Spatially-Resolved Polymer Degradation Via Electron Spin Resonance Imaging (ESRI)

该奖项旨在研究在空气和臭氧/空气混合物存在下，由于紫外线照射和热处理而导致的聚合物降解。 将对含有受阻胺稳定剂（HAS）作为保护添加剂的聚合物进行拟议的研究。 研究的主要方法是对降解过程中形成的氮氧自由基和其他自由基中间体进行电子自旋共振成像（ESRI）。 空间信息将通过在磁场梯度存在下收集ESR谱而编码在光谱中。 1D ESRI将提供自由基强度的空间分布，2D空间光谱ESRI将允许沿样品深度沿着的线形可视化。 实验将作为处理时间、UV源波长和热降解温度的函数进行。 将通过自旋探针ESR、UV、FTIR和差示扫描量热法（DSC）获得其他信息。 将对两类聚合物进行光降解和热降解：1.以苯乙烯、丙烯腈和丁二烯为基料的聚合物，作为均聚物和以不同组合形式作为共聚物。 这一组将包括共聚物聚（苯乙烯-共-丁二烯）、聚（丙烯腈-共-丁二烯）和聚（苯乙烯-共-丙烯腈）以及聚（丙烯腈-丁二烯-苯乙烯）（ABS）。 2.聚丙烯和乙烯的共聚物通过顺序聚合制备。 这些聚合物由半结晶聚丙烯（PP）基质和分散的无定形弹性体组分组成，并具有相分离形态;这些系统的研究将受益于有关聚丙烯降解的丰富文献，但也会带来挑战和优点通过添加弹性体相来改性。 与目前用于探测空间维度的其他（破坏性）方法相比，通过ESRI执行非破坏性分析的能力是一个重要的优势。%预计拟议的研究将：确定降解过程加速的特定形态域;绘制样品深度内mm尺度和微米尺度形态域内稳定剂的消耗图，有助于理解环境因素，例如照射波长和臭氧的影响;并导致非破坏性光谱分析作为用于检测聚合物降解和稳定化中的早期事件的方法。

This award is directed to the study of polymer degradation due to UV irradiation and thermal treatment in the presence of air and ozone/air mixtures. The proposed studies will be performed on polymers containing hindered amine stabilizers (HAS) as protecting additives. The main method of study is electron spin resonance imaging (ESRI) of nitroxides and other radical intermediates formed in the degradation process. Spatial information will be encoded in the spectroscopy by collecting ESR spectra in the presence of magnetic field gradients. 1D ESRI will provide the spatial distribution of the radical intensity, and 2D spatial-spectral ESRI will allow visualization of the line shapes along the sample depth. The experiments will be performed as a function of treatment time, wavelength of the UV source, and temperature in thermal degradation. Additional information will be obtained by spin probe ESR, UV, FTIR, and differential scanning calorimetry (DSC). Photo- and thermal degradation will be performed on two classes of polymers: 1. Polymers based on styrene, acrylonitrile and butadiene, as homopolymers and in different combinations as copolymers. This group will include the copolymers poly(styrene-co-butadiene), poly(acrylonitrile-co-butadiene) and poly(styrene-co-acrylonitrile), and poly(acrylonitrile-butadiene-styrene) (ABS). 2. Copolymers of polypropylene and ethylene prepared by sequential polymerization. These polymers consist of a semicrystalline polypropylene (PP) matrix and a dispersed amorphous elastomeric component, and have a phase-separated morphology; the study of these systems will benefit from the rich literature available on polypropylene degradation, but will present the challenge and advantage of properties modification by addition of the elastomer phase. The ability to perform nondestructive profiling via ESRI is an important advantage compared to other (destructive) methods now in use for probing the spatial dimension.%%%The proposed research is expected to: identify specific morphological domains where the degradation process is accelerated; map the consumption of the stabilizer within the sample depth on the scale of mm, and within the morphological domains on the scale of micrometers, contribute to the understanding of environmental factors, for instance the effect of irradiation wavelength and ozone; and lead to nondestructive spectral profiling as a method for the detection of early events in polymer degradation and stabilization.