Spectroscopic polymer characterization without polymers: Benchmarking quantum chemistry in the gas phase

真实的有机塑料的机械和热性能不仅取决于它们的化学成分，还取决于它们的预处理，这使得精确的理论建模具有挑战性。因此，为重要的聚合物类别创建理想化的桥头是有意义的，在那里理论和实验可以更容易和准确地相互比较。这对于对应于有限聚合物链段的短链分子是可能的。它们允许通过高灵敏度的振动光谱来推断拉伸无限长的链需要多大的力。它们还允许光谱检测临界链长，超过该临界链长，链间吸引力克服链刚度并导致发夹排列。这两个问题都在最丰富的聚合物聚乙烯（PE）的准备工作中得到了解决。聚乙烯以及最重要的水溶性聚合物聚乙二醇（PEG）的特定改性应以类似方式表征。为此，研制了一台灵敏度很高的气相拉曼光谱仪，并将其扩展到同时记录不同的光谱窗口。与精确和近似的量子化学计算的直接比较，应允许后者在机械和分子间性质方面的可靠评估。

The mechanical and thermal properties of real organic plastics depend not only on their chemical composition, but also on their pre-treatment, rendering an accurate theoretical modelling challenging. Therefore, it makes sense to create idealised bridgeheads for important polymer classes, where theory and experiment are more easily and accurately compared to each other. This is possible for short chain molecules which correspond to finite polymer segments. They permit to extrapolate via high sensitivity vibrational spectroscopy how much force is needed to stretch an infinite chain. They further allow to spectroscopically detect the critical chain length, beyond which inter-chain attraction overcomes chain stiffness and leads to hairpin arrangements. Both issues were addressed in preparatory work for the most abundant polymer polyethylene (PE). Specific modifications of polyethylene as well as the most important water soluble polymer polyethylene glycol (PEG) shall be characterized in an analogous way. For this purpose, a very high sensitivity gas phase Raman spectrometer was developed and shall be extended to the simultaneous recording of different spectral windows. The direct comparison with accurate and approximate quantum chemical calculations should allow for a reliable assessment of the latter in terms of mechanical and intermolecular properties.