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首页> 外文会议>NMR spectroscopy of polymers: Innovative strategies for complex macromolecules >Molecular Dynamics and Structure of the Crystalline Region of Isotactic-Polyolefins Characterized by Solid-State NMR
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Molecular Dynamics and Structure of the Crystalline Region of Isotactic-Polyolefins Characterized by Solid-State NMR

机译：固态NMR表征的全同立构聚烯烃结晶区域的分子动力学和结构

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A review is given of recent solid-state NMR work on structure and molecular dynamics of polyolefins such as isotactic poly(l-butene) (iPBl) and isotactic polypropylene (iPP). In iPBl, melt-crystallization leads to metastable form II, and subsequent solid-solid transition results in stable form I. ~1H-~(13)C wide line separation (WISE) and center bands only detection of exchange (CODEX) NMR techniques provided geometric and time-kinetic parameters of molecular dynamics for overall and side chains in both forms at natural abundance. The ~1H line-shape analysis using a two-spin approximation and ~(13)C T_1 results indicate that form Ⅱ chains perform uniaxially rotational diffusions accompanying side-chain conformational transitions in the fast motional limit (correlation time < 10~(-7) s). After irreversible solid transition, ~(13)C CODEX results indicate that crystalline stems and side-chain conformations are completely fixed, up to the melting points (correlation time > 10 s). The effects of the unusual molecular dynamics on the mechanical properties are discussed. The second part of this article deals with a re-investigation (by high resolution ~(13)C NMR) of packing structures of the α form of iPP. Two-Pulse Phase-Modulation decoupling during a rather long acquisition time results in significantly narrowed signals corresponding to ordered packing. The enhanced spectral resolution allows us to properly evaluate order-disorder phenomenon in polymer crystals. From CODEX experiments, lamellar thickness and packing orderapparently suppress helical jumps in the crystalline regions. These experiments provide valuable information on chain-level structures and dynamics, particularly on the variations in lamellae thickness as a function of supercooling.
机译：综述了最近的关于诸如全同立构聚（1-丁烯）（iPB1）和全同立构聚丙烯（iPP）的聚烯烃的结构和分子动力学的固态NMR研究。在iPB1中，熔融结晶导致形成亚稳态的II型，随后的固-固转变导致形成稳定的I型。〜1H-〜（13）C宽线分离（WISE）和中心带仅用于检测交换（CODEX）NMR技术提供了天然丰度下两种形式的整体和侧链分子动力学的几何和时间动力学参数。使用双自旋近似的〜1H线形分析和〜（13）C T_1结果表明，形式Ⅱ链伴随着在快速运动极限（相关时间<10〜（-7 ）s）。经过不可逆的固体转变后，〜（13）C CODEX结果表明，结晶茎和侧链构象已完全固定，直至熔点（相关时间> 10 s）。讨论了异常分子动力学对机械性能的影响。本文的第二部分将对iPP的α形式的堆积结构进行重新研究（通过高分辨率〜（13）C NMR）。在相当长的采集时间内，两脉冲相位调制去耦会导致信号明显变窄，与有序打包相对应。增强的光谱分辨率使我们能够正确评估聚合物晶体中的无序现象。根据CODEX实验，层状厚度和堆积顺序显然可以抑制结晶区域中的螺旋跳跃。这些实验提供了有关链级结构和动力学的有价值的信息，特别是有关薄片厚度随过冷度变化的信息。

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