MALDI-TOF in the characterizations of dendritic-linear block copolymers and stars

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was utilized to study simple poly(ethylene glycol)s (PEG) and a series of amphiphilic copolymers prepared from PEG and dendritic molecules. For the amphiphilic copolymers with branched dendritic structures, MALDI-TOF spectrometry affords more accurate molecular weight data than the conventional gel-permeation chromatography (GPC). For mass lower than 10 000, the molecular weight distribution of the polymer is well-resolved into individual peaks. Using MALDI-TOF in the linear mode, copolymers with molecular masses of up to 43 000 Da were analyzed. For various dendrons attached to the same PEG, a good correlation was observed between calculated and measured data for the expected incremental increase as a function of dendrimer generation. End-group analysis using MALDI-TOF mass spectrometry proved very useful for the analysis of polymers with relatively low molecular weights. The experimental results agree well with the calculated masses of selected oligomers. Such end-group analysis can differentiate between the AB dendritic-linear diblocks, ABA triblocks, and linear PEG. These analyses support our earlier finding that the Williamson ether synthesis utilized in the PEG-dendron coupling reaction indeed converts all of the PEG to the desired block copolymer products.