8718
J. Am. Chem. Soc. 1997, 119, 8718-8719
Scheme 1
The First Polycondensation through a Free Radical
Chain Process
Takeshi Endo,* Nobuo Torii, Toshikazu Takata,†
Tsutomu Yokozawa,‡ and Toshio Koizumi§
Research Laboratory of Resources Utilization
Tokyo Institute of Technology, Nagatsuta-cho
Midori-ku, Yokohama 226, Japan
Scheme 2
Department of Applied Chemistry, College of Engineering
Osaka Prefecture UniVersity, Sakai, Osaka 593, Japan
Department of Applied Chemistry
Faculty of Engineering, Kanagawa UniVersity
Rokkakubashi, Kanagawa-ku, Yokohama 221, Japan
Department of Chemistry, National Defense Academy
Hashirimizu, Yokosuka 239, Japan
addition of thiol to allene as a model reaction similarly proceeds
to give corresponding 1:1 adduct in a certain selectivity.6,8 When
the radical addition of thiophenol to chloroallene (1) (1:1 ratio)
was carried out, we obtained a few products including 1,2-bis-
(phenylthio)propene (2, 15%) and 1-chloro-2-phenylthiopropene
(11%, a formal 1:1 adduct) produced by central carbon attack
of sulfur.9 We noticed the formation of 2, because it could be
emerged presumably through an elimination of hydrogen
chloride from the corresponding 1:2 adduct. To scavenge the
hydrogen chloride evolved during the reaction, propylene oxide
(PO) was added to the reaction system to increase the yield of
2 to 44%. Further, use of 2 mol of thiophenol enhanced the
yield up to 81%, but another 1:1 adduct, 1-chloro-3-phenylthio-
propene (3), was still produced in 9% yield in addition to 10%
of unidentified product (UIP) (Scheme 1). Therefore photo-
initiated radical reaction10 was examined to elevate the product
selectivity by lowering the temperature from 60 to 20 °C. As
a result, the yields of 2 and 3 were 91 and 7%, respectively,
whereas the formation of UIP was almost suppressed.
The polymerization of 1 and aromatic dithiols 4-6 was
conducted at 20 °C for 72 h in toluene under photoirradiation
(Scheme 2, Table 1). The usual workup gave a polymeric
product of which structure was determined mainly by the NMR
spectra as the polymer formed by polycondensation. Typical
1H NMR spectrum of the polymer PS is shown in Figure 1
(top). The simple signal pattern of the spectrum indicated that
the polymer presumably consists only of 1,2-dithiopropene unit,
while the regioisomeric ratio of cis and trans is nearly 1:1. The
13C NMR spectrum supported the proposed structure (Figure
1). The selected results of the polymerizations under varying
conditions are summarized in Table 1.
The polymerization of 1 and 4 was carried out under the
conditions same as those of Scheme 1a (Table 1, run 1) and
gave only 12% yield of polymer with Mn 1300 (peak top value)
which was roughly equal to Mn calculated from the product ratio
of Scheme 1a. In the polymerization under the photoirradiation
at 60 °C (run 2), the yield increased to 24%, although Mn was
fairly low. However, at 20 °C the yield increased to 37% (run
3). With prolonged reaction (run 4), the polymer with Mn 2700
was obtained in 71% yield. It was found that use of dithiol in
slight excess of up to 1.2 equiv enhances both the yield and
molecular weight (runs 5-8). Further loweing of the reaction
temperature (7 °C) affected the results (run 10) little. Decrease
in concentration gave a little better yield and higher Mn
presumably because of the reduced viscosity of the polymeri-
zation system (run 11).
ReceiVed January 21, 1997
The free radical chain reaction is one of the most important
polymerization processes due to its practical advantages, e.g.,
its susceptibility to water much lower than that of ionic
polymerization. The free radical process has been applied only
to addition polymerization and polyaddition. Recent develop-
ment of free radical ring-opening polymerization1 has largely
expanded the possibility of ring-opening polymerizations which
have been limited to ionic process.2 Meanwhile, polyconden-
sations usually proceed with an ionic mechanism via an acid-
or base-catalyzed reaction,3 in addition to those involving
intervention of organometallic intermediates.4 However, to the
best of our knowledge, there has been no example of polycon-
densation through a free radical chain process. Provided
polycondensation through a free radical chain process could
occur, a new entry to polymer synthesis would be opened and
the availability of polycondensation as useful synthetic method
would be enlarged. During our extensive study on polymeri-
zation of allenes and their homologues as vinyl-functionalized
vinyl monomers,5-7 we have recently found the first example
of polycondensation through free radical chain process, which
is disclosed in this paper.
Bisallenes react with dithiols to afford corresponding poly-
addition products in high yields under typical radical conditions
via selective formation of central carbon-sulfur bond.6 Radical
* Author to whom all correspondence should be addressed.
† Osaka Prefecture University.
‡ Kanagawa University.
§ National Defense Academy.
(1) (a) Endo, T. Kobunshi 1986, 35, 272. (b) Endo, T.; Yokozawa, T.
In New Method for Polymer Synthesis; Mijs, W. J., Ed.; Plenum Press:
New York, 1992; p 155. (c) Bailey, W. J.; Chen, P. Y.; Chen, S. C.; Chaio,
W.-B.; Endo, T.; Gapud, B.; Kuruganti, V.; Lin, Y.-N.; Ni, Z.; Pan, C.-Y.;
Shaffer, S. E.; Sidney, L.; Wu, S.-R.; Yamamoto, N.; Yamazaki, N.;
Yonezawa, K.; Zhou, L. L. Makromol. Chem., Macromol. Symp. 1986, 6,
81.
(2) (a) Saegusa, T., Goethals, E., Eds.; Ring-Opening Polymerization;
ACS Symposium Series 59; American Chemical Society: Washington, DC,
1997. (b) Ivin, K. J., Saegusa, T., Eds.; Ring-Opening Polymerization;
Elsevier: New York, 1984.
(3) (a) Marvel, C. S.; Markhart, A. H., Jr. J. Am. Chem. Soc. 1948, 70,
993. (b) Marvel, C. S.; Aldrich, P. H. J. Am. Chem. Soc. 1959, 81, 1978.
(c) Marvel, C. S.; Markhart, A. H., Jr. J. Am. Chem. Soc. 1951, 73, 1064.
(d) Marvel, C. S.; Roberts, W. J. Polym. Sci. 1951, 6, 711. (e) Marvel, C.
S.; Cripps, H. N. J. Polym. Sci. 1952, 8, 313. (f) Marvel, C. S.; Olson, L.
E. J. Polym. Sci. 1957, 26, 23.
(4) For example, see: Ueda, M.; Ichikawa, F. Macromolecules 1988,
21, 1908.
(5) Yokozawa, T.; Tanaka, T.; Endo, T. Chem. Lett. 1987, 1831. (b)
Yokozawa, T.; Ito, N.; Endo, T. Chem. Lett. 1988, 1955. (c) Mizuya, J.;
Yokozawa, T.; Endo, T. J. Polym. Sci., Part A: Polym. Chem. 1990, 28,
2765. (d) Idem. J. Am. Chem. Soc. 1989, 111, 743.
(6) (a) Sato, E.; Yokozawa, T.; Endo, T. Macromolecules 1993, 26, 5185,
5187. (b) Idem. Makromol. Chem., Rapid Commun. 1994, 15, 607. (c)
Idem. J. Polym. Sci., Part A: Polym. Chem. 1996, 34, 669.
(7) (a) Endo, T.; Tomita, I. Prog. Polym. Sci. 1997, 22, 565. (b) Idem.
Trends Macromol. Res. 1994, 1, 151.
(8) (a) Pasto, D. J.; Hermine, G. L. J. Org. Chem. 1990, 55, 685. (b)
Ogawa, A.; Kawakami, J.; Sonoda, N.; Hirao, T. J. Org. Chem. 1996, 61,
4161.
(9) This result was consistent with that of Pasto et al.,8a although they
reported no details such as yield of the products. Other products: abnormal
1:1 adduct, 1-chloro-3-phenylthiopropene (6%), and 1:2 adduct, 1,2-bis-
(phenylthio)-2-chloropropane (19%).
(10) Reaction conditions: Pyrex filter, toluene, 20 °C, 72 h, PO (2 equiv),
and irradiation with a 400 W high-pressure mercury lamp.
S0002-7863(97)00165-0 CCC: $14.00 © 1997 American Chemical Society