POLYMER CONFORMATIONAL STRUCTURE AND DYNAMICS AT THE GLASS-TRANSITION STUDIED BY MULTIDIMENSIONAL C-13 NMR
POLYMER CONFORMATIONAL STRUCTURE AND DYNAMICS AT THE GLASS-TRANSITION STUDIED BY MULTIDIMENSIONAL C-13 NMR
复制标题
多维 C-13 NMR 研究聚合物玻璃化转变的构象结构和动力学
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
H. Spiess
中科院分区：
文献类型：
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作者：
K. Zemke;K. Schmidt;H. Spiess
在各种无定形聚合物如聚丙烯、聚乙酸乙烯酯和聚异丁烯中，利用各向同性化学位移的γ-Gauche效应，通过魔角旋转（MAS）NMR在固态下检测各种主链构象。在聚丙烯中，构象的群体与从溶液13 C NMR确定的特定构型有关。在玻璃化转变温度以上，观察到构象之间的动态交换。的相关函数和运动速率的非指数性是相似的，通过2D交换NMR与慢MAS或静态样品在相同的温度下观察到的扩散重取向。虽然反式和偏置定义的旋转角分布内的聚（丙烯）的优选构象，动力学不适合描述的金刚石晶格上的原子的运动。这特别是通过在3D交换NMR实验中不存在长期取向记忆来证明。为了进一步表征运动的性质，从没有MAS的2D交换谱计算了L = 2和L = 4阶的相关函数。大角度跳跃和各向同性的旋转扩散之间的中间行为进行观察。
In a variety of amorphous polymers such as poly(propylene), poly(vinyl acetate) and poly(isobutylene), various backbone conformations are detected by magic-angle-spinning (MAS) NMR in the solid state, exploiting the γ-gauche effect on the isotropic chemical shifts. In poly(propylene), the populations of the conformations are related to specific configurations determined from solution 13C NMR. Above the glass transition temperature, dynamical exchange between the conformations is observed. The non-exponentiality of the correlation functions and the motional rates are similar of those of the diffuse reorientations observed by 2D exchange NMR with slow MAS or on static samples at the same temperatures. Although trans and gauche define the preferred conformations within the distribution of rotational angles for poly(propylene), the dynamics are not suitably described by motions of the atoms on a diamond lattice. This is demonstrated in particular by the absence of long term orientational memory in 3D exchange NMR experiments. To characterize the nature of the motion further, correlation functions of orders L = 2 and L = 4 have been calculated from 2D exchange spectra without MAS. A behavior intermediate between large-angle jumps and isotropic rotational diffusion is observed.