Phase Behavior of Immiscible Polydimethylsiloxane/Polybutadiene Vitrimer Blends

Vitrimers are polymer networks cross-linked by dynamic covalent bonds that undergo associative exchange, where new bonds form before existing ones break. This mechanism preserves network connectivity while enabling topological rearrangements, rendering vitrimers insoluble yet reprocessable at elevated temperatures. Converting a conventional polymer into a vitrimer enhances mechanical strength, improves chemical resistance, and increases interfacial adhesion with other polymers. Consequently, vitrimers provide a promising strategy for compatibilizing otherwise immiscible polymers. In this talk, we investigate the phase behavior immiscible vitrimer blends composed of polydimethylsiloxane (PDMS) and polybutadiene (PB) with dioxaborolane cross-links that undergo associative exchange. To form the blends, we use photo-initiated thiol-ene click chemistry to cross-link PDMS and PB in solution. We systematically varied the PB weight fraction. Scanning electron microscopy demonstrates that the blends contain micron-sized droplets of the minor polymer within a matrix of the major component. Differential scanning calorimetry suggests that vitrimer blends exhibit enhanced mixing between PDMS and PB, whereas permanently cross-linked blends do not. Small-angle X-ray scattering shows that some vitrimer blends undergo microphase separation, forming cross-link aggregates. We propose potential mechanisms governing the phase behavior.