Journal of Textile Research ›› 2026, Vol. 47 ›› Issue (05): 81-90.doi: 10.13475/j.fzxb.20250900201

• Fiber Materials • Previous Articles     Next Articles

Determination of oligomers in polyamide 66 by ultra-high performance liquid chromatography

MO Hailing1,2, LIU Ke1,2, DAI Junming2, LÜ Wangyang1,2()   

  1. 1 State Key Laboratory of Bio-based Fiber Materials, Zhejiang Sci-Tech University, Hangzhou, Zhejiang 310018, China
    2 Zhejiang Provincial Innovation Center of Advanced Textile Technology, Shaoxing, Zhejiang 312030, China
  • Received:2025-09-01 Revised:2026-03-11 Online:2026-05-15 Published:2026-07-10
  • Contact: Lü Wangyang E-mail:luwy@zstu.edu.cn

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Abstract:

Objective As the influence of oligomers on material properties remains insufficiently understood, their accurate quantification is crucial for evaluating performance, optimizing polymerization, and enhancing quality control. The objective of this study is to develop a reliable analytical method for identifying and quantifying oligomers (C1-C5) in polyamide 66 (PA66). This method provides essential data for process monitoring and helps elucidate structure-property relationships, thereby supporting improved product consistency and advanced manufacturing standards in the polyamide industry.

Method Oligomers were extracted from PA66 using a dissolution-precipitation method. Separation was achieved by preparative liquid chromatography (Prep-LC), followed by qualitative analysis using liquid chromatography-time-of-flight mass spectrometry (LC-TOF-MS). Quantitative determination of C1-C5 oligomers was performed using ultra-high performance liquid chromatography (UPLC) with purified oligomer standards.

Results A highly efficient method for extracting, separating, and quantifying PA66 oligomers was successfully established. Low-molecular-weight oligomers were effectively extracted from PA66 chips using a dissolution-precipitation method. Based on LC-TOF-MS analysis with high-accuracy mass measurement (mass error < 5×10-3 u) and characteristic fragment ion patterns, cyclic and linear oligomers ranging from monomer to hexamer (C1-C6) were clearly identified. After optimizing the liquid chromatographic conditions, a rapid UPLC quantitative method was established and validated. All five target cyclic oligomers (C1-C5) exhibited excellent linearity within the concentration range of 0.008-0.1 g/L (R2 >0.99). The method demonstrated high precision and reliability, with intra-day and inter-day relative standard deviations (RSD) for peak area and retention time below 2.0% and 3.0%, respectively. The analysis time was shorter than 20 min for each sample, significantly improving throughput compared to conventional techniques. When applied to industrial PA66 chip and fiber samples, the total extractable oligomer content was measured to range from 1.2% to 1.6% by mass, with cyclic oligomers accounting for more than 90% of this fraction. The total oligomer content in fiber samples (average 1.388%) was consistently lower than that in their corresponding precursor chips (average 1.483%), indicating possible migration or further condensation of oligomers during the melt-spinning process. Detailed compositional analysis provided species-specific concentration data, revealing that the cyclic monomer and dimer were the most abundant components. The approach offers a robust solution for monitoring oligomer content, providing detailed compositional insights that are critical for evaluating polymerization efficiency and product consistency.

Conclusion This study established a UPLC-based method for the separation and quantification of PA66 oligomers, integrating preparative LC, UPLC-PDA, and LC-TOF-MS. Different from the conventional method for determining the total oligomer content, the method successfully separated and quantified five cyclic oligomers. Quantification was achieved by monitoring at 200 nm and using mixed-standard calibration curves, demonstrating high efficiency, reproducibility, and superior performance over existing methods. Applied to commercial PA66 chips and fibers, the measured oligomer ranges aligned with typical industrial levels, and the observed content differences between physical forms provide a basis for optimizing polymerization and processing formulations. The developed method enables rapid, accurate, and reproducible quantification of PA66 oligomers. It offers significant practical value for quality assurance in industrial production settings. By facilitating precise monitoring of oligomer levels, this approach supports process optimization and helps enhance the final material properties of PA66. Future applications may include monitoring and extended adaptation to other polyamide types.

Key words: polyamide 66, oligomer, ultra-high performance liquid chromatography, dissolution-precipitation method, quantitative analysis, liquid chromatography-time of flight mass spectrometry

CLC Number: 

  • TS102.5

Tab.1

Ultra-high performance liquid chromatography elution procedures"

时间/min 体积分数/%
流动相A 流动相B
0 95.0 5.0
7.0 60.0 40.0
7.5 10.0 90.0
8.5 4.0 96.0
10.0 95.0 5.0
12.0 95.0 5.0

Tab.2

Preparative liquid chromatography elution procedures"

时间/
min		 流速/
(mL·min-1)		 体积分数/%
流动相A 流动相B
1.84 20 95.0 5.0
8.50 20 70.0 30.0
8.60 10 66.0 34.0
9.40 10 58.0 36.0
9.50 20 60.0 40.0
10.00 20 95.0 5.0

Tab.3

Mass spectrometry parameters of PA66 oligomers"

名称 分子式 保留时间/min 理论质荷比 实际质荷比 加合离子类型 绝对质量误差/u
C1 C12H22N2O2 4.06 249.165 7 249.163 7 [M+Na]+ 2.0×10-3
L2 C24H46N4O5 4.36 471.354 6 471.357 2 [M+H]+ -2.6×10-3
C2 (C12H22N2O2)2 5.67 475.326 0 475.326 0 [M+Na]+ 0.0×10-3
L3 C36H68N6O7 5.27 697.522 8 697.527 3 [M+H]+ -4.5×10-3
C3 (C12H22N2O2)3 6.41 701.494 2 701.494 4 [M+Na]+ -0.2×10-3
L4 C48H90N8O9 5.89 923.690 9 923.689 1 [M+H]+ -1.8×10-3
C4 (C12H22N2O2)4 6.81 927.662 3 927.664 0 [M+Na]+ -1.7×10-3
L5 C60H112N10O11 6.30 1 149.859 0 1 149.862 9 [M+2H]2+ -3.9×10-3
C5 (C12H22N2O2)5 7.09 1 153.830 4 1 153.831 3 [M+2Na]2+ -0.9×10-3
L6 C72H134N12O13 6.65 1 375.019 3 1 375.018 3 [M+2H]2+ 1.0×10-3
C6 (C12H22N2O2)6 7.29 1 379.998 5 1 379.997 1 [M+2Na]2+ 1.4×10-3

Fig.1

Oligomers liquid chromatogram extracted by different methods.(a)Oligomers extracted by dissolution-precipitation method; (b)Oligomers extracted by Soxhlet extraction method"

Fig.2

Influence of solvent type on oligomer content in PA66.(a) Liquid chromatograms of FA and HFIP; (b) Statistical analysis results of peek areas of C4 and C5"

Fig.3

Influence of formic acid volume on extraction efficiency of PA66 oligomers"

Fig.4

Influence of injection volume on PA66 oligomer content"

Fig.5

Chromatograms of cyclic oligomers at different wavelengths"

Fig.6

Ultraviolet absorption spectra of partial PA66 cyclic oligomers"

Tab.4

Linear regression equations and coefficients of determination for PA66 cyclic oligomers"

低聚物组分 线性方程 决定系数(R2)
C1 y=9 502 618.92 x + 3 516.14 0.999 6
C2 y=9 184 837.75 x + 3 290.22 0.999 6
C3 y=9 091 985.62 x + 3 225.33 0.999 6
C4 y=6 846 781.39 x + 1 419.33 0.999 3
C5 y=6 079 394.52 x + 398.68 0.994 8

Fig.7

Spectra of oligomer PDAs with repeated injections"

Tab.5

Test results of parallel samples of each cyclic oligomer content in PA66"

低聚物
组分		 环状低聚物含量/% 相对标准
偏差/%
试样1 试样2 试样3
C1 0.372 0.376 0.373 1.951
C2 0.483 0.486 0.488 1.249
C3 0.308 0.307 0.310 0.686
C4 0.288 0.275 0.272 0.868
C5 0.146 0.142 0.145 1.379

Tab.6

Test results of oligomer contents in different samples of PA66"

样品 环状低聚物的含量/% 总含量/%
C1 C2 C3 C4 C5
PA66切片1 0.435 0.521 0.345 0.263 0.100 1.664
PA66切片2 0.366 0.476 0.307 0.260 0.105 1.514
PA66切片3 0.321 0.375 0.248 0.189 0.073 1.206
PA66切片4 0.344 0.410 0.274 0.209 0.085 1.323
PA66切片5 0.332 0.409 0.295 0.219 0.081 1.336
自制PA66切片 0.353 0.469 0.314 0.224 0.122 1.483
自制PA66纤维 0.304 0.445 0.298 0.232 0.108 1.388
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