拉伸状态下高分子弹性体聚集态结构与分子运动的固体高分辨核磁共振研究
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摘要
本文利用固体核磁共振技术，结合专用的原位拉伸装置对拉伸态的天然橡胶(NR)、聚醚酯嵌段共聚物(PEE)、乙烯-辛烯共聚物(POE)和乙烯-丙烯酸甲酯共聚物(EMA)等4个高分子弹性体体系的聚集态结构以及分子运动等进行了系统的研究，所得主要结果如下：
1．设计出可以在4 mm MAS转子中进行拉伸状态下高分子弹性体固体高分辨核磁共振实验的专用插件，该插件具有制作简单、操作方便等特点，放置了该插件的MAS转子最大稳定转速可达到7 kHz。凭借该装置，成功解决了高分子弹性体难以在高速魔角旋转下进行原位拉伸实验的问题，拓展了固体高分辨核磁共振在高分子结构研究中的应用范围。
2．首次通过原位拉伸的固体高分辨核磁共振方法对不同拉伸比的天然橡胶进行了系统的研究。发现未拉伸的天然橡胶样品室温下也存在少量结晶，该结果为天然橡胶在室温下存在结晶的观点提供直接的证据。~(13)C CP／MAS实验结果表明，随着拉伸比的增加，体系中的结晶含量也随之增加。~(13)C T_1，~1H T_2等结果进一步证实不同拉伸比下结晶的存在并对结晶峰进行了归属。定量结果表明，天然橡胶在拉伸比2.0倍左右开始产生拉伸诱导结晶，且在2.0到6.0拉伸比区间内，结晶度和拉伸比呈近似的线性关系。拉伸比大于6.0倍时，拉伸诱导结晶趋缓，发现最大拉伸比(7.0)时的结晶度为19.3％。相对未加炭黑的样品来说，加炭黑的样品在同等拉伸比下表现出较低的结晶度，说明炭黑作为物理交联剂在一定程度上阻止了拉伸诱导结晶的产生。
3．固体核磁共振技术对PEE的研究结果表明，拉伸导致“软段”PTMO的结晶，新产生的结晶量以及这部分结晶的晶片厚度都随着拉伸比的增加而增加，且拉伸引起的结晶主要发生在PTMO非晶区。拉伸对体系中非结晶的高频分子运动并没有明显的影响，拉伸使得结晶区更加趋于完善。结晶厚度表征的结果显示，4.0倍拉伸比时PTMO非晶区与结晶区之间的界面层厚度以及它与4GT结晶区的过渡层厚度分别约为1.1 nm和3.1 nm，拉伸对PTMO链段的影响是均匀的。
4．固体核磁共振对EMA的研究结果表明，随着拉伸比的增加，共聚物中正交晶含量经历了先减少、后增加，然后在断裂伸长比的情况下再大幅度减少的过程，而单斜晶的含量则保持单调的有限增加；~(13)C T_1和自旋扩散实验结果表明，拉伸后的结晶厚度变小，在断裂伸长比之前，体系中结晶度的增加是由一些新的
晶体的产生所导致的;结晶界面层厚度的测定结果显示，其厚度约为1.，nm，
该结果进一步证明，结晶区，3cTI的双指数弛豫行为是由结晶界面层和结晶本
体所造成的。拉伸过程所导致的结晶厚度的降低，使得结晶界面层相对于结晶本
体的含量增加。
5.对POE体系的研究结果表明，高弹性的尸OE不但存在结晶，且结晶中
单斜晶含量明显高于其它的乙烯共聚物。辛烯含量的多少是决定样品聚集态结构
变化的最重要的因素，体系中的结晶度随着辛烯的含量增加而明显降低，单斜晶
和正交晶含量的比值随着共聚单元的增加而增加，说明了较短的乙烯链段，更易
形成单斜晶;较长的乙烯链段易于形成正交晶。不同的样品处理方式也是引起共
聚物聚集态结构变化的重要因素。拉伸对POE弹性体聚集态结构的影响不是一
个单调的过程，在低拉伸比范围内，拉伸会导致结晶度的增加，而进一步增加拉
伸比又会导致对结晶的破坏。在结晶区中含量占优的单斜晶所受到的拉伸的影响
和含量较少的正交晶所受的影响明显不同。正交晶的13cTI弛豫行为随辛烯含
量不同有明显变化，而单斜晶则变化很小，说明正交晶的晶片厚度随着辛烯含量
增加而降低，而单斜晶晶片厚度则无明显变化。通过对不同拉伸比样品，3CTI
弛豫行为的研究发现，拉伸导致正交晶晶片厚度明显变薄，拉伸对于无定形相的
高频分子运动几乎无影响。
拉伸对上述四个弹性体体系的聚集态结构都产生了很大影响，但是影响的程
度和内容因体系而不同，对于本身存在着化学交联(天然橡胶)或者是物理交联
(聚醚酷)的体系而言，拉伸导致了其中本来难以结晶组分的结晶，且结晶度随
着拉伸比增加而增加，与此同时，体系结晶的晶片厚度也会逐渐增加;而对于结
晶性共聚物体系，如EMA和POE，结晶区本来起到了物理交联的作用，在这种
情况下拉伸的影响变得比较复杂，拉伸对于不同晶型的影响有所不同，在拉伸比
较低的情况下体系总体的结晶度会有所增加，说明有新的结晶产生，当接近或达
到断裂伸长比时，体系的结晶度会突然降低，含量占优的结晶会被拉伸所破坏，
含量较低的结晶在整个拉伸过程中受的影响较小。综合4个体系的结果来看，拉
伸对体系中非晶区的高频分子运动几乎没什么的影响。
The morphology and molecular motion of 4 different elastomers, including natural rubber (NR), poly (ester ether) (PEE), ethylene-methyl acrylate (EMA) and ethylene-octene(POE) copolymers, have been systematically investigated by employing an "in-situ stretching" solid-state NMR technique. The main results include:
1. A design of a set of devices for a 4 mm magic angle spinning (MAS) rotor by which "in-situ stretching" solid-state high-resolution NMR investigations of elastomers can be easily performed. A maximum and stable spinning rate of 7 kHz was attainable. Based on these devices, the application of the solid-state high-resolution NMR technique was extended and enabled the stretching behavior of elastomers to be investigated on a molecular level.
2. 13C CP/MAS and DD/MAS spectra, as well as 13C Ti and 1H T2 relaxation times of the individual nuclei were measured for the first time of "in-situ stretched" NR samples. The high-resolution appearance of the NMR spectra suggests that a small amount of crystals do exist in unstretched NR samples at room temperature. A detailed spectral assignment of the crystalline part in the NMR spectrum of both the unstretched and the stretched samples are presented. It was found that the intensity of the crystalline component increases with increasing draw ratio {X). The strain-induced crystallization starts when X is about 2.0. Quantitative experiments suggest that an approximate linear relation between crystallinity and X exists for X in the range of 2.0 to 6.0. The maximum crystallinity obtained was 19.3%. Compared to non-filled samples, the ability of crystallization of the carbon black-filled NR samples was significantly smaller.
3. The morphology and molecular motion of "in-situ stretched" PEE samples were studied by solid-state high-resolution 13C NMR techniques. Strain-induced crystallization of ploy(tetramethylene oxide) (PTMO) was
observed for X.=2.0. The degree of crystallinity of PTMO and the lamellar thickness of the crystallites were found to increase with increasing X. The molecular motion at high frequency of amorphous PTMO was found to be almost independent on X, indicating that the strain-induced crystallization mainly occurs in the "pure" PTMO region. The thickness of the interfacial region between the amorphous and the crystalline phases of PTMO is about 1.1 nm. The corresponding interfacial region between the amorphous PTMO and the crystalline hard segment is about 3.1 nm.
4. The relative content of the orthorhombic crystalline component in EMA samples exhibit a process of decreasing, and then increasing tendencies at lower Xs, and finally a great decreasing at the utmost ratio (b), while the contents of the monodinic components increase monotonously with s. 13C Ti and spin-diffusion experiments demonstrated that the thicknesses of the crystalline lamella decreases upon stretching, while the increase of the crystallinity is mainly due to the newly formed crystals. It was demonstrated further that the origin of the biexponential 13C Ti relaxation behavior of the crystalline region is due to the coexistence of an intermediate and an internal crystalline parts within the sample. The thickness of the intermediate crystalline region was found to be approximately 1.1 nm. The content of this intermediate fraction was found to increase with increasing X.
5. The morphology and molecular motion of POE samples were found to be dependent on the octene content, conditions of crystallization and X. A comparablely high content of monodinic crystals was found in POE samples. With increasing octene content the degree of crystallinity was found to decrease while the ratio of monodinic and orthorhombic crystals (Mono/Orth) increases. All these results indicate that monodinic and orthorhombic crystals are inclined to form by realtively shorter and longer ethylene segments respectively. Moreover, the crystallinity increases with X at low X region. At higher s, the crystallinity, and the fraction of both monodinic and
1．设计出可以在4 mm MAS转子中进行拉伸状态下高分子弹性体固体高分辨核磁共振实验的专用插件，该插件具有制作简单、操作方便等特点，放置了该插件的MAS转子最大稳定转速可达到7 kHz。凭借该装置，成功解决了高分子弹性体难以在高速魔角旋转下进行原位拉伸实验的问题，拓展了固体高分辨核磁共振在高分子结构研究中的应用范围。
2．首次通过原位拉伸的固体高分辨核磁共振方法对不同拉伸比的天然橡胶进行了系统的研究。发现未拉伸的天然橡胶样品室温下也存在少量结晶，该结果为天然橡胶在室温下存在结晶的观点提供直接的证据。~(13)C CP／MAS实验结果表明，随着拉伸比的增加，体系中的结晶含量也随之增加。~(13)C T_1，~1H T_2等结果进一步证实不同拉伸比下结晶的存在并对结晶峰进行了归属。定量结果表明，天然橡胶在拉伸比2.0倍左右开始产生拉伸诱导结晶，且在2.0到6.0拉伸比区间内，结晶度和拉伸比呈近似的线性关系。拉伸比大于6.0倍时，拉伸诱导结晶趋缓，发现最大拉伸比(7.0)时的结晶度为19.3％。相对未加炭黑的样品来说，加炭黑的样品在同等拉伸比下表现出较低的结晶度，说明炭黑作为物理交联剂在一定程度上阻止了拉伸诱导结晶的产生。
3．固体核磁共振技术对PEE的研究结果表明，拉伸导致“软段”PTMO的结晶，新产生的结晶量以及这部分结晶的晶片厚度都随着拉伸比的增加而增加，且拉伸引起的结晶主要发生在PTMO非晶区。拉伸对体系中非结晶的高频分子运动并没有明显的影响，拉伸使得结晶区更加趋于完善。结晶厚度表征的结果显示，4.0倍拉伸比时PTMO非晶区与结晶区之间的界面层厚度以及它与4GT结晶区的过渡层厚度分别约为1.1 nm和3.1 nm，拉伸对PTMO链段的影响是均匀的。
4．固体核磁共振对EMA的研究结果表明，随着拉伸比的增加，共聚物中正交晶含量经历了先减少、后增加，然后在断裂伸长比的情况下再大幅度减少的过程，而单斜晶的含量则保持单调的有限增加；~(13)C T_1和自旋扩散实验结果表明，拉伸后的结晶厚度变小，在断裂伸长比之前，体系中结晶度的增加是由一些新的
晶体的产生所导致的;结晶界面层厚度的测定结果显示，其厚度约为1.，nm，
该结果进一步证明，结晶区，3cTI的双指数弛豫行为是由结晶界面层和结晶本
体所造成的。拉伸过程所导致的结晶厚度的降低，使得结晶界面层相对于结晶本
体的含量增加。
5.对POE体系的研究结果表明，高弹性的尸OE不但存在结晶，且结晶中
单斜晶含量明显高于其它的乙烯共聚物。辛烯含量的多少是决定样品聚集态结构
变化的最重要的因素，体系中的结晶度随着辛烯的含量增加而明显降低，单斜晶
和正交晶含量的比值随着共聚单元的增加而增加，说明了较短的乙烯链段，更易
形成单斜晶;较长的乙烯链段易于形成正交晶。不同的样品处理方式也是引起共
聚物聚集态结构变化的重要因素。拉伸对POE弹性体聚集态结构的影响不是一
个单调的过程，在低拉伸比范围内，拉伸会导致结晶度的增加，而进一步增加拉
伸比又会导致对结晶的破坏。在结晶区中含量占优的单斜晶所受到的拉伸的影响
和含量较少的正交晶所受的影响明显不同。正交晶的13cTI弛豫行为随辛烯含
量不同有明显变化，而单斜晶则变化很小，说明正交晶的晶片厚度随着辛烯含量
增加而降低，而单斜晶晶片厚度则无明显变化。通过对不同拉伸比样品，3CTI
弛豫行为的研究发现，拉伸导致正交晶晶片厚度明显变薄，拉伸对于无定形相的
高频分子运动几乎无影响。
拉伸对上述四个弹性体体系的聚集态结构都产生了很大影响，但是影响的程
度和内容因体系而不同，对于本身存在着化学交联(天然橡胶)或者是物理交联
(聚醚酷)的体系而言，拉伸导致了其中本来难以结晶组分的结晶，且结晶度随
着拉伸比增加而增加，与此同时，体系结晶的晶片厚度也会逐渐增加;而对于结
晶性共聚物体系，如EMA和POE，结晶区本来起到了物理交联的作用，在这种
情况下拉伸的影响变得比较复杂，拉伸对于不同晶型的影响有所不同，在拉伸比
较低的情况下体系总体的结晶度会有所增加，说明有新的结晶产生，当接近或达
到断裂伸长比时，体系的结晶度会突然降低，含量占优的结晶会被拉伸所破坏，
含量较低的结晶在整个拉伸过程中受的影响较小。综合4个体系的结果来看，拉
伸对体系中非晶区的高频分子运动几乎没什么的影响。
The morphology and molecular motion of 4 different elastomers, including natural rubber (NR), poly (ester ether) (PEE), ethylene-methyl acrylate (EMA) and ethylene-octene(POE) copolymers, have been systematically investigated by employing an "in-situ stretching" solid-state NMR technique. The main results include:
1. A design of a set of devices for a 4 mm magic angle spinning (MAS) rotor by which "in-situ stretching" solid-state high-resolution NMR investigations of elastomers can be easily performed. A maximum and stable spinning rate of 7 kHz was attainable. Based on these devices, the application of the solid-state high-resolution NMR technique was extended and enabled the stretching behavior of elastomers to be investigated on a molecular level.
2. 13C CP/MAS and DD/MAS spectra, as well as 13C Ti and 1H T2 relaxation times of the individual nuclei were measured for the first time of "in-situ stretched" NR samples. The high-resolution appearance of the NMR spectra suggests that a small amount of crystals do exist in unstretched NR samples at room temperature. A detailed spectral assignment of the crystalline part in the NMR spectrum of both the unstretched and the stretched samples are presented. It was found that the intensity of the crystalline component increases with increasing draw ratio {X). The strain-induced crystallization starts when X is about 2.0. Quantitative experiments suggest that an approximate linear relation between crystallinity and X exists for X in the range of 2.0 to 6.0. The maximum crystallinity obtained was 19.3%. Compared to non-filled samples, the ability of crystallization of the carbon black-filled NR samples was significantly smaller.
3. The morphology and molecular motion of "in-situ stretched" PEE samples were studied by solid-state high-resolution 13C NMR techniques. Strain-induced crystallization of ploy(tetramethylene oxide) (PTMO) was
observed for X.=2.0. The degree of crystallinity of PTMO and the lamellar thickness of the crystallites were found to increase with increasing X. The molecular motion at high frequency of amorphous PTMO was found to be almost independent on X, indicating that the strain-induced crystallization mainly occurs in the "pure" PTMO region. The thickness of the interfacial region between the amorphous and the crystalline phases of PTMO is about 1.1 nm. The corresponding interfacial region between the amorphous PTMO and the crystalline hard segment is about 3.1 nm.
4. The relative content of the orthorhombic crystalline component in EMA samples exhibit a process of decreasing, and then increasing tendencies at lower Xs, and finally a great decreasing at the utmost ratio (b), while the contents of the monodinic components increase monotonously with s. 13C Ti and spin-diffusion experiments demonstrated that the thicknesses of the crystalline lamella decreases upon stretching, while the increase of the crystallinity is mainly due to the newly formed crystals. It was demonstrated further that the origin of the biexponential 13C Ti relaxation behavior of the crystalline region is due to the coexistence of an intermediate and an internal crystalline parts within the sample. The thickness of the intermediate crystalline region was found to be approximately 1.1 nm. The content of this intermediate fraction was found to increase with increasing X.
5. The morphology and molecular motion of POE samples were found to be dependent on the octene content, conditions of crystallization and X. A comparablely high content of monodinic crystals was found in POE samples. With increasing octene content the degree of crystallinity was found to decrease while the ratio of monodinic and orthorhombic crystals (Mono/Orth) increases. All these results indicate that monodinic and orthorhombic crystals are inclined to form by realtively shorter and longer ethylene segments respectively. Moreover, the crystallinity increases with X at low X region. At higher s, the crystallinity, and the fraction of both monodinic and
引文
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