Employing MALDI-MS on Poly(alkylthiophenes):  Analysis of Molecular Weights, Molecular Weight Distributions, End-Group Structures, and End-Group Modifications

Abstract

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 samples of narrow polydispersity were obtained by fractionation of the polymer by Soxhlet extraction with various solvents. Comparisons between the molecular weights calculated by MALDI and GPC of all fractionated polymer samples showed that GPC calculated molecular weights are a factor of 1.2-2.3 times higher than MALDI. The polydispersities calculated by MALDI were identical or slightly lower than those calculated by GPC. Polymer end-group compositions were also analyzed. We found that more than one type of end-group structure 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 MALDI laser power was high. Larger polymer chains, however, showed no such fragmentation.

Poly(3‐hexylthiophene)‐b‐poly(3‐cyclohexylthiophene): Synthesis, microphase separation, thin film transistors, and photovoltaic applications

“…The number-average molecular weights measured by GPC (107,240 g/mol for HcH63 and 134,260 g/mol for HcH77) seem to be much higher than expected M n from the monomer-to-Ni catalyst ratio (100:1) and this can be explained by over-estimation of measured M n of poly(3-alkylthiophene)s against polystyrene standards. 44 Although the polydispersity index (1.45-1.57) is quite large compared to conventional block copolymers, it is however similar to that reported for other all-conjugated block copolymers such as poly(3-hexylthiophene)-b-poly(3-dodecylthiophene). 43 One possible way to improve the polydispersity is by using asymmetric monomers such as 2-bromo-5-iodo-3-alkylthiophene [38][39][40] and followed by rigorous purification.…”

Synthesis and Transfer of Chirality in Supramolecular Hydrogen Bonded Conjugated Diblock Copolymers

“…It is important to note that GPC tends to overestimate the molar mass of P3ATs. 70 For both polymers low dispersities were obtained, which is in line with the controlled nature of the polymerization. Figure 2.…”

End Group Modification of Regioregular Polythiophene through Postpolymerization Functionalization

“…This is typical since M n of poly(alkylthiophene) by GPC (polystyrene as standards) is found to be off by a factor of 1.5-2. 15 Using this well-defined HT-PHT with H/Br end group structure (2), we performed end group modification as shown in Scheme 1. Since poly(alkylthiophenes) are chemically stable polymers, the ability to modify the end groups off one side of the polymer is similar to polymer or bead supported organic synthesis.…”