Characterization of poly(ethylene oxide)-block-poly(L-lactide) by HPLC and MALDI-TOF mass spectrometry

The analysis of individual blocks in a PEO-PLLA diblock copolymer to the molecular level combining the critical condition HPLC and MALDI-TOF MS was attempted. At the critical condition of PEO block, each oligomeric PLLA block species was resolved by reversed-phase HPLC. It was found that the population with even numbers of LLA residues was far more abundant than the odd-numbered ones. From the analysis of each fractionated peak by MALDI-TOF MS, it was confirmed that the molecular weight distributions of PEO blocks with different numbers of LLA residues are identical within experimental precision and that the Mn of PEO blocks are in good agreement with the SEC analysis result of the precursor MPEO. The loss of lactide units by degradation after the fractionation was also clearly observed.