2036 The Journal of Physical Chemistry, Vol. 97, No. 9, 1993
was complete by 6 h, and thus no quantitative data could be assembled for this system. These results emphasisethe importance of water structure, the role of the relatively hydrophobic and hydrophilic portions of the polymer molecules and their hydrated states in determining the equilibrium structures present in aqueous solution. Naturally these microcalorimetric results for the enthalpies associated with the conformational changes undergone by these polymers in dilute aqueous solution do not give any information on the nature of the events at the molecular level that give rise to the observations reported here. Previous temperature-dependent studits'4~lS~20 using, in the main, noncalorimetric techniques have suggested that transitions are associated with molecule to micelle processes necessarily associated with dehydration. The isothermal results reported here were conducted at the lowtemperature side of the corresponding transition for the studied polymers.9 Indeed Devenand and Selser2Ihave indicated that in dilutesolutionand at temperaturesof 298 and 303 K polyethylene oxidedoes not aggregatein water. Light-scatteringmeasurements of particle mass and high precision density measurementsof partial molar volumes on the experimental solutions used in this work confirm that a temperature driven process does occur for pluronic F87. Importantly for the work reported here these same results show that, under isothermal conditions at 298 K,the system is largely monomeric (Mw= 2430;correspondingto the PO fraction) with only a very small proportion of aggregated material present. We will present elsewhere, in a more complete form light scattering, surface tension, densimetric,small-angle X-ray, FIIR studiesand molar mass determinationsby vapor phaseosmometry to indicate that the isothermal transitionsreported here are indeed associated only with monomeric species of the polymers. The conclusion is, therefore, that the relaxation process under observation in these isothermal studies relates to conformational changes associated with the slow hydration of the polymer following the departure of a molecule from the solid phase to solution. Thus we suppose that the poly(oxypropy1ene) moiety (the hydrophobic portion of the molecule) slowly hydrates under isothermal conditions and this, in the main, is responsible for the observations reported here. The conformation of the polymer molecule entering solution is, therefore, not the equilibrium structure and hence relaxes rather slowly to its preferred orientations upon interaction with water. It is this relaxation which is properly called "aging" and whose time course and relative thermodynamic parameters are reported here for the first time.
Additions and Corrections The HSDSC results reported p r e v i ~ u s l y ~are ~ ~associated, J~ therefore, with the dehydration of this equilibriumconformation of the PO fraction of these ABA copolymers. It remains part of our concerns to demonstrate the general or specific nature of these observations. Further work from this laborabory will explore this issue. Aclrwwledgwat. The award of a Fulbright Scholarship to J.J.I. is gratefully acknowledged. References a d Notes (1) See for example: (a) Krezanoski, J. Z. U S . Patent No 4,188373, 1980. (b) Illum, L.; Hunneyball, I. M.; Davis, S.S . In?. J . Phurm. 1986,29, 53. (c) Park, T. G.; Cohen, S.; Langer, R. Pharm. Res. 1992. 9, 37. (d) Douglas, S. J.; Davis, S. S.;Illum, L. In?. J . Phurm. 1986, 34. 145. (e) Johnston, J. P.; Punjabi, M. A.; Froelich, C. J . Phurm. Res. 1992,9,425. (f) Guzman, M.; Garcia, F. F.; Molpeceres, J.; Aberturas, M. R.Inr. J . Phurm. 1992, 80, 119. (2) Carter, C.; Fisher, T. C.; Hamai, J.; Johnson, C. S.;Meiselman, H. J.; Nash, G. B.; Stuart, J. Clin. Hem. 1992, 12, 109. (3) Kumar, V.;Laouar, L.; Davey, M. R.; Mulligan. B. J.; Lowe, K. C. J . Exp. Bo?. 1992. 43, 487. (4) Schmolka, I. J . Am. Oil Chem. Soc. 1987,54, 110. (5) Gilbert, J. C.; Washington, C.; Davics, L. C.; Hadgraft, J. In?. J . Phurm. 1987, 40, 93. (6) Blou. D.; Hergeth, W. D.; Doring, E.; Witkowski, K.; Waterwig, S . Acta Polym. 1989, 40, 260. (7) Mitchard, N. A.; Beezer, A. E.; R e a . N.; Mitchell, J. C.; Leharne, S.;Chowdhry, B. Z.; Buckton, G., J . Chem. Soc.. Chem. Commun. 1990,900. (8) Beezer, A. E.; Mitchell, J. C.; Rees, N. H.; Armstrong, J. K.; Chowdhry, B. 2.;Leharne, S.;Buckton, G., J . Chem. Res. ( S ) 1991, 254. (9) Mitchard, N. A.; Beezer, A. E.; Mitchell, J. C.; Armstrong, J. K.; Chowdhry, B. Z.; Leharne, S.;Buckton, G., J . Phys. Chem., in press.
(IO) Beezer, A. E.; Mitchard, N. A.; Mitchell, J. C.; Armstrong, J. K.; Chowdhry, B. 2.;Leharne, S.;Buckton, G., J . Chem. Res. (S) 1992. 236. (11) Cole, S. C.; Chowdhry, B. 2. Tibrech 1989. (12) Williams, R. K.; Simard, M. A.; Jolicoeur, C. J. Phys. Chem. 1985, 89, 178. (13) Lianos, P.; Brown, W. J . Phys. Chem. 1992,96, 6439. (14) Yang. L.; &dells. A. D.; Attwood, D.;Booth, C. J. Chem. Soc., Furaduy Trans. 1992,88, 1447. (15) Brown, W.;Schillen, K.; Almgren, M.; Hvidt, S.;Bahadur, P. J . Phys. Chem. 1991, 95, 1850. (16) Privalov, P. L.; Gill, S . J. Adu. Protein Chem. 1989, 39, 191. (17) Privalov, P. L. Ann. Reu. Biophys. Chem. 1989, 18, 47. (1 8) Doi, M.; Edwards, S . F. The Theory of Polymer Dynumics; Oxford University Press: Oxford, UK, 1986. (19) Hansen, L. D.; Lewis, E. A.; Eatough, D. J.; Bergstrom, R.;DegraftJohnson, D. Pharm. Res. 1989, 6, 20. (20) Deng, Y.; Yu,G.; Price, C.; Booth, C. J . Chem. Soc.,Faraduy Truns. 1992. 88, 1441. (21) Devenand, K.; Selser, J. S . Nuture 1990, 343, 739.
ADDITIONS AND CORRECTIONS
1992, Volume 96 Makoto Aratono,' Takanori Takiue, Noribiro Ikeda, Akira Nakamura, nod Kinsi Motomura : Thermodynamic Study on the Interface Formation of Water-Long-chain Alcohol Systems. Page9423. In Figure4,-0.01,-0).02,-0).03,-0.04, and-0.05 of the ordinate should be changed respectively to -0.02, -0.04, -0.06, -0.08, and -0.10.
