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When the initial concentration of 2 was slightly in-
creased (3.3 mol% of 1), the formation of 6a1 and 6a2
was observed. When the concentration of 2 was further
increased (3.9 mol% of 1, and this concentration is
similar to the commercial production of the acetal
copolymer), the formation of 6a1, 6a2 and 6a3 was
observed. The highest concentration of 6a1 was ob-
tained around 25 min, but that of 6a2 and 6a3 was
observed around 15 min and that of 4 increased con-
stantly until the reaction time reached to 40 min. After
the appearance of 6a1, a little later, 4 appeared and 3
appeared around 25 min. The yield of 6a1 was 50% to
the initial ethylene oxide, and that of 6a2 was 20%, and
that of 6a3 was 15%. Apparently, a critical concentra-
tion of 2 is involved for the formation of 6a2 and 6a3.
Just before the consumption of 2, 6a2 and 6a3 were
consumed and, after the consumption of 2 in the reac-
tion mixture, polymerization immediately started to
form a solid crystalline polymer.
Figure 3. Reaction between 1,3-dioxacycloheptane 5c and
ethylene oxide 2. [2]0: 0.55 mol% to 5c, BF3·OBu2: 9.6×10−5
mol/mol-5c, reaction temperature: 30oC.
Thus, considering the studies made by Price et al.,2
Weissermel et al.,3,4 and Collins et al.,5 the following
initiation mechanism for the copolymerization of 1 and
2 may be plausible. The first point is the consumption
of 2 to form 6a1, 6a2 and 6a3. The second point is the
formation of 4 and 3 from 6a1. The third point may be
the copolymerization of 1 with 4, 3, 6a2 and 6a3.
(5 mol% of 5b, the formation of 6b2 and 6b3, which are
the direct reaction products of one mole of 5b and two
moles of 2, and one mole of 5b and three moles of 2,
respectively, was observed. The concentration of 6b1,
6b2, and 6b3 increased constantly until the reaction
time reached to 60 min. For the consumption of 90% of
2, final yield of 6b1 was 80% to the initial ethylene
oxide, and that of 6b2 was 10% and that of 6b3 was 2%,
respectively. The reaction product was confirmed by
gas chromatography and mass spectroscopy. For the
formation of the 6b2, there seemed to exist a critical
concentration of 2. For the formation of 6b3, there also
seemed to exist some critical concentration of 2.
For another ring-expansion reaction, a novel direct
reaction between 1,3-dioxolane and 2 was found.
(Scheme 1; R=CH2CH2, 5b) The reaction procedure
was similar to that of 5a (1). The reaction product was
presumed to be diethylene glycol formal 6b1, triethylene
glycol formal 6b2 and tetraethylene glycol formal 6b3,
respectively.
For another ring-expansion reaction, a novel direct
reaction between 1,3-dioxacycloheptane (1,4-butanediol
formal) and ethylene oxide was found. (Scheme 1;
R=CH2CH2CH2CH2, 5c) The reaction procedure was
similar to that of 5a. The reaction product was pre-
sumed to be 1,3,6-trioxacyclodecane 6c1 and 1,3,6,9-tet-
raoxacyclotridecane 6c2, respectively. Fig. 3 shows the
results of the reaction between 5c and 2. The formation
of 6c1 and 6c2, which are the direct reaction product of
one mole of 5c and one mole of 2 and one mole of 5c
and two moles of 2, respectively, was observed. The
concentration of 6c1 and 6c2 increased constantly until
the reaction time reached to 20 min. For the 100%
consumption of 2, final yield of 6c1 was 82% to initial
ethylene oxide and that of 6c2 was 19%, respectively.
The reaction product was confirmed by mass
spectroscopy.
Fig. 2 shows the reaction of 5b and 2. When the
ethylene oxide concentration in the reaction mixture is
low (1 mol% of 5b), the formation of 6b1, which is the
direct reaction product of one mole of 5b and one mole
of 2, is predominant (selectivity is nearly 99%.). How-
ever, with the increase in ethylene oxide concentration
Based on the observed three novel direct reactions, the
generalization of the reaction between cyclic formals
and ethylene oxide 2 for the ring expansion is thought
to be valid. This new reaction may provide us the
possibility of a new route for synthesizing a new type of
crown ether. We are now determining whether this
ring-expansion reaction is limited only to the reaction
between cyclic formals and ethylene oxide, and how
this reaction can be generalized for other systems.
Figure 2. Reaction between 1,3-dioxolane 5b and ethylene
oxide 2. [2]0: 1.0 mol% to 5b, BF3·OBu2: 3.6×10−5 mol/mol-
5b, reaction temperature: 30oC.