聚合物熔体壁面滑移的流变研究

用平行板流变仪研究了聚二甲基硅氧烷(PDMS)、聚甲基乙烯基硅氧烷(PMVS)、 高密度聚乙烯(HDPE)及聚丙烯(PP)的壁面滑移, 考察了应力/应变数据对平行板的间距依赖性. 稳态剪切流实验结果表明, 相对于HDPE, PMVS的滑移似乎没有临界剪切应力. 动态剪切实验结果表明, 在不同的间距下, 随着应变增大, 剪切应力数据在小振幅和非线性区前期重合, 然后在某一应变处发生分叉, 即剪切应力依赖于间距, 说明发生了壁面滑移或应变不均匀. 按照Cho等提出的应力分解方法, 在分叉点将剪切应力分解为弹性应力和粘性应力后, 考察了影响壁面滑移发生的可能因素. 发现对于4种聚合物熔体, 当发生壁面滑移或应变不均匀现象时, 存在一个无量纲参数τ'max/|G*|, 即最大弹性应力与线性区复数模量的比值在0.26~0.49范围内变化. 在此范围内, 该参数随角频率的增加而缓慢下降, 而且在较大的温度范围内几乎不依赖于温度. 因而弹性应力是导致聚合物熔体壁面滑移或应变不均匀的关键因素.     

振荡剪切对聚乳酸熔体分子链解缠结的研究

利用哈克旋转流变仪在一定的温度和压力条件下对聚乳酸(PLA)熔体施加应变为正弦变化的振荡剪切场,从而对PLA分子链进行高效的降黏解缠.结果表明,当温度为190°C、样品厚度为1.5 mm时,PLA熔体在振动频率和剪切应变分别为3.5 Hz和50%处呈现最佳的降黏效果,其黏度相比于未经处理的熔体黏度下降了3~4个数量级.同时,凝胶渗透色谱(GPC)测试结果表明经过振荡剪切处理的PLA其分子量基本不变,表明熔体黏度的大幅下降是由PLA分子链有效解缠结导致而非分子链降解.示差扫描量热仪(DSC)结果表明,解缠效果最佳的PLA样品相比于未经处理的样品呈现出更低的玻璃化转变温度和较高的结晶度,进一步验证了熔体解缠的效果.不仅如此,我们研究了不同退火时间(1~30 min)和温度(180~200°C)对PLA分子链重新恢复缠结的影响,发现随着退火温度和时间的增加,PLA在120°C下等温结晶的半结晶时间不断增加,并向未经解缠处理的PLA样品的半结晶时间不断靠近,表明振荡剪切导致的解缠能在低温度下保持较长时间,在高温下快速复缠.     

剪切作用下纳米粘土对LDPE熔体粘弹响应的影响

以LDPE/EVA/纳米粘土复合体系为研究模型,考察了剪切作用下,分散良好的纳米粘土对聚合物基体熔体稳态及瞬态粘弹响应的影响.发现剪切作用下,纳米粘土增加了聚合物熔体粘弹特性对剪切速率、剪切应变及剪切作用史的依赖性,改变了相应的依赖关系.稳态剪切时,纳米粘土的加入使体系第一法向应力差(N1)在低剪切速率区变为负值,而在高剪切速率区N1与粘土的含量无关;同时就瞬态剪切应力及N1的应变依赖关系而言,复合体系明显不同于聚合物基体;预剪切对聚合物基体瞬态粘弹响应几乎没有影响,而当纳米粘土的加入量大于3wt%后,与未经预剪切的样品相比较,经预剪切的复合体系的瞬态剪切应力值、应力过冲程度以及稳态剪切应力值均明显下降,且预剪切前后复合体系达到稳态时其瞬态剪切应力差值随纳米粘土含量的增高而线性增加.此外,纳米粘土的添加对聚合物熔体受剪切作用的非线性粘弹响应存在影响.复合体系熔体呈现特异非线性粘弹响应,其缘由被认为是由于纳米粘土在聚合物基体中剥离分散,或聚合物分子链插层于粘土片层间,形成局部有序结构,受剪切作用而排列取向.     

长链支化聚丙烯的非线性流变行为

通过大幅振荡剪切试验方法, 研究了长链支化聚丙烯的非线性流变学行为, 揭示了长链支化结构与非线性黏弹响应的关系. 利用傅里叶变换流变学方法得到试样的三次倍频相对振幅I_3/1与应变的标度关系, 用于界定线性聚丙烯和长链支化聚丙烯非线性流变行为的差异, 并定义了非线性系数来量度长链支化程度. 在高应变下, I_3/1与应变的变化关系可以进一步描述长链支化在非线性流场下的特性, 并得到了长链支化程度与其非线性响应之间的变化关系. 通过应力波的Lissajous曲线分解, 发现了环内和环间黏弹性的差异, 长链支化结构在大应变流场下的非线性黏弹性响应弱于线性结构, 支化程度越高非线性响应越弱.     

聚苯基单醚喹噁啉薄膜的形变机理

非晶聚合物塑性变形机理主要包括银纹化和剪切屈服[1 ,2 ] .银纹化是链段局部排列疏松区域或缺陷在膨胀应力作用下成为银纹核 ,引发银纹 ,银纹 本体界面应变软化 ,银纹微纤拉伸的应变硬化过程 ,使得聚合物银纹微纤沿拉伸方向取向 ,伴随这一过程聚合物的体积增大[3] .剪切屈服是分子链沿拉伸方向的流动以及分子链间的滑移过程 ,这一过程使聚合物形状改变而体积不变 .聚合物的形变机理与聚合物的内在性质如临界缠结分子量 ,缠结密度或硬度等有关[4] .聚苯基单醚喹啉是一种高性能的芳杂环聚合物 ,它的玻璃化转变温度是 2 98℃ ,它具有耐高温…     

线型聚乙烯及其共聚物的挤出畸变与熔体粘弹性的关系

采用恒速型双筒毛细管流变仪研究了一类线型聚乙烯熔体的挤出畸变与熔体非线性粘弹性的关系。实验研究了发生畸变时挤出压力的振荡规律,发现线型大分子或带小侧基的大分子熔体,容易发生壁滑和挤出压力振荡;而有较大侧基、或分子量分布宽、或带大量短支链的熔体,挤出畸变现象较轻。挤出畸变与熔体的弹性及熔体．壁面吸附状态紧密相关。容易发生壁滑和挤出压力振荡的熔体,弹性较大(入口压力降大);在壁面的吸附作用强(壁面临界剪切应力大)。稳态剪切粘度大小与挤出畸变和压力振荡的关系不大;而拉伸应力和拉伸粘度大的熔体较易发生壁滑和挤出压力振荡。     

非线性大应变振荡剪切流场中PP结晶行为的傅立叶转变流变学研究

通过对等规聚丙烯(iPP)过冷熔体施加不同应变的正弦振荡剪切场,研究了大应变振荡剪切流场作用下,等温iPP的流动诱导结晶过程.研究结果表明,施加大应变振荡剪切流场可以明显加速iPP的结晶动力学,且施加的应变越大可以促使iPP结晶动力学加速现象越明显.通过对iPP熔体的应力波形进行傅立叶变换分析发现,由于结晶会引起熔体内部非线性行为改变,傅里叶变化峰值的3倍基频峰值I3与基频峰值I1之比I3/I1可以敏感反映iPP的流动诱导结晶过程.当流变仪施加的应变幅度从10%提高到30%时,I3/I1比值发生突跃的时间则从2500 s迅速减小为600 s.     

通过熔体自由基反应调控聚丙烯体系的链结构和相结构

熔融反应加工是聚合物改性和制备聚合物纳米复合材料的重要途径之一.在此过程中,多数加成聚合物由于受到热、剪切或引发剂作用,通常可原位形成大分子自由基反应中间体.我们系统地研究了如何利用这类大分子自由基调控聚合物分子链的拓扑结构和聚合物纳米复合体系的相结构与界面.然而,某些聚合物大分子自由基,如聚丙烯(PP),受其分子链化学结构决定,在熔融反应条件下非常易于发生降解.研究发现,将可控自由基聚合中调控自由基反应活性的方法应用在熔融反应过程中可以显著抑制PP的降解,促进主反应的发生,在制备长链支化聚合物、调控聚合物纳米复合材料的相结构方面发挥了重要作用.本文介绍了本研究组近几年来通过熔体自由基反应调控PP体系的链结构和相结构的相关研究工作,如实现PP的长链支化,制备高熔体强度PP;在制备PP/C60 、PP/碳纳米管(CNTs)纳米复合材料过程中,利用熔体界面区域所发生的自由基反应,提高了纳米粒子与PP的界面相互作用,改善了纳米粒子在PP中的分散状态等.     

平行壁面间平衡聚合物吸附行为的自洽场分析

采用自洽场理论研究了平衡聚合物在平行壁面间的吸附规律.结果表明,平衡聚合物的吸附行为可根据壁面吸附强度划分为弱吸附和强吸附两个区间.在强吸附区间,平衡聚合物可以形成明确的吸附层,增大吸附强度能够引起平均分子链长的陡增,但不会改变链长分布的指数形式.平衡聚合物的长链分子在强吸附条件下较短链分子更靠近吸附壁面,在弱吸附条件下,则更接近体系中心.通过计算壁面压强发现:在弱吸附作用下,吸附壁面始终受到分子链的推斥作用;在强吸附作用下,分子链对壁面的作用随壁面间距的加大由推斥转变为吸引.平衡聚合物的溶解性和排空效应以及壁面吸附作用之间存在竞争关系,加大排除体积作用参数会引起分子链密度分布的均一化和壁面承受压强的降低.     

超高分子量聚苯乙烯的流变性能

以毛细管流变仪和Hakke转矩流变仪对稀土催化合成的超高分子量聚苯乙烯 (UHMWPS)的流变与加工性能进行了研究 .结果表明 ,UHMWPS最显著的流变特征为超高的熔体粘度和低剪切速率下出现不稳定流动 .不稳定流动与超高分子量聚合物长的松弛时间有关 ,并提出了临界剪切速率与分子量和温度的定量关系式 .较低的分子量和较高的温度有利于提高临界剪切速率 ,改善挤出物外观质量和降低熔体粘度 .分子链极度缠结不仅导致超高的熔体粘度 ,也使UHMWPS链解缠加快 ,导致更高的剪切速率敏感性 .UHMWPS塑化时熔体粘度高 ,转矩大 ,加工性能劣于通用聚苯乙烯 (GPPS)     

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.     

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.     

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.     

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.     

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%).     

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.     

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.