Macrocellular polymer foams from water in oil high internal phase emulsion stabilized solely by polymer Janus nanoparticles: preparation and their application as support for Pd catalyst

In this study, the preparation of styrene/divinylbenzene-based macrocellular polymers of high internal phase emulsions (polyHIPEs) with interconnected open-cell structure as well as their application as support for Pd nanoparticles are presented. Firstly, water in oil high internal phase emulsions (HIPEs) were generated by adding the water stepwise to the oil phase (styrene and divinylbenzene) containing Janus polymer nanoparticles that consist of a linear poly(methyl methacrylate) "tail" and a cross-linked poly(4-vinylpyridine) "head". The generated water in oil HIPEs stabilized solely by Janus polymer nanoparticles were then converted to polyHIPEs foams by polymerizing the external continuous oil phase, followed by the extraction with methanol and the drying under the reduced press. Scanning electron microscopy observation revealed that the as-produced macrocellular polyHIPEs were foam structure with closed and/or partially open-cells. Partial cells covered by a thin polymer film were peeled off during the post-treatment. Some key factors influencing the polyHIPEs morphologies, including emulsifier particles content, the mole ratio of styrene to divinylbenzene and the internal phase volume fraction were investigated, and macrocellular polyHIPEs with interconnected open-cell morphologies could be achieved under optimal conditions. Benefited from the strong interaction between the emulsifier particles embedded in the polyHIPEs and H2PdCl4 precursor, Pd nanoparticles were facilely supported in situ within the macrocellular polyHIPEs without any functional monomers or post-functionalization requirement. The obtained Pd@macrocellular polymer hybrid foams were then applied for the heterogeneous Suzuki-Miyaura carbon-carbon coupling reactions between iodobenzene and benzeneboronic acid, and a high catalytic activity with a good recyclability were demonstrated.