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FULLY AUTOMATED PREPARATIVE COLUMN-BASED FRACTIONATION BY COMPOSITION OR MOLAR MASS


Introduction


Preparative fractionation in a column packed with an inert support is a long used technique for polyolefi ns characterization, as it facilitates the analysis of the fractions to obtain the bivariate distribution of a resin. For decades, fractionation has been an important but challenging and tedious task because it requires manually handling of large volumes of toxic solvents at high temperature.


Thus, the signifi cant amount of time and effort demanded for the operation called for an automatic equipment that avoided solvent handling by the analyst. In the 90’s, Polymer Char developed the instrument PREP mc2


, an automated technique that was able to


fractionate up to 2 grams of polyolefi ns according to their chemical composition (by temperature rising elution fractionation, TREF or by crystallization analysis fractionation, CRYSTAF) or according to their molar mass. Samples were placed into vessels and fractionation was performed automatically according to the selected method in less than 24 hours.


Nevertheless, with this method, fractionation takes place with the absence of a support, and it has started to become evident that, for some polymers, when fractionating by TREF, a support for the solution to adhere to is critical for a good separation of the fractions, as is the case with multiple reactor-catalyst resins.


As a response, Polymer Char introduced the PREP C20, a column- based equipment, which - by adding a support for the solution to crystallize - improves the separation for each of the fractions, and therefore becomes more appropriate for those types of complex resins.


Moreover, for a better understanding of the structure-properties relationship, fractionation techniques are needed in order to separate polymers into fractions, which allow for their subsequent characterization. Often, some of the techniques employed to analyze the fractions require high amounts of polymer, which implies doing several fractionations of the parent sample to achieve the needed amount for the fractions.


In this way, PREP C20 has been designed to fractionate high amounts of polymer, up to 20 grams depending on the sample. Therefore, one unique fractionation will be enough to obtain the fractions amount needed for their complete characterization.


PREP C20 is a powerful and sophisticated equipment designed to fractionate large amounts of polymer in a completely automatic way, which works as a pilot plant eliminating the need of manual handling of high volumes of hot solvent. A column-based instrument in which fractionation can take place according to the basis of Temperature Rising Elution Fractionation (TREF) technique, or according to molar mass using a solvent-non solvent gradient.


Figure 1. PREP C20 main instrument Experimental


To perform a fractionation, the user just needs to place a dry sample into a vessel, select the method and start the process. Once the fractionation is fi nished, the equipment is rinsed and ready to start a new one.


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