Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA.
Appl Spectrosc. 2021 Aug;75(8):963-970. doi: 10.1177/00037028211014165. Epub 2021 May 27.
A pair of attenuated total reflection infrared (ATR IR) spectra obtained during the crystallization of bioplastic copolymer poly[(R)-3-hydroxybutyrate--(R)-3-hydroxyhexanoate] or PHBHx from the melt by spontaneous cooling were examined using the two-trace two-dimensional correlation spectroscopy (2T2D-COS) analysis. Unlike conventional difference spectra, 2T2D spectra showed unexpected details for the patterns of spectral intensity changes, clearly revealing the existence of two distinct populations of crystalline contributions, attributed to the well-ordered primary crystals and the less ordered secondary crystals, in addition to the amorphous component. The 2T2D spectrum sorts out highly overlapped bands associated with different constituents of the system, based on the fundamental properties and constraint imposed on a pair of spectra. Hetero-mode asynchronous 2T2D correlation analysis between the congested CH-stretching region and better resolved carbonyl-stretching region further indicates that the increase in the intensities of certain methyl and methylene bands during the crystallization process is mostly associated with the growth of the well-ordered primary crystals of PHBHx instead of the formation of the secondary crystals in the confined inter-lamellar space.
采用双迹二维相关光谱（2T2D-COS）分析研究了熔体中非晶热塑性共聚酯聚[(R)-3-羟基丁酸-(R)-3-羟基己酸酯]（PHBHx）在自发冷却结晶过程中获得的一对衰减全反射红外（ATR IR）谱。与常规差谱不同，2T2D 谱显示出光谱强度变化模式的意想不到的细节，清楚地揭示了除无定形成分外，还存在两种不同的晶区贡献，分别归因于有序的初生晶体和无序的次生晶体。2T2D 谱基于对一对谱的基本性质和约束，对与体系不同组成部分高度重叠的谱带进行了分类。在拥挤的 CH 伸缩区域和分辨率更好的羰基伸缩区域之间进行的异模态非同步 2T2D 相关分析进一步表明，结晶过程中某些甲基和亚甲基谱带强度的增加主要与 PHBHx 的有序初生晶体的生长有关，而不是在受限的层间空间中形成次生晶体。
