Internal organization of macromonomers and dendronized polymers based on thiophene dendrons
The internal organization of macromonomers (MGs) consisting of all-thiophene dendrons of generation g = 2 and 3 attached to a phenyl core, as well as of the dendronized polymers resulting from polymerization of these macromonomers (PG2 and PG3, respectively), has been investigated using theoretical methods. The conformational preferences of the MGs, determined using density functional theory calculations, are characterized by the relative orientation between dendrons and core. We find that the strain of the MGs increases with the generation number and is alleviated by small conformational re-arrangements of the peripheral thiophene rings. The conformations obtained for the MGs have subsequently been used to construct models for the dendronized polymers. Classical molecular dynamics simulations have evidenced that the interpenetration of dendrons belonging to different repeat units is very small for PG2. In contrast, the degree of interpenetration is found to be very high for PG3, which also shows a significant degree of backfolding (i.e. occurrence of peripheral methyl groups approaching the backbone). Consequently, PG2 behaves as a conventional linear flexible polymer bearing bulk pendant groups, whereas PG3 is better characterized as a semirigid homogeneous cylinder. The two polymers are stabilized by π–π stacking interactions, even though these are significantly more abundant for PG3 than for PG2; the average numbers of interactions per repeat unit are 3.0 and 8.8 for PG2 and PG3, respectively. While in these interactions the thiophene rings can adopt either parallel (sandwich) or perpendicular (T-shaped) dispositions, the former scenario turns out to be the most abundant.