Polymer Characterization by On-Line GPC/NMR

(1)利用凝胶峰化色谱仪与~1H核磁共振波谱仪联用(在线GPC/核磁共振)分析了M_n为3.27×10~(-3)~2.22×10~(^4)的全同立构PMNAs的分子量分布。流动洗脱液中聚合物的相对分子质量是由端基和重复单元引起的核磁共振信号的相对强度直接测定的(不需要常规的校准程序)。由23、40和80个重复单元组成的均匀等规聚甲基丙烯酸甲酯的SEC-核磁共振实验证明，用这种方法测定的分子量分布是准确的。此外，还对GPC/核磁共振定量测量的流速和核磁共振参数进行了优化研究。在相同条件下，750MHzGPC/…谱的信噪比是500MHzGPC/NMR谱的9.2倍。(2)用750MHzGPC/NMR法研究了三元乙丙橡胶的化学组成通过监测三元共聚物样品中的CH_2和CH_3共振得到的色谱图的比较清楚地表明乙烯/丙烯比是摩尔质量的函数。测定采用连续流动洗脱液(氯仿-d，0.2mL/min)。(3)用750MHzGPC/NMR研究了均质同立构(mm=100%)和间同立构(rr=98%)46聚甲基丙烯酸甲酯之间的立体络合反应.在丙酮/丙酮-d_6(95/5)中，st-46mer和it-46聚(st-/it-=0.61)的混合物在-15ﾟC下放置24小时，然后进行凝胶渗透色谱/核磁共振测量(柱温-15ﾟC；探头温度，45ﾟC)。除了非络合46聚体的洗脱峰外，在色谱图的高相对分子质量区域还观察到一个由立体络合物产生的峰。通过监测It-OCH3和St-OCH3的共振峰记录的GPC曲线清楚地表明，非络合物部分主要由It-46mer组成，立体络合物部分的st/it比为1.5~1.7。当探针温度调整到柱温(-15ﾟC)时，由于链段迁移率的损失，在立体络合物部分的凝胶渗透色谱/核磁共振光谱中没有观察到-46mer的共振。较少

(1) A gel peameation chromatograph coupled to a ^1H NMR spectrometer (on-line GPC/NMR) was used to analyze molecular weight distributions of isotactic PMNAs with M_n ranging from 3.27*10^3 to 2.22*10^4. The molecular weight of the polymer in flowing eluate was determined directly (without a conventional calibration procedure) from the relative intensity of NMR signals due to the end-group and repeating units. The molecular weight distribution determined in this manner was proved to be accurate by SEC-NMR experiments on uniform isotactic PMMAs consisting of exactly 23,40, and 80 repeating units. Investigation was also undertaken to optimize flow rate and NMR parameters for quantitative GPC/NMR measurements. The signal-to-noise ratio of 750 MHz GPC/NMR spectra was 9.2 times that obtained previously with 500 MHz GPC/NMR operated under similar conditions.(2) Chemical compositions in ethylene-propylene- (2-ethylidene-5-norbornene) terpolymers (EPDM) were investigated by 750 MHz on-line GPC/ … More NMR.Comparison of the chromatograms obtained by monitoring the CH_2 and CH_3 resonances in a terpolymer sample showed clearly the ethylene/propylene ratio as a function of molar mass. The measurements were carried out with continuous flow of eluent (chloroform-d, 0.2mL/min). Molar mass dependence of a small amount (0.6-1.1mol%) of 2-ethylidene-5-norbornene units in a terpolymer was determined by GPC/NMR using the stop-and-flow technique.(3) Stereocomplexation between uniform isotactic (mm=100%) and syndiotactic (rr=98%) 46mers of MMA was studied by 750 MHz on-line GPC/NMR.A blend of st-46mer and it-46mer (st-/it-=0.61) in acetone/acetone-d_6 (95/5) was allowed to stand at -15ﾟC for 24h, and then subjected to the GPC/NMR measurements (column temp., -15ﾟC ; probe temp., 45ﾟC). Besides the elution peak due to non-complexed 46mers, a peak due to stereocomplex was observed at a high MW region in the chromatogram. The GPC curves recorded by monitoring it-OCH_3 and st-OCH_3 resonances showed clearly that the non-complexed part consisted essentially of it-46mer and st-/it- ratio in the stereocomplex part was 1.5 to 1.7. When probe temperature was adjusted to the column temperature (-15ﾟC), no resonance due to it-46mer was observed in the GPC/NMR spectra of the stereocomplex part because of the loss of segmental mobility. Less