COMMUNICATIONS TO THE EDITOR time. (4) The relaxation time spectra are markedly temperature dependent, broadening as temperature is lowered. The similarity to behavior in many polymer glasses is striking. One alternative explanation that could be given to some of our results is that phase separation occurs in glasses formed from mixtures of simple molecules and that the appearance of secondary relaxation peaks (below Tg)is an artifact due to this. But the near universality of this behavior both in a wide variety of mixtures, and in pure substances as well, leads us to exclude this possibility. Most molecular explanations for the presence of molecular mobility (indicated by secondary relaxation regions below Tg)have been in terms of internal molecular motions involving hindered rotation around chemical b o n d ~ . ~ In J this view these relaxations are extrinsic to the glassy state and arise from intramolecular modes of motion that remain active even when the molecule as a whole is frozen in the glassy matrix. On the basis of our studies, we suggest that relaxations in the glassy state need to be reexamined from the point of view of intermolecular rather than intramolecular degrees of freedom. We are continuing these studies on additional simple glass forming systems and will report this work in detail and discuss implications of this picture on dielectric relaxation in liquids later.
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Figure 1. Postirradiation polymerization of hydrated barium methacrylate at 35". Dose 0.86 Mrad at -78"; in vacuo: A, 0.6 days; 0, 27.6 days; in air: 0, 34 days.
hydrate.2b Our studies have shown it to be a monohydrate and this observation is in agreement with the recent report of Bowden and O'DonnelL2" These workers, however, have studied the dehydration process in air, for comparison with polymerization studies, believing the polymerization to be unaffected by the presence of oxygen. Results obtained in our laboratory indicate that this conclusion is valid only for the monohydrate and anhydrate. At all intermediate states of hydration, the polymerization is observed to be extremely sensitive to the presence of oxygen. In Acknowledgment. We are grateful to the OwenFigure 1 the yields of polymer on postirradiation polyIllinois Foundation and to the Department of Defense merization in vacuo at 35" for 0.6 and 27.6 days are (Grant No. N00014-69-A-0411) for the support of shown as a function of water content. (The loss of this research. water from the crystal hydrates, under the experimental conditions used, is negligible even at the longest (4! N. G.McCrum, B. E. Read, and G . Williams, "Anelastic and Dielectric Effects in Polymeric Solids," John Wiley and Sons, New polymerization times.3 Therefore, the quoted level York, N. Y., 1967. of hydration is the correct one at any time.) A maxi(5) A. E . Woodward and J. A. Sauer in "Physics and Chemistry of mum in the polymerization rate is observed at the the Organic Solid State," Vol. 11, Interscience Publishers, New York, N. Y., 1965, p 638. 0.25 hydrate. In the presence of air, however, while BELFERGRADUATE SCHOOL OF SCIENCE GYANP. JOHARI the rates a t the zero and monohydrate compositions YESHIVA UNJVERSITY MARTINGOLDSTEIN are unchanged, those at all other compositions show NEW YORK,NEWYORK 10033 an inversion relative to the vacuum polymerizations. We have therefore examined the dehydration process RECEIVED NOVEMBER 20, 1969 in vacuo at 47". The results show that dehydration proceeds with no loss in crystallinity. Infrared spectra and X-ray powder diffraction measurements were Dehydration and Polymerization of Barium identical with those reported by Bowden and O'Donnell. In addition, density measurements of monoMethacrylate Monohydrate1 hydrate, anhydrate and intermediate compositions show that there is no collapse of the lattice upon Xir: The thermal degradation of barium methacrylate removal of the water of crystallization. A minor exmonohydrate has recently been reported by Bowden (3%) along the C axis was observed. pansion and O'Donnell.2a An understanding of this process can play an important role in defining the mechanisms of (1) Paper presented in part at the 15th Canadian High Polymer the solid-state polymerizations of acrylate and methForum, Kingston, Ontario, Sept 3-5, 1969. acrylate salts. We report here some additional ob(2) (a) M .J. Bowden and J. H. O'Donnell, J . Phys. Chem., 73, 2871 (1969); (b) J. B. Lando and H. Morawetz, J . Poly. Sci., C, 4, 789 servations on the dehydration phenomenon. (1964). The salt of barium methacrylate has been previ(3) F. M. Costaschuk, D. F. R. Gilson, and L. E. St. Pierre, to be ously reported by Lando and Morawetz to be a dipublished. Volume 74, Number 9
April SO, 1970
COMMUNICATIONS TO THE EDITOR
2036 The oxygen inhibition is rationalized on the basis of increased permeability of crystals rich in defect^^,^ and will be treated more fully in a paper which will follow. Further evidence of the nonessential role of water in maintaining the crystal structure of barium methacrylate is obtained from infrared spectra. The 0-H stretch occurs as a sharp strong absorption at 3562 cm-l, indicative of free 0-H stretching, rather than a broad peak at longer wavelengths which would indicate a hydrogen-bonded species. These results are in contrast to those found for calcium acrylate dihydrate3 where the water of hydration plays an important function in maintaining the crystalline structure.
splitting might follow the same angular dependence as
p proton splitting. This conclusion, however, is not forced on one by the evidence of the p fluorine splitting.
I n symmetrical ketyls of this type, there is no independent means of monitoring the spin distribution unless the carbonyl 13Chfs is measured. Cyclization to a perfluorocyclobutyl ring may well affect the spin distribution within the carbonyl group. Nevertheless, the 37.3-G splitting from the y-fluorines, which are at a 0" dihedral angle with the spin site, lends plausibility to their conclusion. Elementary bonding arguments can be used to rationalize maximum p-fluorine hfs at either the 90" or 0" dihedral angles. If the fluorine atom is at a 90" angle to the p orbitals containing the odd electron, spin (4) G. Adler, J . Poly. Sci., C16, 1215 (1967). transfer can occur by a 1,3 p-7r mechanism, Le., overlap DEPARTMENT OF CHEMISTRY F. If. COSTASCHUK of the and - lobes of the fluorine p orbital with the MCGILLUNIVERSITY D. F. R. GILSON corresponding and - lobes of the radical system. MONTREAL, CANADA L. E. ST. PIERRE (The orthogonal fluorine p orbital js in the nodal plane RECEIVED DECEMBER 3, 1969 of the 7r system. Note, however, that it can interact with the lone-pair electrons on the oxygen.) This situation is shown in I for the specific case of a nitroxide. On the other hand, if the dihedral angle is 0", spin transComment on "Electron Spin Resonance of fer can be achieved by a 1,3 p-u overlap, i.e., interacPerfluorocyclobutanone Ketyl. Long-Range tion of lobe with lobe as shown in 11. Recent INDO calculations predict a maximum p-fluorine hfs at Fluorine Coupling," by J. A. Gerlock and OO.lo If both p-7r and p-a spin transfer mechanisms E. G. Janzen. The Angular Dependence of are operative, the dihedral angle dependence could be p-Fluorine Hyperfine Splitting complicated.
+
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+
Sir: Branching at a carbon attached to a radical site normally reduces the hyperfine splitting (hfs) of the remaining p protons, as referenced to the methyl-substituted radical. This result stems from an increased population of conformers in which the p protons are at dihedral angles greater than 45". The maximum p proton hyperfine splitting is expected at a 0" dihedral angle with a minimum value at a 90" angle.'t2 Perfluorobranching at a trifluoromethyl group, however, increases the hfs of the remaining p fluorines. The fluorine splitting in ditrifluoromethyl nitroxide is 8.2-8.6 G,3 while the p-fluorine splittings in symmetrical nitroxides substituted with CICFzCFz and MeOCOCFzCFz groups are 10.14 and 13.8 G,6 respectively. Similar effects have been noted in perfluoroalkyl-tbutoxy nitroxides6 and perfluoronitroalkane anion radicals.7~~If the conformational properties of perfluoroalkyl groups are similar to those of alkyl groups (an assumption), then the dihedral dependence of p-fluorine hfs might be exactly opposite to that of p protons. Recently, Gerlock and Janzen studied the esr spectrum of perfluorocyclobutanone ketyl,' I n this radical, the p hfs was 82.9 G and the y hfs was 37.3 G, as compared to the 34.7-G splitting found in hexafluoroacetone k e t ~ lwhere , ~ the average dihedral angle is 45'. Since the dihedral angle of the p fluorines in the cyclic ketyl is 25-30", Gerlock and Janzen concluded the p fluorine The Journal of Physical Chemistry
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A definitive answer to the question of the angular dependence of p-fluorine splitting must await experiments in rigid cyclic systems in which the fluorine atoms are at reasonably well-known dihedral angles and in which the spin densities can be monitored. However, if the angular dependence for fluorine splitting is the same as that for proton splitting, it follows from the experimental results cited above that the conformer population in perfluoroalkyl substituted radicals of the above type (1) (a) &I. C. R. Symons, J . Chem. Soc., 277 (1959); (b) H . C. Heller and H. M. McConnell, J . Chem. Phys., 32, 1535 (1960). (2) For a thorough review, David H. Geske in Progr. Phys. Org. Chem., IV, 125 (1967). (3) (a) W.D. Blackley and R. R. Reinhard, J . Amer. Chem. floc., 87,802 (1965); (b) I. 1'. Miroshnichenlto, G. M'.Larin, S. P. Makarov, and A. F. Videnko, Zh Strukt. Khim., 6, 776 (1965). (4) W. D. Blackley, J . Amer. Chem. Soc., 88,480 (1966). (5) E. T. Strom and A. L. Bluhm, Chem. Commun., 115 (1966). (6) A. L. Bluhm and E. T. Strom, unpublished research. (7) J. L. Gerlock and E. G. Janzen, J . Phys. Chem., 72, 1832 (1968). (8) In t h e radicals cited, changes in nitrogen hfs were minor. (9) E. G. Janzen and J. L. Gerlock, J . Phys. Chem., 71, 4577 (1967). (10) K . Morokuma, J. Amer. Chem. SOC., 91, 5412 (1969).
