Thermodynamical Study of Poly(n-hexyl methacrylate) with Some Solvents by Inverse Gas Chromatography Ozlem Yazici, Dolunay Sakar, Ozlem Cankurtaran, Ferdane Karaman Yıldız Technical University, Department of Chemistry 34220, Davutpasa Campus, Esenler-Istanbul, Turkey Received 3 March 2010; accepted 26 January 2011 DOI 10.1002/app.34288 Published online 10 June 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: The retention volume diagrams of ethyl acetate, isobutyl acetate, tert-butyl acetate, benzene, n-hex- ane, n-heptane, n-octane, acetone, chloroform, and acetoni- trile on the poly(n-hexyl methacrylate) (PHMA) were plotted at temperature ranges from 333 to 393 K by inverse gas chromatography technique. Some polymer-solvent ther- modynamic interaction parameters, such as weight fraction activity coefficient, X 1 1 , Flory-Huggins, v 1 12 , hard-core, v  12 , and some exchange parameters such as effective energy, X eff , enthalpy, X 12 , and entropy, Q 12 , were determined for studied solvents at infinite dilution of PHMA at tempera- tures mentioned above. Then the partial molar heat, D H s 1 , and free energy, D G s 1 , of sorption as well as the partial molar heat, D H 1 1 , and free energy, D G 1 1 , of mixing at infi- nite dilution were determined. In addition, the solubility parameter of PHMA, d 2 , was determined as 8.8 (cal/cm 3 ) 1/2 at room temperature by extrapolation of the values of solu- bility parameters from studied temperatures to 298 K. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1815–1822, 2011 Key words: poly (n-hexyl methacrylate); polymer-solvent interactions; inverse gas chromatography; solubility parameter INTRODUCTION Poly(alkyl methacrylate)s are most popular and well known polymers. Owing to their excellent properties such as high transparency, light weight, good mechanical and electrical properties, great resistance to high temperature, aging and chemicals, and easy formability, they are used in architecture, industry, motorization (as constructional materials and organic glasses in buildings, cars, ships, and aircrafts), in agri- culture, medicine, pharmacy as well as in textile, pa- per, and paint industry. 1,2 The ability of alkyl metha- crylates to copolymerize with other monomers allows obtaining special copolymers and terpolymers. Since homopolymers, copolymers, and terpoylmers of alkyl methacrylates are widely used to modify other com- mercial polymers, it is important to study their physi- cochemical properties to design suitable modifications. Inverse gas chromatography (IGC) has been used for investigation of thermal behavior of polymers, interactions of various liquids and gases with poly- meric materials and polymer-polymer miscibility. The method is simple, relatively rapid, and consider- ably accurate, with low cost, and at the same time the required equipment is available almost in all of the laboratories. The physicochemical properties that can be obtained for polymeric systems include weight fraction activity coefficients of solvents at in- finite dilution, interaction parameters of polymers with solvents and polymers, surface energies, molar heats of mixing and sorption, solubility parameter, glass transition and melting points, and crystallinity degree of polymers. 3–5 The exchange parameters of energy, X eff , enthalpy, X 12 , and entropy, Q 12 , in the equation-of-state theory 6,7 were designed to quantify the energy, en- thalpy, and entropy required to exchange a polymer segment adjacent to another polymer segment with a solvent molecule. In theory, it was assumed that their magnitude depends on the chemical nature of the polymer and solvent and independent of the composition of the polymer-solvent mixture. There- fore, the X eff , X 12 , and Q 12 values found at infinitely high polymer concentration from IGC measurements can be used to make simulations using equation of state theory in binary mixtures at lower polymer concentrations as in the case of osmotic pressure measurements. 8–10 It is expected that the exchange parameters of a polymer with solvents in a homologue series should be close to each other. 11–14 It was the first time we have determined exchange enthalpy and entropy pa- rameters of poly (dimethyl siloxane) 15 and poly (methyl methacrylate) 16 with some solvents directly from IGC measurements earlier. The parameters X 12 and Q 12 of these polymers with the studied solvents were comparable with those determined earlier by Correspondence to: D. Sakar (dolunaykar@yahoo.com). Contract grant sponsor: Scientific Research Projects Coordination Center, Yildiz Technical University. Journal of Applied Polymer Science, Vol. 122, 1815–1822 (2011) V C 2011 Wiley Periodicals, Inc.