Macromolecules 1986, 19, 2647-2648
Grant 84-0101. We thank The B. F. Goodrich Co. for supplying the CPVC samples and characterization information and Kuraray Co. and Bayer Ltd.for their kind gifts of ethylene-vinyl acetate copolymers. Registry No. (Et)-(VAc) (copolymer), 24937-78-8.
References and Notes Kambour, R. P.: Bendler. J. T.:. Bouu, R. C. Macromolecules 1983, 16, 753. ten Brinke, G.; Karasz, F. E.; MacKnight, W. J. Macromolecules 1983, 16, 1827. Paul, D. R.; Barlow, J. W. Polymer 1984, 25, 487. Shiomi, T.; Karasz, F. E.; MacKnight, W. J. Macromolecules, in press. Hammer, C. F. Macromolecules 1971, 4, 69. Zakrzewski, G. A. Polymer 1973, 14, 347. Alexandrovich, P. R.; Karasz, F. E.; MacKnight, W. J. Polymer 1977, 18, 1022. Stein, D. J.; Jung, R. H.; Illers, K. H.; Hendus, H. Angew. Makromol. Chem. 1974, 36,89. Fried, J. R.; Karasz, F. E.; MacKnight, W. J. Macromolecules 1978, 11, 150. Chion, J. S.; Paul, D. R.; Barlow, J. W. Polymer 1982,23,1543. Goh, S. H.; Paul, D. R.; Barlow, J. W. Polym. Eng. Sci. 1982, 22, 34. Hall, W. J.; Kruse, R. L.; Mendelson, R. A.; Trementozzi, Q. A. Prepr. Diu. Org. Plast. Chem. 1982, 47, 298. VukoviE, R.; KuregeviE, V.; SegudoviE, N.; Karasz, F. E.; MacKnight, W. J. J. Appl. Polym. Sci. 1983, 28, 3079. VukoviE, R.; Karasz, F. E.; MacKnight, W. J. Polymer 1983, 24, 529. Casper, R.; Morbitzer, L. Angew. Makromol. Chem. 1977,58, 1. Ueda, H.; Karasz, F. E., to be submitted. Fredriksen, 0.;Crowo, J. A. Makromol. Chem. 1967,100,321. Komoroski, R. A.; Parker, R. G.; Shockcor, J. P. Macromolecules 1985, 18, 1257. Randall, J. C. Polymer Sequence Determination; Academic: New York, 1977; Chapter 3. Coleman, M. M.; Zarian, J. J . Polym. Sci., Polym. Phys. Ed. 1979, 17, 837. Lehr, M. H. Polym. Eng. Sci. 1985,25, 1056.
2647
Table I Geometrical Parameters Required for the RIS Analysis" bond bond length/A bond angle angle/deg c-I 2.18 LCCI 109.0 c-c 1.54 LCCO 111.5 c-0 1.43 LCOC 111.5
"References 1 and 2.
'
End-to-End Distance in a,w-Diiodo Derivatives of Ethylene Oxide Oligomers: A Rotational Isomeric State Analysis of the X-ray Scattering Data of Li, Post, and Morawetz AKIHIRO ABE* and KENZABU TASAKI Department of Polymer Chemistry; Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152, Japan. Received April 18, 1986
In an attempt to elucidate conformational characteristics of the oxyethylene chains, Li, Post, and Morawetz' have performed X-ray scattering measurements on a series of a,w-diiodo compounds such as ICHzCHz-(OCHzCH2),-I ( x = 1-3). The scattering function observed on 2,2'-diiododiethyl ether (DDE) in m-xylene was interpreted in terms of the rotational isomeric state (RIS) scheme. The conformational energy difference between the gauche and trans states was estimated for the constituent bonds: E,, = 0 for IC-CC and E, = 0.8 kcal mol-l for CC-OC. The interiodine distance ( r ) deduced from the analysis of the X-ray scattering data tends to increase with x . The experiment was also carried out in ethanol. The observed ( r ) was found to be somewhat smaller in this solvent. Li et al. emphasize the usefulness of the X-ray scattering method in providing unambiguous evidence for the solvent dependence of the flexibility of the chain backbone. In a recent work,2 we have examined conformation-dependent properties of dimethoxyethane (DME) and poly(oxyethy1ene) (POE). The conformational energy 0024-9297/86/2219-2647$01.50/0
Table I1 Standard Values of the Conformational Energies and Statistical Weights bond sequence statistical weight" First-Order Interaction IC-Cob 7 = exp(0.23/RT) cc-OC' p = 0.61 exp(-0.8/RT) oc-CO' u = 0.99 exp(O.B/RT)
Second-Order Interaction IC-c-oc
0 0
oc-c-OC'
u = 0.88 exp(-0.53/RT)
cc-0-cc
aRT expressed in kcal mol-'. *Reference 6. 'References 2 and 3.
parameters were determined by the analysis of the observed NMR vicinal coupling constants 3JHH and 3JcH. In these treatments, statistical weight factors, p and u, defined for bond rotations CC-OC and OC-CO, respectively, are expressed in a general form such as a = cyo exp(-EJRT) (a = p or a). The parameters thus derived were used to estimate various solution properties of P O E 3 Values of the statistical weight parameters established in this manner are as follows: p = 0.61 exp(-0.8/RT) and u = 0.99 exp(0.5/RT), R T being in kcal mol-l. A negative value of E , is due to the gauche oxygen effect characteristic to the OC-CO m ~ i e t y . The ~ ? ~E , value was found to be solvent dependent. A weight of w = 0.88 exp(-0.53 fRT) was assigned to the second-orderinteractions associated with the OCCCCOC arrangement. In the following, we report the results of our analysis on the aforementioned X-ray scattering data. Geometrical Parameters and Statistical Weights Bond lengths and bond angles used in the analysis are listed in Table I.lt2 Statistical weights required for the RIS description of the molecular system are given in Table 11. The expressions for p , u, and 77 are the same as those cited in the preceding section. The conformational energy parameter E, defined for the IC-CO bond was adopted from Raman studies on 2-iodoethyl methyl ether in dioxane.6 In Table 11, the preexponential factor (qo) for 7 is assumed to be unity. The steric interactions taking place between groups separated by four bonds in sequences such as ICGCfOC and CCfOfCC should be of high enerand the weights are set equal to zero. Rotational states were taken to occur at 4cc = 120' and 4 ~ =0 In the following treatment, conformational energies will be altered somewhat around the standard values given in Table 11. Temperatures were taken to be 20 OC. Calculation of the Scattering Function for DDE and Comparison with Experimental Results Following Li et al.,l the scattering functions were calculated for DDE by using the expression' i(s) = C(4srk2)fk[(sins r J / s r k ] (1) k
s = (4ssin 8 ) / A
where fk is the statistical weight of the kth conformer, rk represents the interiodine distance, 28 is the scattering 0 1986 American Chemical Society
2648 Notes
Macromolecules, Vol. 19, No. 10, 1986
Table I11 Locations of the Minimum and Maximum of the Scattering Function of DDE Calculated as a Function of E , with E , Fixed at 0.8 kcal mol-'
E./(kcal mol-')
20minideg 9.8 9.4 9.2 9.1 9.0 9.1
-0.6 -0.3 -0.2 -0.1 0.0 obsd"
28,..ide~ 16.7 15.9 15.6 15.4 15.2 15.5
Measured in m-xylene.]
I-
-4
-6 6
8
10 12 14 16 18 20 2eldeg Figure 1. Scattering functions of DDE: (-) calculated for the
standard set of parameters as indicated in Tables I and 11; (---) observed in m-xylene.'
11
T
7
7 -6
I
2
3
X
Figure 2. Variation of the interiodine distance ( P ) with I. The solid curve indicates the results calculated for the standard set of parameters (Tables I and 11). The experimental values are shown by circles, with error bars indicating the half-width of the peak appearing in the radial distribution curve.' the preceding section: E,, = -0.23 and E, = 0.8 kcal mol-'. The E , value required for oligomers of x = 2 and x = 3 was Since the chains are not too taken to be -0.5 kcal m0l-l.~7~ long, the excluded volume effect was ignored. The results are illustrated in Figure 2, where the experimental values (measured in m-xylene) reported by Li et al.' are also indicated. The calculated values of ( r ) increase with x, in agreement with experimental observations. As stated by Li et al.,' however, experimental uncertainties are rather large, and, therefore, the comparison should not be taken to be a critical test of the theoretical model. Li et al.' noted that the unperturbed 1-1 distance is somewhat solvent dependent. Lower values of ( r ) obtained in ethanol can be explained on the basis of the gauche effect characteristic to the IC-CO and OC-CO moieties.2,6 Brady et a1.lo also noted a small solvent effect in their analysis on a series of a,w-diiodoalkanes. As was discussed in their paperlo, the excluded volume effect should be practically nil in these short-chain molecules. In conclusion, the conformational energies assembled in Table I1 were shown to give a satisfactory agreement with the experimental results obtained in m-xylene. For the terminal bond rotation, i.e., IC-CO, the value of E , (-0.23 kcal mol-l) was taken from the experimental result on 2-iodoethyl methyl ether in dioxane. Since the dielectric constant of m-xylene is similar to that of dioxane, this choice should be reasonableas The X-ray scattering data of a,w-diiodo derivatives are therefore compatible with the RIS model deduced for DME and POE. Acknowledgment. We thank Professor H. Morawetz of Polytechnic University for suggesting this subject. Registry No. DDE, 34270-90-1; I(CH2),(0CH2CH),I, 36839-
angle, and X is the wavelength of the radiation. The conformational energy parameters required for the description of DDE are E, and E,. The minimum (29-) and maximum (20") of the scattering curve were estimated' for several combinations of the energy parameters. The values of 2dmi, and 29,, were found to be insensitive to the choice of E,: for the range E, = 0.6-1.0 kcal mol-', variations in 29- and 29- are less than 0.1'. The results listed in Table I11 are those calculated for E, = 0.8 kcal mol-l. The experimental values obtained in m-xylene1 are shown in the last row. The observed results are well reproduced by the calculation with E, = 0 to -0.2 kcal mol-'. A scattering function calculated by using the standard parameter set, i.e., E , = -0.23 and E , = 0.8 kcal mol-', is shown in Figure 1 (an arbitrary scale for the ordinate), together with the experimental curve reproduced from Li et ala'spaper.' The theoretical values of 20min (9.3') and 29,, (15.7') are in agreement with those observed in m-xylene.' When the measurements are carried out in ethanol, the scattering curve shifts somewhat toward a higher range of 29. The observed values of 20min(10.0') and 29,,, (16.5') 55-1; I(CH2)2(0CH,CH,)J, 36839-56-2. can be matched by adopting E, = -0.6 kcal mol-' (cf. Table References and Notes 111). In view of the experimental data on the conformaLi, H.-M.; Post, B.; Morawetz, H. MakromoE. Chem. 1972,154, tional energies of 2-iodoethyl methyl ether,s variation of 89. E,, from -0.2 (in m-xylene) to -0.6 kcal mol-l (in ethanol) Tasaki, K.; Abe, A. Polym. J . 1985, 17, 641. is highly probable. In general, it is known that 1,2-diAbe, A,; Tasaki, K.; Mark, J. E. Polym. J. (Tokyo) 1985, 17, substituted ethanes such as XCH2CH2Y,where X and Y 883. = halogen or oxygen, exhibit the so-called gauche e f f e ~ t . ~ Abe, A.; Mark, J. E. J. Am. Chem. SOC. 1976, 98, 6468. Abe, A,; Tasaki, K. J . Mol. S t ~ c t .accepted , for publication, In these compounds, gauche forms tend to be more staMoradi-Araghi, A.; Hansen, K. E.; Schwartz, M. Spectrosc. bilized as the polarity of the media increases. On the other Lett. 1978,11,645. Moradi-Araghi, A.; Adame, I. E.; Hansen, hand, E, is less susceptible to the solvent: in our previous K. E.; Schwartz, M. Spectrochim. Acta, Part A 1979,35a, 813. analysis of DME,2nearly the same E, value (0.8 kcal mol-') This expression differs from eq 1 of Li et al.'s paper by inclusion of a factor 4?rrk2. In the present instance, improvement was obtained in cyclohexane and methanol. The best-fit achieved in the agreement by this modification was found t o parameter set for ethanol ( E , = -0.6 and E, = 0.8 kcal be trivial. mol-l) is therefore relevant to the spectroscopic data on The conformational energy differences AH~sm-sauche of 2-iodostructurally related compounds. ethyl methyl ether were estimated to be 0.02 in n-hexane ( e = Estimation of the Unperturbed Interiodine Distance ( r) for Oligomers of x = 1-3 Statistical mechanical averages of the 1-1 distance ( r ) were calculated by using the parameter set established in
1.9),0.23 in dioxane (c = 2.2), and 0.48 in acetonitrile (c = 36.0), units being in kcal mo1-1.6 Orville-Thomas, W. J. Internal Rotation in Molecules; Wiley: New York, 1974. Brady, G. W.; Cohen-Addad, C.; Lyden, E. F. X. J. Chem. Phys. 1969,51, 4309, 4320.
