Sroka-Bartnicka A, Olejniczak S, Ciesielski W, Nosal A, Szymanowski H, Gazicki-Lipman M, Potrzebowski M J
Polish Academy of Sciences, Center of Molecular and Macromolecular Studies, Sienkiewicza 112, 90-363 Łodz, Poland.
J Phys Chem B. 2009 Apr 23;113(16):5464-72. doi: 10.1021/jp900788m.
High resolution solid state (13)C nuclear magnetic resonance (SS NMR) measurements were carried out on poly(p-xylylene) (PPX). The samples comprised vapor-deposited specimens as well as pure alpha and beta polymorphs of this polymer. The measurements were performed using cross-polarization and magic angle spinning (CP/MAS) techniques. Density functional theory gauge-including-atomic-orbital (DFT GIAO) calculations of NMR shielding parameters (13)C sigma(ii) were performed for the optimized geometry and structure of a xylylene trimer, acquired from the X-ray data, including intermolecular interactions. Two-dimensional phase adjusted spinning sideband (2D PASS) correlation was employed for the assignment of the values of the principal elements (13)C delta(ii) of the chemical shift tensor (CST). A comparative analysis of shielding (sigma(ii)) versus chemical shift (delta(ii)) parameters showed substantial differences between the molecular dynamics of alpha and beta polymorphs. This observation was further supported by the measurements of (13)C T(1) relaxation times and the analysis of cross-polarization kinetics. Frequency switched Lee-Goldburg heteronuclear correlation (FSLG HETCOR) for the (1)H-(13)C system was used in order to analyze molecular packing in both polymorphs. As a result of all of the above measurements, new insight into the mechanism of thermal phase transition from the alpha to the beta polymorph of poly(p-xylylene) is presented.
对聚对二甲苯（PPX）进行了高分辨率固态（13）C核磁共振（SS NMR）测量。样品包括气相沉积标本以及该聚合物的纯α和β多晶型物。测量使用交叉极化和魔角旋转（CP/MAS）技术进行。对从X射线数据获得的二甲苯三聚体的优化几何结构和结构进行了密度泛函理论含原子轨道（DFT GIAO）的NMR屏蔽参数（13）C σ（ii）计算，包括分子间相互作用。二维相位调整旋转边带（2D PASS）相关性用于确定化学位移张量（CST）的主元素（13）C δ（ii）值。屏蔽（σ（ii））与化学位移（δ（ii））参数的对比分析表明，α和β多晶型物的分子动力学存在显著差异。（13）C T（1）弛豫时间的测量和交叉极化动力学分析进一步支持了这一观察结果。使用（1）H-（13）C系统的频率切换Lee-Goldburg异核相关性（FSLG HETCOR）来分析两种多晶型物中的分子堆积。上述所有测量结果揭示了聚对二甲苯从α多晶型物到β多晶型物热相变机制的新见解。
