Trans content in atactic polystyrene estimated by double-quantum solid-state NMR
Trans content in atactic polystyrene estimated by double-quantum solid-state NMR
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DOI：
10.1016/s0926-2040(98)00062-9
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发表时间：
1998-09-01
影响因子：
3.2
通讯作者：
Schmidt-Rohr, K
中科院分区：
文献类型：
--
作者：
Dunbar, MG;Novak, BM;Schmidt-Rohr, K
用固体核磁共振研究了25%(CH2)-C-13基团标记的无规聚苯乙烯的构象统计。双量子脉冲序列用于选择统计形成的C-13-C-13自旋对。一项将C-13-C-13分子矢量与C-13化学位移各向异性相关联的实验确定了单个主干扭转角的构象统计。关联两个相邻链段的(CH2)-C-13化学位移各向异性的双量子实验提供了关于两个连续扭转角的信息。光谱分析得到反式含量为68%(+/-10%)。这是第一次对无规聚苯乙烯中的反式/五氯苯比率进行直接实验估计。这里发现的反式含量很好地符合旋转同分异构态模型，但与考虑堆积效应的更精细的原子模型的结果不一致。(C)1998 Elsevier Science B.V.保留所有权利。
The conformational statistics of atactic polystyrene have been investigated by solid-state NMR, on a sample labeled with 25% (CH2)-C-13 groups. Double-quantum pulse sequences are used to select statistically formed C-13-C-13 spin pairs. An experiment correlating the C-13-C-13 infemuelear vector with the C-13 chemical-shift anisotropy determines the conformational statistics of a single backbone torsion angle. Double-quantum experiments correlating the (CH2)-C-13 chemical-shift anisotropies of two adjacent segments provide information on two consecutive torsion angles. The analysis of the spectra yields a trans content of 68% (+/-10%). This represents the first direct experimental estimate of the trans/gauche ratio in atactic polystyrene. The trans content found here agrees well with rotational-isomeric-state models but is inconsistent with results from more elaborate atomistic models that take packing effects into account. (C) 1998 Elsevier Science B.V. All rights reserved.