关键词:  , 聚对苯二甲酸乙二醇酯（PET）, 低聚物, 超高效聚合物色谱, 光电二极管阵列检测器, 示差检测器, 组成

Abstract: Polyethylene terephthalate (PET) is widely used in textile fibers, packaging materials, industrial films and other fields because of its chemical stability, good resilience and high strength. The rapid development of polyester products in all walks of life has also worsened energy shortage and environmental pollution problems. Research on recycled polyester in recent years has contributed to sustainable development. However, oligomers contained in polyester materials can be migrated to fiber surface or deposited on the machine during the production process, affecting product performance and production efficiency. In this study, a method for determining the composition of oligomers in polyester was established, which provides a technical basis for further research on oligomers in recycled polyester. 
In this study, photo-diode array (PDA) and refractive index detector (RID) were connected in series on advanced polymer chromatography (APC) to analyze the mixture standard sample according to the principle of them, and the standard curve and linear equation of each composition oligomer were established by the external standard method. At the same time, we verified the feasibility of the method by repeating experiments. The oligomer content in recycled polyester and virgin polyester was calculated by the linear equation and compared to characterize the differences. It is found that more sensitive and accurate information can be obtained by selecting chromatography at the maximum absorption wavelength of 240 nm. According to the spectral information obtained by RID and PDA, the standard curves plotted have a good linearity within a certain range. It can be seen from the repeatability test that the method is stable and efficient, and is suitable for the detection of oligomers in PET. With the help of standard curve and linear equation, the content of each oligomer in the regenerated and virgin PET fibers was calculated, and it could be seen that the oligomer compositions in PET fibers include cyclic dimers, cyclic dimers containing a diethylene glycol, cyclic trimers…cyclic dodecamers and above. There are many oligomeric species that can be extracted by the one-step precipitation method. Cyclic trimer and cyclic tetramer are the main compositions of PET oligomers, with a relative content of about 60% and 17%, respectively. The total amount of oligomers contained in physically recycled PET is 22.64 mg/g, which is higher than that of virgin PET at 21.03 mg/g, and the total amount of oligomers in chemically recycled PET is 20.73 mg/g, which is lower than that of virgin PET. It is in accordance with the physical and chemical recovery processes. 
In this study, PDA was coupled with RID on APC to extract chromatogram information at 240 nm; the standard curve of each composition oligomer was ploted, so as to establish the quantitative detection method of oligomers in PET. The method is simple and efficient, with better stability. From the calculation results, it is clear that different recovery methods of PET affect its internal oligomer content. Therefore, for different product performance requirements, the selection of suitable PET recovery methods is crucial for its high quality.

Key words: oligomer, APC, PDA, RID, composition