HDPE/HIPS/CB复合材料的制备及PTC性能

以高抗冲击聚苯乙烯(HIPS)和高密度聚乙烯(HDPE)为基体,炭黑(CB)为导电填料,采用熔融法制备聚合物基正电阻率温度系数效应(PTC)复合材料.通过扫描电子显微镜(SEM)研究了CB在复合材料两相基体中的选择分布,采用热敏电阻温度(RT)曲线测试仪研究复合材料PTC性能随CB含量的变化规律.结果表明,在HIPS/CB体系中加入HDPE后,复合材料的渗流阈值降低,PTC强度增强,耐电压强度有所提高.     

HDPE/CB高分子导电复合体系的单轴形变与压阻行为

根据基体形变及其与渗流网络结构之间的关系,研究了高密度聚乙烯(HDPE)/炭黑(CB)复合材料压阻行为的发生机制及其影响稳定性的力学因素.结果表明,单轴压阻行为的产生源于材料受外力变形而导致的渗流网络微结构变化,且这种变化强烈依赖于填料含量.当填料含量较低时(渗流阈值附近),体系电阻率随压力升高而表现为电阻正压力系数行为;当填料含量较高时,体系电阻率随压力升高显现电阻负压力系数效应.完全卸载的零压力下,电阻基线随压缩循环随循环次数增大而发生漂移,这种漂移与轴向残余压缩应变有关,可以通过增加循环次数来加以稳定.交联可以减小残余压缩应变,并抑制高填充复合体系电阻基线的漂移.     

PANI—PBOPy复合材料的制备及介电性能

采用甲基磺酸（MSA）掺杂聚苯胺（PANI）,并以MSA为溶剂,将其与聚（2,6-亚吡啶基）苯并二嗯唑（PBOPy）采用溶液共混法制备了不同PANI质量分数的PANIPBOPy复合材料。采用红外光谱、wXRD、Uv—Vis、TGA以及SEM对复合材料的结构和性能进行了表征。研究了PANI的质量分数、温度、频率等因素对PANIPBOPy复合材料导电性能和介电性能的影响。研究表明：当PANI的质量分数达到20％时,复合材料的电导率增大了10个数量级;复合材料的介电常数和介电损耗则随着PANI质量分数的增加呈现先增大后减小的趋势,随着频率的升高先迅速降低而后趋于稳定,并且随温度升高而增大,40℃时PANI质量分数为15％的复合材料的介电常数约为230。     

基体分子运动对聚偏氟乙烯/碳纤维复合材料的聚合物基正温度系数性能的影响

聚合物基正温度系数(PTC)材料中,基体分子在熔体状态下的运动能力可显著影响填料分布、PTC强度及稳定重复性等,明确其机理有利于高灵敏性且稳定可重复的PTC复合材料的设计与制备.通过探究基体熔体黏度不同的聚偏氟乙烯(PVDF)/碳纤维(CF)的电阻-温度响应行为,可以发现复合材料PTC转变温度区间仅取决于基体化学结构与结晶性,而PTC循环稳定性却受到基体分子运动能力的显著影响.当基体分子运动能力较强时,分子链极易黏附填料在CF表面形成包覆层,导致局部填料间距增大到隧穿距离以上,不利于复合材料导电网络的重建,导致随热循环次数增加,复合材料的室温电阻率有所升高,PTC可重复性略微降低.而对基体分子链缠结明显的PVDF/CF复合材料中,运动能力较弱的分子链不会包覆CF粒子,在多次升温-降温循环后导电通路能恢复到初始状态,复合材料呈现良好的PTC可重复性,将其应用于电路过热保护装置时,复合材料表现出灵敏的温度响应特性及可多次循环的开关特性.     

具有高灵敏性且稳定可重复的正温度系数效应的PVDF/CF导电复合材料

以碳纤维(CF)为填料,聚偏氟乙烯(PVDF)为基体,通过熔融共混法制备PVDF/CF导电复合材料.所得复合材料具有显著的正温度系数(PTC)效应,温度上升到聚合物熔点附近时,电阻率对温度变化敏感.在转折温度区间(155.5~171.0oC,(35)(28)15.5oC)内,其体积电阻率的增加速率约为1.3×105?cm K-1.在不同CF含量下,复合材料表现出不同的PTC行为.随着CF含量的增加,其峰值电阻略有下降.高导电粒子含量下,无负温度系数(NTC)效应.在冷却循环过程,导电网络的重构性良好.复合材料即使经过多次热循环,依然表现出良好的PTC特性重现性.     

交联聚苯乙烯的辐射法制备与性能表征

以苯乙烯、二乙烯基苯(DVB)为共聚单体,60Co作为γ射线辐照源,采用原位本体聚合法制备出交联聚苯乙烯(CLPS)块体材料。采用FT-IR、DSC、TG和DMA等手段对聚合物的结构及性能进行了表征和分析。结果表明,在纯氮气氛中,150~200kGy的吸收剂量,当DVB的质量分数大于1%时,可以得到透明无缺陷的产物。CLPS在380°C以下能够非常稳定地存在,玻璃化温度(Tg)达到127℃;CLPS的拉伸强度和断裂伸长率随DVB质量分数的增加呈先增大后减小的趋势,在1.6%~1.8%时出现最大值,表现出较好的力学性能;在9.3GHz测试条件下,交联剂的含量对CLPS介电常数和介电损耗影响甚微,介电常数为2.48~2.50,介电损耗为4×10-4~6×10-4。     

FeCl3/共轭聚席夫碱复合材料的制备及介电性能

由戊二醛和对苯二胺通过缩合反应合成席夫碱聚合物,并将其与三聚氰胺交联构筑立体网状结构,再与氯化铁配位形成具有"海胆状"结构的FeCl_3/席夫碱复合材料,利用傅里叶红外光谱和扫描电镜对其进行表征。通过对比Fe~(3+)掺杂量分别为0.02、0.03、0.04 mol时复合材料半年前后的电导率、介电常数实部与虚部、介电损耗角正切值和科尔-科尔半圆的改变,发现静置后复合材料介电参数均大幅增长,介电弛豫从无到有,并且在刚合成时其介电常数虚部在3.664×10~6~1.000×10~7 Hz为负值,但经过静置后却转变为正值。其中,静置半年后,Fe~(3+)掺杂量为0.04 mol的席夫碱铁盐聚合物在102 Hz处的介电损耗角正切从0.02升至6.13,电导率从7.15×10~(-7)S·cm~(-1)升至2.19×10~(-5)S·cm~(-1),介电常数实部与虚部也大幅增加,介电损耗机理为二重介电驰豫。     

BaTiO_3包覆粉煤灰漂珠/聚苯胺复合材料的制备及电流变性能

首先利用原位化学氧化聚合法将聚苯胺包覆在粉煤灰漂珠表面(FAFB/PAn),再利用低温溶胶凝胶-水热法制备BaTiO_3包覆FAFB/PAn的复合材料(FAFB/PAn/BaTiO_3),形成内核为空心漂珠、外壳依次为导电层、绝缘层的核/壳结构.采用FTIR、XRD、SEM、数字式四探针以及LCR介电谱仪对FAFB/PAn/BaTiO_3复合材料的结构与性能进行分析;以FAFB/PAn/BaTiO_3为分散相制备的电流变液,对其悬浮性及外加电场下的剪切应力进行测试.FTIR和XRD结果证明了利用本文的实验方法可成功将PAn和BaTiO_3引入到FAFB表面.电导率测试结果表明,复合材料电导率为7.8×10~(-4)S·cm~(-1),相对BaTiO_3提高了近2个数量级.在1~2000 k Hz交变电场频率测试范围内,FAFB/PAn/BaTiO_3具有相对较好的介电性能:当f=1 k Hz时εr最大为598,随电场频率的增加介电常数逐渐减小,对应的介电损耗tanδ最大为1.14,且随电场频率的增加介电损耗逐渐减小,当f=200 k Hz时tanδ=0.75,后趋于平稳.比较了7天的悬浮稳定性发现,FAFB/PAn稳定性最好,悬浮率可达88%,而包覆BaTiO_3后与纯BaTiO_3相当,仅为60%.在电场作用下FAFB/PAn/BaTiO_3表现出较明显的电流变性能,即当E=4.0 k V/mm时,剪切应力达631 Pa,且具有较好的抗击穿能力.     

HDPE/EPDM/CB复合物的PTC效应

聚合物正温度系数 (PTC)材料 ,是由聚合物基体与炭黑、碳纤维、金属粉末等导电填料共混而成的一种功能导电复合材料 ,其特点是 :当温度升高时 ,在聚合物结晶熔点附近 ,材料的电阻率随温度升高急剧增加 ,可发生几个数量级的突跃 .聚合物 PTC材料可用作自限温加热器、过电流保护器、传感器等 ,有广阔的发展前景 .目前对聚合物 PTC材料的研究主要以聚乙烯 [1～ 5]、乙烯 -醋酸乙烯酯共聚物[6] 、偏氟乙烯 [7] 等单一组分聚合物作为基体材料 .本文研究了以高密度聚乙烯 (HDPE) /三元乙丙胶(EPDM)共混物为基体材料的炭黑 (CB)导电复合材…     

碳纳米纸/聚乙烯复合材料的电热性能研究

为改善碳纳米管(CNT)分散性,将CNT先制备成碳纳米纸(CNP),然后将CNP与高密度聚乙烯(HDPE)进行复合压膜形成具有三明治结构的CNP/HDPE复合材料,详细研究了CNP的形貌、孔结构、力学性能以及CNP/HDPE复合材料的电热性能。结果表明:采用悬浮过滤法可获得表面平整、光滑、孔径均匀的碳纳米纸;碳纳米纸孔径大部分集中在20nm~40nm之间;碳纳米纸具有一定的强度和柔韧性。CNP/HDPE复合材料的拉伸强度和拉伸模量略高于纯HDPE;在碳纳米管含量相同时,在相同电压下,CNP/HDPE复合材料其电热性能远高于以共混方式制备的CNT/HDPE复合材料。     

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.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

正丁胺对激光染料荧光谱影响的研究

用正丁胺作为碳源,采用射频辉光放电制备碳膜,选用激光染料R6G和聚乙二醇混合液作为蒸气源,采用单源热蒸发,在蒸发室与染料同时沉积得到混合膜,用拉曼光谱和红外光谱分析了碳膜的结构和键合方式,分析表明:碳膜中存在胺基团和氢原子.混合膜的荧光谱测量结果表明,认为正丁胺对染料荧光谱的影响是因为胺基和氢原子的存在.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.