3 research outputs found
Synthesis of Titanium-Containing Block, Random, End-Functionalized, and Junction-Functionalized Polymers via Ruthenium-Catalyzed Living Radical Polymerization and Direct Observation of Titanium Domains by Electron Microscopy
A series
of well-defined titanium-containing random, diblock, and
triblock copolymers were prepared by ruthenium-catalyzed living radical
polymerization of glycidyl methacrylate followed by amination of the
epoxy group with diethanolamine and titanium complex loading, which
was achieved by reacting the resulting triethanolamine pendent group
with CpTiCl<sub>3</sub> or Cp*TiCl<sub>3</sub> (Cp: cyclopentadienyl;
Cp*: pentamethylcyclopentadienyl). The titanium-containing unit obtained
by this procedure possessed a discrete atrane structure, which contributed
to the formation of soluble well-defined polymers without cross-linking
via uncontrolled intermolecular multisite ligation to the titanium
center. In addition, the Cp* derivatives were highly stable to moisture.
The same strategy was used successfully to construct well-defined
titanium end-functionalized polymers, and an epoxy-functionalized
initiator was used in the ruthenium-catalyzed living radical polymerization
of methyl methacrylate, followed by postreactions with diethanolamine
and Cp*TiCl<sub>3</sub>. The titanium-containing block copolymers
were analyzed by electron energy loss spectroscopy, transmission electron
microscopy, and transmission electron microtomography to directly
observe titanium-containing phases in the microphase-separated block
copolymers
Epitaxial Phase Transition between Double Gyroid and Cylinder Phase in Diblock Copolymer Thin Film
The epitaxial relationship in the
thermal phase transition between
double gyroid (DG) and hexagonally packed cylinder (HEX) phases in
polystyrene-<i>block</i>-polyisoprene thin films on Si wafer
was investigated using transmission electron microtomography and grazing
incidence small-angle X-ray scattering. Two different types of epitaxial
transitions were observed, and they appeared to be selectively favored
depending on the transition direction. One type of epitaxial relationship
prevails in the phase transition from DG to HEX upon heating in which
{121}<sub>DG</sub>, {111}<sub>DG</sub>, and {220}<sub>DG</sub> are
converted to {100}<sub>HEX</sub>, {110}<sub>HEX</sub>, and {001}<sub>HEX</sub>, respectively. The interphase planes are {220}<sub>DG</sub> and {001}<sub>HEX</sub>, and the cylinders meet the {220}<sub>DG</sub> plane perpendicularly (head-on, Type A) at the grain boundary between
DG and HEX. Although there are small dimensional mismatch and distortion
in the location of the cylinders in this epitaxial relationship, all
cylinders are formed along the topologically equivalent DG skeletal
path. On the other hand, in the transition from HEX to DG upon cooling,
another epitaxial relationship as well as the head-on type epitaxy
was observed, in which {100}<sub>HEX</sub>, {110}<sub>HEX</sub>, and
{001}<sub>HEX</sub> are converted to {121}<sub>DG</sub>, {220}<sub>DG</sub>, and {111}<sub>DG</sub>, respectively. The interphase planes
are {220}<sub>DG</sub> and {110}<sub>HEX</sub>, and the cylinders
meet the {220}<sub>DG</sub> plane in parallel (side-on, Type B) at
the grain boundary between HEX and DG. The domain spacing and the
symmetry of the two phases are matched near perfectly, but cylinders
are converted to two different DG skeletal paths. The Type B epitaxy
is hardly observed in the transition from DG to HEX
Morphological Control of Helical Structures of an ABC-Type Triblock Terpolymer by Distribution Control of a Blending Homopolymer in a Block Copolymer Microdomain
The
control of microphase-separated structures in a poly(styrene-<i>block</i>-butadiene-<i>block</i>-methyl methacrylate)
(SBM) was investigated in three dimensions by transmission electron
microtomography. Neat SBM self-assembled into a double-helical structure
of polybutadiene (PB) domains around hexagonally packed core polystyrene
(PS) cylinders in a poly(methyl methacrylate) matrix. When PS homopolymer
with a lower molecular weight than that of the PS block in SBM was
added to the SBM, the PB domains transformed from double-helical structures
to spherical domains, while maintaining the helical trajectories.
In contrast, adding a higher molecular weight PS to the SBM changed
the helical structures from double- to triple-stranded structures
and even to four-stranded structures. The helical structures of the
PB domains were strongly affected by the distribution of the blended
polystyrenes in the core cylindrical PS domains