592 LETTERS TO THE EDITORS

isolated from polyethylene terephthalate film' is ruled out by the molecular weight and by the ease of sublimation (the sublimate formed in polymeriza- tion of ethylene terephthalate is much smaller in amount and much less volatile than that isolated from polyethylene isophthalate preparations).

The strain which causes diaculty in formation of the cyclic dimer of ethylene terephthalate is absent in the case of ethylene isophthalate. No diBculty was experienced in preparing Fisher-Hirschfelder models of the cyclic dimer.

Reference

1. S. D. Ross, E. R. Coburn, W. A. Leach, and W. B. Robinson, J . Polymer Sci., 13, 406 (1954).

C. E. BERR Yerkes Research Laboratory E. I. du Pont de Nemours & Co.. Inc. Buffalo, New York

Received October 21, 1954

Hydroperoxides in Oxidized Polythene

In a recent paper on the infrared investigation of the structure of poly- thene, Rugg et al. drew attention to the presence of a band a t 2.81 p in the spectrum of oxidized polythene at 150 "C.' They attributed the appear- ance of this band to the formation of a hydroperoxide group in the poly- thene. After cooling the oxidized polythene to room temperature they found that the band a t 2.81 p had disappeared. The inference from this observation would be either that the hydroperoxide group decomposed quickly on cooling, or that there is no band a t 2.81 p due to the hydroper- oxide absorption in the spectrum of polythene a t room temperature. The former is improbable, and the latter led us to look more closely at the spec- trum in the 3 p region.

\Ve have confirmed the presence of the band a t 2.81 p (X) in hot oxidized polytliene (spectral curve B), and have shown the wave length of this band to be identical with the wave length of the band due to the OH stretching vibration in tert-butyl hydroperoxide, cumene hydroperoxide, and cyclo- hexene hydroperoxide, examined as dilute solutions in carbon tetrachloride. Therefore we agree that the 2.81 p band in oxidized polythene is consistent with the presence of a hydroperoxide group.

In the spectrum of oxidized polythene cooled to room temperature (spectral curve C) we observed a weak band still present a t 2.81 1.1, but also a very strong broad absorption band at about 2.97 p (this spectral change may be seen on Rugg's diagrams).

LETTERS TO THE EDITORS 593

T z

w c

W

P

I I I /Wavelength in /u 2 1 1 ! -

2 7 29 31

Fig. 1. Evidence of hydroperoxide in oxidized polythene: (A) Polythene untreatedspectrum recorded at 30°C. (B) Heated in air at 150"C.--spectrum recorded at 150°C. (C) Heated in air at 150"C.-spectrum recorded at 30°C. (D) Material of B and C heated in absence of air for 3 hrs.-spectrum recorded at 150°C. (X) Band at 2.81 p assigned to free hydroperoxide group. (Y) Band at 2.97 p assigned to associated hydroperoxide group.

On heating the polythene slowly by stages to 150°C. the intensity of the 2.97 p (Y) band was observed to decrease, and the intensity of the 2.81 p band to increase gradually as the temperature was raised. When the original temperature of 150°C. was reached, the 2.97 1.1 band had decreased to a very weak absorption and the 2.81 p band had attained the original intensity seen before the cooling. This suggests that there is an equilib- rium at all temperatures between an associated and a free hydroperoxide group in oxidized polythene. The equilibrium is displaced toward the as- sociated state a t room temperature, but the free state predominates at 150 "C.

The hydroperoxide group might be expected to decompose on heating. Oxidized polythene was heated in the absence of oxygen a t 150"C., and the band at 2.81 p (assigned to hydroperoxide) was observed to disappear only after 3-4 hours of heating (spectral curve D). This supplies codrmation of the previous assignment of the 2.81 p band to the presence of hydroper- oxide.

The rate of formation of the hydroperoxide must be somewhat faster than the rate of decomposition in free air at 150°C. since the intensity of the hydroperoxide band continued to increase over a period of 20 hours at this temperature. The decomposition products of this hydroperoxide have not

.594 LETTERS To THE EDITORS

been investigated in detail, but the spectrum of oxidized polythene heated in the absence of oxygen for several hours contains bands a t 3.0 and 3.1 p a t room temperature, probably due to an alcoholic OH group and a car- boxylic acid OH group, respectively.

Reference 1. F. M. Rugg, J. J. Smith, and R. C. Bacon, J . Polymer Sci., 13, 535 (1954).

J. D. BURNETT R. G. J. MILLER H. A. WILLIS

Research Department Imperial Chemical Industries Ltd. Plastics Division Welwyn Garden City, Herts., England

Received November 29, 1954

Quaternary Anilinium Salt as an Initiator for Vinyl Polymerization

It has been found that the binary mixture of dimethylaniline and benzyl chloride initiates the polymerization of methyl methacrylate. The poly- merization was still more affected when the corresponding quaternary salt, dimethylbenzylphen ylammonium chloride (I), was used instead of the bi- nary mixture. In this communication, the outline of our finding concerning this new catalyst is briefly described.

A mixture of methyl methacrylate, dimethylaniline, and benzyl chloride was heated under nitrogen in a sealed tube. The reaction temperature was controlled to 70 f 0.1'. The volume ratios of methyl methacrylate, di- methylaniline, and benzyl chloride were 20 : 1 : 5, 20 : 2 : 4, 20 : 3 : 3, and 20 : 4 : 2, respectively.

The degree of polymerization, which was viscometrically determined in chloroform, ranged from 1000 to 2000.

From the result of these experiments, it has been made clear that the rate of polymerization was the highest when the amine and the chloride were used in an equimolecular amount.

Thus it is expected that the initiating action may be correlated with the quaternary salt formation between the amine and the chloride. Compara- tive experiments showed that the quaternary salt (I) was a better catalyst than the equivalent mixture of the components when the polymerization was carried out in a homogeneous system. (An example of the homogene- ous polymerization recipe is 2.5 ml. of the monomer, 0.004 mole of the salt (or the binary mixture), and 1 ml. of methanol.) Hydroquinone thoroughly inhibited the polymerization.

From these facts it may be considered that the species capable of initiat- ing the vinyl polymerization is a radical which is probably a result of the