Polystyrene standards

Molecular
weights were determined by a gel permeation chromatography (GPC) system,
Waters 1515. Isocratic high performance liquid chromatography (HPLC)
pump with a Waters 2410 refractive index detector, a Waters 717 plus
autosampler, and a Rheodyne (Cotati, CA) injection valve with a 20
μL loop. The samples were eluted with CHCl₃ (HPLC
grade) through a linear Styragel HR4E column (Waters) with a molecular-weight
range of 50–100K Da at a flowrate of 1 mL/min. The molecular
weights were determined relative to a polystyrene standards (Polyscience,
Warrington, PA) calibration curve having weight-average molecular
weight (M_w) from 600 to 50 000.

Gel permeation chromatography (GPC) measurements were performed on a Waters 515 system equipped with a refractive index (RI) detector using tetrahydrofuran (THF) as the solvent at a flow rate of 1.0 mL/min, and 60 µL of a 1.0 w/v% solution were injected for each analysis. Calibration was accomplished using polystyrene standards (Polysciences, Warrington, PA, USA).