SANS Study of Polymer−Supercritical Fluid Solutions:  Transitions from Liquid to Supercritical Fluid Solvent Quality

• Published in: Macromolecules Vol. 33; no. 17; pp. 6321 - 6329
• Main Authors: DiNoia, T. P, Kirby, C. F, van Zanten, J. H, McHugh, M. A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 22.08.2000
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties; Solvent effect; Chemical solution; Pressure effect; Mixed solvent; Solution structure; Phase diagram; Butylene derivative copolymer; Ethylene copolymer; Supercritical solvent; Radius of gyration; Experimental study; Conformation
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma000240z

Phase behavior and small-angle neutron scattering (SANS) measurements are reported for poly(ethylene-co-1-butene) (PEB) dissolved in pentane, pentane plus ethane, and supercritical ethane to pressures of 2000 bar and temperatures of 130 and 150 °C. The solution microstructure and solvent quality are probed using the high-concentration isotopic labeling technique at the mixture critical concentration to determine the variation of intra- and intermolecular correlations on approach to the phase boundary with isothermal changes in pressure. The SANS results for the three solutions show that the intramolecular radius of gyration remains close to the unperturbed value over the entire pressure range investigated. However, the intermolecular correlation length changes dramatically as the phase boundary is approached and is approximately 3 times larger in ethane as compared to pentane even at 1000 bar from the phase boundary. The intermolecular correlation length data suggest that ethane is a poorer quality solvent than pentane at conditions close to the phase boundary even though both solvents have similar mass densities.