1926 Sugihara et al.
Macromolecules, Vol. 38, No. 5, 2005
Scheme 1. Unique Physical Gelation of an Aqueous Solution of Double Thermosensitive Diblock Copolymers
assemblies of similar sizes exist in the thermally
induced physical gel. These spherical assemblies (mi-
celles) consist of diblock copolymers with a narrow
MWD. Polydispersity of diblock copolymers would affect
physical gelation behavior and, if it occurs, the transi-
tion sharpness. Thus, thermosensitive physical gelation
was examined with a diblock copolymer having the same
composition (EOEOVE/MOVE ) 1/2) but a broad MWD
(Mn ) 7.0 × 104, Mw/Mn ) 1.81), prepared by mixing
and/or concentration of micelles caused by partial
dehydration of the outer shells as shown in Scheme 1.
Acknowledgment. This study was supported in
part by a grant for “The development of the basic tech-
nologies for the industry system construction harmo-
nized with environment” promoted by Shiga Prefecture
under the program of Collaboration of Regional Entities
for the Advancement of Technological Excellence by
Japan Science and Technology Agency. We express our
special thanks for the center of excellence (21COE) pro-
gram “Creation of Integrated EcoChemistry” of Osaka
University. We also thank Professor M. Shibayama of
the University of Tokyo for his invaluable comments.
We acknowledge Mr. K. Ishiura and Mr. S. Kobukata
of Kuraray Co. for TEM measurement.
various diblock copolymers (EOEOVE100-b-MOVE200
,
EOEOVE200-b-MOVE400, EOEOVE300-b-MOVE600) with
narrow MWDs (Mw/Mn < 1.2). With all diblock copoly-
mers used as samples, thermally induced physical
gelation occurred. In contrast to the diblock copolymers
with narrow MWDs, an aqueous solution of the mixed
diblock copolymers with a broad MWD did not undergo
physical gelation even at 20 wt %. In addition, only
insensitive phase separation was observed in dilute
solution (Figure 11, dotted line). The mixed diblock
copolymers are likely to form micelles with a broad size
distribution. Since smaller micelles do not contribute
to the turbidity of the solution, no drastic change in
transmittance was observed around the TPS of poly-
(EOEOVE). In sharp contrast, diblock copolymers of
uniform length are likely to produce micelles with a
narrow size distribution, which can associate in a
sensitive manner through subsequent packing or inter-
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