Employing MALDI-MS on poly(alkylthiophenes): Analysis of molecular weights, molecular weight distributions, end-group structures, and end-group modifications

Regioregular, head-to-tail coupled, poly(3-alkylthiophenes), synthesized by three different methods, were subjected to MALDI-TOF MS analysis. Polymer samples of both high and low polydispersities were examined. Polymer sample s of narrow polydispersity were obtained by fractionation of the polymer by Soxhlet extraction with various solvents. Comparisons between the molecula r weights calculated by MALDI and GPC of all fractionated polymer samples s howed that GPC calculated molecular weights are a factor of 1.2-2.3 times h igher than MALDI. The polydispersities calculated by MALDI were identical o r slightly lower than those calculated by GPC. Polymer end-group compositio ns were also analyzed. We found that more than one type of end-group struct ure could be detected, and these structures are dependent on the synthetic method employed. Chemical modification of the end-group structure was also performed and monitored by MALDI with successful results. We observed that smaller polymer chains were subject to end-group fragmentation when the MAL DI laser power was high. Larger polymer chains, however, showed no such fra gmentation.