Preparation of smart soft materials using molecular complexesMiyata, Takashi
doi: 10.1038/pj.2010.12pmid: N/A
This article provides a short overview of our research regarding the preparation of smart soft materials using molecular complexes that reversibly associate and dissociate in response to environmental changes. Stimuli-responsive hydrogels that show swelling/shrinking in response to pH and temperature were prepared by copolymerization of a monomer bearing a phosphate group and other various monomers. Hydrogels with phosphate groups were useful tools for the construction of self-regulated drug delivery systems. Furthermore, we proposed a strategy for the preparation of biomolecule-responsive hydrogels that use reversible crosslinks in the networks of biomolecular complexes. Based on this strategy, we have prepared two types of biomolecule-responsive hydrogel that undergo changes in volume in response to target biomolecules. This was accomplished using biomolecular complexes such as antigen–antibody complexes and saccharide-lectin complexes and both a biomolecule-crosslinked hydrogel and a biomolecule-imprinted hydrogel have been synthesized with this approach. Biomolecule-crosslinked hydrogels, such as glucose- and antigen-responsive hydrogels, swelled in the presence of a target biomolecule due to the dissociation of biomolecular complexes that act as reversible crosslinks. On the other hand, biomolecule-imprinted hydrogels, such as tumor marker glycoprotein-responsive hydrogels, shrank in response to a target biomolecule due to the formation of a complex between ligands (lectin and antibody) and the target biomolecule. Thus, biomolecule-responsive hydrogels have many potential applications as smart biomaterials in biomedical fields. Although most smart soft materials prepared using molecular complexes still require further research, they are likely to become important materials in the future.
Synthesis and properties of N-substituted maleimides conjugated with 1,4-phenylene or 2,5-thienylene polymersOnimura, Kenjiro; Matsushima, Mieko; Yamabuki, Kazuhiro; Oishi, Tsutomu
doi: 10.1038/pj.2009.341pmid: N/A
π-Conjugated polymers are particularly interesting in the field of electro-optic materials because of their desirable properties such as electrical conductivity, nonlinear optics and electroluminescence. Coupling polymerizations of 2,3-dibromo-N-substituted maleimide (DBrRMI) (R=benzyl, phenyl, cyclohexyl, n-hexyl and n-dodecyl) were carried out using palladium or nickel catalysts. The number-average molecular weights of poly(RMI-alt-Ph) obtained by Suzuki–Miyaura cross-coupling polymerizations of DBrRMI with benzene-1,4-boronic acid or 2,5-thiophene diboronic acid were 680–1270 by gel permeation chromatographic analyses. By contrast, Yamamoto coupling polymerizations of DBrRMI with diiodobenzene gave random poly(RMI-co-Ph) results. Poly(RMI-co-Ph)s exhibited a higher thermal stability than monomer and poly(RMI-alt-Ph). Copolymers showed strong photoluminescence from yellow to light blue colors in tetrahydrofuran.
A carbon network backbone polymer functionalized with polymer brushesGreco, Jeffrey F; Bianconi, Patricia A
doi: 10.1038/pj.2009.343pmid: N/A
The surface-initiated graft polymerization of polymer brushes attached to an sp3 random carbon network backbone structure is demonstrated. Poly(ethyl acrylate) (PEA), poly(4-fluorostyrene) (PFS) and poly(acrylonitrile) (PAN) brushes were grafted from the network backbone polymer poly(hydridocarbyne), 1, illustrating the breadth of reactivity of the network backbone. Attachment of polymeric/oligomeric chains to the network backbone was observed through two different methods with different polymer systems. First, selective solvent extraction separated a homogeneous mixture of PEA and 1, dissolving PEA in diethyl ether, but leaving 1 behind as a brown precipitate. In contrast, 1 functionalized with PEA brushes completely dissolved, showing that it was not a homogenous mixture of the substrate and free polymeric chains, but a system of covalently bound polymer chains originating from 1. Formation of short chains of PFS at the surface of 1 allowed the use of 19F nuclear magnetic resonance to observe the change in resonance shift and shape for the polymer side chains. Solvent extraction was used to demonstrate that tetrahydrofuran (THF) was able to separate a homogeneous mixture of PAN and 1, dissolving 1 in THF, but leaving PAN behind as a white precipitate.
Tuning the hydrophilic–hydrophobic balance of block-graft copolymers by click strategy: synthesis and characterization of amphiphilic PCL-b-(PαN3CL-g-PBA) copolymersLee, Ren-Shen; Huang, Yi-Ting
doi: 10.1038/pj.2010.6pmid: N/A
The self-organization of amphiphilic block copolymers in water strongly depends on their molecular structure, particularly their hydrophilic–hydrophobic balance. This study proposes tuning the amphiphilicity of block copolymers by a click strategy. This work prepares novel amphiphilic block-graft PCL-b-(PαN3CL-g-PBA) copolymers that comprise poly(ɛ-caprolactone) (PCL) as the hydrophobic segment and poly(α-azido-ɛ-caprolactone-graft-propargyl benzoate) (PαN3CL-g-PBA) as the hydrophilic segment by ring-opening polymerization of 2-chloro-ɛ-caprolactone (ClCL) with hydroxyl-terminated macroinitiator PCL, substituting pendent chloride with sodium azide. This copolymer is subsequently used for grafting propargyl benzoate (PBA) moieties by the Cu(I)-catalyzed Huisgen’s 1,3-dipolar cycloaddition, thus producing a ‘click’ reaction. This research examines characteristics of these copolymers by 1H NMR, FT-IR, GPC, contact angle measurement and differential scanning calorimetry (DSC). Increasing the length of the hydrophilic segment or decreasing the length of the hydrophobic segment significantly increases water uptake and decreases the contact angle of the copolymers. These amphiphilic copolymers self-assembled into micelles in the aqueous phase, which were then examined by fluorescence, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The average micelle size ranges from 90 to 190 nm. The critical micelle concentration (CMC) is from 2.4 to 7.6 mg l−1 at 25 °C. The length of the hydrophilic segment influences the shape of the micelle. The current study describes drug entrapment efficiency and drug loading content of micelles, dependent on the composition of block-graft polymers.
Synthesis of thermoresponsive polysilsesquioxane with methoxyethylamide group and crown etherMatsuoka, Tomonori; Yamamoto, Shin-ichi; Moriya, Osamu; Kashio, Mikihiro; Sugizaki, Toshio
doi: 10.1038/pj.2010.7pmid: N/A
A polysilsesquioxane with a bis(2-methoxyethyl)amide group and 15-crown-5-ether ring (MCPSQ) was newly prepared by the co-condensation of silane coupling reagents, which were obtained from (3-isocyanatopropyl)triethoxysilane and the corresponding amines with the respective groups. MCPSQ showed the expected amphiphilic and thermoresponsive properties. The behaviors of hydrophobic aggregation of MCPSQ in the aqueous solutions containing the chlorides of lithium, potassium and sodium reflected the selective ion recognition property due to the presence of the crown ether. The highest aggregation temperature of 32 °C was observed in the solution containing sodium ion as expected from the coordination ability of the crown ether group. With the use of the sodium salt of 4-phenylazobenzoic acid as an additive in the aqueous solution of MCPSQ, the aggregation temperature was changed according to the photochemical isomerization of the phenylazobenzoate group. The results show the efficient coordination of the sodium salt with the crown ether ring.
Significantly improved performance of rubber/silica composites by addition of sorbic acidGuo, Baochun; Chen, Feng; Lei, Yanda; Chen, Weiwei
doi: 10.1038/pj.2010.4pmid: N/A
Sorbic acid (SA) was used to improve the performance of styrene–butadiene rubber (SBR)/silica composites by direct blending. The mechanisms for the significantly improved performance were studied by X-ray photoelectron spectroscopy, X-ray diffraction and by the determinations of bound rubber content and crosslink density. The strong interfacial bonding between silica and the rubber matrix resulted from SA-intermediated linkages. Significantly improved dispersion of silica by virtue of the interactions between silica and SA was found. Formation of zinc disorbate during compounding of composites was confirmed. The effects of SA content on vulcanization behavior, morphology, mechanical properties and abrasion loss of composites were studied. Significantly improved mechanical properties of SA-modified SBR/silica composites were demonstrated. Changes in vulcanization behavior, morphology and performance were correlated with the interactions between silica and SA and the largely improved dispersion of silica.
New poly(4,4′-dicyano-4″-vinyl-triphenylamine) host material for single-layer Ir complex phosphorescent light-emitting devicesFang, Yi-Kai; Lee, Wen-Ya; Tuan, Chi-Shen; Lu, Ling-Hui; Teng, Wan-Jung; Chen, Wen-Chang
doi: 10.1038/pj.2010.1pmid: N/A
We report a new host material for iridium complex light-emitting devices, poly(4,4′-dicyano-4″-vinyl-triphenylamine) (PCNVTPA), which was synthesized by nitroxide-mediated free radical polymerization. The incorporation of electron-withdrawing cyano groups led to a significant variation in electronic energy levels and luminescence characteristics in comparison with the parent poly(4-vinyltriphenylamine) (PVTPA). The prepared organosoluble PCNVTPA and PVTPA had number-average molecular weights (M
n) of 10 200 and 23 400, respectively. PCNVTPA exhibited higher thermal stability (T
g=211 °C) and photoluminescence (PL) quantum efficiency (PLQY) (20%) compared with PVTPA (T
g=140 °C, PLQY=3%) because of enhanced rigidity from the cyano-substituted group. Cyano substitution also led to lower energy levels (HOMO, LUMO, unit: eV) in PCNVTPA (−5.63, −2.52) than in PVTPA (−5.35, −1.89). The emission peak of the Ir complexes was observed in the PL spectra of PVTPA or PCNVTPA/Ir complex blend through efficient energy transfer from the host polymer to the guest Ir complex. Single-layer phosphorescent electroluminescent devices of indium-tin oxide/PEDOT:PSS/PCNVTPA:Ir complexes/Ca:Al showed maximum luminance (2899 cd m−2) and luminance efficiency (8.84 cd A−1), respectively, which were much higher than those of PVTPA. Such an improvement was probably due to the more efficient hole trapping in Ir complexes by the lower HOMO level or better electron injection from the lower LUMO level of PCNVTPA. The results suggested that the new PCNVTPA could be a good host polymer for the electrophosphorescent device.
Synthesis and characterization of cellulose-b-polystyreneYagi, Shunsuke; Kasuya, Natsuki; Fukuda, Kiyoharu
doi: 10.1038/pj.2009.342pmid: N/A
A block copolymer of cellulose and polystyrene (PS) was synthesized through atom transfer radical polymerization. Macroinitiators (MIs) were prepared by introducing 2-chloroacetamide to the reducing end of cellulose (degree of polymerization=20, 50, 250). Subsequently, MIs were copolymerized with styrene monomer in a system of N,N,N′,N″,N″-pentamethyldiethylenetriamine/CuCl or CuBr/ascorbic acid at 130 °C. The resulting copolymers were characterized by 1H nuclear magnetic resonance and size-exclusion chromatography. The kinetic study indicated that the polymerization was controllable. The efficacy of copolymers in compatibilizing an immiscible cellulose/PS blend was confirmed by microscopic observation. The mechanism of thermal and thermo-oxidative decomposition of the blend was investigated by thermogravimetry.