Discrete oligodimethylsiloxane-oligomethylene di- and triblock co-oligomers: synthesis, self-assembly and molecular organisation

A new class of discrete-length block co-oligomers comprising oligodimethylsiloxane (oDMS) and oligomethylene (oM) is presented. For this, oM blocks containing up to 69 backbone carbons are synthesised via an iterative, Wittig reaction-based strategy. Ligation with oDMS hydrides permits the formation of a library of block co-oligomers (BCOs) in which the block configuration, MW, and composition can be tuned. Differential scanning calorimetry and small-angle X-ray scattering show that all BCOs exhibit microphase separation into well-ordered lamellar morphologies, driven by the crystallisation of the oM blocks. Pre-melting order-order transitions are present for a number of BCOs, resulting in an alteration of the oM crystal packing as well as in changes of the overall microphase-segregated structure. As a result of the discrete nature of the BCO chains, we propose models that describe the molecular organisation within the microphase-segregated structures by evaluating the changes in the lamellar thickness upon varying the BCO architecture.