Youngkyu Chang

Synthesis and photophysical characterization of amphiphilic dendritic–linear–dendritic block copolymers

Amphiphilic dendritic–linear–dendritic triblock copolymers based on hydrophilic linear poly(ethylene oxide) (PEO) and hydrophobic dendritic carbosilane were synthesized with a divergent approach at the allyl end groups of diallyl-terminated PEO. Their micellar characteristics in an aqueous phase were investigated with dynamic light scattering, fluorescence techniques, and transmission electron microscopy. The block copolymer with the dendritic moiety of a third generation could not be dispersed in water. The block copolymers with the first (PEO–D-Si-1G) and second (PEO–D-Si-2G) generations of dendritic carbosilane blocks formed micelles in an aqueous phase. The critical micelle concentrations of PEO–D-Si-1G and PEO–D-Si-2G, determined by a fluorescence technique, were 27 and 16 mg/L, respectively. The mean diameters of the micelles of PEO–D-Si-1G and PEO–D-Si-2G, measured by dynamic light scattering, were 170 and 190 nm, respectively, which suggests that the micelles had a multicore-type structure. The partition equilibrium constants of pyrene in the micellar solution increased with the increasing size of the dendritic block (e.g., 7.68 × 104 for PEO–D-Si-1G and 9.57 × 104 for PEO–D-Si-2G). The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene were 0.06 for PEO–D-Si-1G and 0.09 for PEO–D-Si-2G. The r values were lower than those of the linear polymeric amphiphiles, suggesting that the microviscosity of the dendritic micellar core was lower than that of the linear polymeric analogues.

Hyperbranched poly(ether ketone) analogues with heterocyclic triazine moiety : Synthesis and peripheral functionalization

Hyperbranched poly(ether ketone) with 1,3-s-triazine moiety was prepared by a one-pot polymerization of an AB 2 type monomer, 2,4-bis(4-hydroxyphenyl)-6-(4-(4-(4-fluorobenzyl)phenoxy)phenyl)-1,3,5-s-triazine, which was synthesized from cyanuric chloride. The selective reactivity of three chlorine atoms on cyanuric chloride toward nucleophiles provides a very efficient route for the systematic synthesis of AB 2 type triazine monomers and their hyperbranched polymers. The resulting polymers exhibited a glass transition at 264°C without any indication of crystallinity. The modification of the peripheral hydroxyl groups on the hyperbranched polymers by methoxy, oligoethyleneoxy, or sterayl moieties brought about remarkablechanges in their solubility and glass transition temperatures. The amphiphilic nature of the 2-[2-(2-(2-methoxyethoxy)ethoxy)ethoxy)]ethoxy-terminated pmoly(ether ketone) analogue in an aqueous phase was investigated by using fluorescence techniques and dynamic light scattering. It was found that the analogue forms of self-aggregation at a critical aggregation concentration of 12.6 mg/L. The mean diameter of the aggregates was 320 nm. The steady-state fluorescence anisotropy value (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) in the hydrophobic domain was 0.240.

Synthesis and structural characterisation of hyperbranched poly(benzyl ether) analogs with 1,3,5-s-triazine moiety

Hyperbranched poly(benzyl ether) analogs with the 1,3,5,-s-triazine moiety were prepared by direct polymerization of AB 2 type monomers. 2,4-bis-(4-hydroxyphenyl)-6-(4-bromomethylphenyl)-1,3,5-s-triazine. The triazine rinags: influenced the structural and material charasteristices of these hyperbranched polyems. In the hyperbranched poly(benzyl ether) analogy, only the O-alkylated structure, instead of the C-alkytated branches, was observed, pressibly due to the electron-withdrawing nature of the triazine ring which restrains C-alkylation on the prenyl group of the monomer. The triazine moieties play an impotant role in producing the structural regularity hypobranched poly(benzyl ether) analogs.

A Covalently Interconnected Phosphazene-Silicate Network: Synthesis and Surface Functionalization

A sol-gel precursor was prepared by the reaction of poly[bis(2-(2-hydroxyethoxy)ethoxy)phosphazene] (1) with 3-isocyanatopropyltriethoxysilane. It was then sol-gel polymerized to produce a covalently interconnected phosphazene-silicate network with urethane functionalities. Isocyanato groups were introduced on the surface of the network through coupling by allophanate formation between hexamethylene diisocyanate and urethane functionalities on the gel surface. Heparin was immobilized on the surface of the network by reacting hydroxyl or amino groups of heparin with the surface isocyanato groups. The activity of the immobilized heparin was 4.0% that of free heparin.