APC-MALLS法测定聚酰胺相对分子质量及其分布

Determination of relative molecular mass and its distribution of polyamide by APC-MALLS

以5mmol/L的三氟乙酸钠的六氟异丙醇溶液为溶剂及流动相,采用超高效聚合物色谱-多角度激光光散射仪-示差折光仪检测器,在色谱柱为ACQUITY APC XT 450,200,125,柱温55℃,检测器温度25℃,流动相流速0.5 mL/min,进样量为50μL的条件下,测定聚酰胺6（PA 6）、聚酰胺66（PA 66）的相对分子质量及其分布,探讨了折光指数增量（dn/dc）,试样浓度对测试结果的影响.结果表明：PA 6,PA 66的dn/dc分别为（0.260 3 ±0.009 3）mL/g,（0.243 9 ±0.003 8）mL/g,质量浓度均为2·10^-3 g/mL时,在色谱操作条件下,测得PA 6,PA 66数均相对分子质量分别为20 100,19 100,重均相对分子质量分别为31 400,27 800,相对分子质量分布宽度平均值为1.56,1.46,6次测量的变异系数分别为1.96％,2.26％,试样洗脱峰出现时间均为4.5 ～9 min;该方法重复性和准确性较好,可大幅度缩短测试时间.

The relative molecular mass and distribution of polyamide 6 （ PA 6） and polyamide 66 （ PA 66） were determined by an advanced polymer chromatography-multi-angle laser scattering-refractive index detector with the chromatographic columns of ACQUITY APC XT 450, 200,125 using hexafluoroisopropyl alcohol solution containing 5 mmol/L sodium trifluoroacetate as the solvent and mobile phase under the conditions of column temperature 55 ℃, detector temperature 25 ℃, mobile phase flow rate 0.5 mL/min, injection volumn 50 μL. The effects of the refractive index increment （ dn/dc ） and sample concentration on the determination results were discussed. The results showed that the number-average relative molecular mass of PA 6 and PA 66 was determined as 20 100 and 19 100, the weight-average relative molecular mass as 31 400 and 27 800, the average width of relative molecular mass distribution as 1.56 and 1.46, respectively, under the above chromatographic operation conditions when dn/dc of PA 6 and PA 66 was （0. 260 3 ±0. 009 3） mL/g and （0.243 9 ±0.003 8） mL,/g, respectively, and the mass concentration was both 2 ·10^-3 g/mL; the coefficient of variation for 6 - time measurement was 1.96% and 2.26% of 6 - time, respectively for PA 6 and PA 66, but the elution peaks both appeared in 4.5 - 9.0 min; and this method possessed fairly good repeatability and accuracy and considerably shortened the determination time.