We report a direct one-pot route for the preparation of supramolecules from simple polyacetylene diblock copolymers synthesized by mild ring-opening metathesis polymerization of cyclooctatetraene. This in situ nanoparticlization of conjugated polymer (INCP) approach is advantageous over conventional self-assembly processes because this method does not require any tedious postsynthetic treatments. Also, this direct approach provides intriguing supramolecules with a unique nanostructure resembling a caterpillar. Furthermore, the new supramolecules are highly stable adducts because the polyacetylene core block provides an exceptionally strong driving force for the self-assembly. Even though pristine polyacetylene is unstable in air, the polyacetylene segment in the nanocaterpillar is very stable because it is protected within the shell of the supramolecule.
Dendronized polymers were synthesized from various endo-tricycle[4.2.2.0]deca-3,9-diene (TD) monomers, using a macromonomer approach, via ring-opening metathesis polymerization. The polymerization was achieved in a living manner to give dendronized polymers with high molecularweights and narrow polydispersity index. The resulting polymers showed highly extended conformations both in solution and in the solid state, even with relatively small thirdgeneration ester dendrons, because of the rigid backbone of TD monomers. Using their rigidity, block and gradient copolymers containing TD and norbornene moieties were synthesized. Diblock copolymers were produced by the sequential addition of two dendronized macromonomers, and gradient copolymers were produced in a simple batch reaction, because large differences in reactivity allowed for the simultaneous one-pot polymerization, favoring TD over norbornene. Polymer conformations were confirmed by both scattering analysis in solution and atomic force microscopy (AFM) imaging in thin films. The high-resolution AFM images of both copolymers enabled us to distinguish the structural differences between the two classes of copolymers because the block copolymer showed clear boundary for each block while the gradient copolymer showed gradual changes in height and thickness. Furthermore, a comparison of the rigidities of these two copolymers was performed by scattering analysis in solution.
High generation dendronized polymers with high molecular
weight
were synthesized by ROMP via macromonomer approach. The polymerization
was achieved in living manner and the macromolecules exhibited rod-like
conformation. Correlation between the monomer structures and the conformation
of the final polymers was investigated in detail. The rigid rod conformation
in solution was confirmed by both light scattering and viscometric
analysis and the single polymer chains were visualized by AFM.
Living
ROMP of monomers containing endo-tricyclo[4.2.2.02,5]deca-3,9-diene (TD) moieties was successfully performed
using thermally stable second generation Grubbs and Hoveyda–Grubbs
catalysts. Even slow-initiating catalysts enabled the living polymerization
to give polymers with a narrow polydispersity index and controlled
molecular weight because the unique structure of the TD monomers resulted
in much faster initiation and slower propagation than conventional
norbornene monomers. Kinetic analyses confirmed that the ratio of
initiation/propagation rate (k
i/k
p) of the TD monomers was 10 to 200 times larger
than that of norbornene derivatives. To demonstrate the living nature
of the ROMP, block copolymers were successfully prepared using second
generation Hoveyda–Grubbs catalyst for the first time. In addition,
three-arm star polymers were prepared by core-first approach using
Hoveyda–Grubbs type three-arm initiator, owing to the living
ROMP of TD monomers with this stable catalyst. Also, star diblock
copolymer was prepared with precise molecular weight and narrow PDI
of 1.03. Since these star polymers contained bulky second or third
generation dendrons, these dendronized three-arm star polymers were
visualized under atomic force microscopy (AFM) to confirm the star-shape
topology.
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