All-conjugated block copolymers: from controlled synthesis to chiral expression

In the last two decades, the field of conjugated polymers (CPs) expanded rapidly. Besides the discovery of several controlled chain growth polymerizations and the expansion of the monomer scope, also research toward more complex CPs was performed. Copolymers, e.g. block, gradient and random copolymers, and polymers with different topologies, e.g. hyperbranched, star, circular, graft and toothbrush polymers, were synthesized, but the potential of this field remains large. Because the material properties do not only depend on the molecular structure, but also on the supramolecular structure, also the morphology of CPs is one of the frequently studied topics. For conjugated homopolymers, the aggregation behavior is already well described, but for more complex CPs, like block copolymers, a lot of blind spots remain. Therefore, this dissertation focusses on the controlled synthesis and (chiral) aggregation behavior of conjugated block copolymers. In the first part, the influence of branching of the side chain on the controlled polymerization of 3-alkylthiophenes was investigated. It was found that it reduces the propagation rate constant, leading to remarkably low dispersities. Also the maximal DP that could be obtained in a controlled manner was determined to be 150 and nona-stage polymers were synthesized. Further, it was established that a branched side chain diminishes the long term controlled character of the polymerization and that decomplexation of the Ni-catalyst from the polymer backbone was the main termination reaction. The second part deals with the controlled synthesis and (chiral) aggregation behavior of conjugated triblock copolymers. Triblock copolymers consisting of solely thiophene units, as well as triblock copolymers containing selenophene and (a)chiral thiophene units were synthesized in a controlled manner and by investigating their aggregation behavior, it was found that this is influenced by the order of the blocks. In the third part, block copolymers of electronically different monomers were synthesized. Their chiral aggregation behavior was studied in order to investigate whether block copolymers can be designed to exhibit a set of properties, which cannot be achieved in homopolymers, by transferring properties of one block to the other. In a stepwise approach, a poly(fluorene)-b-poly(thiophene) block copolymer, that exhibits β-phase aggregation and chiral expression (two aggregation features which cannot be obtained together in homopolymers), was designed. In the final part, the influence of the nature and the position of defects on the chiral expression in P3ATs was investigated. Polymers with one head-to-head (HH) or tail-to-tail (TT) defect in predetermined positions and one regioregular polymer were synthesized and their chiral aggregation behavior was compared. It was found that the largest chiral expression was obtained when the defect is situated at the beginning of the polymer chain. A TT defect always decreases the chiral expression, but an HH defect can cause an increased chiral expression compared with a complete regioregular polymer. Also, the effect of mixing polymers with a defect in different positions was investigated. For the polymers with an HH defect, no significant influence was observed, but for the polymers with a TT defect, the chiral expression was relatively lowered or enlarged, depending on the type of mixture that was made. This shows that not only the nature or the position of a defect influences the chiral expression, but also the mixing of polymers with a defect in different positions.

Jaar van publicatie:2019

Toegankelijkheid:Open