Baker Williams fractionation

Two advantages of HPPLC should be mentioned here its general applicability and its only moderate dependence on column activity. The first aspect refers to the fact that solubility and precipitability are common characteristics of a wide variety of polymers. In principle, HPPLC is Baker-Williams fractionation by means of modern HPLC techniques. 

Fig. 28. Distribution of the degree of polymerization of the 10th Baker-Williams fraction (middle fraction, Pw = 1500) of polystyrene sample Ti-Te-1, polymerized anionically in 1,2-dimethoxy-ethane at —48 °C PDC at 15 °C (O) and GPC, not corrected for spreading (strip method, A)...

Fig. 29. Integral distribution of the degree of polymerization for polystyrene sample 0/2 polymerized anionically in tetra-hydropyran at 0 "C, Pw = 1225) and Baker-Williams-pre-fractionated PDC at 15 °C (O) and Baker-Williams fractionation of this sample by Bohm J9) (+). The integral distribution obtained by Bohm is somewhat narrower than that obtained from PDC, because of some different Pw-values (aP = Pw(/ Uz, Bohm had probably taken Pn instead of Pw)...

Elimination of Systematic Errors in the Baker-Williams Fractionation... 

It has been shown recently that elution fractionation driven by solubility - not by the size of the molecules - might represent the solution to this problem. Separation into discrete molar mass fractions, without being influenced by the volume of the molecule, was achieved by utibzing a principle similar to the well-known Baker-Williams fractionation, which involves both temperature and solvent gradient [153]. The interplay between temperature and solvent quality is... 

In column fractionation (157,158) the polymer is precipitated onto an inert support, which is placed at the top of a packed column (159). A solvent mixture of increasing solvent power is pumped through the column a temperature gradient is often maintained. This is known as Baker-Williams fractionation (160). This technique is applicable to all amorphous homopolymers and crystalline ho-mopol5miers above the melting point. For copol5miers and more complex compositions, the same technique may be employed, but the analysis is considerably more difficult. 

Another type of fractionation is called the Successive Solution Fractionation (SSF). In the SSF after phase separation the polymer-lean phase is removed and forms fraction 1. The polymer-rich phase is diluted by addition of solvent up to the initial volume of the feed phase and forms now the feed phase for separation step 2 etc. Continuous thermodynamics has also been applied to Baker-Williams fractionation where the polymer is fractionated in a column using a solvent and a non-solvent. The superposition of a solvent and nonsolvent gradient and a temperature gradient leads to a very high separation efficiency. 

Within this contribution, we focus our attention on two methods, namely the Baker-Williams fractionation (BW) [40,41] and continuous polymer fractionation (CPF) [42]. The B W method leads to fractions with a very low nonuniformity and is deemed to be the most effective technique [43, 44]. CPF allows the isolation of fractions on the 100 g scale. 

Ratzsch MT, Tschersich L, Kehlen H (1990) Simulation of Baker-Williams fractionation by continuous thermodynamics. J Macromol Sci A27 999-1013... 

Two patented large-scale techniques, based on liquid-liquid phase separation, are the continuous polymer fractionation (CPF) and the continuous spin fractionation (CSF)." The experimental setup of these two techniques will be presented in the next two sections (sections 2.04.2.1 and 2.04.2.2), which are followed by the description of two chromatographic methods, namely, the Baker-Williams fractionation (section 2.04.2.3) and the phase distribution chromatography (PDC) (section 2.04.2.4). 

Molecularly very homogeneous fractions with nonuniformities of about 0.05 were obtained in the range of molecular masses from 60 to 600 kg mol" . The inversion of molecular mass in the last three fractions is something that is typical for many Baker-Williams fractionations. 

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