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对四个聚甲基丙烯酸甲酯级分用混合级分法分别进行淋洗柱分级和沉降速度法测定分子量分布的研究,以混合级分的分子量累积分布是否与单一级分累积分布的加和符合,作为分子量分布曲线绝对评价的判据.淋洗柱分级采用苯-甲醇体系,超速离心沉降在丙酮-乙醇体系的θ-温度附近测定.实验结果说明,混合级分的淋洗柱分级曲线与加和曲线比较,显得分子量分布偏窄,分子量小的部分低估,分子量大的部分高估;而用沉降速度法所得混合级分的分子量分布曲线则与加和曲线相符,因此可以用后法所得分子量分布曲线作为评价淋洗柱分级曲线的依据.可以认为淋洗柱分级曲线基本上真实反映试样的分子量分布,但是如用通常方法画出累积分布曲线,则使分布偏窄,对试样中高分子量尾端大大低估.因此如何用分级法分成较少的级分,而对分级数据作出更合理的处理,值得作进一步的研究.
The molecular weight distribution of four polymethylmethacrylate fractions were separated by leaching column and sedimentation velocity separately by mixed fraction method. Whether the cumulative molecular weight distribution of the mixed fraction was the sum of the cumulative distribution of single fraction As the criterion for the absolute evaluation of the molecular weight distribution curve.The leaching column was fractionated by benzene-methanol system and the ultracentrifugation was measured near the θ-temperature of the acetone-ethanol system.The experimental results showed that the leaching column gradation curve Compared with the addition curve, it appears that the molecular weight distribution is narrow, the molecular weight is underestimated, and the molecular weight is overestimated. However, the molecular weight distribution curve of the mixed fraction obtained by the sedimentation rate method is consistent with the additive curve. Therefore, The obtained molecular weight distribution curve is used as the basis for evaluating the leaching column grading curve. It can be considered that the leaching column grading curve basically reflects the molecular weight distribution of the sample. However, if the cumulative distribution curve is drawn by the usual method, the distribution is narrow. The end of high molecular weight sample is greatly underestimated, so how to use the grading method is divided into fewer fractions, while the grading data to make a more reasonable treatment, it is worth Further studies.