Phase behavior, acrylates

Phase behavior studies with poly(ethylene-co-methyl acrylate), poly (ethylene-co-butyl acrylate), poly(ethylene-co-acrylic add), and poly(ethylene-co-methacrylic acid) were performed in the normal alkanes, their olefinic analogs, dimethyl ether, chlorodifluoromethane, and carbon dioxide up to 250 °C and 2,700 bar. The backbone architecture of the copolymers as well as the solvent quality greatly influences the solution behavior in supercritical fluids. The effect of cosolvent was also studied using dimethyl ether and ethanol as cosolvent in butane at varying concentrations of cosolvent, exhibiting that the cosolvent effect diminishes with increasing cosolvent concentrations. 

Figure 1 shows the phase behavior of EMAX (the subscript x denotes the molar acrylate content) copolymers in propylene which is slightly more polar than propane [4,5]. The EMA q curve is at slightly lower pressures than the PE curve since the first few acrylate units interact favorably with the quadrupole of propylene. However, the cloud-point curves shift to higher pressures and temperatures and as the amount of MA units increases to 31 and 41 mol% in the copolymer. EMA41 does not dissolve in propane to temperatures of 200 °C and pressures of 2,000 bar, whereas it is readily soluble in propylene. 

McHugh M A, Rindfleisch F, Kuntz PT, Schmaltz C, Buback M. Cosolvent effect of alkyl acrylates on the phase behavior of poly(alkyl acrylates)-supercritical CO2 mixtures. Pol5mier 1998 39 6049-6052. 

Hansson P, Almgren M. Interaction of alkyltrimethylammonium surfactants with poly(acrylate) and poly(styrenesulfonate) in aqueous solution. Phase behavior and surfactant aggregation numbers. Langmuir 1994 10 2115-2124. 

Hasch, B. M., M. A. Meilchen, S.-H. Lee, and M. A. McHugh. 1992. High pressure phase behavior of mixtures of poly(ethylene-co-methyl acrylate) with low molecular weight hydrocarbons. J. Polym. Sci. Polym. Phys. Ed., 30 1365-1373. 

A considerable amount of work has focused on the design and synthesis of macromolecules for use as emulsifiers for lipophilic materials and as polymeric stabilizers for the colloidal dispersion of lipophilic, hydrocarbon polymers in compressed CO2. It has been shown that fluorinated acrylate homopolymers, such as PFOA, are effective amphiphiles as they possess a lipophilic acrylate-like backbone and C02-philic, fluorinated side chains, as indicated in Figure 4.5-1 [100]. Furthermore, it has been demonstrated that a homopolymer which is physically adsorbed to the surface of a polymer colloid precludes coagulation due to the presence of loops and tails [110]. These fluorinated acrylate homopolymers can be synthesized homogeneously in CO2 as described in an earlier section. The solution properties [111,112] and phase behavior [45] of PFOA in SCCO2 have been thoroughly examined. Additionally, the backbone of these materials can be made more lipophilic in nature by incorporating other monomers to make random copolymers [34]. 

P8 M is not the only polymer forming the isotropic smectic phase. To date, we have observed formation of that phase for a half-dozen chiral polymethacrylates and polysiloxanes. Table 5.1 summarizes the chemical structure and phase behavior of synthesized side-chain homopolymers, which carry chirally substituted side chains derived from asymmetric esters of terephthalic acid and hydroquinone. Such a structure with alternating orientation of carboxylic link groups seems to favour the formation of the IsoSm phase, whereas isomeric derivatives of p-hydroxybenzoic acid, where all carboxylic links have the same orientation, form only conventional Sm A and Sm C phases. Molar mass of all the synthesized homo- and copoly(meth)acrylates is within the range of 1 to 2-10 g mol the poiysilox-anes have the average degree of polymerization, p 35. 

Phase behavior studies showed that the substrate methyl acrylate is fully miscible with CO2 in the pressure range 9-29.5 MPa, whereas the product dihydromuconates are only fully miscible at the concentrations required above a density of 0.4 g cm" ... 

MAE Maeda, Y., Yamamoto, H., and Ikeda, 1., Effects of ionization on the phase behavior of poly(A -isopropylacrylamide-co-acrylic acid) and poly(A, A-diethylacrylamide-co-acrylic acid) in water. Coll. Polym. Sci., 282, 1268, 2004. 

L11 Liu, S., Liu, X., Li, F., Fang, Y., Wang, Y, and Yu, J., Phase behavior of temperature- and pH-sensitive poly(acrylic acid-g-Y-isopropylacrylamide) in dilute aqueous solution, J. Appl. Polym. Sci., 109,4036,2008. 

LEE Lee, S.-H. and McHugh, M.A., The effect of hydrogen bonding on the phase behavior of poly(ethylene-co-acrylic acid)-ethylene-cosolvent mixtures at high pressures, Korean 7. Chem. Eng., 19, 114, 2002. 

In a pioneering work, Stoffer and Bone [32-34] studied the phase behavior of sodium dodecyl sulfate (SDS)-pentanol-methyl methacrylate or methyl acrylate-water systems before and after polymerization. A typical composition of the system was MMA, 41.7% pentanol, 27% SDS, 14.6% water, 16.7%. As the monomers forming the continuous phase of the microemulsion polymerize, phase separation occurs. 

LUF Luft, G. and Subramaruan, N.S., Phase behavior of mixtures of ethylene, methyl acrylate, and copolymers under high pressures, Ind. Eng. Chem. Res., 26, 750, 1987. 

MEI Meilchen, M.A., Hasch, B.M., and McHugh, M.A., Effect of copolymer composition on the phase behavior of mixtures of poly(ethylene-co-methyl acrylate) with propane and chloro-difluoromethane, A/ocTO/Mo/ecM/es, 24, 4874, 1991. 

BYU Byun, H.-S., Hasch, B.M., McHugh, M.A., Mahling, F.-O., Busch, M., and Buback, M., Poly(ethylene-co-butyl acrylate). Phase behavior in ethylene compared to the poly(ethylene-co-methyl aciylate)-ethylene system and aspects of copolymerization kinetics at high pressures, Macroffro/ecw/ra, 29, 1625, 1996. 

LUN Luna-Barcerras, G., Mawson, S., Takishittra, S., DeSimone, J.M., Sanehez, I.C., and Johnstorr, K.P., Phase behavior of poly(l,l-dihydropeifluorooctyl acrylate) in supereritieal caA>ot. dioyiA.Q, Fluid Phase Equil, 146,325, 1998. 

BYU Byun, H.-S. and Choi, T.-H., Effect of the octadecyl acrylate concentration on the phase behavior of poly(octadecyl aciylate)/supercritical CO2 and C2H4 at high pressures, J. Appl. Polym. Sci., 86, 372, 2002. 

Restricting our continuous phase to carbon dioxide means that the monomers in question must be relatively C02-phobic (in other words hydrophilic or at least very polar). Note that this greatly reduces the number of monomers that would be viable candidates for inverse emulsion polymerization in CO2 (or in another supercritical continuous phase) indeed even some water-soluble monomers such as acrylic acid are miscible with CO2 under relatively mild conditions. We will examine the issues surrounding monomer selection and surfactant design as they relate to the phase behavior of the system in the next section. 

Recently, Ye and DeSimone [40] showed that a diblock copolymer of a fluorinated acrylate and a glucose-containing hydrophilic block will support the emulsion polymerization of N-ethyl acrylamide in CO2. Here, the use of a fluorinated azo-initiator that partitions strongly to the CO2 phase (avoiding the monomer droplets) led to the generation of very fine (submicron) particles of polymer. Fluoroacrylates are known to be the most C02-philic materials found to date, and hence their use allows for achievement of the crucial phase behavior conditions shown in Fig. 7.2. 

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