2582
Macromolecules 2003, 36, 2582-2583
dilution) method, even though mixtures of cyclic oligo-
mers were desired, the highest yield of dimer is not
greater than 65% accompanied by considerable amounts
of higher oligomers.3b,5 Recently, new synthetic ap-
proaches using cyclo-depolymerization have been re-
ported.5,10 Although these are significant advances from
the viewpoint of material recycling of polyesters, they
are unsuitable for our requirements because of either
low dimer yields5 or usage of chlorinated solvents and
long reaction times.10
In this communication, we report a simple method for
the selective and quantitative synthesis of macrocyclic
ethylene isophthalate dimer. In this method, the most
important factor is the selection of the solvent and the
leaving groups of substrates. The key point of this
method is that the reaction progresses efficiently in the
form of an azeotropic mixture.
Selective Syn th esis of Ma cr ocyclic Eth ylen e
Isop h th a la te Dim er
Ritsu k o Na ga h a ta ,*,† J u n -ich i Su giya m a ,†
Yu k im ich i Na k a o,‡ Mich ih ik o Asa i,† a n d
Ka zu h ik o Ta k eu ch i†
Research Center of Macromolecular Technology, National
Institute of Advanced Industrial Science and Technology
(AIST), AIST Tsukuba Central 5, 1-1-1, Higashi, Tsukuba,
Ibaraki 305-8565, J apan, and Nanotechnology Research
Institute, National Institute of Advanced Industrial Science
and Technology (AIST), AIST Tsukuba Central 5,
1-1-1, Higashi, Tsukuba, Ibaraki 305-8565, J apan
Received October 8, 2002
Revised Manuscript Received February 19, 2003
Aromatic polyesters (PET, PBT, PEN, etc.) are ex-
tensively employed thermoplastic polymers, used either
alone or in blends for application in textile and film
manufacturing, food packaging, and information sup-
port for the computer industry. New synthetic routes
for polyesters via environmentally friendly entropically
driven ring-opening polymerization of macrocyclic oli-
gomers have been attracting increasing research atten-
tion.1-7 In this new method, chain ring-opening polym-
erization of macrocyclic precursors proceeds without
elimination, leading to two major benefits: industrial
processes will no longer need to emit unwanted reaction
byproducts, and energy losses will be drastically re-
duced. Furthermore, high-quality products without
impurities originating in eliminated byproducts are
expected to be obtained. In conventional high-temper-
ature synthetic processes, polymeric products are af-
fected by hydrolysis and thermal degradation, making
it difficult to prevent discoloration and deterioration of
mechanical properties.
We have already demonstrated that the solid-phase
ring-opening polymerization of polycarbonates and poly-
(ethylene terephthalate) gave high-quality polymers.8,9
When the macrocyclic precursors are strained small ring
size compounds, ring-opening polymerization progresses
at temperatures much lower than their melting points
without solvent. We have also reported that, in the case
of macrocyclic oligomers with low tension in the ring,
the growth reaction of the polymer chain and the
transesterification reaction proceed simultaneously,
interfering with formation of high molecular weight
polymers. These results may provide an important
guiding principle in further molecular design of oligo-
mers.
Ethylene glycol diacetate (EGA, distilled in vacuo,
2.34 g, 16 mmol) and isophthalic acid dimethyl ester
(recrystallized from methanol, 3.88 g, 20 mmol) were
stirred in 30 mL of cyclohexane (previously dried over
calcium hydride, bp 80.8 °C) at 65 °C and treated with
sodium ethoxide (freshly prepared just before the ex-
periment by adding metal sodium to dry ethanol fol-
lowed by drying in vacuo, 4.6 mg, 0.2 mmol) in EGA
(0.56 g, 4 mmol). The reaction that immediately followed
started with the clouding of the solution, in which
methyl acetate (bp 57.8 °C) was evaporated at 55.5 °C
by producing an azeotropic mixture with cyclohexane.11
After 2 h of stirring, the reaction mixture was cooled to
room temperature. White precipitate was filtrated and
dried. On the basis of unreacted monomers in the
filtrate, the conversion was found to be 97.6%. The
purity of the white powder, as measured by GC,12a was
98.4%. Low molecular weight impurity was completely
removed by recrystallization from DMF, producing
white crystals of mp ) 390-401 °C.13 Complete absence
of molecules larger than the dimer was proved by
SEC.12b The structure was confirmed by elemental
analysis12c and high-resolution ESI mass spectrum
analysis.12d
Concerning the synthesis of ethylene isophthalate
copolymers, our knowledge of solid phase ring-opening
polymerization of aromatic polyesters suggests that
cyclic dimer with high melting point is suitable. Oligo-
mers with a larger ring size show less strain in the
molecules, and the reaction leading to the ring-opening
polymerization does not usually progress efficiently. To
our knowledge, to this date no simple and effective
methods for the selective synthesis of macrocyclic eth-
ylene isophthalate dimer have been reported in the
literature. With the high-dilution (or pseudo-high-
Previously, we reported a new synthetic method for
oligo(ethylene terephthalate) by ester-ester exchange
reaction between diethyl terephthalate and ethylene
glycol diacetate in hydrocarbon solutions using an alkali
metal alkoxide as a catalyst, which was based on the
similar idea as described here.14 Comparing various
combinations of solvents and esters, it was found that
in nonazeotropic conditions efficiencies of ester-ester
exchange reactions deteriorate remarkably. A special
† Research Center of Macromolecular Technology.
‡ Nanotechnology Research Institute.
* Corresponding author. E-mail: nagahata-ritsuko@aist.go.jp.
10.1021/ma0257191 CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/22/2003
Nagahata, Ritsuko
