长链支化聚乳酸的多重松弛行为

在辐照法制备长链支化聚乳酸(LCB-PLA)的基础上,采用凝胶渗透色谱-多角度激光光散射联用(SEC-MALLS)表征了LCB-PLA的支化结构,利用动态流变学方法考察了PLA的黏弹松弛行为,计算得到了线型及支化PLA在较宽时间范围内完整的加权松弛时间谱.结果表明,由于长支链的引入及支链长度的增加,导致LCB-PLA松弛时间谱加宽,松弛时间增长,并呈现多重松弛行为.提出了一种计算长链支化聚合物支链长度的方法,可以定量表征LCB-PLA的支链长度以及长支链的分子量.     

螺旋聚(N-炔丙基酰胺)的合成及侧基对螺旋结构稳定性影响

设计并合成了3种带有不同侧基的N-炔丙基酰胺单体(1~3),以红外、核磁、元素分析等技术对单体进行了表征;以[Rh]金属有机配合物为催化剂实施聚合反应得到高产率(近100%)的聚合物,聚合物具有高的立构规整性.利用紫外吸收谱图对聚合物的二级结构进行了表征,聚合物1与聚合物3分别在羰基的α和γ位有支链,聚合物不易形成螺旋结构;聚合物2在羰基的β位有支链,聚合物易于形成稳定的螺旋结构.表明相邻侧链上酰胺基团间形成的氢键及侧链间适当的空间位阻是聚合物形成稳定螺旋的关键因素.     

星形聚苯乙烯本体粘弹性对结构的依赖性

用应力松弛法研完了一组4—12支链星形聚苯乙烯本体的粘弹性。从应力松弛主曲线测定了零切变粘度η_0、稳态柔量J_e~o和其它流变学参数。结果发现,零切变粘度和最大松弛时间τ_m强烈地依赖于聚合物的分子尺寸,并且可以用无扰特性粘度或折合分子量来描述。η_0和τ_m随支化度增大而增大。实验还直接证实了支链长度相同的星形聚合物的J_e~o与支链数目无关,但是星形聚合物的稳态柔量比具有和支链间分子量相同的线形聚合物的稳态柔量大。     

聚合物交联密度定性和定量表征的讨论

聚合物交联密度表征可以分为定性和定量表征。聚合物低交联密度,可以用简便的溶涨法定量表征;聚合物高交联密度,当形变较小时,可以用动态热机械分析法定量表征;聚合物交联密度可以用玻璃化温度定量表征。聚合物交联密度定性表征包括:热学性能表征、力学性能表征、流变学表征、化学方法表征和功能应用表征;其中热学性能表征(差示扫描量热分析法)可以区分分子内交联和分子间交联;通过流变学表征(频率扫描试验)可以有效控制凝胶点,让黏流体转变为凝胶体。     

高分子材料支化结构与流变性的联系串讲北大核心CSCD

高分子链结构为直链型或支化型以及高分子支链的形态、多寡和长度对材料的剪切黏度、黏流活化能、熔体破裂现象等流变性能有显著影响,且与高分子材料成型加工行为密不可分。本文以串讲方式讨论了高分子材料支化结构与流变性能之间的联系。理解、串并、归纳和总结高分子支化结构与流变性之间的联系有利于使学生更加深刻领会《聚合物流变学》课程中高分子材料结构与性能间的关系,串联高分子物理、聚合物流变学、高分子材料成型加工系列专业课程知识。     

怎样上好聚合物流变学

之目的在于探讨工科院校中聚合物流变学课程的教学重点与教学措施,提出了"以高分子物理为依托,服务于聚合物成型工艺,强调课程实用性"的教学思路。聚合物流变学在高分子专业本科教学过程中是承上启下的关键课程,地位与作用明显;聚合物流变学课程又不同于一般流变学课程,有着自身的特点;工科院校中,应突出其实用功能,同时不放弃对经典流变学理论的介绍与适当深入。文中,还对国内外聚合物流变学教材的特点作了评述,对于如何上好聚合物流变学提出了自己的观点。     

高分子材料支化结构与流变性的联系串讲

高分子链结构为直链型或支化型以及高分子支链的形态、多寡和长度对材料的剪切黏度、黏流活化能、熔体破裂现象等流变性能有显著影响,且与高分子材料成型加工行为密不可分。本文以串讲方式讨论了高分子材料支化结构与流变性能之间的联系。理解、串并、归纳和总结高分子支化结构与流变性之间的联系有利于使学生更加深刻领会《聚合物流变学》课程中高分子材料结构与性能间的关系,串联高分子物理、聚合物流变学、高分子材料成型加工系列专业课程知识。     

原位共聚制备的线性低密度聚乙烯的结构特征

采用{[(2-ArN=C(Me))2C5H3N]FeCl2}作为齐聚催化剂[其中Ar=2,4-C6H3(CH3)2和Ar=2-Cl-4-CH3C6H3],商品化的Ziegler-Natta催化剂作为共聚催化剂,分别组成双功能催化体系A[Ziegler-Natta/MAO/TEA/Fe-CH3]和B[Ziegler-Natta/MAO/TEA/Fe-Cl],催化乙烯原位共聚。通过调节不同的聚合条件制备了具有不同支化度、不同分子量及其分布的LLDPE,利用13 C-NMR、流变仪、GPC(示差/光散射)等表征手段,研究了所得高聚物的结构特征。结果表明,该催化体系制备LLDPE样品的支链含量和齐聚物的碳数分布规律是一致的,LLDPE中既有短支链也有较长的支链,聚合物的分子量分布较宽,为聚合物的力学性能和可加工性能提供了更大的调节余地。通过对样品的零剪切粘度、模量、交叉频率、损耗角以及剪切变稀特征等的考察,零剪切粘度与重均分子量的指数关系大于3.8,可以判断被分析的样品含有长支链。分别采用A和B催化剂体系制备的样品作比较,B组样品含有长支链组分,存在较多的高分子量尾端。     

聚合物熔体界面扩散理论与研究方法

本文结合与聚合物加工过程密切相关的界面扩散问题,从动力学和热力学两方面综述了与聚合物界面互扩散相关的基础理论.结合在聚合物界面扩散方面的研究进展,系统介绍了聚合物熔体界面扩散的常用研究方法.对其中的流变学方法的原理及进展作了重点论述,该方法不仅可以有效表征聚合物熔体界面扩散的动力学过程,进一步从分子动力学角度发展并完善聚合物扩散理论,而且对于聚合物加工成型过程的界面结构设计和性能优化起到关键的指导作用.本文最后提出了聚合物熔体界面扩散研究中存在的问题并对其前景进行了展望.     

高分子物理之流变学教学探讨

本文根据高分子行业的发展对人才的需求及高分子专业的培养目标定位,提出了在高等院校高分子专业本科阶段加强教授聚合物流变学内容的必要性,在介绍聚合物流变学的研究内容和研究方法的基础上归纳了其特点和重要性,根据高分子专业课程体系的承接性提出了流变学教学设置,进而结合高分子专业学生特点探讨了聚合物流变学本科教学的讲授内容和课时安排,并对教学过程中采用的教学方法和手段进行了探讨,还提出了在高分子实验中开设与流变学相关的实验促进教学的方法。     

Microstructure characterization of polyethylene using thermo-rheological methods

In the present work, we use the viscoelastic moduli of a large number of industrially available polyethylenes in order to evaluate/test some of the previously proposed correlations between levels of long chain branching and polydispersity with the rheological properties. These correlations together with some new ones can be used to correct for the effects of polydispersity or long chain branching in order to assess the effect of these two molecular features on the rheological properties independently. The effects of short and long chain branching are studied providing a methodology to detect rheologically levels of short and long chain branching.     

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.     

辐照高聚物分子量分布的SEC—LALLS表征

本文分析了长链支化存在下,SEC柱扩展效应对测定数据的影响并导出了基本方程组,给出方程组的解法,并通过计算机数值模拟确证此解法的可行性,同时还讨论了扩展效应、改正参数、实验误差对测定结果的影响。在此基础上,建议了以SEC-LALLS联用技术为核心的表征辐照高聚物分子量分布的系统化方法。     

Effect of branching and molecular weight on the viscoelastic properties of poly(butyl acrylate)

A series of poly(butyl acrylate) samples were prepared by emulsion polymerization with a range of molecular weights and degrees of chain branching. Characterization was performed with NMR (giving the fraction of branching, ranging from approximately 0 to 7%), gel permeation chromatography, viscometry, and determination of the gel fraction. The dynamic mechanical response, that is, the frequency dependence of the storage and loss moduli G′(ω) and G″(ω) was measured from 0.02 to 200 Hz. The occurrence of a significant insoluble fraction in the sample meant that full characterization of the molecular weight distribution was not possible, and so an unambiguous separation of the dependencies of the mechanical response on the degree of long‐chain branching (LCB) and short‐chain branching (SCB) and the molecular weight could not be made; however, trends dependent on the molecular weight alone were insufficient to model the results. At high frequencies, all trends in G′(ω) and G″(ω) could be ascribed to molecular weight dependencies; at low frequencies, the effects of both the molecular weight and total degree of branching could be inferred, with more highly branched samples showing lower storage and loss moduli. Although the relative amounts of SCB and LCB could not be determined, no dynamic features attributable to LCB were observed. The low‐frequency trends could be semiquantitatively fitted with reptation and retraction theory if it was assumed that an increased degree of SCB led to an increased tube size. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3335–3349, 2002     

Crystallizability of ethylene homopolymers by crystallization analysis fractionation

The effect of molecular weight and long‐chain branching on the crystallization analysis fractionation (CRYSTAF) of ethylene homopolymers was investigated. Several ethylene homopolymers were prepared with different molecular weights and levels of long‐chain branching to isolate these effects from the dominant effect of comonomer content on crystallizability measured by CRYSTAF. Molecular weight effects might be significant for samples with number‐average molecular weights below 5000, but this effect can be corrected if terminal methyl groups are taken into account. Long‐chain branching has only a very small effect on the CRYSTAF profile of the samples investigated in this study. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1616–1628, 2001     

Long chain branching indices of low density polyethylenes from size exclusion chromatography and 13C-NMR spectroscopy

Size exclusion chromatography (SEC) and ¹³C-NMR analyses have been used to measure long chain branching indices in low density, free radical-polymerized polyethylenes. Calculation of long chain branching frequency from SEC data requires the assumption of a molecular model. Generally, a randomly branched polymer is assumed, with branches originating at trifunctional branch points. Long chain branch concentrations determined by SEC analysis alone appear to be valid only in a relative sense. The parameters used in the model assumptions vary from polymer to polymer. Despite these limitations, SEC analyses appear to be internally consistent when applied to polyethylenes made by a single manufacturer and process. Comparisons of absolute values of long branch frequency between products from different reactor types require NMR as well as SEC data.     

用凝胶色谱与毛细管粘度计联用法研究顺丁胶的长链支化

本文讨论了用GPC与自动粘度计联用技术测定高聚物长链支化度的方法,将得到的实测关系[η](V)转化成校准关系[η](V_R)后,利用在同一淋出体积流出支化物和线型分子的([η]·M)乘积相等这一普遍原理,计算出各级分的支化因子g_i、总平均支化因子以及产生支化的临界分子量M~*,并讨论了检测器与粘度计连结管死体积△V及虹吸管残留液对支化参数计算值的影响。     

Size Exclusion Chromatography (SEC) of Complex Polymers-Methods of Correction for Imperfect Resolution

Abstract

Herein is reported a review and extension of recently published methods of correction for imperfect resolution (inadequate peak separation and or excessive peak broadening) for the SEC of linear homo and uniform copolymers and complex polymers such as polymers with long chain branching and nonuniform copolymers. Emphasis Is placed on analytical correction methods and absolute detector systems such as the low angle laser light scattering photometer and viscometer in series with a mass detector. Analytical correction methods and absolute detector systems play a vital role in the SEC characterization of complex polymers.