Building-block approach to discrete and sequence-specific oligosiloxanes†

Discrete and sequence-specific oligomers that combine molecular-level structural precision with macroscopic properties have attracted increasing attention in polymer and materials science. This study reports a facile method to selectively synthesize discrete and sequence-specific oligosiloxanes of up to 26-mer in a single flask on a gram scale by incorporating a siloxane building block into a B(C₆F₅)₃-catalyzed one-pot controlled iteration. The building blocks enable the incorporation of a well-defined oligosiloxane unit into an intermediate of controlled iteration in a single step, thereby significantly reducing the number of iterations. The four obtained 26-mers with molecular weights higher than 3400 bearing different Me₂SiO/Ph₂SiO sequences exhibit distinct thermal, structural, and mechanical properties, even though the substituents on the silicon atoms are simple methyl and phenyl groups. These results indicate that controlling the monomer ratio and sequence are both crucial in determining the physical properties of copolymerized polysiloxane (silicone) materials.