Waseda University , Consolidated Research Institute for Advanced Science and Medical Care, 513 Wasedatsurumaki-cho, Shinjuku-ku, Tokyo 162-0041, Japan.
Anal Chem. 2017 Mar 7;89(5):3043-3050. doi: 10.1021/acs.analchem.6b04750. Epub 2017 Feb 17.
We have recently demonstrated a methodology to estimate the percent crystallinity (PC) of polymers directly with Raman spectroscopy and multivariate curve resolution (MCR) by alternating least-squares (ALS). In the MCR-ALS methodology, the Raman spectrum of a semicrystalline polymer is separated into two constituent components (crystalline and molten/amorphous) and their corresponding concentrations. The methodology necessitates that the Raman spectrum at any temperature be a linear combination of two MCR spectral components (one molten and one crystalline). This is true in the case of simple systems such as crystalline pendant alkyl domains in polymers (Samuel et al. Anal. Chem. 2016, 88, 4644). However, in the case of main chain polymer crystals (e.g., polyethylene), the situation can be complicated owing to several molecular changes in the lattice in addition to conformational reorganizations during melting. Under this circumstance, a simple two-state model may not be adequate and we describe the modifications required to treat such systems, keeping the basic principles of the proposed methodology unchanged. A comparative study with wide-angle X-ray scattering (WAXS) and Raman spectroscopy is also performed to substantiate our findings. In addition to estimating percent crystallinity (PC), our methodology is capable of revealing additional information, such as interchain interactions in crystal lattice, that in principle will help distinguishing polymorphic transformations, subtle changes in lamellar lattice dimensions, and other phase changes in polymers.
我们最近展示了一种通过交替最小二乘法（ALS）的拉曼光谱和多元曲线分辨（MCR）直接估计聚合物结晶度（PC）的方法。在 MCR-ALS 方法中，半晶态聚合物的拉曼光谱被分离成两个组成部分（结晶和熔融/无定形）及其相应的浓度。该方法要求任何温度下的拉曼光谱都是两个 MCR 光谱分量（一个熔融和一个结晶）的线性组合。对于简单的系统，如聚合物中的结晶侧基烷基域（Samuel 等人，分析化学，2016 年，88 年，4644），这是正确的。然而，在主链聚合物晶体的情况下（例如，聚乙烯），由于晶格中的几个分子变化以及熔融过程中的构象重排，情况可能会变得复杂。在这种情况下，简单的两态模型可能不够充分，我们描述了处理此类系统所需的修改，同时保持所提出方法的基本原则不变。还与广角 X 射线散射（WAXS）和拉曼光谱进行了比较研究，以证实我们的发现。除了估计结晶度（PC）之外，我们的方法还能够揭示额外的信息，例如晶格中的链间相互作用，这原则上将有助于区分多晶型转变、层状晶格尺寸的细微变化和聚合物中的其他相变化。
