3524 Communications to the Editor
Macromolecules, Vol. 37, No. 10, 2004
Ta ble 1. Ca tion ic P olym er iza tion s of BTOT u n d er Va r iou s Con d ition sa
entry
initiator
temp (°C)
solvent
CH2Cl2
CH2Cl2
CH2Cl2
nitrobenzene
nitrobenzene
[M]0 (mol/L)
conv (%)b
yield (%)c
Mn (Mw/Mn)d
1
2
3
4
5
TfOMe
30
30
30
30
50
1.0
1.0
1.0
0.7
0.7
20
69
74
51
>99
14
61
70
47
96
53 100 (1.31)
43 900 (1.16)
33 400 (1.26)
31 500 (1.11)
20 400 (1.04)
BF4OEt3
BF3OEt2
BF3OEt2
BF3OEt2
a
b
Polymerization conditions: [initiator]0 ) 0.02 M; [BTOT]0/[initiator]0 ) 30; reaction time ) 24 h. Determined by 1H NMR analysis.
c Isolated yield of MeOH-insoluble parts. Estimated by SEC analysis (eluent THF, polystyrene standards) of the crude products.
d
Sch em e 2
1
upon polymerization. Other peaks in both the H and
13C NMR spectra are also consistent with the expected
polymer structure. The isomerization was supported by
the CdO absorption peak at 1643 cm-1 in the IR
spectrum of polyBTOT (see Supporting Information).
Scheme 2 illustrates a plausible mechanism for the ring-
opening polymerization. A nucleophilic attack of the
thiocarbonyl sulfur to the cationic initiator affords
carbenium cation species. Then, the thiocarbonyl sulfur
nucleophilically attacks to the R-position of the ether
oxygen in the cyclic carbenium ion, and the chain
reaction of these processes gives polyBTOT.
transition temperature (Tg) was 23 °C. The Td5’s of
polythiourethanes derived from diisocyanates and dithi-
ols are 76-108 °C,13 indicating that polyBTOT is more
heat-resistant than common polythiourethanes presum-
ably due to the absence of active proton (-NHCOS-)
that may accelerate thermal degradation through hy-
drogen bonding to the carbonyl oxygen in the main
chain. Further, polyBTOT has a high refractive index
(nd ) 1.642), indicating the potential applicability to
optical materials.
In summary, we demonstrated a well-defined synthe-
sis of a polythiourethane by the controlled cationic ring-
opening polymerization of 3-benzyltetrahydro-1,3-ox-
azolidine-2-thione (BTOT). Control of molecular weight
was also achieved by using dithiocarbamate as a ter-
minator. PolyBTOT showed high reflactive index and
thermal stability, which may be applicable to optical
materials.
The relationship between the Mn of the obtained
polymer and the feed ratio of [BTOT]0/[BF3OEt2]0 was
linear, and Mw/Mn was less than 1.1, as shown in Figure
2. Further, a two-stage polymerization experiment was
performed to elucidate the stability of the growing ends.
After the first stage polymerization of BTOT (30 equiv
to BF3OEt2) for 10 h at 50 °C (Mn ) 20 400, Mw/Mn )
1.04), BTOT (30 equiv to BF3OEt2) was fed to react
continuously for an additional 10 h at 50 °C. As a result,
the second monomer was consumed completely to
provide a polymer with higher molecular weight (Mn )
40 400, Mw/Mn ) 1.03), while maintaining a narrow Mw/
Mn. These results indicate that the present polymeri-
zation would proceed through a controlled fashion.
The thermal behavior of polyBTOT obtained in entry
5 was evaluated by thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC), where its
5% weight loss temperature (Td5) was 353 °C and glass
Su p p or tin g In for m a tion Ava ila ble: SEC profiles of the
polymers, IR spectra of BTOT and polyBTOT, plot of Mn vs
[H2O]0/BF3OEt2]0 in polymerization of BTOT, 1H NMR spec-
trum of polymer, scheme showing termination by Et2NCS2-
Na‚3H2O, and Experimental Section. This material is available
Refer en ces a n d Notes
(1) (a) Podkoscienlny, W.; Szubinska, S. J . Appl. Polym. Sci.
1988, 35, 85. (b) Imai, Y.; Kato, A.; Ii, M.; Ueda, M. J . Polym.
Sci., Polym. Lett. Ed. 1979, 79, 579. (c) Imai, Y.; Ueda, M.;
Ii, M. J . Polym. Sci., Polym. Ed. 1979, 17, 85. (d) Imai, Y.;
Ueda, M.; Ii, M. Makromol. Chem. 1978, 179, 2085.
(2) (a) Nemoto, N.; Yoshii, K.; Kameshima, H.; Sanda, F.; Endo,
T. J . Polym. Sci., Part A: Polym. Chem. 2003, 41, 185. (b)
Nemoto, N.; Sanda, F.; Endo, T. Macromolecules 2000, 33,
7229.
(3) Choi, W.; Sanda, F.; Endo, T. Macromolecules 1998, 31,
9093.
(4) Mukaiyama, T.; Kuwajima, I.; Mizui, K. J . Org. Chem. 1996,
31, 32.
(5) (a) Nagai, A.; Ochiai, B.; Endo, T. Chem. Commun. 2003,
24, 3018. (b) Nagai, A.; Miyagawa, T.; Kudo, H.; Endo, T.
Macromolecules 2003, 36, 9335.
(6) For the synthesis of TOT, see: Li, G.; Ohtani, T. Hetero-
cycles 1997, 45, 2471.
(7) Experimental details are given in the Supporting Informa-
tion.
(8) Because SEC analysis of the resulting polymer without
quenching showed a unimodal profile, the bimodal distribu-
tion would originate from the termination process using
MeOH. To clarify the reaction mechanism for the bimodal
distribution, the reaction of BTOT and initiator and MeOH
(1:1:1) is now under investigation, and the results will be
reported elsewhere.
F igu r e 2. Mn and Mw/Mn vs [BTOT]0/[BF3OEt2]0 ratio in the
polymerization of BTOT in nitrobenzene at 50 °C; BF3OEt2
)
(9) A plausible mechanism for the termination by Et2NCS2Na‚
0.033 mmol, [BTOT]0 ) 0.7 M. Conversion of BTOT ) 100%.
3H2O is given in the Supporting Information.