Makromol. Chem. 180, 267-269 (1979)

Short Communication

A Study on Long-lived Propagating Polymer Radicals of Acrylamide Derivatives at Room Temperature

Hitoshi Tanaka, Tsuneyuki Sato, and Takayuki Otsu*

Department of Applied Chemistry, Faculty of Engineering, Osaka City University, Sugimoto-cho, Sumiyoshi-ku, Osaka 558, Japan

(Date of receipt: September 22, 1978)

Long-lived propagating polymer radicals, or so-called living polymer radicals, have been observed by many workers’,’). In general, propagating polymer radicals are unstable, and are often detected only at very low temperature. On the other hand, it has been found that a solid state polymerization of acrylamide (Am) with y-ray irradiation affords a polymer radical which is stable for 6 weeks at 25 T3’.

Recently, we have found that acrylamide and its derivatives such as N-methylacrylamide (NMAm), methacrylamide (MAm), and N-methylmethacrylamide (NMMAm) produce long-lived propagating polymer radicals, when they are polymerized in 1,Cdioxane (Am, MAm, and NMMAm), benzene (NMAm and NMMAm), or carbon tetrachloride (NMMAm) with di-tert- butyl peroxalate (DBPOX) and with di-tert-butyl peroxide (DBPO) in the presence of light at room temperature, in which the systems become heterogeneous as the polymerizations

Fig. 1 Fig. 2

Fig. 1. ESR spectrum of the system N-methylmethacrylamide (NMMAm)/di-tert-butyl peroxalate (DBPOX)/benzene after being reacted for 55 h at room temperature; [NMMAm] =3,27 mol/l, [DBPOX] =4,27.10-2mol/l(SI unit: 1 G=10-4T)

Fig. 2. ESR spectrum of the system N-methylacrylamide (NMAm)/DBPOX/henzene after being reacted for 5 h at room temperature; [NMAm] = 3,87 mol/l, [DBPOX] = 1,78. mol/l

268 H. Tanaka, T. Sato, and T. Otsu

proceed. No polymer radical is, however, observed in the polymerizations of NMMAm in ethanol and of N,N-dimethylacrylamide in benzene, where the polymerization systems are homogeneous during the reactions.

Figs. 1 and 2 show ESR spectra of the systems, NMMAm/DBPOX/benzene and NMAm/DB- POX/benzene, at room temperature. The observed five line ESR spectrum (apparently, AH = 23,2 G) from NMMAm and the three line spectrum (apparently, AH= 24,6 G) from NMAm are assigned to the following propagating polymer radicals 1 and 2, respectively.

CH3 H I

-CH2-CC' I

I c=o I c=o I

H-N-CH3 I

H-N-CH3

1 2

-CHZ-C

In a degassed benzene system, radical 1 is more stable than radical 2, and it is stable for several months at room temperature, although a large proportion of 1 disappears by heating at 70°C for about a day. Radical 1 is found to react easily with oxygen to be converted into a peroxyl radical. The polymerization of NMMAm in 1,4-dioxane gives a similar ESR spectrum to Fig. 1, but the life-time of this radical is not so long as compared with radical 1 produced in benzene.

Similar results were also observed in the photo-sensitized polymerizations of the amide monomers with DBPO at room temperature.

The polymer radical 1 was allowed to react with second monomers to prepare block copolymers. NMMAm was easily converted into polymer radical 1 by DBPOX in benzene at room tempera- ture. During this polymerization, the system became heterogeneous with a yellowish coloration. After complete consumption of NMMAm monomer (two days), the system was heated for additional 3 h at 50°C to decompose the unreacted initiator. To this solution a second monomer was added, and then allowed to stand without stirring at room temperature for a day. During the reaction, the color of the mixture changed slowly from yellow to colorless.

The results obtained are shown in Tab. 1. Although a preliminary solubility test is compatible with the assumption that the polymers formed are block-copolymers, further study is required to get clear-cut evidences. As is shown in Tab. 1, methyl acrylate (MA) was converted into

Tab. 1. Block copolymerizations by using poly(NMMAm) radical 1 in benzene at room temperaturea'

Second monomer

Reaction time in h

Yield in %b)

Methyl acrylate Acrylonitrile Methyl methacrylate

20 24 24

100 41,O 36,l

*) [NMMAm] = 3,27 mol/l, [DBPOX] =0,025 mol/l, [second monomer] = 62,5 vol.- % with respect to

b, Calculated, based on second monomer. whole solution.

A Study on Long-lived Propagating Polymer Radicals. .. 269

polymer in the yield of 100%. The polymer radical 1 prepared from photo-sensitized polymeriza- tion of NMMAm with DBPO gave a similar result.

Fig. 3 shows an ESR spectrum of the reaction mixture of MA and radical 1 produced from the NMMAm/DBPO/hv system. This spectrum is assigned to a mixture of the propagating

Fig. 3. ESR spectrum of the block copolymeri- zation system of poly(NMMAm) radical 1 and methyl acrylate (MA) after being reacted for 4 h at room temperature; NMMAm (2,45 mol/l) was irradiated by a 100 W high pressure mercury lamp in benzene for 2 h at room temperature in the presence of di-tert-butyl peroxide (DBPO) (5,42. lo-’ mol/l), and then MA (5,54mol/l) was added

k 2 0 G - - . (

polymer radical from MA (three line spectrum) and a small amount of radical 1. This indicates that a large proportion of radical 1 is converted into the propagating polymer radical 3 of MA [Eq. (i)] in this system.

Similarly, the reactions of radical 1 with acrylonitrile (AN) and of radical 2 with methyl methacrylate (MMA) gave the propagating polymer radicals from AN and MMA, respectively.

H - -CH2-CC’ I I

COOCH3

3

1 + n CH2=CH I

COOCH3

These results lead not only to an effective method for preparing block-copolymers by a radical mechanism, but also to formation of very stable propagating polymer radicals of various olefinic monomers in such a block copolymerization matrix at room temperature.

More detailed results will be described in a future publication.

B. Ranby, J. F. Rabek, “ESR Spectroscopy in Polymer Research”, Springer-Verlag, New York 1977 *) V. A. Kabanov, J. Polym. Sci., Polym. Symp. 50, 71 (1975) 3, G. Adler,-D. Ballantine, B. Baysal, J. Polym. Sci. 48, 195 (1960)