Mendeleev Commun., 2012, 22, 211–212 – 211 – © 2012 Mendeleev Communications. All rights reserved. Mendeleev Communications The design of nanocomposites with tunable size and spatial distribution of nanoparticles is of key importance for functional properties of such materials. The radiation-chemical reduction of metal ions is a powerful tool for the preparation of metal nano- particles and functional nanocomposites for various prospective applications. 1–7 Recently, 6,8 we have introduced a novel approach to a single-stage fabrication of metal–polymer nanocomposites by radiation-chemical technique, starting from films of triple interpolyelectrolyte complexes of poly(acrylic acid) (PAA)– poly(ethylene imine) (PEI)–metal ion, which are swellable in aqueous solution. Further investigations revealed wide opportu- nities for obtaining metal–polymer nanocomposites with various spatial distributions of nanoparticles from such systems using X-ray irradiation. 8–10 Here we present the preliminary results of studies of the X-ray induced reduction of copper ions in solutions of poly(allylamine) (PAlAm) and mixed triple systems PAlAm–PAA–Cu 2+ , which demonstrated the formation and specific organization of copper nanoparticles in microheterogeneous systems. Note that the triple systems were found to form relatively stable suspensions under weakly acidic conditions, when cooperative interaction between polyanion and polycation are suppressed. In this case, the samples contain labile complexes between certain amino groups and acrylate groups (partial ‘zipping’), which is somewhat different from com- pletely zipped polyelectrolyte films used previously. 6,8–10 The experimental approaches were described in detail else- where. 6 The solutions of 0.3 M PAlAm [obtained by deacidi- fication of poly(allylamine hydrochloride) having average M w of 15 000] containing 0.15 M Cu 2+ (pH 7.9) ions in aqueous– alcohol mixture (10% ethanol) and suspensions of triple systems (0.3 M PAlAm–0.3 M PAA–0.15 M Cu 2+ , pH 3.55) were bubbled with pure argon and irradiated with X-rays using a 5-BKhV-6(W) tube with a tungsten anode (30 kV, 70 mA). Molarity of polymer solutions is based on the concentration of repeating units. The solution and suspensions were irradiated in plastic cells with thin walls and a layer thickness was ~5 mm (note that a half- attenuation length for the 30-keV X-rays in water is ~20 mm, that is, the effect of inhomogeneous dose distribution should be relatively small). The irradiation time varied from 1 to 120 min. The reduction of copper ions and formation of nanoparticles after irradiation were monitored by optical absorption spectro- scopy and transmission electron microscopy (TEM). The basic mechanism of reduction of copper ions and forma- tion of nanoparticles upon irradiation of PEI solutions was described previously. 2,7 Generally speaking, irradiation of aqueous solutions in the absence of oxygen leads to formation of both reducing species (hydrated electrons e – aq and H atoms) and a strong oxidizer (OH radicals). In the presence of alcohol, OH radicals are converted to hydroxyalkyl radicals with reducing properties (CH 3 · CHOH in the case of ethanol) due to hydrogen abstraction reaction. All the reducing radicals (e – aq , H and CH 3 · CHOH) can react with Cu 2+ to yield Cu + ions. The crucial step in preparation of metal copper nanoparticles is the formation of neutral copper atoms (Cu 0 ) from Cu + in a bulk solution, which occurs only due to reaction with the strongest reductant (e – aq ). 2 Further processes include formation of clusters Cu n m+ and, finally, metal nanopar- ticles with surface charge stabilized by interaction with polyelec- trolytes (the nucleation and particle growth in interpolyelectrolyte complexes were considered previously 6,9,10 ). In line with results reported for dilute solutions of PEI–Cu 2+ , 2 the present optical absorption studies demonstrate reduction of Cu 2+ ions (decrease of strong absorption with maximum at ~260 nm) at early stages of the process (1–3 min). Prolonged irradiation (up to 1–2 h) of solu tions containing PAlAm leads to formation of nanoparticles (an intense band at ~570 nm with a shoulder in the range of 400–450 nm, similar to those observed previously 2 ). It is difficult to obtain quantitative optical absorption data for the triple systems (suspen- sions) because of very strong scattering of the samples; however, the radiation-induced color change is similar to that observed for solutions. The formation of relatively small nanoparticles was determined by TEM in the samples irradiated for 2 h, both for solutions (PAlAm only, nanoparticle diameter of 2 to 6 nm) and suspensions (PAlAm + PAA, nanoparticle diameter of 2–4 nm). The microdiffraction data show reflexes of metal copper (broadened due to lattice imperfection), which confirms the identity of nano- particles. Meanwhile, the most striking result (which is the focus of this communication) is concerned with specific spatial organiza- tion of nanoparticles observed in the irradiated triple system. As demonstrated in Figure 1, in addition to formation of small Spatial organization of a metal–polymer nanocomposite obtained by the radiation-induced reduction of copper ions in the poly(allylamine)–poly(acrylic acid)–Cu 2+ system Ayse Bakar, a Viktor V. De, b Aleksei A. Zezin, b,c Sergei S. Abramchuk, b Olgun Güven a and Vladimir I. Feldman* b a Department of Chemistry, Hacettepe University, 06800 Ankara, Turkey. E-mail: guven@hacettepe.edu.tr b Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation. Fax: +7 495 939 4870; e-mail: vladimir.feldman@rad.chem.msu.ru c N. S. Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences, 117393 Moscow, Russian Federation 06.014 DOI: 10.1016/j.mencom.2012. The X-ray-induced reduction of Cu 2+ ions in aqueous–alcoholic suspensions containing poly(allylamine) and poly(acrylic acid) leads to a specific microheterogeneous structure with microdomains (100–200 nm) enriched by small copper nanoparticles (2 to 4 nm), which are dispersed in a continuous matrix.