Branched polymers chromatographic methods

In summary, the approach outlined here is a straightforward method for determining representative values of viscosity ratios [ n ] MA /[ h ] LB I certainly g values significantly less than 1.0 are expected for such highly branched polymers (33). However, the anomalous dependence of g (v) on M[v1a suggests that 1) the core/shell hydrodynamic configuration and/or chromatographic artifacts invalidate universal calibration, and/or 2) the LB elution behavior does not conform to that of polystyrene in the assumed, constant manner. Further work is necessary to elucidate these points. 

This combination of separation and elemental detection allowed them to see several oligomeric series of species in the polysiloxanes, which were compared with the retention times of standard compounds. The series proved to be linear chains, branched chains, and cyclic structures. The chromatographic method was able to give a baseline separation of each of the ohgomers up to 60 units of trimethoxy-polydimethylsiloxane (silicone oils and greases are this type of polymer). 

As shown by a red curve in Eig. 18.8 (right), the CRYSTAE chromatograph starts at T just below T, and upon cooling first, the most crystalline fraction precipitates. The fractionation continues as T decreases crystallizing the macromolecules with increasing branch content. The last data point, at the lowest T, represents highly branched or amorphous polymer, i.e., the fraction which would not crystallize. The first derivative of this curve corresponds to the CCD and is similar in shape to the one obtained in TREE with a T shifted by about 16 °C the shift originates in the difference between the crystallization and dissolution T. The CRYSTAE method has been often reviewed (Hamielec and Soares 1996 Soares et al. 1998 Soares and Hamielec 1999 Pasch et al. 2000 Monrabal 2000, 2011 ... 

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