注塑温度对POM/TPU共混物分散相及力学性能的影响

研究了注塑温度对聚甲醛(POM)/热塑性聚氨酯弹性体(TPU)共混物形态结构和力学性能的影响.实验结果表明,注塑温度影响POM基体相与TPU分散相的粘度比,195℃时两者粘度相当,在剪切流动过程中,TPU可在POM基体中形成条状分散相,可吸收较多的冲击能并阻止银纹的生长以及裂纹的产生,从而较大幅度提高共混物的缺口冲击强度.     

4,4'-二羟基二苯硫醚对聚甲醛结晶和熔融行为的影响

为了探究4,4'-二羟基二苯硫醚(TDP)的添加对聚甲醛(POM)熔融与结晶行为的影响,本文利用熔融共混的方法制备了POM/TDP共混材料。通过差示扫描量热仪(DSC)对共混材料的熔融与结晶行为进行了研究,利用广角X射线衍射仪(WAXD)对共混材料的晶体结构进行了研究。结果表明,在POM中添加TDP后,POM的晶面间距变大,晶体结构变的疏松,使POM的结晶温度(Tc)、结晶焓(ΔHc)、熔融温度(Tm)与熔融焓(ΔHm)均降低。当TDP质量分数增加到30%时,共混物的熔点与结晶温度较纯POM分别下降了15.2和12.8℃。在等温结晶过程中,随着TDP含量的增大,POM完成结晶所需的时间显著加长,共混物的结晶速率逐渐降低,结晶活化能逐渐升高,但TDP的加入对POM的晶型并没有影响。以上结果说明TDP的添加对POM的熔融与结晶行为影响很大,这将为POM结晶行为的调控提供依据。     

弹性体共混改性对聚甲醛结晶行为及力学性能的影响

本文采用不同弹性体——热塑性聚氨酯(TPU)和聚乙烯弹性体乙烯-辛烯共聚物(POE)对聚甲醛(POM)进行增韧改性,研究了纯POM、POM/TPU (85/15)、POM/POE (85/15)三种体系的结晶行为和微观结构演变对材料力学性能的影响。结果表明,由于纯POM在结晶过程中能够形成较大的球晶,球晶边缘无定形区分子耗尽而形成微孔,这些微孔结构导致POM具有较差的缺口冲击强度。弹性体的加入可显著提高POM的结晶速率并大幅减小其球晶尺寸,因此有效减少了微孔数量,从而增加POM的韧性。比较而言,POM/TPU (85/15)的抗冲强度提升更为明显,主要原因在于二者良好的相容性和形成的大量细小球晶;而对于POM/POE体系,二者相容性差,且两者界面对球晶形貌起到了限制作用,因此降低了机械性能。     

热塑性聚氨酯共混物的硬度与冲击性能的关系北大核心CSCD

选取了2种分子组成相同硬度不同的热塑性聚氨酯(TPU),将二者共混后得到了不同硬度的TPU共混物,探究了TPU共混物的硬度与冲击性能的关系。通过落球冲击试验、感压纸测试和冲击前后样品表面温度测试对TPU共混物的冲击性能进行表征。当样品的硬度越低时,峰值冲击力越小,冲击持续时间越长,冲击时的最大应变越大,冲击时样品的受力面积增大,对应的冲击时的峰值应力值减小。不同硬度样品的能量耗散比差别不大,但随硬度降低呈现小幅度上升趋势。冲击后的样品表面温度较冲击前有所上升,说明样品通过热的形式耗散了部分能量,各硬度样品的温度差值较为接近,这与不同硬度样品的能量耗散比的变化规律是相似的。所有样品均具有较高的能量耗散比,TPU能耗散大部分冲击能量,具有良好的抗冲击性能。     

酚醛树脂的增容作用对聚甲醛/丁腈橡胶共混物的韧性、结晶形态和亚微相态的影响

考察了酚醛树脂(Novolak)的增容作用对聚甲醛(POM)/丁腈橡胶(NBR)共混物的韧性、结晶形态和亚微相态的影响.实验结果表明,POM与NBR不相容,直接共混不能提高POM的韧性;添加Novolak后,当NBR质量分数为40%时共混物发生“脆-韧”转变.POM/NBR共混物中POM球晶尺寸大,易形成应力集中点,导致增韧效果不佳;Novolak可通过与POM的分子链间相互作用,改变POM分子链固有的规程和排列方式,使球晶显著减小.亚微相态显示,POM/NBR呈现“海-岛”结构相态,NBR在基体中分散性很差;添加Novolak可提高NBR在基体中的分散性;当NBR质量分数达到40%时,NBR在基体中呈现带状网络结构.网带结构能够终止受外力作用而在基体中产生的银纹和剪切屈服,增加了共混物的破裂能,从而使共混物的韧性显著提高.     

聚甲醛与热塑性酚醛树脂相容性研究

考察了聚甲醛(POM)与热塑性酚醛树脂(Novolak)的相容性;浊点法研究结果表明,POM/Novolak共混物存在一个低位临界相转变温度.DSC测试表明,POM与Novolak共混后,共混物的熔点下降;通过DSC测试得到数据,采用Hoffman-Weeks平衡熔点外推法和Flory熔点下降方程推算出POM与Novolak的相互作用参数(χ)约为-0.032.FTIR研究表明,Novolak的羟基能够与POM的醚氧基形成氢键,导致共混物中Novolak的羟基峰向高频偏移.研究结果表明,POM与Novolak能够达到热力学相容.     

聚乳酸/聚氨酯共混体系相容性研究

采用热塑性聚氨酯弹性体(TPU)作为改性剂来增韧聚乳酸(PLA),通过溶度参数法、聚合物混合焓变法预测了TPU和PLA的相容性,并且通过稀溶液粘度法、动态热机械分析(DMA)及扫描电镜(SEM)对两者相容性进行表征,结果显示PLA和TPU为部分相容体系.共混溶液的粘度与组成含量的变化呈非线性关系;PLA/TPU共混膜的...     

聚(氯乙烯-醋酸乙烯酯)与热塑性聚氨酯的相容性及其共混膜的氧化稳定性

采用溶液法制备了聚(氯乙烯-醋酸乙烯酯)(PVCAc)与热塑性聚醚型聚氨酯(TPU)的共混膜(PUV).通过FT-IR和DSC对膜的形态和相容性进行了研究.与聚氯乙烯(PVC)相比,PVCAc与TPU的相容性明显增强.将PUV膜浸没于H2O2-CoCl2溶液中25 d进行加速氧化实验,结果表明:PUV膜的氧化稳定性优于TPU和TPU/PVC的共混膜(PUC).此外,PUV膜的力学性能明显高于PUC膜.     

微波调控石墨烯-碳纳米管协同增强聚氨酯损伤自修复研究

首先采用溶液共混法制备出石墨烯-碳纳米管(G-CNT)/聚氨酯(TPU)复合材料,然后通过拉伸实验及扫描电子显微镜(SEM)表征来考察该材料的拉伸强度和微波自修复特性,并从力学及材料与微波之间的相互作用等角度对其拉伸强度增强和微波修复机理进行研究.结果表明:在拉伸强度方面,与单一的石墨烯或CNT增强TPU相比,G-CNT之间形成的协同效应使TPU拉伸强度得到进一步提高,当石墨烯和CNT的质量比为3∶1时,G-CNT/TPU抗拉强度较纯TPU提高了67%,较G/TPU提高了18%,较CNT/TPU提高了25%;在材料裂纹的微波修复方面,石墨烯和CNT之间的协同效应使TPU材料自修复效果得到有效提高,当石墨烯和CNT的质量比为3∶1时,G-CNT/TPU修复效果达到最高值117%.     

玻璃纤维对碳纳米管填充聚合物/热塑性聚氨酯共混体系导电性能的影响

研究了表面带有环氧基团的玻璃纤维(GF)对聚丙烯(PP)/热塑性聚氨酯(TPU)/多壁碳纳米管(MWCNT)、 聚甲基丙烯酸甲酯(PMMA)/TPU/MWCNT和聚乳酸(PLA)/TPU/MWCNT体系导电性能的影响. 研究结果表明, 未添加GF时, 由于MWCNTs选择性地分布在TPU分散相中, PP/TPU/MWCNT, PMMA/TPU/MWCNT和PLA/TPU/MWCNT材料的导电性能很差; 加入20%的GF使3个体系的电阻率均大幅度下降, 最高下降约13个数量级, 表明填充GF是一种具有普适性的改善以TPU为分散相的共混体系导电性能的有效方法. GF使体系电阻率降低的机理主要是形成了TPU包覆GF结构, 该结构可以看作长径比较高的导电棒, 可以有效协助导电通路的构建; 同时GF还起到了体积占位的作用, 提高了体系中导电组分在基体中的有效浓度.     

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.     

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.     

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.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

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.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

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.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

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.