Triangular Fractionation Schemes

Gjmbination of the ne hbouring fractions considerably reduces the final number of fractions. Fig. 41a shows the result of a five-step triangular fractionation in which the fraction sizes in the various stages are 

Tiiangalar fraction without combination of fractions (TC 16) and successive extraction (SC IQ of a logarithmic normal function (M = b = 10 ——) 

Evaluation of Spenoer s sommative procedure along the lines pot forward in 3.2 reveals that this method d es not yield a good approximation of the initial distributwn, which, in this case, is (see Table 1). Both examples (5 and 10 fractions) reveal spurmus peaks or shoulders (Fig. 42). 

compared with the more elaborate successive and triangular procedures, these fast techniques yield results that are more accurate than one would presume. 

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Meffroy-Biget (65) and Meyerhoff (66) proposed a triangular scheme which is a combination of precipitation and extraction. In the first step the polymer is separated into two fractions. The next step comprises further separation of either fraction into two portions. Before continuing in this way one may, or may not, combine those two portions out of the four which are closest together in average molecular weight. The two possible triangular fractionation schemes are illustrated in Fig. 26. 

Fig. 26. Triangular fractionation schemes with (a) and without (6) comtaimtion...

Increasing composition of A Increasing composition of B Figure 7.3. Fractional recrystallization of a solution triangular scheme)... 

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