Palladium (Pd)-loaded poly-hydromethylsiloxane (PHMS) microparticles of tunable size and elasticity are prepared in a capillary-based coaxial flow-focusing microfluidic device constructed using off-the-shelf components. Simultaneous droplet formation and chemical cross-linking processes are performed by tuning the dilution of the cross-linking catalyst in the annular flow of the microreactor, resulting in PHMS microparticles synthesized in a single step. The size of the elastomeric microparticles can be tuned by adjusting the flow rate ratio of the polymer and cross-linker mixture to water, while the elasticity can be tuned by the polymer to cross-linker ratio as well as the flow rate ratio of the polymer mixture to cross-linking catalyst mixture. Microparticle elasticity is characterized by the degree of solvent uptake. Application of the synthesized PHMS microparticles in organic synthesis is demonstrated by producing monodispersed Pd-loaded microparticles and utilizing them as microreaction vessels for continuous Suzuki-Miyaura cross-coupling in a Pd-loaded microparticle-packed bed reactor. (C) 2018 American Institute of Chemical Engineers