Synthesis of monodisperse isomeric oligomers based on meta-/para- and linear/star-monomer precursors with Ugi–hydrosilylation orthogonal cycles
Monodisperse discrete oligomers were precisely fabricated through orthogonal cycles of Ugi-4CRs (Ugi four-component reactions) and hydrosilylation coupling reactions. On varying the precursor of the Ugi-4CR (monofunctional and trifunctional) and the monomer of the hydrosilylation reaction (meta- and para-, referred to 3-(dimethylsilyl)aniline and 4-(dimethylsilyl)aniline, respectively), linear and star-shaped meta- or para-oligomers with the same molecular weight and chemical formula but different configurations or topologies were constructed. The configuration and topology can be simultaneously controlled. The four oligomers 6mer-yne-Meta (2907.21 Da), 6mer-yne-Para (2907.31 Da), 6mer-yne-StarMeta (2863.88 Da) and 6mer-yne-StarPara (2863.09 Da) perfectly model the concept of monodisperse isomeric oligomers. Experimental measurements and DFT simulations were conducted to study the different properties of these four oligomers with the same MW but different topologies or configurations. 6mer-yne-StarPara shows larger molecular dimensions (34.2 Å vs. 26.1 Å) and a higher Tg (159.7 °C vs. 148.3 °C) than 6mer-yne-StarMeta due to the different chain folding angles from the primary meta- and para-linkers. This study explores the concept of “monodisperse isomeric oligomers” at the macromolecular level.