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Synthesis of Amphiphilic Rod–Coil P3HT-b-P4VP Carrying a Long Conjugated Block Using NMRP and Click Chemistry

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journal contribution
posted on 10.04.2012 by Ruth H. Lohwasser, Mukundan Thelakkat
We use a combination of click chemistry and nitroxide-mediated radical polymerization (NMRP) for the incorporation of high molecular weight poly­(3-hexylthiophenes) (P3HTs) segments into amphiphilic block copolymers. First, a high molecular weight alkyne-terminated P3HT was synthesized using Kumada catalyst transfer polymerization followed by in-situ end-capping with alkyne and by quenching with methanol. We found out that hydrochloric acid, the best quenching agent for nonfunctionalized P3HTs, leads to addition reactions with the alkyne group and therefore is not suitable for alkyne-terminated P3HT. With the use of copper-catalyzed azide–alkyne click reaction, P3HT-alkoxyamine is formed as a macroinitiator for NMRP. This was used to polymerize 4-vinylpyridine to get amphiphilic rod–coil P3HT-b-P4VP block copolymers with 55 and 77 wt % of poly­(4-vinylpyridine) (P4VP). We investigate how the optical and thermal properties as well as the phase separation behavior depend on the block ratios. These P3HT-b-P4VP copolymers are interesting for hybrid organic photovoltaics as well as for studying the colloidal structures of semiconductor amphiphilic systems. The high molecular weight rod influences the rod–rod interaction as described by the Maier–Saupe parameter μ and therefore has consequences in the microphase separation.