The iterative synthesis of discrete dimethylsiloxane oligomers: A practical guide

Discrete dimethylsiloxane oligomers are interesting building blocks for the synthesis of high chi-low N block co-oligomers (BCOs) forming highly organized nanostructures. Here, a practical guide to the synthesis of molecularly defined oligodimethylsiloxanes (oDMS) from 7-mer to 40-mer via a linear growth strategy is described. The iteration of a hydroxylation reaction and the condensation of mono- or bifunctional hydroxysiloxanes with chloro-octamethyltetrasiloxane results in asymmetric and symmetric siloxanes, respectively. The synthesis contains critical washing and purification steps to remove minor amounts of low and high-molecular weight byproducts, which are detected using Fourier transform infrared spectrometry, gas chromatography-mass spectrometry, and size-exclusion chromatography. The oligomers are obtained on a multigram scale in yields of 94-50% and in high purity with only one molar mass detected. The formation of the chloride, hydroxide or hydride functional groups is adequately analyzed using Si-29 NMR spectroscopy. The hydride terminated siloxane oligomers are used in Karstedt catalyzed hydrosilylation reactions with alkene-functional substrates to obtain oDMS-based oligomers and BCOs. Byproduct formation as a result of isomerization and reduction are followed by H-1 NMR spectroscopy and minimized using dry conditions and low-catalyst loadings.

Automated summary

The article provides a practical guide to the synthesis of molecularly defined oligodimethylsiloxanes (oDMS) via a linear growth strategy. The synthesis involves critical washing and purification steps to remove minor amounts of low and high-molecular weight byproducts, and the oligomers are obtained in high purity with only one molar mass detected. The functional groups formation and byproduct minimization are adequately analyzed and addressed in the study.