High-Pressure Phase Behavior for Poly[dodecyl methacrylate] +

Jul 17, 2009 - Experimental cloud-point curves for poly(dodecyl methacrylate) [P(DDMA)] + dodecyl methacrylate (DDMA) or dimethyl ether (DME) in ...
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Ind. Eng. Chem. Res. 2009, 48, 7821–7827

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High-Pressure Phase Behavior for Poly[dodecyl methacrylate] + Supercritical Solvents + Cosolvents and Carbon Dioxide + Dodecyl Methacrylate Mixture Shuang Liu,† Ha-Yeon Lee,† Soon-Do Yoon,† Ki-Pung Yoo,‡ and Hun-Soo Byun*,† School of Biotechnology and Chemical System Engineering, Chonnam National UniVersity, Yeosu, Jeonnam 550-749, South Korea, and Department of Chemical and Biomolecular Engineering, Sogang UniVersity, Seoul 121-742, South Korea

Experimental cloud-point curves for poly(dodecyl methacrylate) [P(DDMA)] + dodecyl methacrylate (DDMA) or dimethyl ether (DME) in supercritical CO2 are reported for the binary and ternary mixtures up to 473 K and 248.0 MPa. The location of the P(DDMA) + CO2 cloud-point curve shifts to lower temperatures and pressures when DDMA or DME is used as a cosolvent. P(DDMA) does not dissolve in pure CO2 to the temperature of 493 K and the pressure of 260.0 MPa. High-pressure phase behavior data are presented for the CO2 + DDMA system at 313.2-393.2 K and up to ca. 25.2 MPa. The system exhibits type-I phase behavior with a continuous mixture-critical curve, and the system is adequately modeled with the Peng-Robinson equation of state. High-pressure phase behavior data are reported for P(DDMA) in supercritical propane, propylene, butane, and 1-butene. Cloud-point curves for the P(DDMA) in C4 hydrocarbons are at lower temperatures than the P(DDMA) + C3 hydrocarbons curves at fixed pressures. 1. Introduction Thermodynamic knowledge of high-pressure phase behavior experimental data of polymer and supercritical fluid solvents + cosolvent mixtures plays an essential role in the basic design of various polymer processes and related industrial application. In particular, the carbon dioxide among SCF solvents has interested many for a variety of applications including polymer material synthesis, particle generation, foaming, coating, and extraction.1-5 As a result, the attention has been placed on the polymer and chemical thermodynamic understanding of supercritical fluid systems.6,7 The information on the high-pressure behavior for monomer in supercritical carbon dioxide has been valuable in the design of new separation processes in various fields such as polymerization condition, particle formation, particle size, pharmaceutical, and related industries.8 The experiment for the ternary (polymer + supercritical solvents + cosolvents) system is performed to develop the polymer process such as polymer separation, which considers an optimum and economy of processes. The methacrylate-based polymers are widely used in modern plastic technology. The methacrylate monomers and polymers are mainly used for a variety of applications such as prostheses, contact lenses, photopolymer printing plates, adhesives, and coatings.9 Experimental data of phase behavior with the methacrylate polymers in supercritical fluid solvents were reported by Gornert and Sadowski,10 McHugh et al.,11 and Byun et al.12,13 The thermodynamic properties of acrylic polymers were reported by Gaur et al.14 Gornert and Sadowski10 had reported the experimental phase equilibrium data of the poly(methyl methacrylate) (Mw ) 17 900 and 101 000)/methyl methacrylate/carbon dioxide ternary system using a variable-volume view cell. McHugh et al.11 have demonstrated that phase behavior curves for the poly(butyl methacrylate) (Mw ) 100 000 and 320 000) in supercritical CO2 * To whom correspondence should be addressed. Tel.: +82-61-6593296. Fax: +82-61-653-3659. E-mail: [email protected]. † Chonnam National University. ‡ Sogang University.

present the upper critical solution temperature (UCST) curve at pressure up to ∼300.0 MPa and below 503 K. Byun et al.12 have performed experimental phase behavior for poly(hexyl methacrylate) + CO2 + hexyl methacrylate system at temperature range from 334 to 473 K and pressure up to 220.0 MPa using a high-pressure variable volume view cell. The experimental cloud-point data for poly(ethyl methacrylate) and poly(butyl methacrylate) in supercritical CO2 were reported by Byun and McHugh.13 Experimental phase behavior data for binary CO2 + DDMA system are obtained to complement the P(DDMA) + CO2 + DDMA (or DME) studies presented here because there is no literature for phase behavior data available on these mixtures. Tsang and Streett15 reported the vapor-liquid equilibria data for the CO2 + DME mixture. They also demonstrated that the Peng-Robinson equation of state16 provides an adequate representation of the experimental data when kij is -0.020. The phase behavior data for CO2 with DDMA and DME will be obtained if any one of these two binary mixtures form multiple phases in the pressure-temperature-composition regions where these cosolvents are used. The CO2 + DDMA experimental data are also fitted to the Peng-Robinson equation of state16 so that the phase boundary curves can be calculated at elevated operating temperatures and pressures. The goal of this work is to determine the impact of DDMA cosolvent on the phase behavior of the P(DDMA) + CO2 system and the impact of DME on the cloud-point of the P(DDMA) + CO2 mixture. Given that CO2 has been considered as the desirable reaction medium for free radical polymerizations,17 phase behavior data for these ternary P(DDMA) + supercritical CO2 + DDMA mixtures provide the information needed on the regions where homogeneous polymerization can occur in the presence of excess monomer. Binary cloud-point curves are also obtained for P(DDMA) in supercritical propane, propylene, butane, 1-butene, and DME. These data show the effect of solvent polarity on the location of the cloud-point curves. Table 1 lists the critical temperature, critical pressure, critical density, polarizability, dipole moment, and quadrupole moment for the solvents used in this study.18-23 Propane and propylene have similar critical properties and

10.1021/ie900598w CCC: $40.75  2009 American Chemical Society Published on Web 07/17/2009

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Table 1. Critical Temperatures (Tc), Critical Pressures (Pc), Critical Densities (Gc), Polarizabilities (r), Dipole Moments (µ), and Quadrupole Moments (Q) of the Solvents Used in This Study18-23 solvents CO2 propane propylene butane 1-butene dimethyl ether

Pc Fc R × 1025 µ Q × 1026 Tc (K) (MPa) (g/cm3) (cm3) (debye) (erg1/2 cm5/2) 304.3 369.9 365.1 425.3 419.6 400.0

7.38 4.25 4.62 3.80 3.97 5.30

0.469 0.217 0.236 0.228 0.234 0.258

26.5 62.9 62.6 81.4 82.4 52.2

0.0 0.1 0.4 0.0 0.3 1.3

-4.3 1.2 2.5 2.5 1.2

polarizabilities, but propylene, with a double bond, has a significant quadrupole moment that favorably interacts with the weak polar DDMA groups in the polymer. It is evident that there is similarity between butane and 1-butene. Hence, it is possible to determine the impact of quadrupole interactions, essentially independent of dispersion interactions, by comparing the cloud-point curves for each of these pairs of alkane and alkene solvents. On the other hand, the comparison of propane and butane, or propylene and 1-butene, yields information of the effect of solvent size, and hence polarizability on the phase behavior, essentially independent of quadrupole effects. DME has a significant dipole moment that provides an opportunity to compare the impact of dipole interactions with quadrupole interactions found with the alkenes and with CO2. 2. Experimental Section 2.1. Apparatus and Procedure. Figure 1 shows a schematic diagram of the experimental apparatus. The phase behavior measurements are carried out by using a variable-volume view cell that has been described in detail elsewhere.2,24-26 We obtain cloud-point curves for P(DDMA) + supercritical solvents + DDMA (or DME) mixture24,25 and pressure-composition isotherms for CO2 + DDMA mixture using the high-pressure experimental apparatus.2,26 The pressure inside the cell is measured with a Heise gauge (Dresser Ind., model CM-108952, 0-345.0 MPa, accurate to within (0.35 MPa) and high-pressure generator (HIP Inc., model 37-5.75-60). The temperature inside the cell is measured using a platinum-resistance thermometer (Thermometrics Corp., Class A) connected to a digital multimeter (Yokogawa, model 7563, accurate to within (0.005%). The system temperature is typically maintained to within (0.2 K below 473 K. The cell inside is viewed on a video monitor using a camera coupled to a borescope (Olympus Corp., model F100-038-000-50) placed against the outside of the sapphire window. Polymer is loaded into the cell to within (0.001 g, and then the cell is purged with nitrogen followed by supercritical fluid

Figure 2. Experimental cloud-point curves for the P(DDMA) + CO2 + DDMA system with different DDMA concentrations. The polymer concentration is ∼5 wt % for each solution.

solvents to ensure that all of the organic matters are removed. Liquid cosolvent is injected into the cell to within (0.002 g by using a syringe, and supercritical solvent and cosolvent are transferred into the cell gravimetrically to within (0.004 g by using a high-pressure bomb. The polymer + solvent + monomer mixture in the cell is heated to the desired temperature and pressurized until a single phase is achieved. The binary and ternary mixtures are maintained in the one-phase region at the designed temperature for at least 30-40 min so that the cell can reach thermal equilibrium. The pressure is then slowly decreased until the solution becomes cloudy. The cloud-point pressure is defined as the point at which the solution becomes so opaque that it is no longer possible to see the stir bar in the solution. After a cloud point is obtained, the solution is recompressed into a single phase, and the process is repeated. Cloud points are measured for the polymer solutions at a fixed P(DDMA) concentration of 5.0 ( 1.0 wt %. Cloud points are measured and reproduced at least twice to within (0.28 MPa and (0.3 K. Bubble-, dew-, and critical-point transitions for the CO2 + DDMA mixture are measured and reproduced at least twice to within (0.03 MPa and (0.2 K. The uncertainty in the mole fraction of the mixture was less than (0.002. 2.2. Materials. Poly(dodecyl methacrylate)[P(DDMA)] (Mw ) 250 000; Tg ) 208 K; CAS RN 25719-52-2) used in this work was obtained from Scientific Polymer Products, Inc. and used as received. Dodecyl methacrylate (DDMA) (min. 98% purity; CAS RN 142-90-5) used in this work was obtained from Polysciences, Inc. and used as received. To prevent DDMA polymerization, 2,6-di-tert-butyl-4-methyl phenol (Aldrich, 99% purity) was used as an inhibitor at a concentration of 0.005 times the amount of DDMA. Carbon dioxide (99.8% minimum purity) was obtained from Daesung Industrial Co., propane (98% purity) was obtained from LG Gas (E1), and propylene (99.6% purity), butane (97.0% purity), 1-butene (99.5% purity), and dimethyl ether (DME) (99.5% purity) were obtained from Yeochun NCC Co. and used as received. Because the P(DDMA) was supplied in a toluene solution, the polymer solution was placed under vacuum for at least 10 h by the rotary evaporator (Tamato Scientific Co., model RE-47) for toluene removal. 3. Experimental Results and Discussion

Figure 1. Schematic diagram of the experimental apparatus used in this study.

3.1. Phase Behavior for P(DDMA) + SCF CO2 + Cosolvents Mixture. Figure 2 and Table 2 show the cloud-point behavior of the P(DDMA) + CO2 + x wt % DDMA system. P(DDMA) does not dissolve in pure CO2 to the temperature of 493 K and the pressure of 260.0 MPa. The P(DDMA) + CO2

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Table 2. Experimental Cloud-Point (CP) Data for the Poly(dodecyl methacrylate) [P(DDMA)] + CO2 + x wt % Dodecyl Methacrylate (DDMA) System Measured in This Study T/K

P/MPa

transition

5.1 wt % P(DDMA) + 9.8 wt % DDMA 431.1 432.6 433.7 452.7

162.93 154.10 146.03 120.52

CP CP CP CP

5.5 wt % P(DDMA) + 14.3 wt % DDMA 410.3 413.5 423.7 433.9 452.3

173.28 151.72 117.14 101.69 95.83

CP CP CP CP CP

5.1 wt % P(DDMA) + 19.6 wt % DDMA 370.1 370.8 376.2 394.6 415.7 433.3 453.8

173.62 142.79 113.17 88.69 79.10 76.76 75.45

CP CP CP CP CP CP CP

5.6 wt % P(DDMA) + 25.0 wt % DDMA 342.4 355.5 374.6 391.6 412.9 433.5 455.3

109.14 72.28 61.90 58.35 58.00 59.28 60.62

CP CP CP CP CP CP CP

4.9 wt % P(DDMA) + 36.7 wt % DDMA 327.8 353.7 378.1 403.6 428.7 452.8

23.86 27.24 31.03 34.48 37.72 40.55

CP CP CP CP CP CP

+ 9.8 wt % DDMA cloud-point curve has a rapidly negative slope (i.e., upper critical solution temperature (UCST) curve) at a pressure range of 120.0-163.0 MPa and at a temperature range of 431-453 K. The location of the UCST curve is the critical mixture shown with the steep and negative slope at low temperatures. A fluid phase region exists at pressures and temperatures to the right of the UCST line, while a liquid + liquid region exists at pressures and temperatures to the left of the UCST line.27 The P(DDMA) + CO2 + 9.8 wt % DDMA cloud-point curve shifts to ca. 50.0 MPa at 453 K when 19.6 wt % DDMA is added to the solution. The cloud point for the P(DDMA) + CO2 + 19.6 wt % DDMA mixture shows a rapid increase to less than 368 K. The sharp rise of the cloud-point pressure with decreasing temperature is attributed to the increase of solvent + solvent interactions over polymer + solvent interactions. With 36.7 wt % DDMA cosolvent in P(DDMA) + CO2 mixture, the cloud-point curve is now located at pressure as low as 24.0 MPa and temperature to 328 K. The cloud-point curve for the P(DDMA) + CO2 + 36.7 wt % DDMA mixture exhibits LCST (lower critical solution temperature curve) behavior with a positive slope (ca. 1.3 MPa/K). The LCST curve is the critical mixture shown with the steep and positive slope at high temperatures. A fluid phase (single) region exists at pressures and temperatures to the left of the LCST line, while a liquid + liquid region exists at pressures and temperatures to the right of the LCST line.27 Figure 3 and Table 3 show the impact of 44.7 wt % DDMA monomer on the phase behavior of the P(DDMA) + CO2

Figure 3. Impact of 44.7 wt % DDMA monomer (on a polymer-free basis) on the phase behavior of the P(DDMA)-CO2 system. O, fluid f liquid + liquid transition; 9, fluid f liquid + vapor transition; b, liquid + liquid (L + L) f liquid1 + liquid2 + vapor(LLV) transition; - - -, suggested extension of the LLV line. Table 3. Experimental Cloud-Point (CP), Bubble-Point (BP), and Liquid-Liquid-Vapor (LLV) Data for the Poly(dodecyl methacrylate) [P(DDMA)] + CO2 + Dodecyl Methacrylate (DDMA) System Measured in This Study T/K

P/MPa

transition

4.8 wt % P(DDMA) + 44.7 wt % DDMA Cloud-Point Transition 393.4 414.2 435.8 452.2

21.90 25.24 28.69 30.41

CP CP CP CP

Bubble-Point Transition 361.4 370.2 382.9

18.79 19.45 20.70

BP BP BP

Liquid-Liquid-Vapor Transition 396.7

21.67

LLV

system. The cloud-point curve for the P(DDMA) + CO2 + 44.7 wt % DDMA mixture exhibits LCST-type behavior with a positive slope of 1.5 MPa/K at a pressure range of 22.0-30.4 MPa and at a temperature range of 393-453 K. The cloudpoint curve of this system intersects the bubble-point curve at ca. 391 K and ca. 21.5 MPa. The bubble-point curve switches to a liquid + liquid + vapor (LLV) curve28 at temperature greater than 391 K. Figure 4 and Table 4 show the cloud-point curve of the DME concentration for P(DDMA) + CO2 + x wt% DME mixture.

Figure 4. Phase behavior of the DME concentration for P(DDMA) + CO2 + x wt % DME system. The concentration of polymer is ∼5 wt % for each solution.

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Table 4. Experimental Cloud-Point (CP) Data for the Poly(dodecyl methacrylate) [P(DDMA)] + CO2 + Dimethyl Ether (DME) System with Different DME Content Measured in This Study T/K

P/MPa

transition

aij ) (aiiajj)1/2(1 - kij) bmix )

(2)

∑xb

(3)

i i

i

5.7 wt % P(DDMA) + 13.0 wt % DME 426.0 435.6 443.3 454.5 463.6 474.1

179.48 150.17 135.34 124.66 119.14 115.34

Here, kij is the binary interaction parameter determined by fitting P-x isotherms, and aii and bi are pure component parameters defined by Peng and Robinson.16 Table 6 lists the pure component critical temperatures and critical pressures for CO230 and DDMA that are used with the Peng-Robinson equation of state.16 The acentric factors for CO2 and DDMA are 0.225 and 0.779, respectively. The critical property of DDMA is calculated with a group-contribution method,30 and the vapor pressures, needed to calculate the acentric factors, are calculated with the Lee-Kesler method.30 Values for the two binary interaction parameters are determined by minimizing the objection function (OBF).31

CP CP CP CP CP CP

4.7 wt % P(DDMA) + 25.5 wt % DME 375.8 383.9 394.0 412.4 435.1 452.3

169.83 141.90 115.00 97.41 87.76 84.31

CP CP CP CP CP CP

4.3 wt % P(DDMA) + 41.4 wt % DME 333.2 352.2 373.6 393.7 413.2 433.4 454.3

113.28 71.21 60.86 58.10 57.76 58.45 59.48

N

CP CP CP CP CP CP CP

OBF )

i

The P(DDMA) + DME mixture is obtained at a temperature range of 373-453 K and pressures of 7.0-20.0 MPa. The pressure difference between two systems is probably due to whether or not the dipole moment was in DME and carbon dioxide as shown in Table 1. As shown in Figure 4, for the P(DDMA) + CO2 + x wt % DME, 13.0 wt % DME shows the UCST-type behavior with a negative slope, and then the pressure increases rapidly at ca. 423 K. At T < 423 K, the cloud-point curve increases sharply with pressure, suggesting that either polymer + polymer or cosolvent + cosolvent polar interactions dominate the interchange energy and induce the system to phase separately. Hence, the DDMA polymer precipitates out of the binary and ternary mixture probably due to strong polymer + polymer interaction. If the DDMA concentration is increased to 25.5 wt %, the phase behavior exhibits a negative slope in the temperature range of 376-453 K. The 25.5 wt % DDMA cloud-point curve shows a rapid increase in pressure at 388 K because of a large increase in energetics between polymer segment + polymer segment as compared to polymer segment + solvent interaction. With 41.4 wt % DME, the cloud-point curve exhibits UCST region with a negative slope in the temperature range from 333 to 454 K and pressures up to 113.0 MPa. 3.2. Phase Behavior for CO2 + DDMA Mixture. P-x isotherm experimental data for binary CO2 + DDMA mixture are listed in Figure 5 and Table 5. The P-x isotherm for the CO2 + DDMA mixture is consistent with the characteristics expected for type-I phase behavior with a continuous criticalmixture curve.27,29 Liquid-liquid-vapor behavior is not observed for the CO2 + DDMA system. The experimental data in this work are modeled with the Peng-Robinson equation of state16 using the following mixing rules. amix )

∑ ∑xxa

i j ij

i

j

∑

(1)

(

Pexp - Pcal Pexp

)

2

(4)

Figure 5 shows the comparison of experimental data and calculated results for CO2 + DDMA P-x isotherm at temperatures of 313.2, 333.2, 353.2, 373.2, and 393.2 K where the binary interaction parameters, kij ) 0.033, were fit only to the 353.2 K isotherm. When one mixture parameter is used, the fit of the isotherms is significantly better. As previously mentioned, Tsang and Streett15 reported the experimental data for the CO2 + DME mixture, which has a continuous critical-mixture curve with a maximum pressure of 8.0 MPa at ca. 320.2 K. They also demonstrated that the Peng-Robinson equation of state16 provided a very adequate representation of the experimental data if a kij of -0.020 was used. 3.3. Phase Behavior for P(DDMA) + SCF Solvents and Poly[alkyl methacrylate] + SCF Solvents + Alkyl Methacrylate System. Figure 6 and Table 7 show the cloud-point curves of P(DDMA) dissolved in supercritical propane, propylene, butane, 1-butene, and DME obtained in this work. The cloud-point behavior for P(DDMA) + propane, + propylene, + butane, and + 1-butene systems exhibits LCST-type curves with a positive slope. The cloud-point curves for the P(DDMA) + propane and + propylene systems begin at ca. 453 and 31.5 MPa and end at ca. 333 K and ca. 12.2 MPa. In contrast, the cloud-point curves for the P(DDMA) + butane and + 1-butene systems begin at 453 K and 16.0 MPa and end at 375 K and 4.7 MPa. The reason why C3 is higher in pressure than C4 is that C3 is lower in polarizability than C4. The impact of weakly

Figure 5. Comparison of the experimental data (symbols) for the CO2 + dodecyl methacrylate system with calculated data (solid lines) obtained using the Peng-Robinson equation of state with kij ) 0.033.

Ind. Eng. Chem. Res., Vol. 48, No. 16, 2009 Table 5. Experimental Data for the Carbon Dioxide + Dodecyl Methacrylate (DDMA) System Measured in This Studya DDMA mole fraction 0.011 0.020 0.044 0.055 0.102 0.148 0.198 0.227 0.254 0.341 0.386 0.438 0.461 0.556 0.687 0.787 0.011 0.020 0.044 0.055 0.102 0.148 0.198 0.227 0.254 0.341 0.386 0.438 0.461 0.556 0.687 0.787 0.011 0.020 0.044 0.055 0.102 0.148 0.198 0.227 0.254 0.341 0.386 0.438 0.461 0.556 0.687 0.787 0.011 0.020 0.044 0.055 0.102 0.148 0.198 0.227 0.254 0.341 0.386 0.438 0.461 0.556 0.687 0.787 0.011 0.020 0.044 0.055 0.102 0.148 0.198 0.227 0.254 0.341 0.386 0.438 0.461 0.556 0.687 0.787 a

P/MPa T ) 313.2 K 9.07 9.28 9.22 9.18 8.86 8.21 7.48 7.29 6.85 5.72 5.38 4.62 4.30 3.45 2.09 1.47 T ) 333.2 K 13.79 14.21 14.51 14.50 13.28 11.83 10.40 9.91 9.50 7.48 6.86 5.81 5.57 4.32 2.52 1.89 T ) 353.2 K 17.43 18.28 19.05 19.14 17.09 15.66 13.56 12.91 11.95 9.38 8.33 7.27 6.86 5.27 3.00 2.18 T ) 373.2 K 19.97 21.45 22.40 22.49 20.47 18.97 16.26 15.41 14.36 10.97 10.06 8.72 8.21 6.13 3.31 2.36 T ) 393.2 K 21.66 23.78 25.19 25.21 23.21 21.66 18.90 17.76 16.43 12.59 11.60 10.22 9.61 7.03 3.74 2.52

transition DP CP BP BP BP BP BP BP BP BP BP BP BP BP BP BP DP DP CP BP BP BP BP BP BP BP BP BP BP BP BP BP DP DP DP BP BP BP BP BP BP BP BP BP BP BP BP BP DP DP DP CP BP BP BP BP BP BP BP BP BP BP BP BP

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Table 6. Properties of Pure Component for the Peng-Robinson Equation of State compound

Mw

Tc/K

Pc/MPa

ω

carbon dioxide DDMA

44.01 254.4

304.3 694.8

7.38 1.37

0.225 0.779

Table 7. Experimental Cloud-Point (CP) Data for the Poly(dodecyl methacrylate) [P(DDMA)] + Solvents Systems Measured in This Study T/K

P/MPa

transition

5.2 wt % P(DDMA) + 94.8 wt % Propane 334.4 355.6 374.4 394.9 414.7 435.5 453.5

14.66 18.45 21.21 24.31 27.07 29.14 30.52

CP CP CP CP CP CP CP

5.2 wt % P(DDMA) + 94.8 wt % Propylene 332.9 354.4 375.9 394.2 416.0 434.0 455.1

12.24 17.41 21.21 23.97 27.07 29.48 31.55

CP CP CP CP CP CP CP

5.6 wt % P(DDMA) + 94.4 wt % n-Butane 374.9 393.4 412.3 433.1 454.1

4.66 7.76 10.86 13.62 16.03

CP CP CP CP CP

4.9 wt % P(DDMA) + 95.1 wt % 1-Butene 394.0 413.1 435.0 453.7

5.45 8.79 12.59 14.66

CP CP CP CP

4.2 wt % P(DDMA) + 95.8 wt % DME 374.2 394.2 414.0 434.8

7.07 11.55 15.35 18.79

CP CP CP CP

pressures less than 20.0 MPa and temperatures as low as 373 K. DME has a larger dipole moment than any of the other SCF solvents. Nevertheless, it is shown between the C3 and C4 hydrocarbons. Figure 7 provides an interesting comparison between the cloud-point curves of P(DDA) + DDA (9 and 14 wt %)32 and poly(DDMA) + DDMA (9 and 14 wt %) in supercritical CO2.

DP DP DP DP BP BP BP BP BP BP BP BP BP BP BP BP

BP is bubble point, DP is dew point, and CP is critical point.

polar P(DDMA) + solvent interactions is further demonstrated with the P(DDMA) + DME cloud-point curve, which is at

Figure 6. Effect of the phase behavior of P(DDMA) dissolved in supercritical propane, propylene, butane, 1-butene, and DME. The concentration of polymers is ∼5 wt % for each solution.

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concentration is ∼9 wt % except for the P(DMA) + CO2 + 6.7 wt % DMA solution. 4. Conclusions

Figure 7. Impact of the dodecyl acrylate and dodecyl methacrylate on the cloud-point curves of poly(dodecyl acrylate) [P(DDA), Mw ) 50 000, Tg ) 243.2 K] and poly(dodecyl methacrylate) [P(DDMA), Mw ) 250 000, Tg ) 218.2 K] in supercritical CO2. Tg is the glass transition temperature, and Mw is the weight-average molecular weight. The polymer concentration is ∼5 wt % for both solutions, and the cosolvent concentrations of DDA and DDMA are 9 and 14 wt %, respectively.

The CO2 + DDMA system exhibits type-I behavior. The P-x bubble-point curve is a convex, which indicates that CO2 exhibits a high solubility in DDMA, probably due to the formation of a weak complex between the carboxylic oxygen in DDMA and the carbon in CO2. Cloud-point data are presented for binary and ternary mixtures of the poly(dodecyl methacrylate) [P(DDMA)] + CO2 + DDMA system with DDMA concentration of 9.8-36.7 wt %. With 44.7 wt % DDMA added to the P(DDMA) + CO2 mixture, the cloud-point curve shows the typical appearance of a positive slope boundary. P(DDMA) does not dissolve in pure CO2 to the temperature of 493 K and to the pressure of 260.0 MPa. The liquid DDMA monomers provide favorable intermolecular interactions between the polymer segments and the solvent molecules, which help dissolution of the polymer. The location of the P(DDMA) + CO2 cloud-point curve shifts to lower temperatures and pressures when DDMA or DME is added to the P(DDMA) + CO2 solution. The P(DDMA) + C4 hydrocarbons cloud-point curves are ∼120 K higher than the P(DDMA) + C3 hydrocarbons curves at fixed pressures. Acknowledgment This work was financially supported by Chonnam National University, 2007. Literature Cited

Figure 8. Impact of the straight chain alkyl tail of the methacrylate group on the cloud-point curves of poly(hexyl methacrylate) [P(HMA), Mw ) 90 000, Tg ) 268.2 K], poly(octyl methacrylate) [P(OMA), Mw ) 100 000, Tg ) 253.2 K], poly(decyl methacrylate) [P(DMA), Mw ) 100 000, Tg ) 203.2 K], and poly(dodecyl methacrylate) [P(DDMA), Mw ) 250 000, Tg ) 208.2 K] in supercritical CO2. The concentration of polymer is ∼5 wt % for each solution. The cosolvent concentration is ∼9 wt % for each solution except for the P(DMA) + CO2 + 6.7 wt % DMA solution.

The P(DDA) + CO2 + 9 wt % DDA and + 14 wt % DDA curve is shifted to lower temperatures by ∼20 K (9 wt %) and ∼0 K (14 wt %) at a fixed pressure of 140.0 MPa. If the locations of these cloud-point curves are fixed only by the free volumes of the polymer, higher, not lower, temperatures will be needed to dissolve P(DDA) as compared to P(DDMA) because P(DDMA) has the larger free volume of the two methacrylates. If the locations of the curves are fixed by molecular weight, the P(DDA) curve will be at lower pressure and temperatures again because the molecular weight of the P(DDA), 50 000, is lower than that of P(DDMA), 250 000. From an interchange energy viewpoint, quadrupolar CO2 is expected to interact approximately to the same extent with the weakly polar methacrylate groups in P(DDA) and P(DDMA). Figure 8 shows the impact of the straight chain alkyl tail of the methacrylate group on the cloud-point curves of poly(hexyl methacrylate) [P(HMA), Mw ) 90 000, Tg ) 268.2 K],33 poly(octyl methacrylate) [P(OMA), Mw ) 100 000, Tg ) 253.2 K],34 poly(decyl methacrylate) [P(DMA), Mw ) 100 000, Tg ) 203.2 K],35 and poly(dodecyl methacrylate) [P(DDMA), Mw ) 250 000, Tg ) 208.2 K] in supercritical CO2. The concentration of polymer is ∼5 wt % for each solution, while cosolvent

(1) Giles, M. R.; Griffiths, R. M. T.; Irvine, D. J.; Howdle, S. M. The Polymerization of Functionalized Methacrylate Monomers in Supercritical Carbon Dioxide. Eur. Polym. J. 2003, 39, 1785–1790. (2) Shin, J.; Bae, W.; Kim, B. G.; Lee, J. C.; Byun, H. S.; Kim, H. Phase Behavior of a Ternary System of Poly[p-perfluorooctyl-ethylene(oxy, thio, sulfonyl) methyl styrene] and Poly[p-decyl(oxy, thio, sulfonyl) methyl styrene] in Supercritical Solvents. J. Supercrit. Fluids 2008, 47, 1–7. (3) Charpentier, P. A.; Kennedy, K. A.; DeSimone, J. M.; Roberts, G. W. Continuous Polymerization in Supercritical Carbon Dioxide: Chain-Growth Precipitation Polymerization. Macromolecules 1999, 32, 5973–5975. (4) Liu, T.; Garner, P.; DeSimone, J. M.; Roberts, G. W.; Bothun, G. D. Particle Formation in Precipitation Polymerization: Continuous Precipitation Polymerization of Acrylic Acid in Supercritical Carbon Dioxide. Macromolecules 2006, 39, 6489–6494. (5) Yuvaraj, H.; Hwang, H. S.; Jung, Y. S.; Kim, J. H.; Hong, S. S.; Lim, K. T. Dispersion Polymerization of Styrene in Supercritical CO2 in the Presence of Non-fluorous Random Copolymeric Stabilizers. J. Supercrit. Fluids 2007, 42, 351–358. (6) Kirby, C. F.; McHugh, M. A. Phase Behavior of Polymers in Supercritical Fluid Solvents. Chem. ReV. 1999, 99, 565–602. (7) Liu, K.; Kiran, E. High-pressure Solution Blending of Poly(εcaprolactone) with Poly(methyl methacrylate) in Acetone + Carbon Dioxide. Polymer 2008, 49, 1555–1561. (8) Kikic, I. Polymer-Supercritical Fluid Interactions. J. Supercrit. Fluids 2009, 47, 458–465. (9) Waegemaekers, T. H. J. M.; Bensink, M. P. M. Mutation Research/ Genetic. Toxicology 1984, 137, 95–102. (10) Gornert, M.; Sadowski, G. Phase-equlibrium Measurement and Modeling of the PMMA/MMA/Carbon Dioxide Ternary System. J. Supercrit. Fluids 2008, 46, 218–225. (11) Rindfleisch, F.; DiNoia, T. P.; McHugh, M. A. Solubility of Polymers and Copolymers in Supercritical CO2. J. Phys. Chem. 1996, 100, 15581–15587. (12) Byun, H. S.; Lee, D. H. Phase Behavior of the Poly(neopentyl methacrylate) + Supercritical Fluid Solvents + Neopentyl Methacrylate System and CO2 + Noepentyl Methacrylate Mixtures at High Pressure. J. Chem. Eng. Data 2007, 48, 805–812.

Ind. Eng. Chem. Res., Vol. 48, No. 16, 2009 (13) Byun, H. S.; McHugh, M. A. Impact of “Free” Monomer Concentration on the Phase Behavior of Supercritical Carbon DioxidePolymer Mixtures. Ind. Eng. Chem. Res. 2000, 39, 4658–4662. (14) Gaur, U.; Lau, S. F.; Wunderlich, B. B.; Wunderlich, B. J. Phys. Chem. Ref. Data 1982, 11, 1065–1089. (15) Tsang, C. Y.; Streett, W. B. Vapor-Liquid Equilibrium in the System Carbon Dioxide/Dimethyl Ether. J. Chem. Eng. Data 1981, 26, 155–159. (16) Peng, D. Y.; Robinson, D. B. A New Two-Constant Equation of State. Ind. Eng. Chem. Res. Fundam. 1976, 15, 59–63. (17) DeSimone, J. M.; Guan, Z.; Elsbernd, C. S. Synthesis of Fluoropolymers in Supercritical Carbon Dioxide. Science 1992, 257, 945–947. (18) Zeman, L.; Patterson, D. J. Phys. Chem. 1972, 76, 1214–1219. (19) Daubert, T. E.; Danner, R. P. Physical and Thermodynamic Properties of Pure Chemicals; Hemisphere Publishing: New York, 1989. (20) Prausniz, J. M.; Lichtenthaler, R. N.; de Azevedo, E. G. Molecular Thermodynamics of Fluid-Phase Equilibria, 2nd ed.; Prentice-Hall: Englewood Cliffs, NJ, 1986. (21) Meyer, G.; Toennies, J. P. Determination of Quadrupole Moments of Light Hydrocarbon Molecules from Rotationally Inelastic State Scattering Cross Sections. Chem. Phys. 1980, 52, 39–46. (22) Benson, R. C.; Flygare, W. H. The Molecular Zeeman Effect in Propane and Comparison of the Magnetic Susceptibility Anisotropies with Cyclopropene and Other Small Ring Compounds. Chem. Phys. Lett. 1969, 4, 141–143. (23) Albrecht, K. L.; Stein, F. P.; Han, S. J.; Gregg, C. J.; Radosz, M. Phase Equilibria of Saturated and Unsaturated Polyisoprene in Sub- and Supercritical Ethane, Ethylene, Propylene, and Dimethyl Ether. Fluid Phase Equilib. 1996, 117, 84–91. (24) Liu, S.; Lim, J. S.; Kang, J. W.; Byun, H. S. Measurement of High Pressure Phase Behavior for Benzyl (Meth)Acrylate in Supercritical Carbon Dioxide from (313.2 to 393.2) K and Pressure from (6 to 24) MPa. J. Chem. Eng. Data 2008, 53, 175–179. (25) Lora, M.; McHugh, M. A. Phase Behavior and Modeling of the Poly(methyl methacrylate)-CO2-Methyl Methacrylate System. Fluid Phase Equilib. 1999, 157, 285–297. (26) Byun, H. S.; McHugh, M. A. High Pressure Phase Behavior of Poly[isopropyl acrylate] and Poly[isopropyl methacrylate] in Supercritical

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Fluid (SCF) Solvent and SCF Solvent + Cosolvent Mixtures. J. Supercrit. Fluids 2007, 41, 482–491. (27) McHugh, M. A.; Krukonis, V. J. Supercritical Fluid Extraction: Principles and Practice; Butterworth: Boston, MA, 1994. (28) Condo, P. D.; Radosz, M. Equation of State for Monomer and Polymers. Fluid Phase Equilib. 1996, 117, 1–10. (29) Scott, R. L.; van Konynenburg, P. B. Static Properties of Solutions: van der Waals and Related Models for Hydrocarbon System. Discuss. Faraday Soc. 1970, 49, 87–97. (30) Poling, B. E.; Prausnitz, J. M.; O’Connell, J. P. The Properties of Gases and Liquid, 5th ed.; McGraw-Hill: New York, 2001. (31) Kuester, J. L.; Mize, J. H. Optimization Techniques with Fortran; McGraw-Hill: New York, 1973. (32) Byun, H. S.; Yoo, K. P. Phase Behavior of Binary and Ternary Mixtures for Poly[dodecyl (meth)acrylate] + Cosolvent and Dodecyl (meth)acrylate in Supercritical Fluid Solvents. The 5th International Symposium on Supercritical Fluids (Supergreen 2007); Hoam Convention Center (Seoul National University), Seoul, Korea, Nov. 28-Dec. 1, 2007; p 71. (33) Byun, H. S.; Kim, J. G.; Yang, J. S. Phase Behavior on the Binary and Ternary System of Poly(hexyl acrylate) and Poly(hexyl methacrylate) with Supercritical Solvents. Ind. Chem. Eng. Res. 2004, 43, 1543–1552. (34) Byun, H. S.; Yoo, K. P. Phase Behavior on the Poly[octyl (meth)acrylate] + Supercritical Solvents + Monomer and CO2 + Monomer Mixtures at High Pressure. J. Supercrit. Fluids 2007, 41, 472–481. (35) Byun, H. S.; Lee, D. H. Phase Behavior of Binary and Ternary Mixtures of Poly(decyl acrylate)-Supercritical Solvents-Decyl Acrylate and Poly(decyl methacrylate)-CO2-Decyl Methacrylate. Ind. Chem. Eng. Res. 2006, 45, 3373–3380.

ReceiVed for reView April 14, 2009 ReVised manuscript receiVed June 22, 2009 Accepted July 7, 2009 IE900598W