SEC was measured with a Waters Acquity APC system, equipped with Acquity Column Manager -S, Sample Manager -pFTN, Isocratic Solvent Manager, Acquity RI Detector and Acquity TUV Detector (Waters Corporation, USA). The used columns are Acquity APC XT 45, 125 and 200. Dimethylformamide (DMF, Fisher Scientific) was used as eluent with a flow speed of 0.6 mL min -1 and at a temperature of 40°C. The system was calibrated with PMMA standards (Polymer Standard Service). The data was analysed using the software Empower 3 and Origin software.