Gel permeation chromatography (GPC) was performed employing N,N-dimethylformamide (DMF) with lithium bromide (5 g L -1 ) as eluent and GRAM columns (300 x 8 mm, 10 µm particle size, PSS Mainz) with 100 and 3000 Å pore sizes. The samples were measured on a SEC 1260 Infinity system (Agilent Technologies) at a flow rate of 0.5 mL min -1 at 23 °C, using a refractive index detector (Agilent Technologies). The calibration was done with narrowly distributed polystyrene standards (PSS calibration kit) and toluene (HPLC grade) was used as internal standard.