2014 年 7 月 Vol.32 No.7 July 2014 Chinese Journal of Chromatography 746 ~ 752 Article DOI: / SP.J Determination of thermodynami

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1 2014 年 7 月 Vol.32 No.7 July 2014 Chinese Journal of Chromatography 746 ~ 752 Article DOI: / SP.J Determination of thermodynamic properties of poly( cyclohexyl methacrylate) by inverse gas chromatography Ismet KAYA 1, Cigdem Yigit PALA 1,2 (1. Canakkale Onsekiz Mart University, Faculty of Sciences and Arts, Department of Chemistry, Polymer Synthesis and Analysis Laboratory, Canakkale 17020, Turkey; 2. Kaleseramik AR GE Research, Kaleseramik R &D Center, Kaleseramik Canakkale Kalebodur Ceramic Industries Inc., Canakkale 17020, Turkey) Abstract: In this work, some thermodynamic properties of poly( cyclohexyl methacrylate) were studied by inverse gas chromatography ( IGC). For this purpose, the polymeric substance was coated on Chromosorb W and which was filled into a glass column. The retention times ( t r ) of the probes were determined from the interactions of poly ( cyclohexyl methacrylate) with n pentane, n hexane, n heptane, n octane, n decane, methanol, ethanol, 2 propanol, butanol, acetone, ethyl methyl ketone, benzene, toluene and o xylene by IGC technique. Then, the specific volume ( V 0 g ) was determined for each probe molecule. By using ( 1 / T; lnv 0 g ) graphics, the glass transition temperature of poly( cyclohexyl methacrylate) was found to be 373 K. The adsorp tion heat under the glass transition temperature (ΔH a ), and partial molar heat of sorption above the glass tran sition (ΔH S 1 ), partial molar free energy of sorption (ΔG S 1 ) and partial molar entropy of sorption (ΔS S 1 ) belong ing to sorption for every probe were calculated. The partial molar heat of mixing at infinite dilution ( ), partial molar free energy of mixing at infinite dilution ( ΔG 1 ), Flory Huggins interaction parameter ( χ 12 ) and weight fraction activity coefficient (a 1 ) values of polymer solute systems were calculated at different col umn temperatures. The solubility parameters (δ 2 ) of the polymer were obtained by IGC technique. Key words: inverse gas chromatography ( IGC); poly( cyclohexyl methacrylate); thermodynamic properties CLC number: O658 Document code: A Article IC: (2014) The methacrylate polymers are widely used in the manufacture of prostheses, contact lenses, adhesives, coatings, etc. [1]. The thermodynam ic properties and solubility of polymers are param eters that must be known for application of poly mer synthesis, economic production of polymeric materials and the process that used for this pur pose. These parameters can be investigated with the inverse gas chromatography ( IGC) technique. In this technique, the polymer is coated onto sup ported material and then filled into chromato graphic columns. The solvents with known prop erties pass through the column by carrier gas and leave the column at different times according to the interest of the polymer. IGC technique has been used for the determination of some proper ties of the polymers such as the solubility parame ters, melting point and glass transition tempera ture [2]. This method is of convenience and eco nomics of operation. The basic tools for IGC are inexpensive, rugged, widely available, and suit able for routine laboratory applications. IGC data might be collected quite rapidly over extended temperature ranges [3]. As the molecular weights of the polymeric substances are very high and the polymeric substances are non volatile, IGC meth od has been used to investigate the properties of these substances instead of normal gas chroma tography. IGC was developed by Smidsrod and Guillet [ 4] and applied to many polymeric sys tems. The information in the processing steps of polymers are important parameters for higher pol ymer quality. The thermodynamic of polymer sys tems affects how these processing steps can be carried out. Therefore, the knowledge of thermo dynamic data of polymer solutions is a necessity Corresponding author. Fax: , E mail: kayaismet@ hotmail.com. Received date:

2 第 7 期 Ismet KAYA, et al: Determination of thermodynamic properties of poly( cyclohexyl methacrylate) by inverse gas chromatography 747 for the improvement of industrial processes. In this paper, we have examined the interac tions of poly( cyclohexyl methacrylate) with alco hols ( polar) and alkanes ( nonpolar), acetone, ethyl methyl ketone, benzene, toluene and o xy lene solute probes by using IGC in the tempera ture range of K. Flory Huggins interac tion parameter ( χ 12 ) and weight fraction activity coefficient (a 1 ) of poly( cyclohexyl methac rylate) solute systems selected were determined by IGC technique. Also, we have determined the solubility parameter ( δ 2 ) of the poly( cyclohexyl methacrylate) by IGC technique. The glass transi tion temperature ( T g ) of poly ( cyclohexyl meth acrylate) was found to be 373 and 371 K from IGC and differential scanning calorimetry ( DSC ) measurements, respectively. 1 Theoretical The probe specific retention volume (V 0 g), cor rected to 0 was calculated from the standard chromatographic relation: V 0 = (Δt F 273 2) / (w T g r) 3 / 2[(P i / P 0 ) 2-1] / [(P i / P 0 ) 3-1] (1) where Δt ( = t p -t g ) is the difference between the retention times of the probe (t p ) and the methane (t g ); F is the flow rate of the carrier gas meas ured at room temperature (T r ); w is the mass of the polymeric stationary phase; P i and P 0 are the inlet and outlet pressures, respectively. The partial molar heat of sorption ( ΔH S 1 ) and the partial molar free energy of sorption (ΔG S 1 ) of the probe adsorbed by the polymer, is given by Equation (2) and (3) [5-8]: ΔH S = 1 -R[δln(V0 g) / δ(1 / T)] (2) ΔG S = -RTln[M 1 1V 0 g / (273 2R)] (3) By incorporating Equation (2) and (3) we cal culated the entropy of sorption of solutes as fol lows: ΔS S = 1 (ΔHS 1 -ΔGS 1 ) / T (4) The adsorption heat of probes adsorbed by the poly( cyclohexyl methacrylate) is given by the fol lowing equation where ΔH a is the adsorption en thalpy and R is the ideal gas constant [9]: δln (V 0 g) / δ(1 / T)= -ΔH a / R (5) The weight fraction activity coefficient, ( a 1 / w 1 ), the partial molar free energy ( ΔG 1 ) and the average partial molar heat of mixing ( ) at infinite dilution were calculated according to the following equations. Heats of vaporization (ΔH v ) for the probes were obtained from the heats of solution and heats of mixing by using the following relation [9]: (a 1 ) = ln[273 2R / (P 0 1 V 0 g M 1 )] - P 0 1(B 11 -V 1 ) / (RT) (6) where B 11 is the second viral coefficient of the or ganic solute in the gaseous state; P 0 1 is the vapor pressure of the probes at the column temperature (T, K); M 1 is the molecular weight of the probe; V 1 is the molar volume of the solute. The values of P 0 1 and B 11 have been calculated in literatures [10-12]. ΔG 1 = RT(a 1 ) (7) = R[δln (a 1 ) / δ(1 / T)] (8) ΔH v = -ΔHS 1 (9) The molar volume of the solute ( V 1 ) was cal culated using the following equation [11]: V 1 = V c / q r (10) where V c is the critical molar volume and q r is the reduced density of the solute given by the follow ing equation. q r = 1 20+( z c )(1-T / T c ) (0 8z c+0 31) (11) where z c is the critical compressibility factor and T c is critical temperature [13]. The Flory Huggins parameter ( χ 12 ) characteri zing the interactions of a vapor phase probe with a polymer is determined by Equation (12): χ 12 = ln[273 2Rv 2 / (P 0 1V 0 gv 1 )] - P 0 1[(B 11 -V 1 ) / (RT)] -1 (12) where R is the gas constant; v 2 is the specific vol ume of the polymer. Solubility parameter of the probe is calculated as follows [14]: δ 1 = [(ΔH v -RT) / V 1 ] 1/ 2 (13) where δ 1 is solubility parameter of probes; ΔH v is the molar enthalpy of vaporization for the probe at temperature T (K).

3 748 色谱第 32 卷 The solubility parameter of the polymer ( δ 2 ) can be calculated by using the following equation: δ 2 1 / (RT) -χ 12 / V 1 = [2δ 2 / (RT)]δ 1 -δ 2 2 / (RT) (14) If the left hand side of this equation is plotted against δ 1, a straight line with a slope of 2δ 2 / RT and an intercept of ( - δ 2 2 / RT ) is obtained. The solubility parameter of polymer (δ 2 ) can be deter mined from both the slope and intercept of the straight line [15]. The studies indicated that the inverse gas chromatography method gives good information on polymeric systems after careful analysis [9-12,14,16-18]. The Flory Huggins in teraction parameter (χ 12) and solubility parameter (δ 2 ) of naphthenic and paraffinic base oils had been determined from Emam M. N. et al. by IGC technique [19]. 2 Experimental 2.1 Materials Fourteen polar and non polar probes were used in this study. They were selected to provide differ ent chemical natures and polarities. n Pentane, n hexane, n heptane, n octane, n decane, metha nol, ethanol, 2 propanol, butanol, acetone, ethyl methyl ketone, benzene, toluene and o xylene, were from Aldrich Chemical Co. Poly( cyclohexyl methacrylate) was supplied by Across Organics in powder form of Registry No Poly ( cy clohexyl methacrylate ) was in white powder form. Refractive index (n20/ D) and density of po ly (cyclohexyl methacrylate) were and 1 1 g / ml at 25, respectively. Chromosorb W (45-60 mesh) was supplied from Sigma Chemical Co. 2.2 Instrumentation and procedure of ther modynamic studies A Shimadzu GC 2010 model gas chromatograph equipped with a dual flame ionization detector was used. Dried nitrogen gas ( research grade) was used as carrier gas. Methane was used as a non interacting marker to correct the dead volume in the column. Pressures at inlet of the column read from GC were used to compute corrected re tention volumes by the usual procedure. Flow rates were measured with a soap bubble flow me ter at the end of the column. A flow rate of about 15 cm 3 / min was used throughout our experiment. The glass tube (2 1 m 3 2 mm i. d.) was washed with acetone and was annealed prior to use. A column packing material was prepared by coating mesh size Chromosorb W treated with poly mer. An amount of 0 5 g poly(cyclohexyl methac rylate) was dissolved in 100 ml of tetrahydrofu ran ( THF). An amount of 5 g of the solid sup porting material was added to this solution and kept stirring afterwards. The solvent was removed by continuous stirring and slow evaporation under partial vacuum in a rotary evaporator. The pre pared material was packed into the glass tube [14, 16]. The column was conditioned with fast carrier gas ( N 2 ) flow rate for 48 h prior to use. The probes were injected into the column with an auto sampler. Three consecutive injections were made for each probe at each set of measurement and three values of retention time with inverse gas chromatography method were averaged. An injec tion volume was selected as 0 1 μl. Methane was synthesized in the laboratory by the reaction of sodium acetate with sodium hydroxide [10]. DSC analyses were carried out between ( in N 2, 10 / min) using Perkin Elmer Pyris Sap phire DSC. 3 Results and Discussion The specific retention volumes ( V 0 g ) of 14 probes were obtained by loading poly( cyclohexyl methacrylate) at a series of temperatures. Probes of different chemical natures and polarities ( n al kanes, alcohols, ketones, aromatics) were se lected for this study. The V 0 g values of these probes were calculated according to Equation (1) and are given in Table 1 and Fig. 1, respectively. The averages of three values of retention time measured with inverse gas chromatography meth od were used in calculation of V 0 g of each probe at different temperatures. V 0 g values changed with the molecular weight of each group of solvents. Also, V 0 g values of probes on poly(cyclohexyl methacry late) were decreased with increased temperature. According to IGC and DSC analyses, T g of poly

4 第 7 期 Ismet KAYA, et al: Determination of thermodynamic properties of poly( cyclohexyl methacrylate) by inverse gas chromatography 749 Probe Table 1 Variation of V 0 g of selected organic solvent systems at different column temperatures using poly( cyclohexyl methacrylate) as stationary phase V 0 g / (cm 3 / g) 353 K 363 K 373 K 383 K 393 K 403 K 413 K 423 K 433 K 443 K 453 K n Pentane n Hexane n Heptane n Octane n Decane Methanol Ethanol Propanol Butanol Acetone EMK Benzene Toluene o Xylene EMK: ethyl methyl ketone. ( cyclohexyl methacrylate) was found as 100 and 98, respectively. The ( a 1 ) Probe Table 2 and χ 12 values obtained using Equation (6) and (12) respectively are shown in Table 2. The values of χ 12 greater than 0 5 repre sent unfavorable polymer solvent interactions while values lower than 0 5 indicate favorable in teractions in dilute polymer solutions [ 17]. The following rules have been formulated by Guillet et al [ 15]: ( a 1 ) < 5: good solvents; 5 < ( a 1 / w 1 ) <10: moderate solvents; (a 1 ) >10: bad solvents. The ( a 1 ) data in Table 2 indicate that n pentane, acetone and benzene are good solvents; n hexane, n heptane, methanol, ethanol, 2 Poly(cyclohexyl methacrylate) solute interaction coefficient (χ 12 ) and weight fraction activity coefficients (a 1 ) of selected organic solvents at various temperatures (a 1 ) 423 K 433 K 443 K 453 K χ K 433 K 443 K 453 K n Pentane n Hexane n Heptane n Octane n Decane Methanol Ethanol Propanol Butanol Acetone EMK Benzene Toluene o Xylene Fig. 1 V 0 g of selected probes at different temperatures

5 750 色谱第 32 卷 propanol, butanol, ethyl methyl ketone, toluene and o xylene are moderate solvents; n octane, n decane are bad solvents for poly ( cyclohexyl methacrylate). Similar results were obtained ac cording to the interaction parameters. χ 12 and ΔG 1 were found to be related to the number of carbons in the series and temperature. χ 12, ΔG 1, (a 1 ) and at infinite dilution of the solutes showed dependence on the number of carbons in the series ( except for alcohols). These values increased with increasing number of carbons in the series. But in all series, the values of χ 12, ( a 1 ) and ΔG 1 decreased with in crease in the column temperature. ΔG 1 and ΔG S 1 calculated from Equation (7) and (3) respective ly, are shown in Table 3. Table 3 (ΔG) 1 and ΔG1 S of sorption by using poly(cyclohexyl methacrylate) as the stationary phase and selected organic solvents as mobile phase Probe (ΔG) 1 / (cal / mol) ΔG1 S / (cal / mol) 423 K 433 K 443 K 453 K 383 K 393 K 403 K n Pentane n Hexane n Heptane n Octane n Decane Methanol Ethanol Propanol Butanol Acetone EMK Benzene Toluene o Xylene values of probes at infinite dilution were calculated using Eqation ( 8). ln ( a 1 ) were plotted against T -1 / K -1 ( Fig. 2). ΔH a and ΔH S 1 of poly ( cyclohexyl methacrylate ) probe systems were calculated by plotting lnv 0 g against T -1 / K -1 using Equation ( 5) and ( 2), respectively. ΔH v values of probes were found according to Equa tion ( 9). Table 4 shows the experimentally ob tained sorption heats (ΔH S 1 ), molar heats of mix ing ( ) and adsorption heats ( ΔH a ) in tem perature ranges of K, K and K, respectively. Fig. 2 Variation of (a 1 ) with T -1 / K -1 for (a) n pentane, n hexane, n heptane, n octane, n decane; (b) methanol, ethanol, 2 propanol, butanol; ( c) acetone, ethyl methyl ketone, benzene, toluene and o xylene The number of carbon atoms of each probe is different from each other. ΔH a becomes more ex othermic with increasing CH 2 groups in each group of probes due to the increasing surface are as of probes. ΔH S 1 becomes more exothermic with more CH 2 groups in each group probe. The attrac tion forces between poly ( cyclohexyl methacry late) and ketones are actually a combination of

6 第 7 期 Ismet KAYA, et al: Determination of thermodynamic properties of poly( cyclohexyl methacrylate) by inverse gas chromatography 751 two types: dispersive forces between the CH 2 groups of the ketones and the methyl group of poly( cyclohexyl methacrylate ) and the interac tion of the C = O groups of the ketones with the C = O groups of poly( cyclohexyl methacrylate) via dipole dipole interactions. Also, alcohols have higher exothermic ΔH S 1 values than hydrocarbons, ketones and aromatics since there are hydrogen bond interactions between poly( cyclohexyl meth acrylate) and alcohols. ΔG S 1 of these probes on poly( cyclohexyl methacrylate) are of positive val ues. According to thermodynamic rules, ΔG is of negative value for spontaneous events. For this reason, interactions between polymer and probes are weak. values of n hydrocarbons changed from 3 84 to 6 27 kcal / mol as seen from Table 4. values of alcohols changed from 3 88 to 5 39 kcal / mol, while the values of ketones changed from 3 40 to 3 88 kcal / mol and the values of aro matics changed from 1 36 to 1 98 kcal / mol. Based upon these results the probes with low values were accepted as solvent polymer sys tems and the others were taken as non solvent polymer systems. Table 4 ΔH1( S K), ( K), ΔH a ( K), and ΔH v of selected organic solvents on poly( cyclohexyl methacrylate) Solvent ΔH1 S / ΔH a / / ΔH v / (kcal / mol) (kcal / mol) (kcal / mol) (kcal / mol) Calculated according to Equation (9) From Ref. [13] n Pentane n Hexane n Heptane n Octane n Decane Methanol Ethanol Propanol Butanol Acetone EMK Benzene Toluene o Xylene DiPaola Baranyi et al [7] determined that values for aromatic solvents changed from kcal / mol to 0 3 kcal / mol in polystyrene ( PS), and from 0 3 kcal / mol to 1 1 kcal / mol in polym ethyl acrylate (PMA). These values for the same polymers changed from 0 6 kcal / mol to 2 5 kcal / mol and from 2 5 kcal / mol to 4 1 kcal / mol in n hydrocarbons. According to these results the probes with small values were suitable for solvent polymer systems and those with large values were suitable for nonsolvent polymer systems [7]. The solubility parameter (δ 2 ) of a polymer can be determined by Equation (14) [18]. δ 2 was de termined from either slope or intercept of a straight line obtained by plotting the left hand side of Equation (14) versus δ 1 (Fig. 3). δ 2 of poly (cyclohexyl methacrylate ) was found as 5 17, 4 60, 4 18, 3 74 ( cal / cm 3 ) 0 5 and 5 17, 4 38, 3 87, 3 22 (cal / cm 3 ) 0 5 at 423, 433, 443 and 453 K, respectively (Table 5). Table 5 T / K Slope Intercept Variation of δ 2 with poly(cyclohexly methacrylate) temperature Calculated from slope δ 2 / (cal / cm 3 ) 0.5 Calculated from intercept These values were in compliance with the val ues found previously [20]. The solubility parame ters obtained from the slopes and intercepts of the plots were in good agreement with each other. Comparing the δ 2 values of poly(cyclohexyl meth acrylate ) at different temperatures, it showed that the solubility parameters decreased with

7 752 色谱第 32 卷 Fig. 3 Variation of the term [δ 2 1 / (RT) -χ 12 / V 1 ] with δ 1 at the column temperatures of (a) 423 K, (b) 433 K, (c) 443 K and (d) 453 K for poly(cyclohexyl methacrylate) increasing temperature. 4 Conclusions Inverse gas chromatography technique was suc cessfully applied to determine the glass transition temperature of poly ( cyclohexyl methacrylate ). Some thermodynamic properties were obtained for poly( cyclohexyl methacrylate) solute systems such as adsorption heat, partial molar heat of sorption, partial molar free energy of sorption, partial molar heat of mixing at infinite dilution, partial molar free energy of mixing at infinite dilu tion, Flory Huggins interaction parameter and weight fraction activity coefficient values. The solubility parameter of the polymer was deter mined with inverse gas chromatography tech nique. The results obtained are in good agreement with those of polymer solvents and polymer non solvents systems. The technique is relatively un complicated and the data reduction is carried out by a computer. References: [1] Jang Y S, Kang J W, Byun H S. J Ind Eng Chem, 2010, 16 (4): 598 [2] Aydin S. [ MS Dissertation]. Istanbul, Turkey: Yildiz Tech nique University, 2005 [3] Shyamala M, Pragati Ranjan S, Sharma J V C. International Journal of Pharma Sciences, 2013, 3(2): 201 [4] Guillet J E, Purnel J H. New Developments in Gas Chroma tography: 322 Progress in Gas Chromatography. New York, USA: Wiley Interscience, 1973: 323, 187 [5] Smidsrod O, Guillet J E. Macromolecules, 1969, 2(3): 272 [6] Braun J M, Guillet J E. Macromolecules, 1977, 10(1): 101 [7] DiPaola Baranyi G, Guillet J E. Macromolecules, 1978, 11 (1): 228 [8] Galin M, Maslinco L. Macromolecules, 1985, 18(11): 2192 [9] Kaya I, Ozdemir E. Polymer, 1999, 40 (9): 2405 [10] Kaya I. [ PhD Dissertation]. Elazig, Turkey: Firat Universi ty, 1995 [11] Kaya I, Demirelli K. Polymer, 2000, 41(8): 2855 [12] Papadopoulou S K, Panayiotou C. J Chromatogr A, 2012, 1229: 230 [13] Reid C R, Prausnitz J M, Sherwood T K. The Properties of Gases and Liquids. 2nd ed. New York, USA: McGraw Hill, 1977 [14] Kaya I, Ozdemir E, Coskun M. J Macromol Sci A, 1996, A33(1): 37 [15] Guillet J E, Purnel J H. Advances in Analytical Chemistry and Instrumentation Gas Chromatography. New York, USA: John Wiley & Sons, 1973 [16] Pala C Y. [ MS Dissertation ]. Canakkale, Turkey: Canakkale Onsekiz Mart University, 2013 [17] Klein J, Jeberien H E. Macromol Chem Phys, 1980, 181 (6): 1237 [18] Kaya I, Ilter Z, Senol D. Polymer, 2002, 43(24): 6455 [19] Emam M N, Ahmed E E. Chinese Journal of Chromatogra phy, 2007, 25(6): 871 [20] Bicerano J. Prediction of Polymer Properties. 3rd ed. New York, USA: Marcel Dekker, Inc., 2002

İsmet KAYA Department of Chemistry, Faculty of Sciences and Arts, Department of Chemistry, Faculty of Sciences and Arts, Received

İsmet KAYA Department of Chemistry, Faculty of Sciences and Arts, Department of Chemistry, Faculty of Sciences and Arts, Received Turk J Chem 23 (1999), 171 179. c TÜBİTAK A study of the thermodynamic properties of poly [2-(3-mesityl-3-methylcyclobutyl)-2-hydroxyethyl methacrylate] at infinite dilution using inverse gas chromatography