Viscosity studies of certain alkyl phosphates and their aqueous mixtures

Abstract

critical limits of solubility limited by the temperatures 27.9 and 830°C and by the concentrations 34.7 and 73.7 wt %, respectively. The determination of solubility using two methods (cloud point and refractometry) has given identical results except for the methylvinylketone phase a t higher temperatures (refer to Figure 1, hatched section) where the refractometer (circles) indicated a higher methylvinylketone content and therefore a lower water solubility in the methylvinylketone phase. Although measurements by the cloud point method are commonly more accurate (it is possible to weigh the samples into the sealed test tubes very precisely by differential weighing, the lower limit of turbidity detection is less than 0.1), i t is less suitable than refractometry for this particular system because of the polymerization activity of the methylvinylketone. Even with 0.05 w t % of diethylhydroxylamine added as stabilizer, a partial polymerization occurs a t higher temperatures, as the sample is exposed to the influence of heat and light a rather long time (on the order of several hours). Since polymers affect the cloud point considerably, even in small amounts, the authors tend to the opinion that the refractometric method of determination gives more truthful results. The same concentration of polymers affects the change of cloud point more than the refractive index of the mixture. Besides, the possibility of an error in the refractometric method was decreased by changing the samples for each temperat,ure measurement, and the calibration measurements were made with mixtures containing only pure methylvinylketone without polymers.