micrograph (TEM), X‐ray diffraction (XRD), ¹³C‐NMR, and thermal analysis (TGA/DSC) techniques. These studies showed the homogenous dispersion of γ‐Fe₂O₃ in the polyimide matrix with an increase in the thermal stability of the composite films on γ‐Fe₂O₃ loadings. Magnetization measurements (magnetic hysteresis traces) have shown very high values of coercive force indicating their possible use in memory devices and in other related applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 834–840, 2007     

Ruthenium(II)‐Catalyzed Protocol for Preparation of Diverse α,β‐ and β,β‐Dihaloenones from Diazodicarbonyls

Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.

     

Michael Reaction of Nitroalkanes with β‐Nitroacrylates under a Solid Promoter: Advanced Regio‐ and Diastereoselective Synthesis of Nitro‐Functionalized α,β‐Unsaturated Esters and 1,3‐Butadiene‐2‐carboxylates

A new class of nitro‐functionalized α,β‐unsaturated esters has been prepared by a regio‐ and diastereoselective Michael addition of nitroalkanes to β‐nitroacrylates, performed at room temperature, under carbonate on polymer as promoter, and in the presence of ethyl acetate as eco‐friendly solvent. Moreover, by the modular choice of the reaction conditions the method allows the synthesis of 1,3‐butadiene‐2‐carboxylates.     

Multi‐Enzymatic Synthesis of Optically Pure β‐Hydroxy α‐Amino Acids

A novel enzymatic production system of optically pure β‐hydroxy α‐amino acids was developed. Two enzymes were used for the system: an N‐succinyl L ‐amino acid β‐hydroxylase (SadA) belonging to the iron(II)/α‐ketoglutarate‐dependent dioxygenase superfamily and an N‐succinyl L ‐amino acid desuccinylase (LasA). The genes encoding the two enzymes are part of a gene set responsible for the biosynthesis of peptidyl compounds found in the Burkholderia ambifaria AMMD genome. SadA stereoselectively hydroxylated several N‐succinyl aliphatic L ‐amino acids and produced N‐succinyl β‐hydroxy L ‐amino acids, such as N‐succinyl‐L ‐β‐hydroxyvaline, N‐succinyl‐L ‐threonine, (2S,3R)‐N‐succinyl‐L ‐β‐hydroxyisoleucine, and N‐succinyl‐L ‐threo‐β‐hydroxyleucine. LasA catalyzed the desuccinylation of various N‐succinyl‐L ‐amino acids. Surprisingly, LasA is the first amide bond‐forming enzyme belonging to the amidohydrolase superfamily, and has succinylation activity towards the amino group of L ‐leucine. By combining SadA and LasA in a preparative scale production using N‐succinyl‐L ‐leucine as substrate, 2.3 mmol of L ‐threo‐β‐hydroxyleucine were successfully produced with 93% conversion and over 99% of diastereomeric excess. Consequently, the new production system described in this study has advantages in optical purity and reaction efficiency for application in the mass production of several β‐hydroxy α‐amino acids.

     

Surface modification of aramid fibers with γ‐ray radiation for improving interfacial bonding strength with epoxy resin

Co⁶⁰ γ‐ray radiation as a simple and convenient method for surface modification of Armos aramid fibers was introduced in this article. Two kinds of gas mediums, N₂ and air, were chosen to modify aramid fiber surface by γ‐ray irradiation. After fiber surface treatment, the interlaminar shear strength values of aramid/epoxy composites were enhanced by about 17.7 and 15.8%, respectively. Surface elements of aramid fibers were determined by XPS, the analysis of which showed that the ratio of oxygen/carbon was increased. The crystalline state of aramid fibers was determined by X‐ray diffraction instrument. The surface topography of fibers was analyzed by atomic force microscopy and scanning electron microscope. The degree of surface roughness and the wettability of fiber surface were both enhanced by γ‐ray radiation. The results indicated that γ‐ray irradiation technique, which is a suitable way of batch process for industrialization, can significantly improve the surface properties of aramid fibers reinforced epoxy resin matrix composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

环氧基硅烷改性氰酸酯树脂的性能研究

采用环氧基硅烷(ESi)对双酚A型二氰酸酯树脂(BCE)进行改性,研究了ESi用量对ESi/BCE体系力学性能和动态力学性能等影响。结果表明:适量的ESi可以明显提高BCE的韧性和强度;当w(ESi)=6%时,ESi/BCE改性体系的力学性能最好,其冲击强度和弯曲强度分别从10.1 kJ/m2、94.11 MPa提高到14.49 kJ/m2、110.94 MPa;ESi/BCE体系的交联密度降至适度是其韧性提高的主要原因,并且其玻璃化转变温度(Tg)低于纯BCE体系(但降幅不大)。     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

Organocatalytic Enantioselective Aziridination of α‐Substituted α,β‐Unsaturated Aldehydes: Asymmetric Synthesis of Terminal Aziridines

The first example of a highly enantioselective organocatalytic aziridination of α‐substituted α,β‐unsaturated aldehydes is presented. The reaction is catalyzed by simple chiral amines and gives access to highly functional terminal azirdines containing an α‐tertiary amine stereocenter in high yields and enantiomeric ratios (95.5:4.5–98:2).