The iterative synthesis of discrete dimethylsiloxane oligomers: A practical guide

Abstract

Discrete dimethylsiloxane oligomers are interesting building blocks for the synthesis of high χ–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 29Si 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 1H NMR spectroscopy and minimized using dry conditions and low‐catalyst loadings.

Determination of the critical chain length for macromolecular crystallization using structurally flexible polyketones

“…Interestingly, recent developments, such as the iterative exponential growth (IEG) strategy, facilitate an efficient synthetic access to discrete oligomers. 9,10 Over the past few decades, a wide variety of discrete oligomers including oligo((meth)acrylate)s, 11,12 oligo(ethylene imine)s, 13–15 oligo(caprolactone)s, 16–18 oligo(siloxane)s, 19–22 oligo(thiophene)s, 23–25 and oligo(peptide)s 26–29 have been investigated. These oligomers aid in discovering length-specific properties, for example, aggregation, folding, host–guest interactions, and light absorption, which are otherwise hidden in polydisperse polymers.…”

Oligodimethylsiloxane-Oligoproline Block Co-Oligomers: the Interplay between Aggregation and Phase Segregation in Bulk and Solution

“…The mono- and dihydride functionalized o DMS blocks were obtained from the robust synthetic strategy for the synthesis of discrete o DMS described in previous work ( Scheme 2 ). 53 Proline oligomers with an N -terminal 5-hexenoic acid residue were obtained by standard solid phase peptide synthesis ( Scheme 2 and Scheme S1 ). Cleavage from the resin with trifluoroacetic acid (TFA) followed by removal of TFA by ion exchange yielded the peptides with 3, 6, or 9 proline units in 36–75% yields.…”

Properties and applications of precision oligomer materials; where organic and polymer chemistry join forces

“…The iterative synthesis of discrete oligo dimethylsiloxanes (oDMS) has received significant attention in the field of macro-organic chemistry 57 and has recently been described by the Meijer group. 58,59 The general strategies toward both asymmetric (with a single endgroup for further functionalization) and symmetric (both endgroups functionalizable) are depicted in Figure 3. Formation of the oligosiloxanes was reliant on two key steps: (1) transformation of a siloxane hydride into the corresponding silanol and (2) subsequent condensation of the silanol with the chlorosilane building block 3.…”