Ryohei Kikuchi

Synthesis and Characterization of New Polyimides Containing Nitrile Groups

Two new nitrile-containing diamine monomers, 4-[bis(4-aminophenyl)amino]benzonitrile and 4-[4-(1-cyanopropoxy)phenyl]2,6-bis(4-aminophenyl)pyridine were synthesized. The diamine monomers were reacted with various tetracarboxylic dianhydrides, followed by cyclodehydration (imidization) without isolation to produce a series of novel polyimides with pendant nitrile groups on the side chain. The polymers were obtained in quantitative yields with high molecular weight. Among them, polymers derived from ODPA and 6FDA showed good solubility, they could dissolve in polar solvents such as DMF, NMP, DMSO and even pyridine and m-cresol. These tough, transparent and flexible polyimide films had a tensile strength of 80–120 MPa, an elongation at break of 4–12% and a tensile modulus of 1.2–2.3 GPa. The polymers obtained exhibited high glass transition temperatures between 305 and 360 C. Moreover, they were fairly stable up to a temperature around or above 400 C and lost 10% weight in the range of 500–590 C and 470–580 C in nitrogen and air, respectively. Together the dielectric constants of the polyimides were measured to be 3.10–3.73 at 10 GHz. On the other hand, blank polyimides with no – CN groups were also prepared for comparison and the results revealed that the nitrile group affected the thermal property of polyimides as well as the electrical properties. Introduction of the –CN groups would increase the glass transition temperature and also the dielectric constant.

Adsorption of hyperbranched polysiloxysilane modified with triethoxy group onto the silicon wafer

Triethoxysilyl functionalized hyperbranched polsiloxysilanes at the focal (FT-HBPSs) and terminal (TT-HBPSs) positions were synthesized to investigate adsorption behavior onto a silicon wafer surface. The surface of the silicon wafer adsorbed with the HBPSs was characterized by X-ray photoelectron spectroscopy, atomic force microscopy (AFM), static and dynamic water contact angle measurements. The AFM images indicated the formation size of dot-like structures were approximately 200 nm. The presence of vinyl terminal groups of FT-HBPSs permitted conversion of the surface from a non-polar hydrocarbon to a polar hydroxylated or carboxylated structures. After the polarity was changed, the surface properties were also studied using the above surface analysis techniques. The dynamic contact angle measurement indicated that the silicon wafer surface modified by FT-HBPSs was more hydrophilic in water than TT-HBPS. This behavior can be explained by the difference of connecting points between HBPS and the silicon wafer surface.

Star-Shaped Thermoresponsive Polymers with Various Functional Groups for Cell Sheet Engineering

This study demonstrates the facile preparation of poly(N-isopropylacrylamide) (PNIPAM)-immobilized Petri dishes by drop-casting a star-shaped copolymer of hyperbranched polystyrene (HBPS) possessing PNIPAM arms (HBPS-g-PNIPAM) functionalized with polar groups. HBPS was synthesized via reversible addition-fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP), and HBPS polymers with different terminal structures were prepared by changing the monomer structure. HBPS-g-PNIPAM was synthesized by the grafting of PNIPAM from each terminal of HBPS. To tune the cell adhesion and detachment properties, polar functional groups such as carboxylic acid and dimethylamino groups were introduced to HBPS-g-PNIPAM. Based on surface characterization using scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements, the advantage of the hyperbranched structure for the PNIPAM immobilization was evident in terms of the uniformity, stability, and thermoresponsiveness. Successful cell sheet harvesting was demonstrated on dishes coated with HBPS-g-PNIPAM. In addition, the cell adhesion and detachment properties could be tuned by the introduction of polar functional groups.