Experiments for the determination of molecular weight distribution by turbidimetric measurements

✍ Scribed by J. Springer; K. Ueberreiter; W. Weinle

• Publisher: Elsevier Science
• Year: 1970
• Tongue: English
• Weight: 334 KB
• Volume: 6
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(70)90188-6

✦ Synopsis

Disadvantages of turbidity measurements obtained by adding a non-solvent can be avoided by a precipitation with programmed decrease of the temperature. Turbidimetric curves for samples of polystyrene of different distribution and tool wt. were recorded by means of the method involving decrease of the temperature in methylcyclohexane. The tool. wt. distribution of samples was determined by fractional precipitation. The partial concentration of the high molecular portion governs the appearance of the first traces of turbidity, and not the average tool. wt. The concentration of solutions and the cooling rate were chosen in such a way that the maximum turbidity remained constant and independent of the cooling rate. This could be performed for concentrations up to I "5.10 -3 [.g cm -a ] and cooling rates of 1-4-0-5[deg min-1]. A relation exists between the homogeneity E = M,,/Mo and a parameter ~¢ of the turbidity curves E = m exp(n 5), in which m and n are dependent constants for the system investigated (5 = A~-/,m,,; ~-=,, = maximum turbidity; AT = ,rso._s.--*rso.+s.; Tso is the temperature of 50 per cent maximum turbidity).