Preparative gel-chromatography Quantitative analysis of polycarbonates Hydrolysis of polycarbonates Polycarbonate samples (e.g. foils) can be readily and rapidly hydrolyzed by means of semi-concentrated ammonia under pressure (1 g polycarbonate in 40 ml semi-concentrated ammonia, 3 h at 13OOC). The hydrolysis products Bisphenol A and polyethylene glycol can be quantitatively separated from each other as well as from the urea formed (from the -0-CO-0-groups of the polycarbonate+ ammonia) as well as from any possible glycerol and determined very accurately via gravimetry. The hydrolysis product freed from excess ammonia is separated as mobile phase on Sephadex LH-20 via methanol (Figure 1) or acetone (Figure 2). In both cases, the separation time can be essentially reduced bya higherflow rate andlorshortercolumn. Forpracticalpurposes,the separation by means of acetone as eluent is most suitable even when larger amounts (20-30 weight-% relative to the polymer) of the pore-structure stabilizer glycerol are present in the foils (see Figure 2, peak 3). MW/mg 6000/25092/660 18/250 601216 228/841

No abstract

An efficient system for preparative reversed-phase separations with packed glass columns is described. The advantage of this system is the use of relatively simple and inexpensive equipment.Column performance, load capacity, effect of the feed volume and the feed concentration on peak broadening are shown. The influence of the selectivity and the capacity factors on column load have been measured.The effect of the column dimensions is demonstrated by means of practical applications. The loading capacity of a column depends on the thermodynamic proporties of the separation system used. It is therefore not expedient in preparative chromatography to correlate the loading capacity of a column by means of grams dissolved per grams of adsorbent.

No abstract

Quantitative analysis of terephthalates Linear calibration curveDepending upon the reaction conditions, the ester interchange of dimethyl terephthalate (DMT) with excess ethylene glycol can afford, in addition to the diol and the separated methanol, various amounts of the three different diesters of terephthalic acid, viz. diglycol-(DGT), monoglycol monomethyl-(MTG), and dimethyl terephthalate (DMT). Qualitative thin-layer and column-chromatographic separations of diglycol-and monoglycol monomethyl terephthalate have already been carried out in connection with studies on polyethylene glycol terephthalate oligomers [l ,2] .The quantitative gas-chromatographic methyl ester group determination [3,4] after alkaline saponification does not give sufficient information to determine in which form the methyl ester groups are present. Pure monoglycol monomethyl terephthalate and a 1 : 1 mixture of diglycol and dimethyl terephthalate produce the same gas-chromatographic result. Compounds with high boiling points, such as diglycol terephthalate, must be converted into more volatile derivatives [5,6] prior to gas-chromatographic analysis. Particularly in the separation of strongly polar and highboiling compounds, high-performance liquid chromatography is far more suitable than gas chromatography, as is shown by a practical example described below. Figure 1 shows the quantitative separation ofaglycolicsolution of DGT, MTG, and DMT on LiChrosorb RP8(5 pm) with a mixture of methanollwater(65:35).The ethylene glycol doesnot impedethe quantitative determination since it appears before the DGT peak and is not indicated by the UV detector. Figure 2 shows the calibration curves of the three terephthalic esters with the aid of the corresponding test fractograms.The content of diester in mgl ml solution can be read directly from the extension line of the peaks. By this method it is possible to determine quantitatively a diester content in the reaction mixture down to 1%. In the case of the DGT this would be < 0.005 mglml, at an injected amount of 20 pI this would amount to < 0.10 pglinjection.