纤维素接枝共聚

<正> 引言聚合物是由称之为单体的简单低分子量分子组成的高分子量物质。如果一个聚合物是由两种或两种以上的不同单体组成,这个聚合物就叫做共聚物。共聚物可根据其骨架中单体的序列分成四种类型。 (1)无规共聚物:在此聚合物中单体排列无一定的规律,其分布是完全任意的。如果用A和B来分别代表两种不同的单体,则无规共聚物可表达为:     

聚丙烯催化合金结构表征

用IR、DSC、NMR分析了聚丙烯催化合金中乙丙共聚物的微结构 ,发现在一定条件下合成的乙丙共聚物主要由两部分组成 :无规乙丙共聚物和各种不同序列长度的乙丙嵌段物组成 .加上丙烯均聚物 ,聚丙烯催化合金是一种具有多分散性结构的混合物 .这种特殊的结构是聚丙烯催化合金具有高抗冲性的主要原因     

蚕丝中蛋白构象含量与其力学性质间的关系

丝蛋白 (Ｆｉｂｒｏｉｎ)是一种具有优异力学性能的天然有机高分子材料 ,蚕丝是最具代表性的一种 .它既有较高的强度 ,又有较强的韧性 ,其强度甚至超过钢丝 .但蚕丝具有如此优异力学性能的机理还不很清楚[1～ 3 ] .通常认为在丝蛋白中有 3种二级结构 (构象 ) ,即α 螺旋 (α ｈｅｌｉｘ) ,β 片层 ( β ｓｈｅｅｔ)和无规线团 (Ｒａｎｄｏｍｃｏｉｌ) [4,5] .α 螺旋是由链内氢键引起的蛋白结构 ,而 β 片层是由链间氢键引起的蛋白结构 .但有研究表明[3 ,6] ,丝蛋白中还存在另一种由 4个氨基酸残基组成的发夹式结构 :β 转角 ( β ｔｕｒｎ)…     

尼龙—1010SAXS研究

用一维电子密度相关函数方法,分析了国产尼龙-1010不同拉伸比时的SAXS现象,由实验相关函数曲线可算得长周期(L),中间层厚(d_(tr)),片晶层厚(d_?),非晶层厚(A_?),平均片层厚(d),积分不变量(Q),比内表面O_s以及(η_c-η_a)等数值及其变化规律。实验结果表明尼龙-1010的结晶结构是由结晶层、非晶层以及结晶-非品中间层三部分组成。     

乙基醋酸纤维素液晶相的织态结构观察

乙基醋酸纤维素/二氯乙酸胆甾型液晶溶液的液晶相和各向同性相在两相共存时,表现出明显的相分离行为。在胆甾相中,液晶相的织态结构随浓度而变化,可以形成园盘结构、油纹结构以及取向微区的无规堆集结构。在前两种结构中,分子链排列层垂直于玻片表面,螺旋结构的轴向与玻片表面平行。     

聚苯乙烯/硅烷偶联剂修饰蒙脱土纳米复合材料的制备与表征

用硅烷偶联剂修饰蒙脱土，制备了聚苯乙烯/蒙脱土纳米复合材料，并用XRD、FTIR、TEM和TGA等对样品进行了表征，发现硅烷偶联剂对蒙脱土表面进行了良好的修饰；苯乙烯单体在蒙脱土层间的聚合导致蒙脱土片层剥离并无规分散在聚合物基体中，片层长度为100-200nm，厚度小于10nm。     

棱子蟹壳的组份形态及存在关系的电子显微镜分析

利用电子显微镜对蟹壳中的甲壳质、蛋白质和无机盐三者的形态及存在关系进行了观察研究,发现甲壳质在壳体中呈纤维状互相交错成无规的网络结构,并平行于壳面分层生长;蛋白质以甲壳质为骨架,沿甲壳质层以片状生长;无机盐呈蜂窝状多孔的结晶结构,充填在甲壳质与蛋白质组成的层与层之间的空隙。     

裂解色谱法分析苯乙烯-丙烯酰胺共聚物

本文报道了用裂解色谱法分析一种新型的苯乙烯-丙烯酰胺共聚物的研究结果。考察了裂解温度、共聚物组成同主要裂解产物之间的相关性。提出了用相关曲线对不同类型共聚物的组成进行定量测定和鉴别的方法。讨论了由于分子链结构的差别导致无规和嵌段共聚物的不同的裂解行为。     

HIPS/OMMT纳米复合材料的燃烧性能与其残余物炭层结构特征研究

采用SEM、XRD、TGA等分析方法对高抗冲聚苯乙烯/有机蒙脱土(HIPS/OMMT)纳米复合材料在燃烧过程中形成的炭渣残余物结构特征进行了研究,包括炭层断面形态,片层结构及炭渣热稳定性等.结果表明复合材料在热释放速率峰值之后,形成了具有阻燃作用的炭层结构,其特征是在炭层表面形成了一层比较薄但密实的皮层,皮层之下是较厚的一层蜂窝层,这种"皮-窝"结构赋予炭层良好的阻隔热的作用,减缓了热分解过程.XRD分析还表明原有插层结构经过燃烧已破坏,在皮-窝炭层中都已消失,结合SEM观察结果,蒙脱土片层多以剥离的单片层无规分布,皮层和窝层中聚合物已基本烧蚀,只剩下片状的蒙脱土聚集在一起形成了一种纳米尺寸的网状结构并包含了一定量的分解温度很高的碳质物质,不仅形成了稳定的保护层,而且碳质物质的生成也降低了材料分解挥发速率.窝层含有大量尺寸较大的空穴结构,隔气效果不如皮层,但显著地增大了炭层的体积,整体上能起到较大的隔热作用.二者共同构筑的皮-窝炭层结构在复合材料的燃烧过程中起到了阻燃的作用.     

抗冲共聚聚丙烯的结晶与相形态

用POM、DSC、WAXD、DMA、AFM对两种乙烯含量、相对分子量及其分布、橡胶相含量几乎完全相同的、韧性差异很大的抗冲共聚聚丙烯(IPC)的结晶、相形态进行了研究.实验结果表明,两者的结晶形态、结晶行为相似.相比IPC-B,IPC-A中分散相和基体的相容性较好.IPC基体、分散相的组成分析发现,分散相的外层为软的乙丙无规共聚物(EPR),内部为硬的聚乙烯(PE)晶区,构成一种复杂的包藏结构.IPC的增韧效果主要来自于相形态和分散状况的贡献.提出了IPC的相结构模型,以描述IPC多相体系的相结构及两种IPC中E-b-P的作用与差异.     

聚环氧乙烷的双层片晶

聚环氧乙烷(M_n=7000)的双层片晶形态用透射电镜和差示扫描量热计进行了研究。在结晶温区54—56℃,现察到双层片晶,高于这个温区,同时看到双层片晶及单层片晶,低于这个温区,只看到单层片晶。双层片晶的熔点稍高于单层片晶。根据非整数次折迭链晶向整数次折迭链晶的转变,讨论了双层片晶和单层片晶的生长过程。在双层片晶界面上的H键降低了表面自由能,这是形成双层片晶的主要原因。     

偏氟乙烯-四氟乙烯共聚物高取向薄膜的形态结构研究

聚偏氟乙烯(PVF₂)至少有四种晶相结构,即α、β、γ和δ相,PVF₂的压电性和热电性直接依赖其β相结构。 本工作报导以特殊的熔体拉伸方法制备不同组成偏氯乙烯(VF₂)和四氟乙烯(VF₄)的共聚物高取向薄膜与对其结构的研究结果。     

随星形聚氧化乙烯的分子拓扑形状演变的单层片晶图案

以不同臂(Arm)数的星形聚氧化乙烯(PEO)为对象,系统地研究了其在不同温度下结晶的晶体冰花图案.实验中采用的星形PEO样品,其臂数分别为3,4和8(3-arm-PEO,4-arm-PEO和8-arm-PEO)且每臂的分子量均为5000,线形PEO其分子量为5000.显然,随着星形PEO分子臂数的增加,分子拓扑形状的各向异性不断减小.在单层片晶冰花图案研究中发现,随着结晶温度逐渐向平衡熔点靠近,这些PEO样品的结晶冰花图案具有从树枝状晶体转变为海藻状晶体,然后转变为非规整的紧凑形晶体,最后变成多面晶体的变化规律.对细节的分析进一步表明,随着星形PEO分子臂数的增加,由于分子的各向异性减小,导致冰花状晶体的各向异性程度不断减弱,因此从树枝状晶体到海藻状晶体和从树枝状晶体到多面晶体的转变温度也都逐渐降低.将这些转变温度对臂数作图获得的一张形态相图(morphology diagram)说明了星形PEO结晶图案的分子形状依赖性,也阐明了冰花图案形成的大分子拓扑形状效应.     

Co60γ-射线辐照对熔融结晶聚乙烯形态的影响——Ⅰ.形态的保持和破坏效应

本系列工作的此部分系用小角激光光散射,小角χ光散射,广角χ光衍射等技术考察了高密度聚乙烯的球晶、片晶和微晶等宏观和微观结构在不同辐照条件下的行为和变化,发现辐照交联对聚乙烯球晶结构有保持效应,且这种效应随辐照剂量的增大而加强;辐照交联对聚乙烯的片层结构也有保持效应,但对片晶内部却有破坏效应,辐照导致了聚乙烯结晶的晶胞膨胀,用"片晶内部破坏"机理解释χ光小角散射积分不变量随辐照剂量单调下降比用"片晶表面破坏"机理解释更为合适。     

聚乙烯片晶辐照破坏机理的电子显微镜研究

用透射电子显微镜观察了高密度辐照聚乙烯的形态结构,并通过统计方法定量地分析了其结构与辐照剂量的关系。发现室温辐照聚乙烯的片晶形态不随辐照剂量而变化。若将室温辐照聚乙烯重新熔融,然后再于125℃下等温结晶4h后,其片晶厚度则随辐照剂量的增加而变薄,长周期亦随之变短。小角X射线散射的测试结果与上述结果符合得很好。室温辐照聚乙烯及其125℃重结晶试样的电子显微镜数据从又一直观角度验证了辐照聚乙烯“片晶内部破坏机理”的正确性。     

Effect of random copolymerization on growth transition and morphology change in polypropylene

The growth rate of an ethylene-propylene random copolymer with a 2.8% w/w ethylene content was studied in a similar manner to polypropylene. A growth regime transition associated with a birefringence change was observed at 130C, while the same phenomena appeared at 138C in isotactic polypropylene. In both polymers positive birefringence corresponds to Regime III, whereas negative birefringence of spherulites is associated with Regime II. The birefringence change is attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae at low temperature (Regime III) and preferentially radiating lamellae at higher temperature (Regime II). We confirm that such a morphological change can be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. Thus, quadritic morphology seems to have a partly kinetic origin. The shift of the transition temperature in the copolymer is due to the rejection of ethylene segments at the surface of crystalline lamellae of polypropylene.     

Heat of fusion and lamellar structure of polyethylene single crystal mats

Recently published results for solution crystallized PE single crystals have shown, that the experimental heat of fusionH ^* is higher, if the solvent is exchanged to silicon oil (oil suspension samples) as compared with dried mats. This has been interpreted by the collapse of the original hollow pyramids during drying, inducing lateral defects within the lamellae. The present investigation does not confirm this unexpected result.H ^* of dried mats (T _c 66 to 91 °C) and of the corresponding oil suspension samples agree within the rather small limits of experimental error. The crystallinities as derived fromH ^*, density or WAXS are in excellent agreement.SEM micrographs of cold fractured dried mats show their spongy macromorphology, but TEM micrographs of stained ultra-thin sections reveal the lamellar morphology of the walls, consisting of curved lamellae and stacked hollow pyramides. If a dried mat is sintered at room temperature, a dense transparent film is obtained with a rather regular stacked morphology of large flat lamellae.H ^* of these films agrees with that of the original mat.Dedicated to Professor Dr. F. H. Müller.     

On the origin of the “core‐free” morphology in microinjection‐molded HDPE

This study investigates the morphology of a high‐density polyethylene processed with microinjection molding. Previous work pointed out that a “core‐free” morphology exists for a micropart (150‐μm thick), contrasting with the well‐known “skin‐core” morphology of a conventional part (1.5‐mm thick). Local analyses are now conducted in every structural layer of these samples. Transmission electron microscopy observations reveal highly oriented crystalline lamellae perpendicular to the flow direction in the micropart. Image analysis also shows that lamellae are thinner. Wide‐angle X‐ray diffraction measurements using a microfocused beam highlight that highly oriented shish–kebab morphologies are found through the micropart thickness, with corresponding orientation function close to 0.8. For the macropart, quiescent crystallized morphologies are found with few oriented structures. Finally, the morphology within the micropart is more homogeneous, but the crystalline structures created are disturbed due to the combined effects of flow‐induced crystallization and thermal crystallization during processing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1470–1478, 2011     

Structure formation in metal complex/polymer hybrid nanomaterials prepared by miniemulsion

Polymer/complex hybrid nanostructures were prepared using a variety of hydrophobic metal β-diketonato complexes. The mechanism of structure formation was investigated by electron paramagnetic resonance (EPR) spectroscopy and small-angle X-ray scattering (SAXS) in the liquid phase. Structure formation is attributed to an interaction between free coordination sites of metal β-diketonato complexes and coordinating anionic surfactants. Lamellar structures are already present in the miniemulsion. By subsequent polymerization the lamellae can be embedded in a great variety of different polymeric matrices. The morphology of the lamellar structures, as elucidated by transmission electron microscopy (TEM), can be controlled by the choice of anionic surfactant. Using sodium alkylsulfates and sodium dodecylphosphate, "nano-onions" are formed, while sodium carboxylates lead to "kebab-like" structures. The composition of the hybrid nanostructures can be described as bilayer lamellae, embedded in a polymeric matrix. The metal complexes are separated by surfactant molecules which are arranged tail-to-tail; by increasing the carbon chain length of the surfactant the layer distance of the structured nanomaterial can be adjusted between 2 and 5 nm.     

Effect of annealing on microstructure and mechanical properties of polypropylene random copolymer

In this work, polypropylene random copolymer (PPR) was taken as an example to study the changes of mechanical properties related to its microstructure evolution. Firstly, the toughness and fracture morphology were analyzed by notched Izod impact test and scanning electron microscope. Annealing at relative lower temperatures (<100°C), mechanical properties are slightly enhanced, which should be pointed out that significant improvements have been observed when annealing at relative higher temperatures (>100°C). Secondly, the study was conducted from the conventional differential scanning calorimetry, wide angle X-ray diffraction, and small-angle X-ray scattering to analyses the changes in the crystalline and amorphous regions. Dynamic thermomechanical analysis was employed to explore the changes of molecular mobility in samples after annealing at different temperatures. Moreover, to find out the stress transfer between the crystalline regions and the amorphous regions, we did further analysis of the typical stress–strain curves and proposed the mechanism of microstructure evolution during annealing process. The results shown that amorphous rearranged and formed thinner lamellae when annealing at relative low temperature. While annealing at higher temperatures, the mobile and rigid amorphous regions rearranged into more perfect lamellae and the density of stress transmitters was increased significantly.