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粘度法测定高聚物的特性粘数,一般是由η_(sp)/c或hlη_r/c对c作图,外推至→0求得。此法手续烦琐而费时。梅朗(S.H.Maron)提出了以下公式[η]=(η_(sp)-γlnη_r)/((1+r)c) (1)以计算高聚物的特性粘数。在给定高聚物——溶剂体系中,γ是与高聚物分子量无关的常数,也就是,每种高聚物—溶剂体系有一个确定的γ值。如果在给定体系中,测得高聚物一个样品的γ值,此值即可用于同一高聚物的不同分子量样品的特性粘数的计算中。梅朗测得聚苯乙烯—甲苯体系在30℃和醋酸纤维素—丙酮体系在25℃时的γ值分别为2.73和5.33,以此二值分别代入式(1),计算得到的特性粘数值的误差在要求的范围之内。我们采用此法测定聚氯乙烯的特性粘数,确定聚氯乙烯—环已酮体系在25℃时其γ值为2.21。测得不同浓度的聚氯乙烯环已酮溶液的η_(sp)和lnη_r,以此γ值(2.21)代入式(1)计算得到的特性粘数值与其外推值列于下表。
Viscosity method for the determination of the intrinsic viscosity of polymers, generally by η sp / c or hlη_r / c mapping of c, extrapolated to → 0 obtained. This procedure is cumbersome and time-consuming. S.H.Maron proposed the following equation [η] = (η_ (sp) -γlnη_r) / ((1 + r) c) (1) to calculate the intrinsic viscosity of the polymer. In a given polymer-solvent system, γ is a constant unrelated to the molecular weight of the polymer, that is, each polymer-solvent system has a defined γ value. If, in a given system, the gamma value of a sample of a polymer is measured, this value is used to calculate the intrinsic viscosity of different molecular weight samples of the same polymer. Melan measured the polystyrene-toluene system at 30 ℃ and cellulose acetate - acetone system at 25 ℃ when the γ values were 2.73 and 5.33, respectively, the two were substituted into equation (1), the calculated intrinsic viscosity value The error is within the required range. We use this method to determine the inherent viscosity of polyvinyl chloride, PVC - cyclohexanone system was determined at 25 ℃ its γ value of 2.21. Measured η 2 (sp) and ln η_r of different concentrations of cyclohexyl ketone solution of polyvinyl chloride, the γ value (2.21) substituted into equation (1) calculated intrinsic viscosity values and their extrapolated values are shown in the following table.