348 JOURNAL OF POLYMER SCIENCE VOL. XXII, ISSUE NO. 101 (1956)

3. A. Charlesby, Proc. Roy. Soc., A222, 60 (1954). 4. A. Charlesby, J. Polymer Sci., 11, 513 (1953). 5. P. Alexander and A. Charlesby, Proc.. Roy. Soc., A230, 136 (1955). 6. P. Alexander and M. Fox, Nature, 169, 572 (1952); Trans. Faruday Soc., 50, 605

7. L. A. Wall and M. Magat, J. chim. phys., 50, 308 (1953). 8. P. Alexander and A. Charlesby in, Radiobiology Symposium, 1954, Bacq and

9. A. Charlesby, Proc. Roy. Soc., A215, 187 (1952).

(1954).

Alexander, eds., Butterworths, London, 1955, p. 49.

10. Nathalie Bach, Proc. Zd. Confer. Peaeeful Uses Atomic Energy, Vol. 7, UNO,

11. A. Chapiro, J. chim. phys., 22, 246 (1952). 12. M. Burton and J. L. Magee, J. Am. Chem. Soc., 72, 1965 (1950). 13. P: Alexander and M. Fox, Nature, 170,1022 (1952). P. Alexander, Z. M. Bacq,

N. Y., 1956, p. 538.

S. F. Cousens, M. Fox, A. Herve, and J. Lazar, Radiation Research, 2, 392 (1955).

Chester Beatty Research Institute Royal Cancer Hospital Fulham Road, London, S.W. 3 England

The Chemistry Department Imperial College London England

Received July 31, 1956

P. ALEXANDER

D. TOMS

The I f rared Spectrum of Zinc Stearate and the Vulcanization of Natural Rubber

The infrared spectrum of zinc stearate shows strong absorption bands in the regions of 6.5 and 7.1 p.' These bands have been found in many metal- lic salts of carboxylic acids2 and are attributed to the carboxylate ion -COO-, which is a resonance hybrid.3

Compounded rubbers containing zinc oxide and stearic acid were re- ported' to have an absorption band a t 6.5 p, due to the formation of zinc stearate. We have noted the presence of this band a t 6.5 p and also one a t 7.1 p. (In smoked sheet there is an impurity band a t 6.5 ~ 1 , ~ which we have found to be absent in purified r ~ b b e r . ~ )

It has been reported that on vulcanizing a rubber compound (containing vulcanizing ingredients) the intensity of the 6.5 p band decrease~.l*~ This disappearance has been ascribed to the destruction of zinc stearate as vul- canization

We have confirmed that on vulcanization the band a t 6.5 p decreases in intensity. However, on re-examination after 18 hours it was found that the 6.5 p band had returned to approximately its original strength (see Fig. 1).

LETTERS TO THE EDITORS 349

The spectrum of natural rubber shows negligible change when determined a t temperatures in the range 20-140°C.s In a similar temperature range the spectrum of zinc stearate shows only minor changes, such as are to be expected from changes of state.'

I n the case of zinc stearate in natural rubber (smoked sheet) there are major changes in the strength of the bands in the 6.5 and 7.1 p regions a t elevated temperatures (see Fig. 2).

a a

m a

0

6.0 7.0

B

I .O 7.0

C D

t.0 7.0 6.0 7.0 MICRONS -

Fig. 1. Changes in the infrared spectrum of a natural rubber com- pound during vulcanization. (A) Original rubber compound. (B) After 20 minutes at 100°C. (D) After 18 hours at 20°C. (C) After 2 hours a t 100°C.

i D C

0 7.0 6.0 7.0 6.0 7.0 6.0 7.0 MICRONS

Fig. 2. Changes in the infrared spectrum of a mixture of zinc stearate and natural rubber at elevated temperatures. (A) 28°C. (B) 90°C. (C) 96°C. (D) After 18 hours at room temperature (about 20'C.).

350 JOURNAL OF POLYMER SCIENCE VOL. XXII, ISSUE NO. 101 (1956)

These observations can only be interpreted in terms of an interaction be- tween the natural rubber and the zinc stearate. The effects show that cau- tion must be exercised when interpreting changes in the infrared spectrum of natural rubber on vulcanization. It is clear that changes in the infra- red spectrum of zinc stearate and natural rubber mixtures can occur on thermal treatment and are not a specific characteristic of the reactions oc- curring during the vulcanization of natural rubber.

We would like to express our thanks to Dr. L. J. Bellamy for his very helpful advice and criticism, and also to the Imperial Smelting Corporation Limited for the award of Research Fellowship to one of us (B. E.).

References

1. Sheppard, N., and Sutherland, G. B. B. M., Trans. Furaday Soc., 41, 261 (1945);

2. Duval, Lecomte, and Douville, Ann. phys., 17, 5 (1942). 3. Bellamy, L. J., The Znfra-Red Spectrum of Complex Molecules, Methuen, London,

4. Dinsmore, H., and Smith, D. C., Anal. Chem., 20,11(1948). 5. In a sample kindly supplied by Mr. W. R. Dean. 6. The infrared spectra were determined at elevated temperatures in a cell similar to

that of Brown and Holliday, J . Sci. Znst., 28, 27 (1951). 7. Richards, R. E. and Thompson, H. W., Proc. Roy. Soc. (London), 195, l (1948).

Rubber Chem. and Technol., 19, 67 (1946).

1954, p. 149.

National College of Rubber Technology Northern Polytechnic Holloway, London, England

Received August 21, 1956

BRYAN ELLIS H. PYSZORA

Some Group IV Tetrahalide-Alcohol Complexes as Solvents f o r Polyamides

We may list the known solvents for polyamides as follows: (a) acids such as formic and sulfuric acids; (b) aromatic hydroxy compounds such as phenol and the cresols; (c) alcoholic solutions of certain inorganic salts, e.g., lithium and calcium chlorides in methanol; (6, some halogenated alcohols; and (el a few electron-accepting molecules such as antimony and arsenic trich1orides.'s2 We wish to describe here two solvents of class (c ) , titanium tetrachloride-methanol and stannic chloride-methanol, which show remarkably good solvent properties for nylon.

These solvents were prepared by dropping the metal chloride into a flask containing the alcohol a t O O C . , with appropriate precautions to exclude moisture from the system. A very rapid exothermic reaction takes place with the separation of, in the case of titanium, bright yellow crystals of a complex on addition of approximately a half molar equivalent of the metal halide. With the stannic system, the crystals are colorless. The complexes may be separated and washed with carbon tetrachloride prior to redissolving in excess methanol to give solvents which show no