Lower critical solution temperature behavior of ethylene propylene copolymers in multicomponent solvents

Abstract

SynopsisThe lower critical solution temperature (LCST) locus for ethylene-propylene copolymers has been determined as a function of pressure in a variety of single and multicomponent solvents. The lower critical end-point temperature (LCEP), which is the intersection of the LCST locus with the vapor-pressure curve, was found to be predictable from the solvent density as previously established for singlecomponent solvents by Charlet and Delmas. Dissolving a lowmolecular hydrocarbon gas such as propylene in an alkane has a dramatic effect on lowering the LCEP, and can reduce phase-separation temperatures to levels at which this technique becomes attractive as a practical method for polymer recovery from diluents such as those used in solution polymerizations. Temperatures considerably above the LCEP are needed to minimize the residual polymer concentration in the solvent in the two-liquid-phase region. The solvent critical temperature must be approached for essentially complete elimination of the polymer from the solvent phase. The LCST locus was found to be a linear function of pressure for all of the systems investigated, and the slope of the line, d(LCST)/dP, could be well correlated as a function of solvent density and critical temperature. From the relationship between the LCEP and solvent density and the correlation for d(LCST)/dP, the location of the LCST locus can be readily predicted from a knowledge of solvent properties. INTRODUCTIONIt has long been recognized that most solutions of amorphous, nonpolar polymers in nonpolar solvents show a positive or endothermic heat of mixing, and that below a certain critical temperature (upper critical solution temperature or UCST) phase separation of the polymer solution occurs. This positive heat of mixing arises from the replacement of energetically preferred solvent-solvent and polymer-polymer contacts by unlike solvent-polymer contacts when a solution is formed.demonstrated that polymer-solvent systems also have a lower critical solution temperature (LCST), so that separation of the solution into multiple phases results from raising the solution temperature. Furthermore, since the LCST usually occurs at temperatures approaching the solvent critical temperature, pressures above atmospheric accompany it, and unlike the UCST, the LCST tends to be very pressure dependent. IRAN1 AND COZEWITHEssentially, as the system temperature approaches the critical temperature of the solvent, the solvent molecules tend toward a gas-like configuration, with all distinction between liquid and gas finally disappearing at the critical point. However, the very high-molecular weight polymer is far removed from its critical point and, consequently, undergoes no such 'dilation' effect as the temperature is raised. Accordingly, the polymer has a contracting effect on the solvent molecules, confining them to a more rigid matrix, and this lesser degree of spatial disorder for the solvent between the dilated and confined states results in a decreased entropy of mixing which leads to phase se...

INEXPENSIVE CO{sub 2} THICKENING AGENTS FOR IMPROVED MOBILITY CONTROL OF CO{sub 2} FLOODS

“…The cloud-point loci exhibit a maximum value at about 5 wt% PMA at each temperature. The maximum in cloud-point pressure near 5 wt% which characterizes the PMA-CO 2 and PVAc-CO 2 mixtures has been previously observed for other polymer-solvent mixtures Meilchen, et al 1991;Allen and Baker, 1965;Irani and Cozewith 1986;Lee. et al 1994).…”

Phase behavior of poly(ethylene-co-norbornene) in C6 hydrocarbon solvents: Effect of polymer concentration and solvent structure

“…Figure 4 shows P-x isotherms for the PEN 53 /n-hexane at 60, 90 and 120 o C. The P-x curves obviously reveal that the isotherms have a maximum at the concentrations around 5 wt% PEN 53 , suggesting that at these polymer concentrations, the cloud-point pressures are reasonably close to the true mixture-critical point. [10][11][12][13] It should be noted that at 90 and 120 o C the P-x isotherms of PEN 53 /n-hexane system are approximately flat between copolymer concentrations of 5 to 12 wt%. Therefore, cloud-point pressures are measured at fixed copolymer concentrations 5~12 wt% in this study.…”

“…Cloud-point pressures of copolymer solutions typically have maxima at concentrations lower than 15 wt% polymer. [10][11][12][13] …”

Cosolvency effect of SF6 on the solubility of poly(tetrafluoroethylene-co-19 mol % hexafluoropropylene) in supercritical CO2 and CHF3

“…11,16 Polymer solubilities are reported as cloud points obtained at a fixed polymer composition of Ϸ5 wt %, the expected maximum in the P-x isotherms. 11,[17][18][19] 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 solution. Cloud points obtained in this manner are identical to those defined as the point at which there is a 90% drop in transmitted light through the solution.…”