2067
YOTES
Oct., 1962
MICRONS 15
6
17
16
18
19
PO
04
z 06
NICL *, CaEa I
5000
3000
2000
1500
1000
,
I
900
700
800
600
500
CM.-‘.
Fig. 1.-Infrared
absorption spectrum of nitryl perchlorate.
spectra thus should resemble each other. In Table I their fundamental vibrations are listed. These agree exactly in activity and rather closely in frequency, with the exception of the v 2 bending mode which occurs a t a distinctly lower frequency (15 to 20%) in KO2+ than in COz. Discussion of the CIOIL- fundamental frequencies is sufficiently ~ o m p l e t ethat ~ , ~it need not be repeated here. Acknowledgment.-The authors are grateful for the considerable assistance of Niiss Ruth Kossatz and her staff of the Infrared Department in carrying out this work. It was supported in part by the U. S. Air Force.
However, it is barely resolved from the envelope due to the other CY- and P-protons. Replacement of the @-hydrogens by deuterium removes all proton-proton spin coupling in the backbone hydrocarbon chain and allows the a-protons in isotactic, syndiotactic, and heterotactic environments to be resolved clearly under appropriate conditions. The proton resonance spectrum of poly-P,b-dideuteriostyrene has been reported previously, but the experimental conditions were not suitable for resolution of the individual peaks.8
Experimental The proton resonance spectra were obtained in a manner described previously.4 The spectra were obtained on 15 wt. % solutions of polymer in benzene enclosed in a sealed tube at 100’. Peak positions are listed in p.p.m. to high PROTON RESONANCE SPECTRB ,4KD field of benzene as an internal reference. The p,p-dideuT A c r I C r w OF POLYSTYRENE AKD teriostyrene was obtained from Merck, Sharp and Dohme of Canada Ltd. and was reputed to be of better than 98% IlEUTERIOPOLYSTYRENES1~2 isotopic purity. The polystyrenes were prepared by standBY S.BROWNSTEIN, S. BYWATER, AND D. J. WORSFOLD ard methods using anionic, cationic, and free radical initiators as described before for a-methylstyrene.4 Dzvzszon of A p p l i e d Chamastry, Nataonal Research Counczl, Ottawa, Canada Recczved Aprzl 1.4. 1988
Results
It has been shown that there are large solvent
effects upon chemical shifts when aromatic moleObservations of polymer tacticity by proton cules are dissolved in aromatic ~ o l v e n t s . ~Adresonance spectroscopy have now been made on vantage was taken of this fact to maximize the several polymer sy~tems.3-~However, only with chemical shifts of the a-protons by choosing a polymethyl methacrylate and poly-a-methylsty- solvent which shifted them relative to the other rene have peaks due to isotactic, syndiotactic, and protons in the molecule. Benzene was found to heterotaetic environments been clearly resolved. have the greatest effect of the many solvents Usually, spin coupling of protons on adjacent which were tried. The spectrum of isotactic carbon atoms produces several lines for each polystyrene in benzene as solvent is shown in Fig. chemically unique species and when their chemical 1. It may be compared with one published preshift is small compared to the spin coupling between v i o u ~ l y to , ~ show the improvement in separation them, only a broad envelope of absorption is ob- of peaks which may be obtained by appropriate tained. One method of removing this obstacle choice of solvent. For comparison, the spectrum is to substitute deuterium for some of the protons. of a polystyrene polymerized by sodium naphthenide The smaller spin coupling constants and almost in tetrahydrofuran is included. This polymer infinite chemical shift combine to simplify the is primarily syndiotactic, as will be shown by the spectrum This has been done with polypropylene, measurements on a deuterated sample. but the choice of sites for deuterium substitution Line widths in proton resonance spectroscopy was such that some chemically non-equivalent are a function of the viscosity of the medium.’O protons were spin coupled.6 As a result, peaks For polymer solutions the macroscopic viscosity due to all three possible tacticities could not be is not the significant quantity since the line width resolved clearly. A separate peak for the a- of the solvent is generally much narrower than proton in isotactic polystyrene has been r e p ~ r t e d . ~those of the protons in the polymer chain. The (1) Issued as N.R.C. No. 7014. degree of segmental motion and internal rotation (2) Presented in part a t the symposium on “Spectroscopy of High along the polymer chain appear to be primarily Polymers,” American Chemical Society National Meeting, Atlantic responsible for broadening of the absorption peaks. City, 1962. (8) F. A. Bovey, G. V. D. Tiers, and G. Filipovich, J . Polgmer Sei., (3) F. A. Bovey and G. V. D. Tiers, J. Polymer Scz., 44,173 (1960).
(4) 5. Brownstein, S. Bywater, and D. J. Worsfold, Makromol. C h e n . , 48, 12‘7 (1961). ( 5 ) U Johnsen, J. Polymet Sci., 64,56 (1961). (6) F. Stehling, Paper #45,Division of Polymer Chemistry, American Chemical Society National Meeting, Washington, March, 1962. (7) R. J. Kern and S. V. Pustinger, Nature, 186, 236 (1960).
38, 73 (1959). (9) A. A. Bothner-By and R. E. Glick, J. Chem. Phys., 26, 1651 (1957). (IO) J. A. Poph, W. G. Schneider, and H. J. Bernstein, “High Resolution Nuclear Magnetic Resonance,” McGraw-Hill Book Co., New York, N. Y., 1959, p. 204.
NOTES
2068 5.52
5.57
A
(a (b) Fig. I .-Proton resonance spectra of polystyrenes: ( a ) isotactic; (b) anionic, primarily syndiotactic.
Vol. 66
Conclusion The proton resonance spectra of poly-p,Pdideuteriostyrene shorn separate peaks due to aprotons in iso-, hetero-, and syndiotactic environments. All the usual methods of polymerization, except by Ziegler catalysts, yield polymers which are largely syndiotactic. T H E EFFECT OF PRESSURE ON RADIOLYSIS OF POTASSIUM NITRATE1 BY TLNG-HO CHENAND EVERETT R. JOHNSON
4.77\ -J4
StOLws Institute of Technology, Hoboken, N e w Jersey Recezved April %8>196%
(a 1
(b)
Fig. 2.-Proton resonance spectra of poly-p,p-dideuteriostyrene: (a) polymerized by BF3 in toluene a t -78'; (b) Dolvmerized bv Na in tetrahydrofuran a t 20".
Potassium nitrate undergoes decomposition by ionizing (gamma) radiation to yield nitrite ion and oxygen,2-5 vix.
KKOs -m+
KKOZ
+
(1) A plot of the nitrite yield us. dose shows three By determining the spectra at a sufficiently elevated temperature, the rate of segmental motion distinct regions: an initial curved portion, and two is sufficient to average the local magnetic environ- apparent straight line regions where the yield apments. The temperature required depends upon pears to be linear with dose. Neglecting the initial the polymeric species, but is largely independent curved portion and concentrating only on the linear of the average molecular weight of the polymer.11 regions, it is apparent that there is a "break" ~ ~has been found For polystyrene in benzene, a temperature of 90' in the nitrite yield c u r ~ 2 J It that coincident with this break, the lattice underis adequate to remove most of the effects of local goes a 1% density change and just prior to the magnetic broadening. The positions of the peaks due to a-hydrogens break, a transition resembling a lambda type tranin isotactic, heterotactic, and syndiotactic en- sition.S,6 Also, an isotope effect of 12% has been Yironments for a variety of polydeuteriostyrenes found prior to the break, but none following the are listed in Table I. Some representative spectra break.2b The exact nature of this transition are shown in Fig. 2 . It can be seen that the line is not known, but was postulated to be initiated by widths are too great, compared with the separation the internal pressure exerted by the trapped oxygen between the lines, to make quantitative estimates from (1) and possibly the mismatch of nitrite ions. of the relative amounts of iso-, hetero-, and syn- It was believed that the application of external diotactic species present in the polymer. The pressure might prevent the transition referred to increased line widths, compared with the methyl above from occurring, or delay its appearance. protons of poly-a-methylstyrene, may be due to With this idea in mind C.P. KNOB was irradiated under about 1900 p.s.i. of He a t the center of a cylindrical co-60 source. The identical geometry TABLE I was used in obtaining all the values shown in Fig. 1. POLYMER PE.4K POSITIONS Dose was determined by Fricke dosimetry with a Synprecision of better than *1.5%. The minimum Temp., 180- Hetero- dioSolvent 'C. tactic tactic tactic Catalyst over-all precision in these determinations is better than i2%. The dose rate was 18 X lo1* ear'.' Toluene -78 4 75 . 5 07 SnClr Tetrahydrofuran 20 4 77 4 93 5 11 Na g,/hr. Benzene 60 4 77 4 88 5 11 AIBW Samples of K S 0 3 (about 0.6 g,) contained in XitromethaneBF3 a 2-mm. i d . Pyrex tube were placed inside a ethylene distainless steel tube. This tube, sealed by a swagechloride -78 4 7 5 4 88 5 07 lok, was connected directly to a helium cylinder Toluene -78 4 75 4 84 5 04 BF3 outside the source. The nitrite ion yield was obButyllithium Toluene -30 4 81 4 91 5 09 tained with and without helium pressure. I t was AlEt3/TiC14 Benzene 25 4 a2 calculated that the maximum energy absorbed by unresolved proton-deuterium spin coupling or the helium was less than 0.3%. incomplete motional averaging of the local mag(1) Research supported in part by 4EC AT(30-1-)-1824 and in part netic environment. In all the polymer samples by NSF grant G-19116. (2) (a) J Cunningham and H G Heal Trans Faraday SOC 64, studied, except that prepared by a Ziegler catalyst, 1856 (1938); (b) J Cunnlngham, .I P h y s C h e m , 66. 628 (1S6l). the syndiotactic species are predominant. How(3) G Henmg R. Lees and M S Matheson, J C h e m P h y s . 21, ever, there seems to be relatirely less of this type 664 (1953) (4) C J. IIochanadel and T. W Davis, zbzd , 27, 333 (1957) in the cationic polymers, compared with the anionic ( 6 ) J Forten and E R Johnson, P h y s Chem. SoEzds 15, 218 or free radical polymers. (1980) (11)
sult@.
S,Brownstein, S.
B y w a t e r , and D . 21.Wiles, unpublished re-
'/e02
(6) E R Johnson and J Forten Dwcusatone F a i a d a y Soc., 81, 238 (lQ61).
