Effects of Some Solvents on the Thermal and Free-Volume Properties of Poly(4-vinylpyridine) Complexes A. Mazroua, 1 E. Gomaa 2 1 Petrochemical Department, Petroleum Research Institute, Naser City, Cairo, Egypt 2 Physics Department, Faculty of Science, Ain Shams University, Abbassia 11566, Cairo, Egypt Received 5 June 2007; accepted 26 February 2008 DOI 10.1002/app.28416 Published online 9 July 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Modified poly(4-vinylpyridine) (P4VP) and its complexes were prepared with different solvents such as benzene, toluene, and xylene as well as potassium chloride (KCl) and copper chloride (CuCl 2 ). Fourier transform infrared spectroscopy, thermal analysis, and positron annihilation spectroscopy were used to investi- gate the properties of the modified P4VP and its com- plexes. It was concluded that complexes were formed between the polymer and solvents via quaternization of nitrogen in the ring with the solvents and also with KCl and CuCl 2 2H 2 O. Furthermore, the modified P4VP–CuCl 2 complexes were more stable than the modified P4VP– KCl complexes, and these complexes were more stable than the P4VP–solvent complexes. Ortho-positronium components (s 3 , I 3 ) were used to estimate the nanoscale free-volume hole size (V f ) and the free-volume fraction (f %). The free-volume hole size and its fractions depended on the addition of solvents and metals to the poly- mer. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 331– 340, 2008 Key words: FTIR; NMR; stabilization; thermal properties INTRODUCTION Polymer–metal complexes are now of great interest. Different polymers are commonly used in industry to produce a large variety of useful items for every- day personal and industrial uses as well. 1,2 It has been demonstrated that the thermophysical proper- ties of polymeric ligands can be modified by coordi- nation to transition-metal complexes. 3–6 CuCl 2 2H 2 O salt is an attractive candidate for forming coordina- tion complexes with the pyridine moieties of poly(4- vinylpyridine) (P4VP), such as a soluble copper–pyr- idine complex of the CuCl 2 (Py) 2 type. 7 On the other hand, octahedral divalent ruthenium is an attractive candidate for forming coordination complexes with the lone nitrogen pair of pyridine in the side group of P4VP or copolymers containing 4-vinyl repeat units. 8 Poly(2-vinylpyridine) (P2VP) and its metal-based derivatives have been synthesized and characterized through analytical measurements, molar mass mea- surements, and thermal analysis. 9 These complexes have been prepared 10–13 by the complexation of P2VP with metal salts. The conductivity of 2-vinyl- pyridine (2VP) has been found to increase by many orders of magnitude on combination with transition metals such as copper, cobalt, and platinum. The nitrogen atom of the pyridine groups of the organic polymer is coordinatively bonded to the copper cen- ter as suggested by X-ray photoelectron spectros- copy, ultraviolet spectroscopy, differential scanning calorimetry, and Fourier transform infrared (FTIR) techniques. 14 It has also been found that a P2VP– cobalt complex has the highest conductivity values among the complexes that have been studied. 13 The reaction of poly(2-vinyl pyridine) with cobalt chlo- ride and zinc chloride produces compounds with the stoichiometry of [Co(2VP) 2.5 (H 2 O)Cl 2 ] n and [Zn(2VP) 2.5 Cl 2 ] n . In the cobalt complex compound, the cobalt ion exists in both octahedral and tetrahe- dral environments, whereas in the zinc ion, it is in a tetrahedral environment. 15 P2VP and P4VP have been partly complexed with Co(II), Ni(II), and Zn(II) transition-metal ions. Ther- mal degradation is initiated at a low temperature, and the complexes decompose even near the thresh- old temperature for weight loss. 16 It is known that thermal treatment might influence the free-volume properties of a polymer. The free- volume hole size (V f ) is defined as a space that is not occupied by the macromolecules, and its value is equal to the difference between the specific and occupied volumes of the polymeric system. 17 The free volume, which may influence the physical and chemical properties of the polymer, can be detected with a positron used as a probe. 18,19 Correspondence to: E. Gomaa (ehsan.gomaa@yahoo.com). Journal of Applied Polymer Science, Vol. 110, 331–340 (2008) V V C 2008 Wiley Periodicals, Inc.