Polymer Journal, Vol. 6, No. 3, pp 230-233 (1974)
The Heats of Dilution of the Oligomeric Ethylene Oxide Benzene System
Yoshihiro BABA, Haruyoshi KATAYAMA, and Akihiro KAGEMOTO
Department of General Education, Osaka Institute of Technology, Omiya Asahi-ku, Osaka, 535 Japan. (Received September 25, 1973)
ABSTRACT: In a previous paper,1 we have reported the heats of dilution of the oligo-ethylene oxide-alcohol systems at 25°C. The interaction heat parameter X1 in creases as the chain length of the alcohols increases. In order to obtain some further information about the behavior of the oligomer in solution, the heat of dilution of the oligo-ethylene oxide-benzene system has been measured at 25°C. The interaction heat parameter seems to be considerably dependent on the molecular weight of the oligomer; the results obtained show the opposite dependence to that found in the oligo-ethylene oxide-alcohol solutions. KEY WORDS Oligomer / Ethylene Oxide / Benzene / Heat of Dilu- tion / Xi-Parameter /
As reported in a previous paper,1 we have from Sanyo Kasei Co. Ltd., and was used measured the heat of dilution of the oligomeric without further purification. ethylene oxide-alcohol systems at 25°C. It The molecular weights of the oligo-ethylene was found that all the systems were endothermic oxides in this study were about 200, 300, 600, in contrast with the exothermic values obtained and 1000. for the aqueous solution of oligomeric ethylene The solvent, benzene, was purified by the oxide,2 and that the interaction heat parameter, ordinary method. 5 Xi, between the oligomer and solvent increases as the chain length of the alcohols increases. RESULTS AND DISCUSSION Such behavior of the Xi-parameter suggested that the attraction acting between the OH- and-O The heat of dilution of oligo-ethylene oxide groups of the oligomer and the HO-groups of was measured by using the twin microcalorimeter the alcohol is compensated more or less by the at 25°C. The heat of dilution was measured repulsion operating between the HO-groups and over the concentration range from 1.00 to 0.128- CH2-groups. volume fraction of the oligomer by successive In this paper, in order to obtain some further additions of 5 or 10-cm3 portions of the solvent information about the behavior of the oligomer to a solution of known concentration. in the solution, the heat of dilution of the The results obtained are summarized in Table oligomeric ethylene oxide-benzene system has I. This system is endothermic. Assuming that been measured. the simple van Laar equation can be applied to an oligomer solution, we have the following EXPERIMENTAL equation for the heat of dilution, ,JHd, from the initial volume fraction of polymer,
230 The Heats of Dilution of the Oligomeric Ethylene Oxide-Benzene System
Table I. Heats of dilution of the oligomeric in Figure 1. According to eq 1, i1Hctf iln1 should
ethylene oxide-benzene system at 25°C vary linearly with RT¢2¢z', but these plots are not linear, indicating that the interaction heat V, -' V', ,I,' Jflct, cm 3 '1'2 cm3 y,2 cal parameter depends on the concentration of oligomer. a) Mn=200 Let us assume that the interaction heat 5 1.000 11 0.455 0.067 5.350 0.296 parameter, XH, is expressed by: 6 1.000 13 0.462 0.078 6.404 0.299 10 1.000 15 0.667 0.059 5.590 0.253 XH=X1+X2molecule play a 17 0.588 25 0.400 0.090 4.903 0.393 hydrophobic role. We suggested that the 17 0.588 26 0.385 0.101 5.283 0.391 attraction acting between the HO- and -0- 20 0.200 28 0.143 0.090 0.373 0.248 22 0.455 30 0.333 0.090 2.928 0.364 groups of the oligomer, and the HO-groups of 24 0.167 34 0.118 0.112 0.571 0.412 the alcohols is compensated more or less by the 25 0.400 34 0.294 0.101 2.442 0.348 repulsion operating between the HO-groups and
26 0.385 34 0.294 0.090 1.672 0.279 CH2-groups. However, the Xi parameter of the 27 0.370 32 0.313 0.056 1.104 0.288 oligo-ethylene oxide-benzene system seems to 28 0.143 33 0.121 0.056 0.198 0.345 be considerably dependent on the molecular ----••••••••••••••ow•--•••••••••••••••••••••••••••••••••••••••••••••••••••••••••·--•••••••••••••• weight of oligomer in the opposite manner to d) Mn=lO00 10 0.300 13 0.231 0.034 0.531 0.385 that found in the oligoethylene oxide-alcohol 10 0.303 16 0.189 0.067 1.202 0.528 solutions. 18 0.128 27 0.047 0.101 0.108 0.302 It may be shown that the attraction acting 19 0.159 27 0.059 0.090 0.172 0.345 between the HO-groups of the oligomer and 33 0.303 39 0.256 0.067 1.357 0.439 the benzene molecule is larger than the repulsion 33 0.303 40 0.250 0.078 1.334 0.380 operating between the -0- groups of the 51 0.196 60 0.166 0.101 0. 957 0.492 oligomer and the benzene molecule as the chain length of the oligo-ethylene oxide increases. This is the same dependence as in the usual
Polymer J., Vol. 6, No. 3, 1974 231 Y. BABA, H. KATAYAMA, and A. KAGEMOTO
100
Mn ···-200 0 /I O 50 200 400 RT,cf{ cal mor' Figure 1. Heats of dilution per mole of solvent vs. the concentration of the oligomeric ethylene oxides-benzene system at 25°C. vinyl polymer solutions;2 the Xi parameter Table II. The interaction heat parameter of the decreases as the molecular weight of oligomer oligomeric ethylene oxide-benzene system increases. This dependence of the interaction heat Mo"Iar weight, Interaction heat parameter parameter on the molecular weight has been Mn X2 X1 theoretically derived by Huggins. 6 But our 200 1.09 -1.08 results can not be quantitatively compared with 300 0.64 -0.56 hi~ theory because of the lack of information 600 0.40 -0.19 concerning the chain configuration in the 1000 0.30 -0.51 polymer solution. Our results can also be qualitatively explained 3.0 () 2.0 ... Q) ;:; O-·-CsHs Ee. 0 tl·-·C4H.0H 0 0. 1.0 O--·C2Hs0H g .c: _§ 0 i -1.0 Figure 2. Interaction heat parameter, Xi, vs. the logarithm of the molecular weight of oligomeric ethylene oxides in various solvents. 232 Polymer J., Vol. 6, No. 3, 1974 The Heats of Dilution of the Oligomeric Ethylene Oxide-Benzene System by application of Flory's polymer solution A ( 7) theory. 7 X1= aan1;2 We can consider a random coil with a radius where A is (Z(Z-2)Llw)/(RTZ(j)312 ). As the of gyration (s0) for a polymer which is formed number of segments (n) is identical with the from a number of segments (n). The volume ratio of the molecular weight of the polymer of a polymer solution (V) with a radius of (M) to that of the polymer unit (M ), the gyration and expansion factor (a) is expressed 0 interaction heat parameter Xi is: as follows: A' 3 3 V=firs0 a X1= aaM1;2 ( 8 ) = ¾ir(i-)3/2na;2aa aa ( 3 ) where A' is (Z(Z-2)LlwM/12 )/(RTZ(j)312). As where a is the distance between one segment seen in eq 8, the interaction heat parameter, Xi, and the next segment of the polymer. If the decreases as molecular weight of the polymer expansion of the polymer is due to the volume increases. But definite information cannot be of the solvent, the number of solvent particles obtained due to the lack of the expansion factor (ns) in the volume of polymer solution is ex for the chain conformation in the polymer pressed as follows: solution in eq 8. Even allowing for such uncertainty, our results seem to be qualitatively ( 4) explained by using eq 8. The contact number (Nsp) between segments of polymer and solvent in the polymer solution is REFERENCES N. _ Z(Z-2)nNs 1. A. Kagemoto, Y. Itoi, Y. Baba, and R. Fuji ( 5) sp-ZNs+(Z-2)n shiro, Makromol. Chem., 150, 255 (1971). 2. A. Kagemoto, S. Murakami, and R. Fujishiro, where Z is the number of coordination of the ibid., 105, 154 (1967). solvent or polymer segment. 3. A. Kagemoto and R. Fujishiro, Bull. Chem. The interaction heat parameter Xi is expressed Soc., Japan, 39, 15 (1966). 4. A. Kagemoto and R. Fujishiro, ibid., 40, 11 as a function of the contact number (Nsp) and (1967). (ns) the solvent number by 5. A. Weissberger and E. S. Proskauen, "Organic LlwNsp Solvent," Interscience Publishers, N. Y., 1955, X1=~~~ ( 6) p. 315. RTns 6. M. L. Huggins, J. Amer. Chem. Soc., 86, 3535 where Llw expresses the interaction energy given (1964). by Hildebrand and Scott8 as follows: 7. P. J. Flory, "Principles of Polymer Chemistry," Cornell Univ. Press, Ithaca, N. Y., 1953, Chap. 11. 8. J. H. Hildebrand, J.M. Prausnitz, and R. L. From eq 3, 4, and 5, the interaction heat Scott, "Regular and Related Solutions," van parameter is expresses as, Nostrand, Reinhold, N. Y., 1970, Chap. 6, p 85. Polymer J., Vol. 6, No. 3, 1974 233