A comparison of the properties of two structurally equivalent but regiochemically different mono-alkylated polybithiophenes prepared through AABB-type stille polycondensation

Abstract

Previous routes to polymers with mono-alkylated bithiophenes have proceeded through polymerization of monoalkyl-2,2′-bithiophene monomers through oxidative or AB-type cross-coupling polymerizations. The resulting polymer regiochemistry affects both the location and orientation of the polymer side-chains. In contrast, AABB-type cross-coupling polymerizations can control the location and in some cases the orientation of the side-chains. To study how this control can impact polymer properties, two poly(monodecyl-2,2′- bithiophene) polymers have been synthesized through Stille AABB-type polycondensations of 2,5-bis(trimethylstannyl)thiophene with different monomers. The alkyl side-chains are located on every other thiophene, but polymer 1 consists of both head-to-tail and head-to-head dyads, whereas polymer 2 is made up of only head-to-head dyads. 1H NMR, 13C NMR, and heteronuclear single quantum correlation spectroscopy are used to confirm and contrast the polymer regiochemistries. The physical properties of the two polymers are analyzed using UV-vis spectroscopy, differential scanning calorimetry, and grazing-incidence X-ray diffraction. Polymer 2 is found to display significantly more aggregation in solution than 1, and it displays different thermal properties. The film properties of polymers 1 and 2, however, are very similar, with nearly identical UV-vis profiles and d-spacing values as determined by grazing incidence X-ray diffraction. © 2012 Wiley Periodicals, Inc.