A fast and efficient way of obtaining the average molecular weight of block copolymers via DOSY

Abstract

Diffusion-ordered NMR spectroscopy (DOSY) allows for solvent-independent molecular weight calibration with low lab variability. Methyl methacrylate standards have been used to calibrate DOSY data for various solvents. Following the Stokes–Einstein equation, a high correlation of the data was obtained when the viscosity of the solvent was taken into account. Moreover, the inter-laboratory and inter-polymer consistency was confirmed by using the pMMA calibration obtained on an NMR system in Germany, which was applied to polystyrene diffusion coefficients that were obtained in Australia. Furthermore, the molecular weight of polymers with added complexity, such as block copolymers, is determined with diffusion data. Butyl acrylate (BA), methyl acrylate (MA), PEG methyl ether acrylate (PEGMEA) and MMA are used as building blocks to synthesize the block copolymers. Firstly, DOSY calibration curves are prepared for the synthesized homopolymers pBA and pPEGMEA. Then, the diffusion data are compared to block copolymers with different compositions of pBA-b-pMA, pBA-b-pPEGMEA and pMMA-b-pPEGMEA and an accurate determination of the molecular weight of the block copolymers could be achieved using the homopolymer calibration curves.