A NUCLEAR MAGNETIC RESONANCE STUDY OF syn-anti ISOMERISM IN KETOXIMES

Abstract

NUCLEsR 31AGNETIC RESONANCE O F Sy?Z-anti ISOMERISM IN KETOXIMES 49 1 of P(O), however, as it is reasonable to expect much of Ihe effects of correlation to cancel. In any case the entire polymer chain would collapse to within A' of the surface as P(0,t') for the polymer given by Fig. 2 approaches unity.A significant point with regard to equation 15 and the curves of Fig. 2 is that P(0) may bevery sensitive to 8 over a certain range of 8. In considering the thermodynamics of chain adsorption*J the number of anchoring segments v = P(O)t is an important factor. It is seen that for e going from 0 to 0.9, v may vary over a wide range (-a factor of ten) if, say K-10 a t 0 = 0 (or K-1 a t 8 = 0.9 if K O remains constant). Any isotherm equation should take this variation of v into account if agreement with experiments is to he expected. Comparison of Calculations with DataRecently Fontana and Thomas13 have carried out some very interesting experiments bearing on the problem of the configuration of adsorbed polymers. They were able to directly determine P(0) for poly-(alkyl methacrylate), PLMA, adsorbed onto silica by infrared spectrometry.Their investigation showed that, for this system, P(0) is relatively independent of 8 over a wide range of e. Since it is clear from their work that the mechanism of adsorption involves hydrogen bonding between the surface hydroxyl groups on (13) E. J. I'ontana and J. R. Thomas, J . Phys. Chem., 66, 480 (1961).the silica and the carbonyl groups on the polymer, e is very likely relatively large (>5kT) for this case. Thus, their data is consistent with the idea that this system is operating a t the upper regions of the curves in Fig. 2 where P(0) is relatively insensitive to 8.These investigators found, however, that the relatively constant value for P(0) was not unity but instead about 0.4. This, as the authors point out, most probably is a result of the combination of polymer backbone inflexibility and availability of properly spaced adsorption sites. It is to be expected that as P(0) approaches a value as high as 0.4 the chain becomes relatively rigid (as compared to the solution configuration) and surface site spacing and surface uniformity requirements become more critical. Furthermore, under these conditions both intermolecular and intramolecular overlapping of portions of the chains will lead to smaller P(0) because of steric effects. Alternatively it may be stated that at P(0) = 0.4 the entire PLMA chain is collapsed t o the surface to the extent that equation 18 might be more appropriate.Acknowledgments.-The author wishes to acknowledge the very helpful suggestions and discussions concerning the problem with Drs. 0. L. Isomerism of the syn-anti kind has been detected for the first time in several aliphatic ketoxinies and ketoxime ethers and is indicated by the presence of two resonance lines for the protons on carbon atoms next to the >C=KOH or >C=SOR group. The separation of these two lines depends on (a) the presence of aromatic compounds, acids or bases in the oxime solution, ...

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