Synthesis and characterization of an optical active triblock copolymer via atom transfer radical polymerization

An optical active triblock copolymer poly(N-methacryloyl-L-leucine methyl ester)-b-polysulfone-b-poly(N-methaeryloyl-L-leucine methey ester) (PMALM-b-PSF-b-PMALM) with predetermined structure and narrow molecular weight distribution was synthesized via atom transfer radical polymerization (ATRP) using polysulfone macroinitiator and CuBr/Me6TREN complex system. The structure was verified by H-1-NMR, GPC and end group titration techniques. DSC, thermogravimetry analysis (TGA) and circular dichroism (CD) were used to study the thermal and optical properties. The mole ratio of PMALM block to PSF block calculated from TGA has a good agreement with the result calculated from H-1-NMR. Both a reversion and an increase of the absolute value of specific rotation in the transformation from MALM to PMALM-b-PSF-b-PMALM were observed, which were probably caused by some kind of stereostructure of the main chain formed during the polymerization due to the intermolecular hydrogen-bonding. The random conformation of PMALM blocks was verified by CD spectra and the linear relationship between the specific rotation and the polarity of CH3 OH/CCl4 mixed solvent.