POLYMER LETTERS vOL. 6, PP. 659-662 (1968)

PHOTOPOLYMERIZATION BY BINARY SYSTEMS CONTAINING CARBON TETRACHLORIDE

It has been reported in the literature that the anthracene-carbon tetra- cohloride (1) system generates free radicals under near-ultraviolet (3650 A) radiation. It has a l so been reported that carbon tetrachloride solu- tions (2) of some nitrogen bases produce the hydrochloride after storage overnight on the laboratory bench exposed to daylight. This led us to examine these systems as initiators of bulk polymerization. Many of these systems are found to be good initiators even under illumination from a tungsten filament lamp in Pyrex g l a s s vesse ls , and some results are shown in Table I . Besides tri-n-butyl amine which has been includ- ed in Table I , several other tertiary amines like triethyl amine, tri-n- amyl amine, N,N-diethyl dodecylamine, and N,N-dimethyl octadecyl- amine were a l so efficient but no quantitative study was made with them.

The polymerization was carried out in sealed tubes (Pyrex g lass ) a t 5OoC in a thermostated water bath of Pyrex g l a s s covered on all s ides with thick black paper with only a sma l l round opening on one s ide for the light source (500 W 220 V tungsten filament lamp), the tube being about 12 cm away from the filament. Evidently the effective wavelength lies in the very weakly absorbed visible region as all UV must have

0 2 4 ' 6

TIME IN HOURS - Fig. 1. Photopolymerization of methyl methacrylate by phenanthrene-

carbon tetrachloride a t 50°C: phenanthrene concentration, 0.162 moles/l; carbon tetrachloride concentration, 33.3% (v/v).

65 9

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POLYMER LETTERS 66 1

. PHENANTHRENE <MOLES/LITRE) - 0 0 1 02 a3

A[ I I - (RELATIVE LIGHT INTENSlTYIzd

0 0-2 0'4 06 08 I'O cl

Fig. 2 . Photopolymerization of methyl methacrylate by phenanthrene- carbon tetrachloride at 5OoC: (A) carbon tetrachloride concentration, 33.3% (v/v); time, 6 hr; (B) phenanthrene concentration, 0.073 moles/l; time, 3 hr; (C) carbon tetrachloride concentration, 33.3% (v/v); phenan- threne concentration, 0.16 moles/l; t ime , 6 hr.

been filtered out by the g lass window, the g l a s s wall of the container, and the interposing layer of water. Control experiments were performed and it was found that in the dark conversion was negligible at 5OoC in most cases . Table I records the photo as well a s the thermal polymer- ization in the dark, the photopolymerization yields being corrected for any yield due to the latter effect.

The yield was good and dependent on the time of exposure (Fig. 1); the yield-time curve tended to be autocatalytic towards the end and on long exposure crosslinked gel was obtained. The variation of yield with concentration of phenanthrene and carbon tetrachloride is shown in Fig- ure 2, which indicates the existence of an optimum concentration. There is a rough square-root correlation between yield and intensity of light (Fig. 2). [ T ] ] changes somewhat with the progress of polymerization (Fig. 1). In the case of methyl methacrylate the polymerization was not in- hibited by oxygen and the polymerization could be carried out in open test tubes but hydroquinone and 2,2-diphenyl-l-picryl hydrazyl inhibited

66 2 POLYMER LETTERS

very effectively. Of other monomers, vinyl acetate and acrylic acid could not be polymerized by any of these initiators, and a-methyl sty- rene failed with phenanthrene-carbon tetrachloride.

this s tage of the work but it is assumed that it must be a free-radical process on analogy with the original reactions (1,2). However, as no halogen end group could be detected by dye techniques (3) in the result- ing polymers, the free radicals (CC14 + - CC13 + * C1) might have reacted with the second component to give other radicals, which initiated the polymerization. Further work is in progress.

No definite mechanism is suggested for the polymerization reaction at

Thanks are due to the Council of Scientific and Industrial Research, Government of India, for financial ass i s tance to B. S.

References

(1) E. J . Bowen and K. K. Rohatgi, Discussions Faraday SOC., 14, (2) R. F. Collins, Chem. Ind. (London), 1957, 704; D. P. Stevenson

(3) M . K. Saha, P. Ghosh, and S. R. Pali t , J . Polymer Sci. A, 2, 1365

146 (1953).

and G. M. Coppinger, J . Am. Chem. SOC., 84, 149 (1962).

(1964).

Bhaskar Sen Santi R. Pali t

Department of Physical Chemistry Indian Association for the Cultivation of Science Jadavpur, Calcutta-32, India

Received March 27, 1968 Revised June 14, 1968