Analytical Instrumentation


Although at this stage the polymer is already segregated in layers or crystalline structures of different composition, the technique still requires a second temperature cycle to collect those fractions. This is achieved by pumping solvent meanwhile the temperature is being increased (elution step). The eluent dissolves fractions of increasing crystallinity, or decreasing branch content, as temperature rises. Figure 2 shows the fractionation of a complex dual reactor LLDPE polyolefin.

Fractionation According to Molar Mass

Molar mass fractionation has been implemented in PREP C20 using a solvent-non solvent gradient through the column at a constant temperature. Narrow fractions of increasing molar mass can be obtained as shown in Figure 3. The graph shows the molar mass distribution of a LLDPE and its fractions obtained with molar mass fractionation mode.

Figure 2. TREF curves of fractions obtained with PREP C20 and their LLDPE parent sample. Future and Other Perspectives

Developed initially for polyolefins, PREP C20 can also be used for other polymers depending on the solvents required for dissolution.

Currently, fractionation takes place according TREF and molar mass modes, but other fractionation techniques such as thermal gradient interaction chromatography (TGIC) and solvent gradient interaction chromatography (SGIC) will be implemented soon.


Fractionation of polyolefins has always been a difficult and physically demanding task due to the manual manipulation of large volumes of hot solvent. After the first automation techniques, new complex polymers have shown to require a support to achieve a proper fractionation.

In this way, a column-based fractionation equipment has been developed, which also enables the fractionation of larger amounts of sample, in a completely automatic way.

Figure 3. Molar Mass distribution of fractions obtained with PREP C20 and their LLDPE parent sample.

The main steps of fractionation are performed automatically following the selected method parameters:

1. The vessel is filled with solvent and heated up for dissolution with stirring at high temperature.

2. Column loading with the sample dissolved at high temperature.

3. Crystallization step following the selected temperature ramp (when subambient conditions are required, PREP C20 can work without the need of liquid coolants down to minus 20ºC).

4. Elution step and fractions collection by pumping solvent at selected increasing isothermal steps (composition mode) or selected non-solvent percentage at a fixed temperature (molar mass mode). For TREF mode, the concentration of the different fractions that are coming out of the column is monitored with an infrared detector, which facilitates the

fractionation comprehension, so the analyst can modify the fractionation methods (elution volumes) according to his needs.

The control program allows the user to define different methods according to their needs. Therefore, dissolution temperatures or times, crystallization rates, elution volumes, etc. can be adjusted for each kind or amount of sample.

Fractionation According

to Composition (TREF mode) Chemical composition fractionation, in semi crystalline polymers, is based on differences in crystallizability of the polymer composition, and it is typically performed by crystallization at a slow cooling rate. Fractionation occurs by deposition of layers of decreasing crystallinity or increasing branch content, onto an inert support in the column, as temperature decreases.

Author Contact Details Dr. Almudena Fernández, Analytical Department- Polymer Char (Spain) Nuria Mayo, Analytical Department- Polymer Char (Spain) Stephany Gamiz, Engineering Department - Polymer Char (Spain) Rebeca Chiva, Engineering Department - Polymer Char (Spain) Dr. Benjamín Monrabal, R&D Director – Polymer Char (Spain)

Polymer Characterization, S.A. • Gustave Eiffel 8, Paterna, Valencia Technology Park | E-46980 Spain Tel: +34 96 131 81 20 • Email: sonia.camarasa @ • Web: www.

The automated control program allows analysts to create their own methods adjusted to their samples and needs.

Fractions are automatically collected in bottles, and it is possible to check the process performance thanks to an interactive software.


1. L. Wild and T. Ryle, Polym. Prepr. Am. Chem. Soc. Polym. Chem. Div., 18, 182 (1977).

2. T.E Davis and R.L. Tobias, Journal of Polymer Science. Vol 1, 227-243 (1961)

3. “Polymer Fractionation” F. Francuskiewicz. Edited by Springer (1994).

4. “Temperature rinsing elution fractionation and crystallization analysis fractionation” B. Monrabal Encyclopedia of Analytical Chemistry. Edited by R.A. Meyers pp. 8074–8094. Wiley & Sons Ltd, (2000).


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