全同立构聚丙烯晶体结构的对称性研究

本文利用对称理论,研究了全同立构聚丙烯的α(型)晶及β(型)晶的可能的晶体结构.1.推导了与C2/c空间群有关的有色空间群,研究了聚丙烯分子链在它们中的排布,得出其中5种是聚丙烯α(型)晶晶体结构可能存在的空间群;2.从晶畴理论出发,得出具有Cc空间群与P2_(1/c)空间群的两种晶畴共存于一个体系中,3.聚丙烯β(型)晶的晶体结构的可能排列方式是聚丙烯分子链按R型晶胞的半无规排列。     

间同立构聚丙烯在聚乙烯(100)晶面上的附生行为研究

利用电子显微镜的欠焦成像和电子衍射技术对间同立构聚丙烯(sPP)在高密度聚乙烯(HDPE)的(100)晶面上的结晶行为进行了研究,明场结果表明,sPP能在HDPE的(100)晶面上附生生长,形成相互交叉的草席状片晶结构,电子衍射结果证明,附生生长的sPP与HDPE的接触面为(100)晶面,sPP与HDPE的分子链方向成固定的±37.交角,说明sPP在纤维取向的HDPE基质上附生结晶不仅仅是HDPE的(110)晶面对sPP有取向成核作用,(100)HDPE晶面也可作为sPP晶体的取向成核点.     

结晶性间同立构1,2-聚丁二烯的单晶结构

近十几年来 ,结晶性间同立构 1 ,2 -聚丁二烯引起人们的广泛关注 ,但绝大多数研究工作集中在聚合物的制备、物理性质和应用方面[1～ 3] ,对于其结晶行为和晶体结构则未见报道 .原因是间同立构 1 ,2 -聚丁二烯分子侧链含有大量的双键 ,在较高温度下很容易交联 ,特别是高间规度的聚合物 ,由于其熔融温度高 (>2 0 0℃ )则更易产生交联 ,这给结晶行为和结构研究带来很大困难 .结晶性间同立构 1 ,2 -聚丁二烯的晶体结构为平面锯齿链正交堆砌 ,Pacm空间群[4 ] .我们曾报道了结晶性间同立构 1 ,2 -聚丁二烯的合成和溶液浇铸膜的板条状结构[5] ,本…     

聚丙烯表面的计算机模拟

用计算机模拟的方法详细研究了聚丙烯薄膜表面分子级别的结构 .采用无定形本体聚丙烯产生初始的随机父链 ,将一条随机父链在二维边界条件下进行塌陷 ,研究薄膜在真空中的构型 .用 10 0个重复单元的父链生成厚度为 3 5nm的薄膜 .发现薄膜内部密度等于聚丙烯的本体密度 ,而离自由表面 0 8nm处薄膜的密度开始跌落 .主链键在内部随机取向 ,在自由表面附近则明显沿薄膜表面平面取向 ,键开始有序取向的程度大致与质量密度相对于本体密度的减小一致 .与聚丙烯本体相比 ,薄膜表面中CH2 CH 的反式结构和旁式结构是增加的 ,这是因为分子链能更好的沿薄膜平面舒展 .同时通过聚丙烯无定形本体 (3D周期性 )和薄膜 (2D周期性 )中的链的能量的差异计算了薄膜内部能量对表面能量的贡献 .     

用DSC研究聚丙烯共混物中的成核作用

本文用示差扫描量热仪(DSC)研究了等规聚丙烯(IPP)/聚对苯二甲酸乙二酯(PE)、IPP/尼龙6、IPP/SBS、IPP/ABS、IPP/高密度聚乙烯(PE)和IPP/聚苯乙烯(PS)六种共混物中各高聚物对IPP过冷结晶温度的影响,结果说明,在IPP/尼龙6和IPP/PET中,尼龙6和PET共混中分别使IPP的过冷结晶温度提高7K左右。本文还研究了在不同降温速率和不同熔体温度下,PET和尼龙6对IPP的成核作用。同时还说明了第二种高聚物对IPP的成核作用与其熔点的高低无关。     

间同立构1,2-聚丁二烯的合成和形态结构研究

间同立构 1 ,2 -聚丁二烯自 1 955年问世以来 ,引起人们的广泛关注 ,但绝大多数研究工作集中在聚合物的合成方面[1～ 3] ,对其形态结构方面的研究却很少报道[4 ] ,原因是该聚合物分子侧链含有大量双链 ,在较高温度下 (>1 50℃ )很容易产生热交联 ,这给结构研究造成了很大困难 .间同立构 1 ,2 -聚丁二烯的性能取决于间规度 ,低间规度聚合物呈现弹性体特征 ,而高间规度聚合物则是一种半结晶性塑料 ,其结晶为平面锯齿链正交堆砌 ,Pacm空间群[4 ] .本文采用一种新的催化体系 ,使合成的 1 ,2 -聚丁二烯间规度可以调控 .同时首次报道了结晶性间规…     

立构复合PL(D) LA-TMC无规共聚物的制备、结构与性能

以辛酸亚锡为催化剂,通过开环聚合法制备了聚左旋乳酸-三亚甲基碳酸酯(PLLA-TMC)和聚右旋乳酸-三亚甲基碳酸酯(PDLA-TMC)无规共聚物.利用共聚物中PLLA/PDLA链段形成立构复合体,通过溶液浇注法制备了PLLA-TMC/PDLA-TMC立构复合聚乳酸材料(sc-PLA-TMC).研究结果表明,聚合物链中的柔性TMC单元可以增强L(D)LA链段的运动能力,有助于不同旋光性的LA链段形成立构复合晶体,但也使得L(D)LA链段的规整度和序列长度降低.即随着共聚物链段中柔性TMC单元摩尔含量的增加,sc-PLA-TMC中同质结晶能力降低.当TMC含量≥5%时,仅生成熔点200℃的PLLA/PDLA立构复合结晶,表明sc-PLA-TMC的耐热性有所提高.蛋白酶K降解实验表明,PL(D)LA-TMC共聚物的降解速率不但比PLLA高,而且可通过共聚物中TMC含量进行调控.     

自成核对间同立构1,2-聚丁二烯结晶行为的影响

间同立构 1 ,2 -聚丁二烯自 1 95 5年问世以来 ,引起人们的广泛关注 ,但其形态结构方面的研究却很少报道 [1] .原因是间同立构 1 ,2 -聚丁二烯分子侧链含有大量双键 ,在较高温度下 ( >1 5 0℃ )很容易产生热交联 ,严重影响该聚合物的结晶行为 .我们曾报道了结晶性间同立构 1 ,2 -聚丁二烯的合成和溶液浇铸膜的板条状结构以及单晶结构 [2 ,3] .本文研究了间同立构 1 ,2 -聚丁二烯的自成核过程、结晶行为和形态结构 .自成核 ( Self- seeding nu-cleation)是指聚合物自身的微小晶粒作为晶核而诱导结晶生长的一种成核方式 ,它具有很高的成核效…     

聚丙烯/丁基橡胶共混体系的研究

本文研究了丁基橡胶(IIR)对等规聚丙烯(IPP)结晶行为的影响以及IPP/IIR共混物的形态与性能的关系。IIR对IPP的熔点、结晶度、结晶温度均无明显影响,但能抑制IPP球晶的增长,少量IIR是IPP的有效成核剂。IIR用量超过30份时,共混物的抗冲击强度迅速增加,但其抗张强度随IIR用量的增加而降低。在130℃热处理2小时,IPP/IIR(100/20)的抗冲击强度提高了近4倍。     

丙烯聚合用TiCl_4/MgCl_2催化剂的研究——聚合温度和烷基铝的影响

研究了不同助催化剂和不同聚合温度对催化剂TiCl4/MgCl2/9,9-双(甲氧基甲基)芴(BMMF)丙烯聚合性能的影响.研究结果发现该催化剂在高温(100℃)聚合时,采用还原能力和络合能力较弱的烷基铝(Hex3Al)为助催化剂可以得到高的立构选择性(97%)和高活性.100℃聚合时不同的助催化剂对催化剂得到的聚丙烯结构有重要影响.助催化剂为Me3Al聚合得到的中等等规聚丙烯含量比其他烷基铝高.助催化剂为Et3Al聚合得到聚丙烯链结构中含有少量乙烯共聚单元;而助催化剂为Me3Al,iBu3Al和Hex3Al聚合得到聚丙烯链结构中没有发现共聚单元.     

Quasiharmonic treatment of infrared and raman vibrational frequency shifts induced by tensile deformation of polymer chains. II. Application to the polyoxymethylene and isotactic polypropylene single chains and the three-dimensional orthorhombic polyethylene crystal

Quasiharmonic equations are derived for stress-induced vibrational frequency shifts in the infrared and Raman spectra of polymer chains subjected to a tensile stress. The expressions are applied to the helical chains of polyoxymethylene and isotactic polypropylene. Observed frequency shifts can be reproduced well by using reasonable anharmonic force constants. A semiquantitative interpretation is given for the close relationship between stress-induced vibrational frequency shifts and the deformation mechanism of the polymer chains. Stress-induced frequency shifts are also calculated for an orthorhombic polyethylene crystal subjected to uniaxial tension along the chain axis or to hydrostatic pressure. The results consistently and reasonably reproduce observed data, not only for the intramolecular vibrational modes but also for the external lattice modes. © 1992 John Wiley & Sons, Inc.     

The conformational structures of defect-containing chains in the crystalline regions of isotactic polypropylene

Calculations were performed to assign defect-resonance patterns observed in solid-state ¹³C NMR spectra obtained from the crystalline regions of isotactic polypropylene. The spectral features of interest are associated with stereo, regio, and comonomer-type defects, which can typically be found in metallocene-synthesized polymers. The calculations were carried out as follows: a model of the crystalline region of defect-free isotactic polypropylene was constructed from available X-ray data corresponding to the α-lattice. A series of irregularities including ethylene comonomer, stereo-mrrm, regio 2,1-erythro, and butylene-comonomer defects were introduced one at a time at various positions in a specific stem occupying a central position in the model crystallite. Low-lying conformations were then obtained from simulated annealing calculations that were initiated from these structures. Finally, quantum mechanical calculations were performed on the representative segments of the defect-containing chains excised from the annealed crystallites and the calculated chemical shifts were compared to the observed resonances. The results of the calculations were used as a basis for interpreting the NMR intensities of defect-related resonances in terms of the partitioning of defects and to help establish the conformational structures of the defect-containing stems.     

硅烷类外给电子体的取代基变化对丙烯聚合影响的研究

合成了2种新型硅烷化合物双环己基二甲氧基硅烷(Donor-H)、双哌啶二甲氧基硅烷(Donor-Py),将其与工业化的环己基甲基二甲氧基硅烷(Donor-C)分别作为外给电子体,用于MgCl2负载的Ziegler-Natta催化剂催化丙烯聚合,通过DSC、GPC、SSA和13C-NMR等分析手段研究了3种外给电子体取代基的变化对催化剂的催化活性、氢调敏感性、聚丙烯的等规度、分子量分布、结晶能力、等规序列分布的影响.结果表明,随着外给电子体取代基体积的增大,外给电子体的给电子能力逐渐增强.与Donor-C相比,随着外给电子体取代基体积的增大,合成的具有较大取代基的Donor-H和Donor-Py用于丙烯聚合时都表现优异的催化性能,特别是新型含有N杂原子的氨基硅烷类Donor-Py为外给电子体的催化剂的催化活性和制备的聚丙烯的等规度最高,聚丙烯的熔融指数可调范围最宽,结晶能力更强.氨基硅烷类Donor-Py制备的聚丙烯SSA热分级后的高等规组分含量最多,可高达64.5%,聚丙烯等规序列长度最长,聚丙烯的等规序列分布最窄,而且13C-NMR结果也表明聚丙烯等规序列长度MSL最长,聚丙烯的分子链最规整.     

Epitaxial growth of isotactic polypropylene on oriented polyethylene from solution

Oriented polyethylene (PE) films with surfaces bounded by the (100) plane were prepared. On the film surfaces, isotactic polypropylene (iPP) was crystallized epitaxially from solution as quadrits with their sides parallel and perpendicular to the polyethylene chain axis. In the through wide-angle x-ray diffraction pattern (taken with incident x-rays normal to the polyethylene film surface), the 111 iPP reflections was observed on the meridian (Parallel to the polyethylene chain axis). In the edge patterns (taken with x-rays incident on the edge of the polyethylene film), 040 and 060 reflections were observed on the equator. From the diffraction patterns, the following lattice coincidence was observed between polyethylene and isotactic polypropylene: (010)iPP//(100) PE, [101]iPP//[001] PE. The Small-angle x-ray scattering patterns showed that edge-on isotactic polypropylene lamellae 9 nm thick were arranged with their long axes inclined at an angle of 40° from the polyethylene axis. Molecular chains were oriented within the lamellae normal to the surfaces.     

Spectroscopic study of α- and β-phase isotactic polypropylene and of atactic polypropylene in solution

Raman spectroscopy is used to investigate the conformation and packing of isotactic crystalline α-phase polypropylene compared with lower-order β-phase isotactic polypropylene and to study the solution behavior of atactic polypropylene. The high-frequency region of the spectrum is analyzed in light of a normal-mode calculation that takes into account the methyl-group vibrations. This region is sensitive to both chain conformation and packing, and because of the high intensity of the methyl and methylene high-frequency stretching modes, it can be used to probe small changes in intermolecular or intramolecular order. Differences in the thermal behavior between the two solid isotactic polypropylene samples are explained interms of packing defects which exist in the β-phase form. In the solution study, we demonstrate that, for molecules in which bands sensitive to intermolecular interactions exist, as is the case of the methyl and methylene vibrations of polypropylene, spectroscopic techniques can be used to estimate the minimum overlap concentration.     

Synthesis of polypropylene block copolymers from brominated styrene-terminated isotactic polypropylene

Isotactic polypropylene block copolymers, isotactic-polypropylene-block-poly (methyl methacrylate) (i-PP-b-PMMA) and isotactic-polypropylene-block-polystyrene (i-PP-b-PS), were prepared by atom transfer radical polymerization (ATRP) using a brominated styrene-terminated isotactic polypropylene macroinitiator synthesized from bromination of styrene-terminated isotactic polypropylene. The styrene-terminated isotactic polypropylene can be obtained by polymerization of propylene in the presence of styrene and hydrogen chain transfer agents using a rac-Me₂Si[2-methyl-4-(1-naphyl)Ind]₂ZrCl₂ as catalyst. The molecular weights of isotactic polypropylene block copolymers were controlled by altering the amount of hydrogen used in the polymerization of propylene and the amount of monomer used in the blocking reaction. The effect of i-PP-b-PS block copolymer on PP-PS blends and that of i-PP-b-PMMA block copolymer on PP-PMMA blends were studied by scanning electron microscopy.     

The enhanced nucleating ability of carbon nanotube-supported β-nucleating agent in isotactic polypropylene

A kind of β-nucleating agent, calcium pimelate, for polypropylene (PP) was chemically supported onto the surface of multi-wall carbon nanotubes, and the effect of the multi-wall carbon nanotube-supported β-nucleating agent on the mechanical properties and morphology of isotactic polypropylene composites was investigated. The composites of isotactic polypropylene and multi-wall carbon nanotube-supported β-nucleating agent exhibited excellent impact toughness compared with pure isotactic polypropylene and β-nucleated isotactic polypropylene, being more than seven times over that of pure isotactic polypropylene and more than three times over that of β-nucleated isotactic polypropylene. The excellent impact behaviors of the composites were also evidenced by the fracture morphology based on scanning electron microscopy observations. Differential scanning calorimetry and wide-angle X-ray diffraction results verified the enhanced nucleating ability of the multi-wall carbon nanotube-supported β-nucleating agent, which greatly improved the impact toughness without significantly deteriorating the strength and stiffness of the polypropylene composites.     

Effect of the initial maleic anhydride content on the grafting of maleic anhydride onto isotactic polypropylene

A series of ¹³C‐enriched maleic anhydride grafted isotactic polypropylene samples were prepared in solution at 170 °C by changes in the initial maleic anhydride content. The NMR spectra of the samples showed that the signals of the maleic anhydride attached to the tertiary carbons of the isotactic polypropylene chains increased considerably with increasing maleic anhydride content, whereas the signals of the maleic anhydride on the radical chain ends (with a single bond) arising from β scission did not. On the other hand, the signals of the maleic anhydride on the radical chain ends with double bonds increased markedly with increasing maleic anhydride content, and this suggested that β scission could occur extensively after maleic anhydride was attached to the tertiary carbons. As a result, the molecular weight of the grafted polypropylene decreased significantly with increasing maleic anhydride content in this study. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5529–5534, 2005     

Application of successive self-nucleation and annealing to study the stereo-defects distribution of biaxially oriented polypropylene

The stereo-defects distribution of polypropylene of the two industry biaxially oriented polypropylene （BOPP） samples T28FE and F28SO with different processing properties was studied through successive self-nucleation and annealing （SSA） technique. It was found that there were more medium isotactic components in sample F28SO, and the isotactic sequence length of polypropylene of sample F28SO was shorter and the isotactic sequence length distribution of polypropylene of sample F28SO was broader, which could be processed well at high-speed orientation during the processing of BOPP films. This result indicates that the isotactic sequence length distribution of polypropylene is related to the processing speed during preparing BOPP films, and the stereo-defects distribution of polypropylene has an important influence on its processing ability.     

Measurements of infrared frequency shifts in stressed polymers

A difference-spectrum method is used to measure vibrational frequency shifts in mechanically stressed polymers. It is shown that the peak-to-peak height of the difference-spectrum intensity profile is a linear function of small frequency shifts with a slope inversely proportional to the band halfwidth for Lorentzian or Gaussian bands. The method is applied to measure frequency shifts in uniaxially stressed ultraoriented isotactic polypropylene films, using a double beam infrared grating dispersion spectrometer with a nonstressed sample in the reference beam. It is shown that frequency shifts can be measured with an accuracy of better than 0.01 cm^?1 using the difference-spectrum method.