先进固体NMR技术研究高分子结构与动力学

随着固体NMR理论和谱仪硬件技术的不断发展,近年来固体NMR技术在高分子多尺度结构与动力学研究领域中正发挥着越来越重要的作用. 多脉冲及高速魔角旋转（MAS）等质子高分辨技术的发展使得高灵敏度的¹H谱可有效地用于高分子化学结构与链间相互作用的检测;基于化学键（J-耦合）相关和通过空间（偶极耦合）相互作用的各种二维异核相关谱NMR新技术,使得复杂高分子的链结构得以严格解析. 基于MAS下同核和异核偶极-偶极相互作用、化学位移各向异性等各向异性相互作用重聚的系列新技术,使得研究者可在采用高分辨¹H或¹³C 检测信号的同时检测准静态下的各向异性相互作用,进而获得与之密切相关的结构和动力学信息. 通过质子偶极滤波技术可有效检测多相聚合物中的界面相与相区尺寸、高分子共混物中的相容性等问题. 在动力学的研究中,通过质子间自旋扩散的有效压制技术和化学位移各向异性的重聚,目前已经可以有效地获取链段上单个化学键的快速局域运动以及链段的超慢分子运动. 上述丰富的多尺度NMR技术可以使研究者在不同空间和时间尺度上对高分子聚合物的微观结构、相分离和动力学行为等进行详细的研究,进而阐明高分子微观结构与宏观性能的关联. 该文以固体NMR中最主要的2类核（¹H和¹³C）的检测技术为主线,简单介绍近年来固体NMR领域的一些最新研究进展及其在高分子结构和动力学研究中的应用.     

固体NMR 研究PMMA 纳米复合材料结构与受限链运动

聚合物/无机纳米复合材料的微观结构和动力学决定了其宏观性能,阐明无机纳米材料对复合材料结构和动力学的影响,对认识材料结构-性能关系及设计新材料都具有重要意义．该文通过乳液聚合方法合成了聚甲基丙烯酸甲酯/锂藻土(PMMA/Laponite)纳米复合材料,采用1H MAS 和¹³C CPMAS、弛豫时间及¹³C 化学位移各向异性谱(SUPER)等多种固体NMR 技术,详细研究了无机纳米材料的界面改性及其对纳米复合材料的微观结构和动力学的影响．¹H MAS 和¹³C CPMAS 实验表明,有机改性剂与锂藻土形成强的有机-无机界面相互作用,¹³C 纵向弛豫时间实验表明,PMMA 及其锂藻土纳米复合物均含有刚性和柔性两个组分,而纳米复合物中的聚合物链运动相对较低,特别是其中PMMA 的酯基分子运动明显受限．进一步的¹³C SUPER 实验表明,PMMA 酯基的化学位移各向异性在加入锂藻土后发生变化,预示酯基与锂藻土表面的羟基可能存在氢键作用而导致聚合物的链段运动进一步受限,上述纳米尺度受限效应提高了复合材料的玻璃化转变温度．     

SMMA/SMA共聚物共混物的自由体积的热动态特性与相分离行为的PALS研究

基于自由体积理论，利用正电子湮灭寿命谱仪(PALS)分别研究在不同升温速率条件下，聚苯乙烯-甲基丙烯酸甲酯共聚物(SMMA)和聚苯乙烯-马来酸酐共聚物(SMA)混合物(30/70)的自由体积参数的温度依赖性，探索相容共混物相行为的热动态特性.在PALS实验中，在玻璃化转变温度T_g以上，当结构松弛的弛豫时间与等温停留时间相当，发现在某一段温度范围内，共混物的自由体积参数随着温度的变化明显地偏离线性关系.从自由体积孔的浓度I₃值在该段的变化趋势，初步推断共混物在该温 关键词： 正电子湮没 正电子素 聚合物共混物 相分离     

聚酰胺66溶液弛豫行为的NMR研究

用1D和2D NMR技术归属了聚酰胺66的1H和13C的NMR共振信号,并通过聚酰胺66溶液温度和浓度改变对氢核弛豫时间的影响,得到了其分子运动信息.结果表明随着温度的升高,聚酰胺66链间氢键逐渐解离,大分子链间相互作用逐渐减弱.而解离出来的链段又与溶剂小分子可以形成新的氢键,使聚酰胺66链卷曲并包含着部分溶剂分子一起运动.随着溶液浓度的增大,由于分子链间距变小,使得分子间作用力增强,链缠结程度加大,使链运动受限.     

紫外光辐照镍系聚丁二烯的NMR研究

用¹H NMR谱,¹³C NMR谱,二维谱,X-射线衍射等方法研究了镍系高顺式聚丁二烯橡胶(NiBR) 在强紫外（UV）光辐照前后的微观结构变化和分子运动情况. 分析表明NiBR样品随着UV光辐照时间的增加,侧链乙烯基端基双键比主链端基双键更易发生氧化反应;并且随着NiBR样品的各基团的半峰宽值逐渐增加,表明NiBR在UV辐照过程中发生了部分交联反应. 样品的X-射线衍射谱图中结晶峰强度随UV光辐照时间的增加逐渐降低,表明样品的晶形无序程度增加了. 自旋-晶格弛豫时间（T₁）和自旋-自旋弛豫时间（T₂）值给出了有关NiBR辐照前后分子运动变化的信息.      

聚合物侧基NMR弛豫相关函数

本文导出了聚合物为链段运动时,侧基进行非等价二位置和三位置跃迁内旋转、随机自由扩散内旋转以及受阻内旋转时的NMR弛豫相关函数,同时给出了相应的谱密度函数,并讨论了两个应用实例。     

固体高分辨NMR研究PPU/PMAs,AB-交联聚合物中的分子运动和相容性

本文使用固体高分辨NMR测量了PPU/PMAs,AB-交联聚合物中PPU的侧甲基的¹³C自旋-晶格弛豫时间(T₁)。使用内旋转运动的平均谱密度函数分析了PPU侧甲基的内旋转和PMA的侧基的多重内旋转运动。结果表明PMA中的侧基距主链越远,其旋转速度越快并且PPU侧甲基的内旋转速度随ABCP中PMA侧链长度增加而变快。还使用质子的T_1ρ和T₂及自旋扩散研究了体系的相容性和相行为。得到了有关相应尺度下的每相的组成和软相微区尺度的信息。     

晶型转变对尼龙11分子链运动的影响

为进一步认识分子链运动与晶型之间的关系,用熔融、冰水淬火和退火等方法制备了α和δ′两种晶型的尼龙11薄膜试样.42Hz～5MHz的介电松弛谱显示了两种不同晶型试样的分子运动特征.不同频率下的介电温度谱显示α型结晶中代表分子链段运动的主松弛较δ′型结晶出现在更高温度,说明退火引起的δ′向α晶型转变使分子链段运动受到了限制.研究结果还显示,α和δ′型结晶中分子链局域松弛运动的活化能基本相同,但α型的松弛时间较δ′型的大,松弛强度则较δ′型的小,表明晶型转变使尼龙11的分子链局域松弛运动也受到了一定程度的抑制.     

聚酯聚氨酯分子动力学的核磁共振研究

测量了对聚酯聚氨酯在浓溶液状态下质子自旋-晶格弛豫时间随温度的变化,对其中有代表性的基团进行了详细的研究,根据BPP理论用各向同性模型计算分子局部运动的相关时间,从计算结果来看,聚酯聚氨酯的局部分子运动是符合BPP理论的,硬链段的局部分子运动比软链段的局部分子运动要慢得多,两者相差至少一个数量级以上;质子的自旋-晶格弛豫时间主要是偶极-偶极作用的影响;强烈的氢键有相互作用使得硬链段基因的局部运动相关时间接近;通过形成氢键不同的NH峰的相关时间和活化能的观察可以研究软、硬段间的相互作用。     

典型高分子材料的固体核磁共振研究

本论文通过固体核磁共振（NMR）谱及动力学参量的测量,并结合X-射线衍射技术和DSC测量等研究了两种典型高分子材料的相结构、链的运动以及相与相之间的关系.  乙烯-醋酸乙烯共聚物( EVA) 是最主要的乙烯共聚物之一. 研究发现,EVA的相组成非常复杂,共有5个不同的组分. 除了PE中所观察到的常规单斜晶相和刚性的正交晶相外,我们发现还存在第三个晶相分量－运动性较强的晶相（SOCP,可能是转动相）. 它不仅拥有自己的熔点,而且它的化学位移和分子运动性不同于刚性正交晶相（LOCP）. 另一方面,非晶相也由两种不同的分量组成：运动受限的各相异性的非晶界面相和高度可动的橡胶型的非晶相. 我们进一步详细研究了EVA中的晶区链动力学和非晶区的低温冻结行为. 实验发现,在正交晶相中,高分子链以180° flip-flop方式运动,同时伴随沿链方向的平移型跳跃运动,并引起正交晶相和非晶相之间的长程链扩散,通过NOE的测量证实了这种相间链扩散的存在,并进一步通过实验证实这种相间链扩散是一种受限扩散而不是自由扩散. 同时非晶相的两个组分具有不同的低温冻结行为：当温度低于-弛豫转变温度时,橡胶型的非晶相中的长程分子运动被冻结,但仍存在分子的局域运动;而界面非晶在低温时冻结成一种有序取向结构,并用质子自旋扩散实验证实该有序结构与正交晶相相邻近.  少量纳米级片层状粘土分散在聚合物中就可赋予材料许多优异的性能,我们用固体NMR技术对EVA/REC复合材料的结构和其中粘土的分散性质进行研究,发现上述复合材料中所形成的晶体类型不仅依赖于各组分的性质还依赖于所形成的复合材料的类型.  偏氟乙烯/三氟乙烯共聚物（P（VDF-TrFE））是最主要的铁电高聚物之一. 我们利用变温固体¹⁹F MAS NMR 谱及弛豫数据的测量详细研究了电子辐照对P(VDF-TrFE)共聚物的分子结构、构型、运动性以及相变等的影响. 发现,电子辐照不仅改变了分子链段的构型和运动性,同时也改变了局部分子化学结构. 电子辐照促使铁电相向顺电相(或者非晶相)转变,与此同时诱发了富含VDF和含-TrFE链段从全反式的构型到混合的反式-旁式构型的转变. 电子辐照加剧顺电区域中的分子运动而在高温熔融态中(>100 ℃）,分子的运动反而受限.     

Glass Transition Behavior and Dynamic Fragility of PMMA-SAN Miscible Blend-Clay Nanocomposites

An investigation of the segmental dynamics and glass transition behavior of a miscible polymer blend composed of poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN) and its melt intercalated nanocomposite by dynamic mechanical analysis is presented. The principle goal was to address the effect of intercalation on local molecular structure and dynamics. The results showed that the intercalation of polymer chains in the galleries of organoclay (Cloisite 30B) led to a lower temperature dependence of the relaxation time (fragility) and activation energy of α-relaxation. Moreover, calculation of the distribution of the segmental dispersion showed a narrower dispersion in the glass transition region so that the Kohlrausch-Williams-Watts (KWW) distribution parameter (β_KWW) increased from 0.21 for neat PMMA to 0.34 for the 50/50 PMMA/SAN blend nanocomposite containing 3 wt% organoclay. Furthermore, the relaxation behavior of the blends showed a negative deviation from mixture law predictions based on the responses of the neat PMMA and SAN. These behaviors were attributed to the lack of specific interactions between the blend components (PMMA, SAN, and nanoclay layers) and the less cooperative behavior, i.e., less constraint for segmental relaxation, of the intercalated chains.     

Application of129Xe NMR to polymer blends

¹²⁹Xe NMR experiments on two different polymer blends are described. The first system, a blend of polypropylene (PP) and the copolymer of polypropylene and polyethylene (EP), shows separate domains of polypropylene and of the copolymer. The latter phase forms rubbery domains in the polypropylene matrix. The second system is the compatible blend of polyvinylidenefluoride and polymethylmethacrylate. For the incompatible blend two Xe resonances are found, one for Xe absorbed in the matrix and one for Xe in the rubbery EP phase. The chemical shift of the Xe absorbed in the rubbery phase can be related to the polyethylene content of the copolymer. The line widths and chemical shifts are affected by the polymer motions as a function of the temperature. Although the system has two very different glass transition temperatures, it is striking to see that upon approaching the polypropylene glass transition temperature the Xe resonance of Xe in the rubbery phase is also affected. Due to the dipolar interaction between Xe spins and polymer proton spins, cross-polarization experiments can be performed. This allows the measurement of correlated NMR spectra. The compatible blend shows only one line with a chemical shift proportional to the composition.     

Glassy dynamics of polymers confined to nanoporous glasses revealed by relaxational and scattering experiments

The glassy dynamics of poly(propylene glycol) (PPG) and poly(dimethyl siloxane) (PDMS) confined to a nanoporous host system revealed by dielectric spectroscopy, temperature-modulated DSC and neutron scattering is compared. For both systems the relaxation rates estimated from dielectric spectroscopy and temperature-modulated DSC agree quantitatively indicating that both experiments sense the glass transition. For PPG the segmental dynamics is determined by a counterbalance of adsorption and confinement effect. The former results form an interaction of the confined macromolecules with the internal surfaces. A confinement effect originates from an inherent length scale on which the underlying molecular motions take place. The increment of the specific-heat capacity at the glass transition vanishes at a finite length scale of 1.8 nm. Both results support the conception that a characteristic length scale is relevant for glassy dynamics. For PDMS only a confinement effect is observed which is much stronger than that for PPG. Down to a pore size of 7.5 nm, the temperature dependence of the relaxation times follows the Vogel-Fulcher-Tammann dependence. At a pore size of 5 nm this changes to an Arrhenius-like behaviour with a low activation energy. At the same pore size vanishes for PDMS. Quasielastic neutron scattering experiments reveal that also the diffusive character of the relevant molecular motions --found to be characteristic above the glass transition-- seems to disappear at this length scale. These results gives further strong support that the glass transition has to be characterised by an inherent length scale of the relevant molecular motions.Received: 1 January 2003, Published online: 14 October 2003PACS: 64.70.Pf Glass transitions - 77.22.Gm Dielectric loss and relaxation - 61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling     

A review of the slow relaxation processes in the glass–rubber transition region of amorphous polymers

This article is a review that introduces several articles about slow relaxation processes, also known as slower segmental dynamics. According to the literature, the coupling effect and free volume holes are two important elements for slower micro-dynamics. In addition, the slower processes of many-body systems (blend and diluted systems) are summarised. A good numerical method for detecting multiple modes in the glass–rubber transition region is introduced.     

环氧树脂高温分子链松弛与玻璃化转变特性

环氧树脂是电力设备中广泛应用的一种绝缘材料, 其介电性能受到分子链运动特性的影响. 本文制备了直径为50 mm、厚度为1 mm的环氧树脂试样, 采用差示扫描量热仪和宽频介电谱仪测试了环氧树脂的玻璃化转变温度和介电特性. 实验结果表明, 环氧树脂的玻璃化转变温度为105 ℃, 在玻璃化转变温度以上, 高频段出现了由分子链段运动造成的松弛过程, 低频段出现了由载流子在材料中迁移造成的直流电导过程. 发现环氧树脂不同尺寸分子链段的松弛时间不同, 其松弛时间分布较宽, 计算得到了分子链段在不同温度下的松弛时间分布特性. 分子链松弛峰频率和直流电导随温度的变化关系服从Vogel-Tammann-Fulcher公式. 拟合实验结果得到分子链松弛峰频率和直流电导的Vogel温度和强度系数. 由Vogel温度计算得到了与差示扫描量热测试结果一致的玻璃化转变温度, 约为102 ℃. 结果表明玻璃化转变温度以上环氧树脂的自由体积增大, 分子链段有足够的空间来响应外电场从而产生分子链松弛极化, 载流子有足够的能量在材料中迁移形成电导.     

Poly ethylene oxide (PEO)–LiI polymer electrolytes embedded with CdO nanoparticles

Improvement of electrical conductivity of poly ethylene oxide (PEO)–LiI polymer electrolytes is necessary for their use in solid state lithium ion battery. In this study a new kind of PEO–LiI-based polymer electrolytes embedded with CdO nanoparticles with improved electrical conductivity has been prepared and characterized. The electron microscopic studies confirm that CdO nanoparticles of average size 2.5 nm are dispersed in the PEO matrix. The glass transition temperature of the PEO–LiI electrolyte decreases with the introduction of CdO nanoparticle in the polymer matrix. X-ray diffraction, electron microscopic, and differential scanning calorimetry studies show that the amorphous phase of PEO increases with the introduction of CdO nanoparticle and that the increase in amorphous phase is maximum for 0.10 wt% CdO doping. The electrical conductivity of the sample with 0.10 wt% CdO increases by three orders in magnitude than that of the PEO–LiI electrolyte. The electrical conductivity of PEO–LiI electrolyte embedded with CdO nanoparticle exhibits VTF behavior with reciprocal temperature indicating a strong coupling between the ionic and the polymer chain segmental motions.     

Mobility in thin polymer films ranging from local segmental motion, Rouse modes to whole chain motion: A coupling model consideration

Large increases of mobility of local segmental relaxation observed in polymer films as the film thickness is decreased, as evidenced by decreases of the glass temperature, are not found for relaxation mechanisms that have longer length scales including the Rouse relaxation modes and the diffusion of entire polymer chains. We show that the coupling model predictions, when extended to consider polymer thin films, are consistent with a large increase of the mobility of the local segmental motions and the lack of such a change for the Rouse modes and the diffusion of entire polymer chains. There are two effects that can reduce the coupling parameter of the local segmental relaxation in thin films. One is the chain orientation that is induced parallel to the surface when the film thickness h becomes smaller than the end-to-end distance of the chains and the other is a finite-size effect when h is no longer large compared to the cooperative length scale. Extremely thin ( ≈ 1.5 nm) films obtained by intercalating a polymer into layered silicates have thickness significantly less than the cooperative length scale near the bulk polymer glass transition temperature. As a result, the coupling parameter of the local segmental relaxation in such thin films is reduced almost to zero. With this plausible assumption, we show the coupling model can explain quantitatively the large decrease of the local segmental relaxation time found experimentally. Received 1 August 2001 and Received in final form 1 December 2001     

Miscibility, Crystallization, and Rheological Behavior of Solution Casting Poly(3-hydroxybutyrate)/poly(ethylene succinate) Blends Probed by Differential Scanning Calorimetry, Rheology, and Optical Microscope Techniques

应用差示扫描量热、流变及偏光显微镜等方法研究了聚3-羟基丁酸酯/聚丁二酸乙二醇酯(PHB/PES)共混体系的相容性、结晶和流变行为．相图显示该共混体系有两个玻璃化转变,但PHB的熔点随其含量的减少而降低,这个结果证明该共混体系是部分相容的,同时应用偏光显微镜观察体系结晶形态的发展证实了这个结论．依赖于结晶温度和组成,PHB和PES能同时结晶,也能分步结晶,且PHB的球晶生长速率随PES含量的增加而增大．对于部分相容的聚合物共混体系,共混组成对球晶生长速率的影响也做了详细地讨论．     

Correlation Between Segmental Dynamics,Glass Transition,and Lithium Ion Conduction in Poly(Methyl Methacrylate)/Ionic Liquid Mixture

A solid-state membrane of a polymer/ionic liquid miscible mixture, poly(methyl methacrylate) (PMMA) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) doped with lithium perchlorate (LiClO₄), was prepared and characterized. Miscibility, segmental dynamics, glass transition and ionic conductivity were investigated. Based on the results from differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA), the system is fully miscible and of single phase. Broadening of the glass transition was observed when increasing the amount of ionic liquid, which can be attributed to mobility and flexibility differences between the polymer and ionic liquid. A large dynamical asymmetry and intrinsic mobility difference allow segmental and structural motion/relaxation over a wider temperature range by increasing the amount of ionic liquid. Saturation recovery spin–lattice relaxation time (T₁) versus temperature obtained from ⁷Li nuclear magnetic resonance (NMR) showed high mobility of lithium ions, which was almost temperature independent. Lithium ion conductivity significantly increases with increasing ionic liquid amount. It is concluded that lithium ion mobility and its conduction is positively correlated to segmental dynamics of ion carriers in this model system, which is more noticeable in mixtures with higher amounts of the ionic liquid.     

Solid electrolyte membranes from semi-interpenetrating polymer networks of PEG-grafted polymethacrylates and poly(methyl methacrylate)

Solid polymer electrolyte membranes were prepared as semi-interpenetrating networks by photo-induced polymerization of mixtures of poly(ethylene glycol) (PEG) methacrylate macromonomers in the presence of poly(methyl methacrylate) (PMMA) and lithium bis(trifluoromethanesulfonyl)imide salt. The composition of the membranes was varied with respect to the PMMA content, the degree of cross-linking, and the salt concentration. Infrared analysis of the membranes indicated that the lithium ions were coordinated by the PEG side chains. Calorimetry results showed a single glass transition for the blend membranes. However, dynamic mechanical measurements, as well as a closer analysis of the calorimetry data, revealed that the blends were heterogeneous systems. The ionic conductivity of the membranes increased with the content of PEG-grafted polymethacrylate, and was found to exceed 10^− 5 S cm^− 1 at 30 °C for membranes containing more than 85 wt.% of this component in the polymer blend.