CHARACTERIZATION OF PDMS MODEL JUNCTIONS AND NETWORKS BY SOLUTION AND SOLID-STATE SI-29 NMR-SPECTROSCOPY
CHARACTERIZATION OF PDMS MODEL JUNCTIONS AND NETWORKS BY SOLUTION AND SOLID-STATE SI-29 NMR-SPECTROSCOPY
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DOI：
10.1002/polb.1986.090240602
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发表时间：
1986-06-01
影响因子：
--
通讯作者：
HIMSTEDT, A
中科院分区：
文献类型：
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作者：
BESHAH, K;MARK, JE;HIMSTEDT, A
利用29 Si溶液和固态交叉极化/魔角自旋（CP/MAS）核磁共振（NMR）技术研究了聚二甲基硅氧烷（PDMS）模型端链弹性体网络的结构特征。拓扑（网络）功能的结构部分，它决定网络的机械性能，其化学（光谱）功能，这是由NMR报告之间的关系进行了讨论。对应于化学官能团类内拓扑官能团变化的二阶光谱位移通常在这些网络中得到足够好的解析，以允许对各种结构特征进行积极识别。基本的PDMS重复单元，OSi（CH 3）2 <$$>，被发现具有轴对称的化学位移张量，在TMS的低场下，σ <$= −56.8 ppm，σ <$= −4.4 ppm。这种轴对称性并不是由围绕链轴的快速重新定向引起的。NMR光谱揭示了模型端连接网络中的缺陷。在乙烯基端基连接体系的情况下，缺陷归因于弹性无效环的形成。羟基末端连接的系统包含环或三官能连接（在链偶联发生之前水解）和悬挂链末端。CP/MAS技术在从不含顺磁掺杂的网络中获取光谱的时间上比标准溶液技术减少了一个数量级。PDMS系统的13 C光谱不如29 Si光谱提供的信息丰富。
The application of29Si solution and solid‐state cross‐polarization/magic‐angle spinning (CP/MAS) nuclear magnetic resonance (NMR) techniques to the study of structural features in polydimethylsiloxane (PDMS) model endlinked elastomeric networks is explored. The relationship between the topological (network) functionality of a structural moiety, which determines network mechanical properties, and its chemical (spectral) functionality, which is reported by the NMR, is discussed. The second‐order spectral shifts corresponding to topographical functionality variation within a chemical functionality class are usually sufficiently well resolved in these networks to allow positive identification of a variety of structural features. The basic PDMS repeat unit, OSi(CH3)2, is found to possess an axially symmetric chemical shift tensor with σ∥= −56.8 ppm downfield from TMS, and σ⊥= −4.4 ppm. This axial symmetry does not result from rapid reorientation about the chain axis. The NMR spectrum reveals defects in model endlinked networks. In the case of vinyl‐endlinked systems, the defects are ascribed to the formation of elastically ineffective loops. Hydroxyl‐endlinked systems contain either loops or else trifunctional junctions (hydrolyzed before chain coupling could take place) and dangling chain ends. The CP/MAS technique provides an order‐of‐magnitude reduction over standard solution techniques in the time to acquire a spectrum from a network not containing paramagnetic doping.13C spectra of PDMS systems are not as informative as29Si spectra.