684
Chemistry Letters 2000
Convenient Synthesis of Poly(butylene succinate) Catalyzed by Distannoxane
Hiroyuki Takahashi, Teruaki Hayakawa, and Mitsuru Ueda*
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552
(Received March 27, 2000; CL-000283)
A convenient method for the synthesis of poly(butylene suc-
cinate) (1) of high molecular weight has been developed. This
polyester was prepared readily by the distannoxane-catalyzed
polycondensation of succinic acid (2) with 1,4-butanediol (3) in
decalin at 190 °C under azeotropic condition. The polycondensa-
tion proceeded in decalin-melted polymer two-phase, giving 1
with the number average molecular weight of 150000.
Because, the reported esterification of carboxylic acids in the
presence of the distannoxane catalyst was carried out using a
large excess of alcohols.8 The reaction proceeded slow at 100
°C but gave a quantitative yield of the 3-phenylpropionic butyl
ester after 24 h.
On the basis of the model reaction, the distannoxane-cat-
alyzed polyesterification of 2 and 3 was investigated. In the
distannoxane-catalyzed esterification, it is reported that the
reverse reaction (hydrolysis) cannot occur, and removal of the
formed water is unnecessary.8 Thus, direct polycondensation
was carried out in bulk in the presence of 4 (1 mol%) at 120 °C
under nitrogen atmosphere. This polymerization produced 1
with a number average molecular weight (Mn) of 4000 (relative
to polystyrene standard), which means the water concentration
is about 0.2 mol% when an equilibrium constant for the poly-
esterification is 4. The polyesterification catalyzed by distan-
noxane gave 1 without removing the water. The molecular
weight of polymer obtained, however, was not enough to make
films and fibers. The water concentration must be lowered to
achieve a high degree of polymerization. Then, water was
removed by a slow flow of nitrogen at 120 °C. This method
was somewhat effective to improve the Mn of 1 (Mn = 9000).
Driving an equilibrium constant toward polyester can be carried
out more efficiently with azeotropic distillation. Therefore, a
mixture of equimolar amounts of each monomer and the cata-
lyst (0.01 or 1 mol%) in solvent was refluxed in a Dean-Stark
apparatus (Scheme 2). A typical polymerization was carried
Aliphatic polyesters are currently receiving considerable
attention for their applications in biodegradable fibers, film,
bottles, and injection-molded products.1 Most of aliphatic poly-
esters for the commercial uses are prepared from cyclic esters
and biosynthesis.2,3 Recently, much attention has been paid to
the synthesis of aliphatic polyesters from aliphatic dicarboxylic
acid and diols. However, it was very difficult to prepare
aliphatic polyesters with high molecular weights because of low
thermal and hydrolytic stability. Thus, high molecular weight
polymers are prepared by the polymerization of chain extender,
such as diisocyanates or diphenyl carbonates, with hydroxy ter-
minated prepolymers from diacids and diols.4,5 Quite recently,
new methods using a direct polycondensation of 2 with diols in
solvents and in bulk under high vacuum have been developed to
obtain aliphatic polyesters with high molecular weights.6,7
However, these methods still require a high vacuum system.
Thus, more simple method would be expected to develop.
Otera et al. reported that distannoxane catalysts were very
effective for esterfication of carboxylic acids with alcohols,8
and applied successfully these catalysts for the synthesis of
poly(L-lactic acid).9 These findings prompted us to develop a
new synthetic method for aliphatic polyesters having high
molecular weights by a direct polyesterfication of aliphatic
dicarboxylic acids with diols.
In this paper, we report the successful synthesis of high
molecular weight 1 from 2 and 3 in the presence of 1-chloro-3-
hydroxy-1,1,3,3-tetrabutyldistannoxane catalyst (4) under
atmospheric pressure.
Before attempting the polymer synthesis, we first studied
the catalytic effects of 4 on the reaction of equimolar amounts
of 3-phenylpropionic acid and 1-butanol in bulk (Scheme 1).
out as follows. A mixture of 2 (20.0 mmol, 2.362 g) and 3
(20.0 mmol, 1.802 g) in the presence of 4 (0.01 or 1 mol%) was
placed in a 50 cm3 round-bottom flask equipped with Dean-
Stark apparatus and a condenser. The mixture was stirred at
120 °C for 1 h, and then the solvent was added. The mixture
was refluxed for 24 or 72 h. After the polymerization, the mix-
ture was cooled to room temperature, the solvent was removed
by decantation. The polymer was dissolved in 20 cm3 of chlo-
roform and the resulting solution was poured into a large
amount of hexane. The polymer was obtained almost quantita-
tively. These results are summarized in Table 1.
When p-chlorotoluene (Run 1) was used for the solvent,
the polymerization proceeded in homogeneous state. On the
other hand, the polymerization in nonane (Run 2) proceeded in
Copyright © 2000 The Chemical Society of Japan