Multifunctional polymer-assisted spontaneous transformation of thin gold films into nanoparticles

In this document, we report an efficient synthesis of well-defined, soluble, high molecular weight, film-forming aromatic multifunctional homopolymers bearing two distinct functional groups per repeating unit. The polymers were obtained in nearly quantitative yields by a one-pot, room-temperature, non-stoichiometric superacid-catalyzed step-polymerization of derivatives of pyruvic acid with aromatic hydrocarbons. It was found that thin gold films (2–12 nm) sputtered onto the surface of a multifunctional homopolymer (PTBC) containing carboxy- and bromomethyl- functionalities in every repeating unit undergo spontaneous, solvent-free, room-temperature, quantitative transformation into nanoparticles. For the first time, the key factors affecting film-to-particle transformation were revealed. Internal factors are dependent on the polymer structure, its homogeneity, and the composition of the polymer/metal interface, while external factors include gold-film thickness, temperature and ageing atmosphere. By varying the functional-group combinations and aromatic fragments, a set of multifunctional homopolymers has been synthesized and it was found that the presence in the homopolymer of a repeating unit of two phenylene rings and two functional groups – bromomethyl and carbonyl – attached to the same carbon backbone atom (forming a so-called "Reactive site") is critically important for film-particle transformation. The process is accelerated with increasing temperature, proceeds in ambient air, and is halted in a vacuum. The average grain size of the nanoparticles increased from 3 to 18 nm over a week at room temperature and from 5 to 27 nm over the same period at 40 °C. The size and shape of the nanoparticles are modulated by controlling the thickness of the gold film, the temperature and the ambient atmosphere. The transformation represents a very simple, one-step, environmentally-friendly process that is not dependent on any other chemical reagents, requires no previous temperature or high-energy processing, and can easily be scaled up to fabricate high-purity, fully accessible polymer-(film- or nanofiber-) supported gold nanoparticles of long-term stability.