Ken-ichi Fukukawa

Synthesis and Characterization of Core-Shell Star Copolymers for In Vivo PET Imaging Applications

The synthesis of core-shell star copolymers via living free radical polymerization provides a convenient route to three-dimensional nanostructures having a poly(ethylene glycol) outer shell, a hydrophilic inner shell bearing reactive functional groups, and a central hydrophobic core. By starting with well-defined linear diblock copolymers, the thickness of each layer, overall size/molecular weight, and the number of internal reactive functional groups can be controlled accurately, permitting detailed structure/performance information to be obtained. Functionalization of these polymeric nanoparticles with a DOTA-ligand capable of chelating radioactive (64)Cu nuclei enabled the biodistribution and in vivo positron emission tomography (PET) imaging of these materials to be studied and correlated directly to the initial structure. Results indicate that nanoparticles with increasing PEG shell thickness show increased blood circulation and low accumulation in excretory organs, suggesting application as in vivo carriers for imaging, targeting, and therapeutic groups.

Synthesis and characterization of silicon-containing block copolymers from nitroxide-mediated living free radical polymerization

High etch resistance to oxygen plasma for silicon-containing polymers, and the high thermal and mechanical robustness of the etching product, silicon oxide, make it attractive to design novel silicon-containing block copolymers for direct patterning of nanostructures on a desired substrate. Here, we report the synthesis of a series of block copolymers from silicon-containing styrenic monomers and styrene (St) or 4-acetoxystyrene (AcOSt) using living free radical polymerization via a α-hydride nitroxide-mediated unimer (a-H unimer). Controlled polymerization with narrow polydispersity (PDI < 1.25) and high yield (up to 80%) were achieved by optimizing polymerization time and temperature, addition of solvents, use of rate accelerants, monomer addition sequence, and solvent polarity. Block copolymer morphologies before and after O 2 plasma were studied using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). When silicon-containing block formed the major phase and silicon concentration was greater than 12 wt %, the morphology and domain size were maintained after O 2 plasma.

Theoretical and Experimental Studies on the Mechanism of Coloration of Polyimides

The mechanism of coloration of polyimides is investigated theoretically and experimentally. Since light is considered to be absorbed by polyimides via charge-transfer excitation, we used the long-range-corrected time-dependent density functional theory recently developed by Tawada et al. [Y. Tawada, T. Tsuneda, S. Yanagisawa, T. Yanai, K. Hirao J. Chem. Phys.2004, 120, 8425] for the calculation of excitation energies and oscillator strengths. Classical molecular dynamic simulations for packed chain models of polyimides were also performed to analyze the structural information of polyimides in condensed phase. In order to predict the transparency of polyimide film, we developed a theoretical method by combining the results of electronic structure calculations and those of molecular dynamics simulations. We compare our theoretical results with experimental ones and discuss the difference between them. As a result, we clarify the new mechanism of coloration and obtain results for the theoretical UV/Visible spectra.

Synthesis and Characterization of Silicon-Containing Block Copolymers from Nitroxide-Mediated Living Free Radical Polymerization

High etch resistance to oxygen plasma for silicon-containing polymers, and the high thermal and mechanical robustness of the etching product, silicon oxide, make it attractive to design novel silicon-containing block copolymers for direct patterning of nanostructures on a desired substrate. Here, we report the synthesis of a series of block copolymers from silicon-containing styrenic monomers and styrene (St) or 4-acetoxystyrene (AcOSt) using living free radical polymerization via a α-hydride nitroxide-mediated unimer (a-H unimer). Controlled polymerization with narrow polydispersity (PDI < 1.25) and high yield (up to 80%) were achieved by optimizing polymerization time and temperature, addition of solvents, use of rate accelerants, monomer addition sequence, and solvent polarity. Block copolymer morphologies before and after O 2 plasma were studied using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). When silicon-containing block formed the major phase and silicon concentration was greater than 12 wt %, the morphology and domain size were maintained after O 2 plasma.

SYNTHESIS AND CHARACTERIZATION OF SILICON-CONTAINING BLOCK COPOLYMERS FROM NITROXIDE-MEDIATED LIVING FREE RADICAL POLYMERIZATION

High etch resistance to oxygen plasma for silicon-containing polymers, and the high thermal and mechanical robustness of the etching product, silicon oxide, make it attractive to design novel silicon-containing block copolymers for direct patterning of nanostructures on a desired substrate. Here, we report the synthesis of a series of block copolymers from silicon-containing styrenic monomers and styrene (St) or 4-acetoxystyrene (AcOSt) using living free radical polymerization via a α-hydride nitroxide-mediated unimer (a-H unimer). Controlled polymerization with narrow polydispersity (PDI < 1.25) and high yield (up to 80%) were achieved by optimizing polymerization time and temperature, addition of solvents, use of rate accelerants, monomer addition sequence, and solvent polarity. Block copolymer morphologies before and after O 2 plasma were studied using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). When silicon-containing block formed the major phase and silicon concentration was greater than 12 wt %, the morphology and domain size were maintained after O 2 plasma.