激光小角光散射测定高聚物的分子量

本工作建议了一种比较方便可行的、用已知瑞利因子的溶剂标定激光小角散射光度计的方法。纯溶剂的瑞利值R_θ与其散射强度比(G_θ/G_0)有如下关系:R_θ/n=φ(G_θ/G_0)-δ],式中n为溶剂折光指数;φ为仪器常数;δ为与背景有关的参数。以已知瑞利值的甲苯、苯、环己烷、氯仿及四氯化碳的R_θ/n对测定的(G_θ/G_0)值作图,得到了较好的线性关系,从直线斜率可定φ值。以此方法标定的仪器测定了十个聚苯乙烯窄分布试样均得到了满意的结果。

DETERMINATION OF MOLECULAR WEIGHT OF POLYMER BY LOW ANGLE LASER LIGHT SCATTERING

Low angle laser light scattering is a useful method for the measurement of molecular weight of polymer. In this work a convenient calibration method has been devised by using pure organic liquids of known Rayleigh factors to evaluate the instrument constant and the background simultaneously for a low angle laser light scattering photometer made in our laboratory.Considering the major background comes from the light scattered in the cell and the probability of stray light passing through the field stop is small, the Eayleigh factor may be rewritten as Rθ/n=φ(Gθ/G0)-δ] for small scattering angles, where Gθ, G, are electrical signals propotional to the radiant power in the direction φ and in the direction of incident beam respectively, n is reflective index of liquid, δ is a factor related to the background, φ is an instrument constant. A linear relationship is obtained from the plot of Rθ/n vs (Gθ/Gθ) of the pure liquids such as toluene, benzen, cyclo-hexane, carbon tetrachloride and chloroform used for calibration. The slope of the straight line is φ and the intercept φδ is related to background. Performance of this instrument and the calibration method has been evaluated by measuring ten polystyrene samples of narrow MWD and good results were obtained.