辛醇改性纳米二氧化硅表面的研究

纳米粒子由于粒径小,所以具有很高的比表面积,表面原子处于高度活化状态,使得表面能很高,粒子易于团聚,填充未经表面处理的纳米粒子,不但起不到特殊作用,反而会成为复合材料的力学弱点。所以要对纳米粒子进行表面改性,提高分散性,增加纳米粒子与聚合物间的界面结合力。用醇类对许多粉体进行酯化反应是常用的表面改性方法。金属氧化物与醇的反应是酯化反应[1]。酯化反应修饰法对于表面为弱酸性和中性的纳米粒子最为有效,例如SiO2等。醇的羟基与SiO2的表面羟基发生反应脱掉一分子水,达到表面接枝的目的。方程式为:这样R基团接枝到SiO2的表面,由于R基团是亲油性的,从而增加了极性的SiO2纳米粒子与有机物的润湿性。为了推动反应正向进行,关键在于及时将产生的水份引出反应体系。目前国内外用醇对纳米粒子进行表面改性主要采用常规回流法和高压反应釜法[2]。由于微波照射具有对物质高效、均匀的加热作用,同时还具有电磁场对反应分子间行为的直接作用而引起的所谓“非热效应”,所以本实验采用微波照射法用正辛醇对SiO2纳米微粒进行表面酯化反应并与常规回流法进行比较。关于该方面的研究报道国内外较少。1实验部分1.1实验原料纳米SiO2:(10~20nm...     

可聚合纳米SiO2杂化材料的制备及其性能研究

利用异佛尔酮二异氰酸酯(IPDI)和纳米SiO2表面-OH基团反应的特点,制备了表面含-NCO基团的纳米SiO2,用端羟基聚丙二醇醚(PPG)对其扩链并进一步和丙烯酸羟乙酯(HEA)反应,制备了丙烯酸酯封端、IPDI和PPG连接纳米SiO2粒子的纳米SiO2杂化材料.用红外光谱(FTIR)、热失重(TGA)和扫描电镜(...     

新型室温酯化法接枝聚合物改性SiO_2纳米微粒

提出了一种在室温、大气环境等温和条件下通过酯化反应将端羧基聚合物链接枝到纳米SiO2微球表面从而制备有机/无机复合纳米微粒的新方法.该方法通过以下两个步骤得以实现,即第一,用3-环氧丙基三甲氧基硅烷对纳米SiO2微球表面进行改性处理,接着将引入到纳米SiO2表面的环氧基团转化为烷羟基基团;第二,通过引入到纳米SiO2微球表面的烷羟基与聚合物中的端羧基在室温下发生酯化反应,从而将聚合物接枝到纳米SiO2表面制得复合微球.利用XPS、FTIR、TEM和TGA等测试手段对纳米SiO2的改性过程以及聚合物接枝后得到的复合微球进行了表征.研究结果表明,该室温酯化接枝方法具有较高的接枝率,接枝到无机纳米微粒表面的聚合物占复合微球质量的55wt%～70wt%;接枝聚合物后,纳米SiO2微球的粒径从40nm增加到64～75nm,从而得到了以SiO2为核、以聚合物为壳的有机-无机复合微球.     

合成聚对苯二甲酸丙二醇酯负载型催化剂钛酸四丁酯/纳米二氧化硅的制备

以钛酸酯偶联剂(TMC-201)为改性剂,采用超声波分散方法对亲水性纳米二氧化硅(nano-SiO2)进行了表面改性。采用浸渍法将钛酯四丁酯(Ti(OC4H9)4)负载于表面改性的nano-SiO2上,制备了纳米级Ti(OC4H9)4/nano-SiO2负载型催化剂。考察了偶联剂用量、温度、时间对纳米SiO2表面改性的影响,研究了负载时间、负载温度和Ti(OC4H9)4用量对表面改性后纳米SiO2负载Ti(OC4H9)4的影响。结果表明,当TMC-201质量分数为35%、反应温度为90℃、反应时间为3.5 h时,纳米SiO2粒子表面接枝的偶联剂量最大;在室温下,负载48 h,Ti(OC4H9)4用量为表面改性纳米SiO2量的1/2时得到的Ti(OC4H9)4/nano-SiO2负载型催化剂负载Ti(OC4H9)4量最大;运用ICP-AES、FESEM等测试技术对修饰后的纳米SiO2及Ti(OC4H9)4/nano-SiO2负载型催化剂进行了表征;将Ti(OC4H9)4/nano-SiO2负载型催化剂用于聚对苯二甲酸丙二醇酯(PTT)聚酯合成的结果表明,与均相Ti(OC4H9)4催化剂相比,Ti(OC4H9)4/nano-SiO2负载型催化剂催化合成PTT聚酯过程中酯化时间177 min,与均相催化剂催化酯化时间相近,在缩聚2 h后得到PTT的特性粘度高达1.05,证明该负载型催化剂具有高的催化活性,既可催化酯化反应又可催化缩聚反应。     

不同聚合物对纳米SiO2表面改性的研究进展

纳米SiO2由于具有无味、无毒、无污染等特性,因而被广泛用作无机纳米填料。纳米SiO2极易团聚,从而限制了它的广泛应用。但纳米SiO2表面富含大量的硅羟基,可对其进行表面改性。纳米SiO2表面改性的方法较多,主要有表面物理改性和表面化学改性两种,其中表面化学改性中又以聚合物改性的效果最好。本文综述了国内外利用不同的聚合物——亲水性、疏水性和两亲性聚合物对纳米SiO2表面的化学改性,并对其应用进行了分析,展望了其发展前景。     

具有双亲特性的水相哑铃型SiO2纳米粒子的制备

以纳米SiO2水溶胶为原料,3?氨丙基三乙氧基硅烷(APTES)和3?氯丙基三乙氧基硅烷(CPTES)为改性剂,在水基环境下分别对SiO2纳米粒子进行改性,得到了具有亲水特性的APTES改性SiO2粒子和具有亲油特性的CPTES改性SiO2粒子水溶胶。2种粒子按不同比例混合,利用接枝在SiO2粒子表面氨基和氯丙基的取代反应,使得2种具有亲水/亲油特性的改性SiO2纳米粒子偶联,制备了粒径为40~50 nm的哑铃型SiO2纳米粒子。并通过透射电镜(TEM)、傅里叶变换红外光谱(FT?IR)、X射线光电子能谱(XPS)以及动态光散射(DLS)等方法对其进行了系统表征。结果表明,2种粒子成功偶联形成了具有哑铃型结构的水相SiO2纳米粒子,该粒子两面具有不同的亲水性,粒径近似等于APTES改性SiO2粒子和CPTES改性SiO2粒子的粒径之和。     

微波辐射下纳米二氧化硅接枝正辛醇的表面改性

在微波辐射下用正辛醇对SiO2纳米粒子进行表面接枝改性。改性SiO2纳米粒子的表征结果显示其亲油疏水性得到了很大提高。     

原子转移自由基聚合接枝改性纳米SiO2的研究进展

纳米SiO2粒子极易团聚,在有机介质中难以均匀分散,从而大大地限制了其优异性能的发挥,有必要对其进行化学改性处理。原子转移自由基聚合(atom transfer radical polymerization,ATRP)是对纳米SiO2粒子进行接枝改性的一种有效途径,通过ATRP对纳米SiO2粒子进行表面改性,可以制备集无机纳米粒子和聚合物的优点于一身的SiO2-聚合物复合材料,且接枝链的长度及分子量分布可控,拓展了纳米SiO2的应用领域。本文主要综述了ATRP、RATRP(reverse ATRP)、AGET ATRP(activators generated by electron transferATRP)和ARGET ATRP(activators regenerated by electron transfer ATRP)方法对纳米SiO2接枝改性的研究现状。     

微波水热改性制备S2 /Fe2O3-SiO2固体酸及催化性能

对共沉淀法得到的Fe2O3-SiO2混合氧化物前驱物进行微波水热改性处理，经浸渍（NH4）2S2O8后再焙烧得S2O8^2-／Fe2O3-SiO2固体酸催化剂。用XRD、TEM、N2气吸附／脱附及化学分析方法对其进行了表征，用乙酸／丁醇酯化催化反应评估固体酸的催化性能，并与通常条件下制得的催化剂进行了比较。结果显示，引入SiO2会延迟Fe2O3晶体的形成与长大；对前驱物用250W的微波水热改性处理1．5h，制得的固体酸具有适中的比表面积、均匀的孔径分布，含硫量为6．02％，比表面积为37．1m^2／g。该固体酸对乙酸丁醇酯化反应有很高的催化活性，催化酯化反应3h，乙酸的转化率高达97．7％。     

二氧化硅-聚丙烯腈核-壳结构复合纳米粒子的制备与表征

以甲基丙烯酸-3-(三甲氧基硅基)丙酯改性的SiO2纳米粒子为种子,采用乳液聚合法制备了粒径分布较窄的SiO2-聚丙烯腈(SiO2-PAN)核-壳结构复合纳米粒子。采用动态光散射、傅里叶红外光谱、透射电镜和扫描电镜表征了复合纳米粒子的粒径及分布、组成、形态和结构,并研究了表面活性剂的加入方式、反应温度及交联剂的引入对制备SiO2-PAN复合纳米粒子的影响。结果表明:SiO2-PAN复合纳米粒子为核-壳结构。采用半连续加入表面活性剂的方法,可以成功抑制乳液聚合中次级粒子的生成。通过增加表面活性剂的初始加入量、加快表面活性剂的补加速率,或降低反应温度,可使SiO2-PAN复合纳米粒子的粒径变小。反应温度的降低以及交联剂的引入使SiO2-PAN复合纳米粒子的表面变得平滑。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Microwave-assisted copper-catalyzed stereoselective ring expansion of three-membered heterocycles with α-diazo-β-dicarbonyl compounds

Microwave-assisted copper-catalyzed ring expansions of three-membered heterocycles with α-diazo-β-dicarbonyl compounds were investigated. Thiiranes generated 3-acyl-5,6-dihydro-1,4-oxathiines in the presence of copper sulfate and trans-3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis-thiiranes through an intramolecular S_N2 process. Oxiranes gave rise to 2-acyl-5,6-dihydro-1,4-dioxines under the catalysis of copper hexafluoroacetylacetonate and cis-3-acyl-5,6-dihydro-1,4-dioxines as stereospecific products for 1,2-disubstituted cis-oxiranes via an intimate ion-pair mechanism. The current method provides a direct and simple strategy in efficient preparation of 3-acyl-5,6-dihydro-1,4-oxathiines and 2-acyl-5,6-dihydro-1,4-dioxines, important agents in medicinal and agricultural chemistry, from readily available thiiranes and oxiranes, respectively.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.