February 15, 1942
ANALYTICAL EDITION
bons used in this work, and for supplying certain data regarding these carbons.
( l ) Andress,
Literature Cited K*, and Berl* E*, z' physik' Chem', 122, 81
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Z . angew. Chem., 35, 722 (1922). (2) Bell, S. H., and Philip, J. C., J . Chem. SOC.,1934, 1164. (3) Berl, E., and Herbert, W., Z . angew. Chem., 43, 904 (1930). (4) Burstin, H., and Winkler, J., Przemysl Chem., 13, 114 (1929).
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(6) Fieldner, A. C., Oberfell, G. G., Teague, 12. C., and Lawrence, J. N., Ihid.. 11. 524 11919). (7) Herbst, H.. kolloid 2.,'38, 314 (1926). (8) Macy, R., J . P h y s . Chem., 35, 1397 (1931). (9) Pearce, J. N., and McKinley, L., Ihid.,32, 360 (1925). and Rowe,-4.W., J , 4 1 n , Chem, so,., 44, 684 (10) Richards,T.w-., (1922). PRESENTED before the Division of dnalvtical and Micro Chemistrv a t t h e 102nd Meeting of the AXERICAN CHEMICAL SOCIETY, .itlantic City, N J.
Turbidimetric Determination of Polymerized Hydrocarbons in Solution BASSETT FERGUSON, JR., AND MARK D. SNYDER, Ugite Sales Corporation, Chester, Penna.
I
X DEALING with unsaturated hydrocarbons subject to polymerization it is frequently necessary to determine the polymer content in a solution of the monomer. As the polymer is usually relatively high boiling, the monomer may be flash-distilled under vacuum and the residue weighed and considered polymer. This method is more or less inaccurate, especially for small quantities of polymer. Some users of these materials have empirical specifications for maximum polymer content based on the insolubility of the polymer in methanol or petroleum naphtha. If a given dilution of the sample with one of these solvents does not produce a distinct cloud of precipitate, the polymer content may be assumed to be below the predetermined value. No mention has been found in the literature, however, of extending this principle to give an accurate analytical method. To obtain a rapid and accurate analytical method for the analysis of polystyrene in solution of styrene and other aromatics, the dilutions for maximum sensitivity of the sample with methanol and petroleum naphtha were determined. It was found that two parts of absolute methanol added to one part of sample will give a distinct cloud when 0.0005 per
cent of polymer is present in the original sample, and nine parts of Atlantic Refining Co.'s S o . 44 naphtha added to one part of sample will give a distinct cloud when 0.005per cent of polymer is present. Furthermore, at these dilutions the effect on the polymer solubility of small changes in temperature is small. Analyses are normally performed at a room temperature of 20" to 25" C., but it' was found that differences in results are negligible betn-een 15" and 30" C. Using these optimum dilutions, a set of standards \vas made up covering t'he range of 0.0005 to 0.3 per cent polymer direct'ly. Higher polymer contents could be measured by first diluting the sample 10 to 1 or 100 to 1 with xylene. As had been feared, hon-ever, the standards containing the higher polymer concentrations deteriorated in a fen- weeks' time, owing to the settling of the precipit'ated polymer. Some means of measuring the turbidity vias then sought. Measurement of the height of a column of the liquid through which fine print could be read (as used in the kauri-butanol test) was tried, but great differences were found between different operators' ability to distinguish the fine print through the turbid liquid. A Burgess-Parr sulfur turbidimeter (Arthur H. Thomas Co. catalog No. 9334) proved to be a satisfactory instrument for the measurement. A column of liquid is placed above an incandescent filament of standard (adjustable) intensity and a movable tube dipping into the liquid indicates the point of extinction of the filament by the turbid liquid. Figure 1 shows per cent of polymer corresponding t o turbidimeter readings for 2 t o 1 methanol dilution and 9 to 1 S o . 44 naphtha dilution. For low polymer concentrations, 200 ml. of absolute methanol are added t o 100 ml. of sample in a stoppered cylinder and mixed by inverting several times. After 15 minutes the mixture is poured into the turbidimeter and a reading is taken using 0.5 or 1 volt on the filament, depending on the turbidity. For somewhat higher polymer concentrations, 180 ml. of S o . 44 naphtha are added to 20 ml. of sample and the same procedure is followed. For polymer concentrations above the scale, 10 to 1 or 100 to 1 dilutions of the original sample with toluene or xylene may be used.
The turbidity increases during the first few minutes after adding the methanol or naphtha, but approaches a maximum after approximately 10 minutes. The 15-minute period was chosen so that time differences of a minute or two in making readings make no appreciable difference on the result. A number of other polymers are known to be precipitated from a solution of the monomer b y methanol and certain other solvents and it is believed that this method could be readily adapted to polymer analysis in such cases.
