Immiscible Polydimethylsiloxane/Polybutadiene Vitrimer Blends

Vitrimers are covalently cross-linked polymer networks that undergo molecular network rearrangement via associative exchange. Conversion to vitrimer chemistry offers a viable alternative for improving miscibility between incompatible polymers. This poster displays findings from polydimethylsiloxane (PDMS) and polybutadiene (PB) blends containing dioxaborolane cross-links that undergo associative exchange. PDMS/PB blends were synthesized using photo-initiated thiol-ene click chemistry. PB weight percent and cross-link density were systematically varied. A PDMS/PB permanently cross-linked blend was made as a control. Solution state morphology prior to cross-linking determines the dry blend morphology. Scanning electron microscopy indicated that cross-link chemistry – either dynamic or permanent – does not have a significant effect on droplet size. Differential scanning calorimetry determined that dynamic cross-linking exhibited improved mixing compared to permanent cross-linking. Small angle X-ray scattering identified that some vitrimer blends form cross-link aggregates. Linear viscoelasticity measurements revealed fast and slow relaxation regimes. The fast regime is associated with segmental motions. The slow regime, independent of blend composition, follows time-temperature and time-composition superposition.