Self-Assembly of Heteroarms Core-Shell Polymeric Nanoparticles (HCPNs) and Templated Synthesis of Gold Nanoparticles within HCPNs and the Superparticles

摘要

Here we report the self-assembly of heteroarm core-shell polymeric nanoparticles (HCPNs) into spherical superparticles and Synthesis of gold nanoparticles within the HCPNs and the superparticles. HCPNs with polystyrene (PS)/poly(4-vinylpyridine) (P4VP) as the heteroarms and the cross-linked network poly(4VP-co-divinylbenzene) as the core were synthesized via a two-step anionic polymerization method. In the first step, living PS chains were prepared by initiating styrene using n-butyllithium in THF. In the second step, copolymerization of 4VP and DVB was initiated by the living PS chains. The HCPNs thus prepared have two features in the structure. (1) The HCPNs are large (the average hydrodynamic radius < R-h > of the HCPNs in DMF is 111 nm, whereas < R-h > of reported heteroarms star polymers are less than 10 nm) and flexible when they are dispersed in the solvents such as DNF and acidic water. (2) The PS arms are designed to be considerably longer than the P4VP arms. These two features led to interesting behaviors of the HCPNs in both the common solvent and the selective solvents for the heteroarms. In DMF, the common solvent, the HCPNs were swollen and with a < R-h > of 111 nm. In toluene, the selective solvent for PS, the longer PS arms shielded the short insoluble P4VP chains so that the HCPNs were individually dispersed with a < R-h > of 80 nm; the short P4VP arms collapsed, and the core shrank. In acidic water, which is a selective solvent for the shorter P4VP arms, the HCPNs self-assembled into large spherical superparticles with an average < R-h > of 187 nm. The above-mentioned two structural features are thought necessary for the regular self-assembly of such large and isotropic HCPNs. Furthermore, both HCPNs in toluene and the superparticles in acidic aqueous solution were used as templates to prepare gold nanoparticles (Au NPs). When HCPNs in toluene were used as the template, the Au NPs with a size of ca. 2-7 nm were scattered at the periphery of the cross-linked cores, forming raspberry-like morphology. When the superparticles were used as the template, the morphology of AuNP/superparticle composite nanoparticles depended on the solvent composition. In 0.1 M aqueous HCl solution, Au NPs were located at the periphery of the superparticles, forming gold shells with a thickness of ca. 50 nm. However, in 0.1 M HCl aqueous solution/DMF mixed solvent (9:1, v/v), the HAuCl4 precursor could penetrate into the P4VP domains within the superparticles, forming dendron-like Au NP clusters within the template after the reduction.