Mixing discrete block co-oligomers: When does it behave like a disperse sample?

Blends of block copolymers (BCPs) have great potential for applications in nanotechnology as the desired dimensions and complex nanopatterns can be designed upon mixing BCPs with other BCPs or homopolymers. Recently, we explored the synthesis of a series of discrete oligo(dimethylsiloxane) block co-oligomers (BCOs) and studied their phase behavior. Here, we disclose our results on blending oligomers of different lengths of discrete hydrazone end-functionalized oligo(dimethylsiloxanes) to study the effect of mixing on the morphological order. These mixtures possess a certain dispersity (Ð) as a result of the composition of the mixture. We have found that a distinct boundary exists between a good and poor morphological order at Ð ~ 1.10. As a result, the domain spacings of the low dispersity mixtures can be tuned by the molecular composition of the mixture, creating a wider spectrum of morphologies. Furthermore, we compare a hydrazone end-functionalized siloxane with a dispersity as a result of mixing with its analog having a similar dispersity but resulting from traditional polymerization. Finally, a discrete BCO was mixed with a disperse BCO of similar size and composition. The discrete BCO is immiscible in the disperse BCO which emphasizes the differences in interactions within disperse and discrete oligomers. These results demonstrate that the entropic and enthalpic contributions to nanoscale order in a system composed of discrete components are different compared to disperse BCPs and BCOs.