Abstract
In this study, the effects of probe quantities on retention volume and the physical and thermodynamic results of polymer-probe systems were investigated. For this purpose, by using inverse gas chromatographic method. Alcohols and alkanes with different chemical and physical properties were injected as probes on homopolymer (2-cyclohexylidene-1,3-dioxolane-4-yl-methyl methacrylate) (CHMMA). Probe quantities of 0.3, 0.6, and 0.9 μl were selected, and an injection was made at every 10°C between 40 and 150°C. In addition, 3 μl volume probes were tried but reproducible results were not obtained in these volumes and the detector was observed to be out of order after several injections. It has been observed that the specific retention volume of alcohols and alkanes partially increased by increasing the injection amount. A linear relationship was observed between probe quantities and specific retention volume. This linear relationship is apparent from the specific retention volume values, where the probes are independent of the physical and chemical structures. It was observed that the results obtained in all three injections were close to each other and within acceptable limits. The glass transition temperature of the polymer was determined to be a of 60°C. The thermodynamic data calculated for the injection of different amounts of probes were close to each other.
1. Introduction
The inverse gas chromatography (IGC) is a widely used method for studying the physicochemical and surface properties of polymer-solvent systems of polymers. The method is simple, economical, fast, and accurate.
The IGC method developed by Smidsrod and Guillet was used successfully to determine the physicochemical and surface properties of polymeric materials [1]. Many parameters such as glass transition temperatures, adsorption heats, the weight fraction activity coefficients, free energies, enthalpies of mixing, solubility parameters, interaction parameter, diffusion coefficient, and surface properties of the polymers can be calculated with this method [2, 3]. Vinyl polymers containing the 1,3-dioxane group in their structure have many properties such as negative electron beam, good resistance to dry etching, and herbicide function [4]. Properties of poly (acetyl benzofuran methyl methacrylate) and copolymers made by acrylonitrile are investigated by inverse gas chromatography. The properties of these structurally similar polymers were successfully determined by inverse gas chromatography [5]. The solubility and surface thermodynamics of the polypyrrole chloride were investigated by inverse gas chromatography, and some probes interacted with the polymer but all probes did not dissolve the polymer [6].
In this study, physicochemical properties of poly(2-cyclohexylidene-1,3-dioxolane-4-yl-methyl methacrylate) (CHMMA) were investigated by inverse gas chromatography. In addition, the effect of the probe quantity on the retention volume and polymer-probe system was investigated. The basis of the method is to find out the retention time of the probe injected into the column as a function of time, after the polymers to be examined have been coated with a supporting sheath.
2. Materials and Methods
The probe specific retention volumes, , are calculated from the standard chromatographic relation [7]: where is the retention times of the probe, is the flow rate of the carrier gas measured at room temperature, is the mass of the polymeric stationary phase, is the column temperature, and and are inlet and outlet pressures, respectively.
The molar heat (enthalpy) () and the molar free energy () of sorption of the probe absorbed by the polymer are given by the following equation [8]:
By incorporating equation (2), we calculated the entropy of sorption of solutes as follows: where is the probe specific retention volume, is the column temperature (K), is the molecular weight of the probe, and is the gas constant. The adsorption enthalpy of probes adsorbed by the polymer, , is given by the following equation [9]:
Partial molar free energy of mixing (cal/mol) and partial molar entalphy (cal/mol) at infinite dilution are calculated according to the following equations [10]:
The weight fraction activity coefficient, , of the solute probe at infinite dilution is calculated according to the following equation [11]:
The polymer-solute interaction parameter , at infinite dilution of different solutes used in this work, is defined by the following equation: where is the gas constant, is the specific volume of the polymer, is the molar volume of the solute, is the vapor pressure, and is the second virial coefficient of the solute in the gaseous state. , , and were calculated at the column temperature.
Second virial coefficients, , were computed using the following equation [12]: where and are the critical molar volume and the critical temperature of the solute, respectively, and is the number of carbon atoms in the solute.
The solubility parameters of polymers, , can be determined by using the following relation:
If the left-hand side of this equation is plotted against , then a straight line with a slope of () and an intercept of is obtained. Solubility parameters of the polymer, , can be calculated from both the slope and intercept of the straight line [13].
Ethyl alcohol, 1-propyl alcohol, 1-butyl alcohol, 1-pentyl alcohol, n-hexane, n-heptane, n-octane, and n-nonane were used as probes in chromatographic purity from the Merck & Company. Chromosorb W (80-100 Mesh) from the Polymer SIĞMA Company was coated 10% by weight on the polymer. The coated polymer weight is 0.228 grams. The 2-cyclohexylidene-1,3-dioxolane-4-yl-methyl methacrylate (CHMMA) polymer used in the experiment was synthesized for the first time in the laboratory of the Department of Chemistry of Fırat University [14]. GC-2010 model Shimadzu brand gas chromatography was performed by adding apparatus suitable for filled column analysis. This column is a polymer steel barrel with a diameter of 3.2 mm and a length of 1 m. The injection and detector were set at 200°C and 220°C, respectively. Helium gas was used as the carrier gas, and the flow rate was set at 30 ml/min. The FID detector was used during this process. Methane was used to determine the column dead volume. Polar and nonpolar probes of 0.3, 0.6, 0.9, and 3 μl volumes were injected every 10°C in the range of 40-150°C. All parameters of the study were inspected by a computer software program connected to the GC-2010 brand device.
3. Results and Discussion
The specific retention volumes of the probes which are calculated from equation (1) are given in Tables 1(a) and 1(b). As seen in the tables, there is a linear relationship between probe volume and retention volume, and as the amount of probe increases, its retention volume increases. In a study performed by Munk et al., a linear relationship between the retention time of the probes and the retention volume was found in the injection range [15]. The retention time or retention volume increases with the injection volume linearly [16]. The physical and thermodynamic values obtained from all three probe quantities (belonging to the polymer-probe system) were found to be close to each other and within acceptable limits. Repeatable results were not obtained at 3 μl injection, and the detector was extinguished at the end of a few injections. As a result, low-volume injections were the preferred choice for achieving accurate results for the polymer-solvent system. The glass transition temperatures of the polymers (), the solubility parameters (), the adsorption temperatures on the polymers under the glass transition temperature of the probes (), enthalpies of sorption (), free energies (), entropy (), enthalpy partial molar free energies (), weight fraction activity coefficients, , and Florry-Huggins interaction parameters () were calculated.
As shown in Figures 1(a)–1(c), the glass transition temperature of the CHMMA polymer in the graphs , 1/T drawn for each of the three injections was found to be about 60°C.As shown in Table 2, the adsorption heats () on the CHMMA polymer of the probes under glass transition temperatures, negative values, indicate that all probes interact with the polymer. While the values of were found to be positive in the area of sorption on above 353-383 K, and were found to be negative, as seen in Tables 3–5. These values are in agreement with the polymer-nonsolvent systems [5]. The positive values of and and the negative values of are compatible with previously published works about dioxolane ring containing polymer-probe systems [17]. Thermodynamic data for the infinite dilution state are supportive for polymer-nonsolvent systems. As can seen be in Table 6, partial molar free energies increased with the increase in the number of carbons in the probs. But, in all probes, decreased with increasing column temperature. Partial molar enthalpy () values of the mixture of infinitely dilute from data given in Table 7 between 393 and 423 K were found. values were calculated from the slope of the lines given in Figures 2–4 according to equation (5). As seen in Table 8, the enthalpy () values of the infinite diluted state, calculated from all three injections, are positive as they should be in polymer-nonsolvent systems [18]. Whether probes can solve the polymer can be understood from the relationship given below [19]. According to the following: (i): good solvent(ii): moderate solvent(iii): bad solvent
(a)
(b)
(c)
It has been found that alkane and alcohols (CHMMA) used as probes are bad solvents at low temperatures for the polymer. As shown in Tables 9 and 10, at high temperatures, alkanes can solve the polymer better than alcohols and this result is understood from the Flory-Huggins () parameters and the weight fraction activity coefficients, . The Flory-Huggins () value must be less than 0.5 in order for the probes to resolve the polymer. At high temperatures, the solubility parameters () of the probes and the solubility parameters () of the polymers were calculated. The difference between solubility parameters () must be less than 2 for the probe to be capable of solving the polymer [20]. The solubility parameter of a polymer, (), can be determined from either the slope or the intercept of a straight line obtained by plotting the left-hand side of equation (10) [10]. The values found in Tables 11 and 12 were used to determine the solubility parameter of the polymer. The solubility parameter of poly(CHMMA) was determined from either the slope or intercepts shown in Figures 5(a), 6(a), and 7(a), 5.922 (cal/cm3)0.5 or 6.617 (cal/cm3)0.5, 5.933 (cal/cm3)0.5 or 6.608 (cal/cm3)0.5, and 5.904 (cal/cm3)0.5 or 6.561 (cal/cm3)0.5 at 423 K, respectively. In addition, the solubility parameters of the polymer calculated at 413 K were found from the slopes and intercept of the lines in Figures 5(b), 6(b), and 7(b). The solubility parameter values of the polymer calculated for each of the three injections given in Table 13 are similar.
(a)
(b)
(a)
(b)
(a)
(b)
4. Conclusion
As a result, characterization of polymeric materials and thermodynamic information of polymer-probe systems can be obtained easily, quickly, and economically with inverse gas chromatography technique. It was observed that the specific retention volume was linearly changed with the amount of the probe. The specific retention volume was found to be independent of the physical and chemical properties of the probes. Results are suitable for polymer-nonsolvent systems. It was observed that the physicochemical results obtained from the retention volume values of the probes in the volume of 0.3, 0.6, and 0.9 μl were close to each other and within acceptable limits. Additionally, the injections of probes in the volume of 3 μl was tried but no reproducible results were obtained and it has been observed that the detector went out after a few injections. As the amount of probes increases, it is difficult to obtain reproducible results. For this reason, low-volume injections may be preferred both for achieving correct results and for saving time and substances.
Data Availability
The data used to support the findings of this study are available from the corresponding author upon request.
Conflicts of Interest
The author declares that they have no conflicts of interest.