Influence of Composition of Amphiphilic Double-Crystalline P3HT-<i>b</i>-PEG Block Copolymers on Structure Formation in Aqueous Solution

A series of poly(3-hexylthiophene)-block-poly(ethylene glycol) (P3HT-b-PEG) with constant P3HT block length block and variable PEG block lengths are presented. Alkyne-functionalized P3HT with high absolute molecular weight of 11.4 kg/mol is combined with azide-functionalized PEGs via copper-catalyzed alkyne–azide cycloaddition (CuAAC). The resulting P3HT-b-PEG block copolymers have PEG weight fractions between 15 and 64 wt %. In bulk materials the crystallinity in the conjugated block is similar to pure P3HT, while the crystallinity of PEG is influenced with decreasing PEG block length. On addition of MeOH as a nonsolvent for the P3HT block, these block copolymers are able to form stable micellar aggregates if the PEG fraction is >31 wt %. In AFM, DLS, and cryo-TEM, P3HT-b-PEG micelles are found to have a spherical or cylindrical shape with diameters of around 25 nm and lengths between 40 nm and some hundred nanometers. It is found that short PEG blocks lead to bigger block copolymer micelles. Thus, a correlation of composition on solution structure and its consequences on the crystallization of both blocks is given.