凝胶渗透色谱-光散射联用表征聚合物摩尔质量的实验教学改革

doi:10.3724/SP.J.1123.2023.12005

摘要/Abstract

摘要：

凝胶渗透色谱-光散射(gel permeation chromatography-light scatting, GPC-LS)联用是目前最常用的表征聚合物摩尔质量的方法之一,具有灵敏度高、结果准确等特点,在科学研究与生产实践中得到了广泛应用。“凝胶渗透色谱-光散射联用表征聚合物摩尔质量”是《高分子物理实验》课程中一个重要的教学内容。然而,目前的GPC-LS实验教学内容简单,缺乏深度。本文在该实验项目原有内容的基础上进行扩充,重新设计出多套实验项目:(1)选取商品化的聚苯乙烯为实验样品,利用GPC-LS对其摩尔质量、摩尔质量分布以及回转半径等分子结构参数进行表征;(2)选取两种分子结构参数接近的聚丙烯腈样品,借助质量微分分布曲线揭示这两种样品在摩尔质量分布中的细微差别;(3)选取一系列不同摩尔质量的聚乙二醇为实验样品,通过比较其色谱图分析摩尔质量的高低对色谱峰的影响;(4)选取3种不同的聚合物(聚丙烯腈、聚甲基丙烯酸甲酯、聚β-环糊精)样品,借助构象图对其分子链的构象进行分析。此外,本文对实验教学方法进行了改革,将被动学习转变为主动学习,提高了学生的自主学习能力。通过本实验项目的教学改革探索,使学生能更加全面地理解凝胶渗透色谱-光散射联用的原理及应用,开拓了学生的知识视野,激发了学生的学习热情,提升了实验教学效果。

关键词: 凝胶渗透色谱-光散射联用, 验证性实验, 设计性实验, 教学改革

Abstract:

Gel permeation chromatography coupled with light scattering (GPC-LS) is among the most common methods for determining the molar masses of polymers. GPC-LS is widely used in polymer science research and has been adopted for many industrial applications owing to its high sensitivity, accuracy, and precision. The determination of polymer molar masses using GPC-LS is an important experimental component of the “Polymer Physics Experiments” course. However, the present GPC-LS experimental teaching content tends to be overly simplistic and lacking in depth. Herein, the original experimental content is expanded and multiple sets of experiments are redesigned: (1) Using commercial polystyrene as an experimental sample, the molar mass, molar mass distribution, radius of gyration, and other molecular structure parameters are determined using GPC-LS; (2) Using two polyacrylonitriles with similar molecular structure parameters, subtle differences in the molar mass distributions of the samples are explored using differential mass distribution curves; (3) By comparing the chromatograms of a series of polyethylene glycols with different molar masses, the effect of molar mass on chromatographic peaks is investigated; and (4) For three different polymers (polyacrylonitrile, poly(methyl methacrylate), and poly(β-cyclodextrin)), the polymer chain conformations are analyzed using conformation plots (i.e., radius of gyration vs. molar mass). In addition, the experimental teaching method is modified to convert passive learning into active learning, thereby improving the students’ self-directed learning ability. This experimental teaching reform will help students obtain a more comprehensive understanding of GPC-LS principles and applications, stimulate their enthusiasm for learning, and improve the teaching quality of the experimental course.

Key words: gel permeation chromatography coupled with light scattering (GPC-LS), confirmatory experiment, designing experiment, teaching reform

中图分类号:

O658

乔从德, 杨文轲, 李仲伟, 刘钦泽, 姚金水. 凝胶渗透色谱-光散射联用表征聚合物摩尔质量的实验教学改革[J]. 色谱, 2024, 42(8): 812-818.

QIAO Congde, YANG Wenke, LI Zhongwei, LIU Qinze, YAO Jinshui. Experimental teaching reform of polymer molar mass determination using gel permeation chromatography coupled with light scattering[J]. Chinese Journal of Chromatography, 2024, 42(8): 812-818.

图/表 7

图1 (a)聚苯乙烯样品的色谱图以及(b)光散射峰中某一级分的Zimm模式图

Fig. 1 (a) Chromatograms of polystyrene sample, and (b) Zimm plot for one data slice from the LS peak LS: light scatting detection; dRI: refractive index detection. Conditions: solvent, 0.05 mol/L LiBr in DMF; flow rate, 1.0 mL/min; column temperature, 60 ℃. Results: slice index, 354; model, Zimm; fit degree, 1; abscissa position, 11.725 min; mass concentration, 0.1565 mg/mL; molar mass, (4.691±0.007)×105 g/mol; radius of gyration, (22.5 ± 0.2) nm; dn/dc, 0.159 mL/g; R2= 0.9957.

图2 聚苯乙烯样品的(a)摩尔质量-洗脱时间及(b)回转半径-洗脱时间曲线

Fig. 2 Curves of (a) molar mass versus elution time and (b) radius of gyration versus elution time for polystyrene sample Conditions: solvent, 0.05 mol/L LiBr in DMF; flow rate, 1.0 mL/min; column temperature, 60 ℃.

表1 聚苯乙烯样品的GPC-LS测试项目及结果

Table 1 GPC-LS test items and results of polystyrene sample

Molecular structural parameter	Content	Result	Uncertainty
Molar mass moments/(g/mol)	M_n	1.686×10⁵	0.2%
	M_p	3.045×10⁵	0.1%
	M_w	2.959×10⁵	0.1%
	M_z	4.381×10⁵	0.3%
Polydispersity	M_w/M_n	1.755	0.2%
	M_z/M_n	2.599	0.4%
Radius of gyration/nm	R_gn	13.7	4%
	R_gw	17.9	2%
	R_gz	22.2	1%

图3 两种聚丙腈样品的(a)色谱图及其(b)质量微分分布曲线

Fig. 3 (a) Chromatograms and (b) differential weight fraction curves of two polyacrylonitrile (PAN) samples Conditions: solvent, 0.05 mol/L LiBr in DMF; flow rate, 1.0 mL/min; column temperature, 60 ℃.

图4 不同摩尔质量PEG的色谱图

Fig. 4 Chromatograms of polyethylene glycol with different molar masses Conditions: solvent, 0.1 mol/L NaNO3 and 0.2 g/L NaN3 in water; flow rate, 0.5 mL/min; column temperature, 35 ℃.

表2 不同摩尔质量PEG的测试结果

Table 2 Determination results of polyethylene glycol with different molar masses

Label M_w/(g/mol)	Determined M_w/(g/mol)	Uncertainty
1000	1260	13%
2000	2210	12%
4000	4450	12%
6000	7760	9%
10000	8130	10%
20000	17430	6%

图5 不同聚合物样品的回转半径与摩尔质量间的标度关系

Fig. 5 Scaling relationship between radius of gyration and molar masses for different polymer samples PMMA: polymethyl methacrylate; poly(β-CD): poly(β-cyclodextrin). Conditions: solvent, 0.05 mol/L LiBr in DMF; flow rate, 1.0 mL/min; column temperature, 60 ℃.

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