Norio Tsubokawa

Grafting of ‘dendrimer-like’ highly branched polymer onto ultrafine silica surface

Abstract To modify ultrafine silica surface, the grafting of polyamidoamine dendrimer, a new class of topological macromolecules, onto the silica surface was investigated. Introduction of amino groups as an initiator site on the silica surface was achieved by the treatment of the silica with γ-aminopropyltriethoxysilane. Polyamidoamine dendrimer was propagated from silica surface by repeating two processes: (1) Michael addition of methyl acrylate to surface amino groups, and (2) amidation of the resulting esters with ethylenediamine. The amino group content of the resulting silica increased from 0.40 mmol/g to 8.30 mmol/g after 10th generation. In addition, the percentage of grafting increased with increasing generation and reached to 575.7% after 10th generation. However, these values were considerably smaller than the theoretical values. This indicates that the propagation of dendrimer grafting from silica surface was not achieved theoretically and ‘dendrimer-like’ highly branched polymer was grafted onto the surface, because of steric hindrance of grafted dendrimer. The effects of amino group content as an initiator site and reaction conditions on the grafting of the polymer onto silica surface were also investigated. Dendrimer-like highly branched polymer grafted ultrafine silicas gave a stable dispersion in a good solvent for the polyamidoamine dendrimer.

Radical Grafting from Carbon Black. Graft Polymerization of Vinyl Monomers Initiated by Peroxyester Groups Introduced onto Carbon Black Surface

AbstractCarbon blacks having tert-butyl peroxyester groups (1, 2, and 3) were prepared by the reaction of acyl chloride groups on carbon black with tert-butyl hydroperoxide. The introduction of acyl chloride groups onto carbon black was achieved by three methods: (1) reaction of a carboxyl group with thionyl chloride, (2) reaction of a phenolic hydroxyl group with adipoyl chloride, and (3) reaction of thionyl chloride with a carboxyl group introduced by the treatment of aromatic ring of carbon black with 4,4′-azobis(4-cyanovaleric acid). Carbon black 1 has no ability to initiate the graft polymerization of methyl methacrylate (MMA) because phenyl radical formed on the carbon black by decomposition of the peroxyester groups inhibited the polymerization. On the contrary, carbon blacks 2 and 3 were able to initiate the graft polymerization of MMA at 70–90°C and PMMA was effectively grafted onto the surface based on the propagation of the polymer from the alkyl radicals formed on the surface. The percentage of grafting of PMMA at 70°C by use of 3 as initiator increased to about 80% with progress of polymerization. Furthermore, the graft polymerization of several vinyl monomers initiated by 3 was investigated.

Surface modification of chitosan powder by grafting of 'dendrimer-like' hyperbranched polymer onto the surface

Abstract To modify the surface of chitosan powder, grafting of hyperbranched dendritic polyamidoamine, a new class of topological macromolecules, onto the surface was investigated. It was found that hyperbranched dendritic polyamidoamine was propagated from chitosan powder surface by repeating two processes: (1) Michael addition of methyl acrylate (MA) to surface amino groups and (2) amidation of the resulting esters with ethylenediamine to give polyamidoamine dendrimer-grafted chitosan powder. However, theoretical propagation of polyamidoamine dendrimer from chitosan powder surface was hardly achieved, because (a) Michael addition and amination proceeded in heterogeneous systems and (b) the grafting of dendritic polyamidoamine was blocked by grafted chains due to steric hindrance. It was found that the average particle size of hyperbranched dendritic polyamidoamine-grafted chitosan powder was decreased by grafting of dendritic polyamidoamine. Furthermore, living poly(2-methyl-2-oxazoline) and living poly(isobutyl vinyl ether) with controlled molecular weight and narrow molecular weight distribution readily postgrafted to the hyperbranched dendritic polyamidoamine-grafted chitosan powder by termination of the corresponding living polymer cation with terminal amino groups of the dendritic polyamidoamine-grafted chitosan powder.

Novel gas sensor from polymer-grafted carbon black: Vapor response of electric resistance of conducting composites prepared from poly(ethylene-block-ethylene oxide)-grafted carbon black

A crystalline block copolymer of poly(ethylene-block-ethylene oxide) (PE-b-PEO) was successfully grafted onto a carbon black surface by direct condensation of its terminal hydroxyl groups with carboxyl groups on the surface using N,N′-dicyclohexylcarbodiimide as a condensing agent. The electric resistance of the composite from PE-b-PEO (PEO content is above 50 wt %)-grafted carbon black drastically increased to 104–106 times of the initial resistance in a vapor of dichloromethane, chloroform, tetrahydrofuran, and carbon tetrachloride, which are good solvents for PE-b-PEO, and returned immediately to the initial resistance when the composite was transferred in dry air. However, the change of the electric resistance of these composites was less than one-tenth in a poor solvent vapor at the same condition. The response of the electric resistance was reproducible and stable even after exposure to a good solvent vapor and dry air with 30 cycles or exposure to the vapor over 24 h. The effect of PEO content on the vapor response was also investigated. The composite from PE-b-PEO-grafted carbon black responded to the low vapor concentration with a linear relationship between the electric resistance and the concentration of the vapor in dry air. This indicates that the composite can be applied as a novel gas sensor.

Curing of Epoxy Resin by Ultrafine Silica Modified by Grafting of Hyperbranched Polyamidoamine Using Dendrimer Synthesis Methodology

Hyperbranched polyamidoamine–grafted silica was prepared according to dendrimer synthesis methodology. The modified silica was dispersed uniformly in epoxy resin, and the curing of epoxy resin proceeded successfully by heating in the presence of the modified silica; the gel fraction of the epoxy resin cured by the hyperbranched polyamidoamine–grafted silica (grafting = 80.2%) reached 77% at 170°C after 48 h. The gel fraction increased with increasing terminal amino group content of the hyperbranched polyamidoamine–grafted silica. In addition, the curing ability of the silica increased by complexation of the terminal amino groups of the grafted polyamidoamine with boron trifluoride. The modulus of elasticity of the curing materials obtained using the modified silica as a curing agent was lower than that using conventional a curing agent such as ethylenediamine in the presence of untreated silica. On the other hand, the heat resistance of the curing product using the modified silica was superior to that using ethylenediamine, but no difference in glass-transition temperature was observed. It is expected that hyperbranched polyamidoamine grafted-silica is incorporated uniformly with chemical bonds in the matrix of the epoxy resin.

A novel gas sensor from polymer-grafted carbon black: responsiveness of electric resistance of conducting composite from LDPE and PE-b-PEO-grafted carbon black in various vapors

The composite of low-density polyethylene (LDPE) filled with carbon black (CB) having high dispersibility and stability was successfully obtained by the use of poly(ethylene-block-ethylene oxide) (PE-b-PEO)-grafted CB. The response of the electric resistance of the composite against solvent vapors was examined. The electric resistance drastically increased by 104–106 times the initial resistance in a nonpolar solvent vapor such as cyclohexane, and carbon tetrachloride vapor at 40 °C and returned immediately to its initial resistance when the composite was transferred to dry air. However, the electric resistance increased only several times in the polar solvent vapor, such as water and alcohol, at the same temperature. The responsiveness of electric resistance is excellently reproducible and is also stable in cyclohexane vapor and dry air. The effect of temperature on the responsiveness against cyclohexane vapor is also discussed. It is concluded that the composite of LDPE filled with PE-b-PEO-grafted CB could be a promising material to use when preparing gas sensors. Copyright

The free radical polymerization of vinyl monomers in the presence of carbon black

Abstract The polymerization of vinyl monomers has been carried out in the presence of furnace blacks using initiators such as 2,2′-azobisisobutyronitrile (AIBN) and benzoyl peroxide (Bz 2 O 2 ) in nitrogen or oxygen atmosphere. The results indicate that free radicals form by the decomposition of initiators reacting with carbon blacks to give active sites on their surface which then capture either the free radicals or the growing polymer radicals. Using the monomers with negative e values, such as styrene and vinyl acetate, a marked retardation was observed in Bz 2 O 2 -initiated polymerization in the presence of furnace blacks, while a moderate inhibition was found in the polymerization initiated by AIBN. The polymerization reaction using Bz 2 O 2 was found to be very sensitive to oxygen in the presence of furnace blacks and the involvement of oxygen was found to promote grafting onto the surface of carbon black by the growing polymer radicals, consequently giving polymer-grafted particles while hindering the formation of homopolymers. Furthermore, the reaction of Bz 2 O 2 with the surface of furnace blacks in oxygen atmosphere has been studied in carbon tetrachloride at 45°C. The resulting carbon blacks show an increase in the number of surface quinone groups with an increase in reaction time.

Grafting of hyperbranched polymers onto ultrafine silica : postgraft polymerization of vinyl monomers initiated by pendant initiating groups of polymer chains grafted onto the surface

Abstract The grafting of polymers having pendant peroxycarbonate groups onto ultrafine silica surface and the radical postgraft polymerization of vinyl monomers initiated by the initiating groups of polymer chains grafted onto silica surface were investigated. The grafting of polymers having pendant peroxycarbonate groups onto the silica surface was achieved by the copolymerization of vinyl acetate (VAc) with t-butylperoxy-2-methacryloyloxyethylcarbonate (HEPO) initiated by azo groups introduced onto silica surface: the introduction of azo groups onto silica surface was achieved by the reaction of 4,4′-azobis(4-cyanopentanoic acid) with amino groups previously introduced onto the surface. The percentage of grafting (the proportion of grafted polymer to silica) of poly(VAc–co-HEPO) onto the surface was about 51% at 80.0°C after 3 h. The amount of pendant peroxycarbonate groups of grafted chain was determined to be 0.55 mmol/g. Radical postgraft polymerization of various vinyl monomers, such as methyl methacrylate, glycidyl methacrylate, 2-hydroxyethyl methacrylate, vinyl acetate, and N-vinyl-2-pyrrolidinone was initiated by the pendant peroxycarbonate groups of grafted poly(VAc–co-HEPO) to give the corresponding hyperbranched polymer-grafted silica. It was found that the grafting of hydrophilic or hydrophobic polymers readily controls the surface wettability to water.

Novel vapor sensor from polymer-grafted carbon black: effects of heat-treatment and γ-ray radiation-treatment on the response of sensor material in cyclohexane vapor

Polyethylene (PE) was grafted onto carbon black surface by γ-ray radiation of the PE-adsorbed carbon black. Vapor sensor composite materials were prepared from the PE-grafted carbon black and PE as a matrix polymer. The effects of heat-treatment and γ-ray radiation-treatment on the response of the electric resistance of the sensor material against cyclohexane vapor were investigated. The heat-treatment of the composite improved the crystallinity of the matrix PE, and thus increased the responsiveness against cyclohexane vapor about five times that of the untreated one. The γ-ray radiation-treatment slightly decreased the responsiveness against cyclohexane vapor, because the γ-ray radiation-treatment induced the crosslinking of PE. On the contrary, the stability and reproducibility of the vapor sensor material remarkably improved. By the heat-treatment followed by the γ-ray radiation-treatment, a novel stable and reproducible sensor material was obtained, which allowed to identify and to quantify certain vapors in air accurately.

Graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto silica surface by Michael addition

The introduction of peroxycarbonate groups onto a silica surface and the graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto a silica surface were investigated. The introduction of peroxycarbonate groups onto a silica surface was achieved by Michael addition of amino groups introduced onto the silica surface to t-butylperoxy-2-methacryloyloxyethylcarbonate (HEPO). The amount of peroxycarbonate groups was determined to be 0.17 mmol/g. The graft polymerization of various vinyl monomers such as styrene (St), N-vinyl-2-pyrrolidinone (NVPD), and 2-hydroxyethyl methacrylate (HEMA) was initiated by peroxycarbonate groups introduced onto the silica surface to give the corresponding polymer-grafted silicas. The percentage of poly(St)-grafting reached about 120% after 5 h. This means that 1.20 g of poly(St) is grafted onto 1.0 g of silica. The surface of poly(St)-grafted silica shows a hydrophobic nature, but the surfaces of poly(NVPD) and poly(HEMA)-grafted silica show a hydrophilic nature. Furthermore, the poly(St)-grafted silica was found to give a stable colloidal dispersion in a good solvent for the grafted polymer.