Silane-Bridged Electroless Ni-Plating on Submicron Polymer Spheres

Abstract

The silane coupling agent (3-trimethoxysilyl propryl methacrylate) was used to functionalize the surface of submicron polymer spheres (sized 168-650 nm) for bridging the polymer core (polystyrene crosslinked with divinylbenzene) and the metal coating shell. The submicron polymer spheres were synthesized by emulsifier-free emulsion polymerization in the presence of NaOH. The metal shell was created by electroless plating. The performance of silane coupling agent, as the bondage between the core and the shell, was compared, in terms of thermal, mechanical and electrical properties, to that of polymer spheres functionalized with -COOH groups. The silane bridge provided more opportunities for binding with metal and the bondage is stable, leading to a denser and more uniform distribution of metal coating, as observed by FESEM studies. The silane bridge was proven to be more durable than the case of -COOH by ball mill tests. Besides bridging with the metal, neighboring silyl groups also form Si-O-Si 2-dimensional network by condensation between two Si-OHs, which further stabilized the bondage between the polymer core and the metal shell.KEY WORDS: Silane Coupling Agent / Submicron Polymer Sphere / Electroless Plating / Core-Shell Structure / Ni Plating / A polymeric microsphere coated with a metallic film (similar to a core-shell structure) would exhibit good electrical conductivity. Due to its spherical geometry, and meanwhile, the major weight portion of the electric-conducting microsphere is occupied by the polymer core, the material has physical properties (e.g., density), as well as price, that are different from metal particles of similar size.In recent years, considerable efforts have been directed to the design and selection of fabrication method for the core polymer microspheres' preparation and metal film coating to obtain the metal coated polymer microspheres with specific electrical, mechanical and chemical properties. Such polymeric microspheres with metallic surfaces have potential applications in interface science, heterogeneous catalysis, electronics etc. [1][2][3] In the literature, a few different approaches have been developed to produce uniformly sized core polymer microsphere colloid, such as suspension polymerization, 1,4 emulsion polymerization, 5 and dispersion polymerization. 6-9 Although by traditional emulsion polymerization, the diameters of the core polymer microspheres could be reduced to submicron scale, but the size distribution could undesirably wide. Better control over the size distribution of the submicron polymer cores calls for the need of alternative strategy. 2,5 Zhang et al. 10demonstrated that the emulsifier-free emulsion polymerization is a process that is capable of obtaining submicron scaled polymer spheres with narrow distribution of particle size. They also pointed out that the merit of such process is the spherical geometry of the product. 10The method of metallic coating is another technological issue in fabricating such material. Metallic coating can be achieved by dir...

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