Polymers

2173 KiB

Open AccessFeature PaperArticle

pH-Responsive Intra- and Inter-Molecularly Micelle Formation of Anionic Diblock Copolymer in Water

by Masanobu Mizusaki, Yoshihiko Shimada, Yotaro Morishima and Shin-ichi Yusa

Polymers 2016, 8(2), 56; https://doi.org/10.3390/polym8020056 - 19 Feb 2016

Cited by 3 | Viewed by 6693

Poly(sodium2-(acrylamido)-2-methylpropanesulfonate)-block-poly(sodium11-(acrylamido)undecanoate) (PAMPS–PAaU) was synthesized via reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. The “living” polymerization of PAaU was evidenced by the fact that the molecular weight distribution was narrow (M_w/M_n = 1.23). The pH-induced association behavior [...] Read more.

Poly(sodium2-(acrylamido)-2-methylpropanesulfonate)-block-poly(sodium11-(acrylamido)undecanoate) (PAMPS–PAaU) was synthesized via reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. The “living” polymerization of PAaU was evidenced by the fact that the molecular weight distribution was narrow (M_w/M_n = 1.23). The pH-induced association behavior of PAMPS–PAaU in 0.1 M NaCl aqueous solutions as a function of solution pH was investigated by ¹H NMR spin-spin relaxation time, dynamic light scattering (DLS), static light scattering (SLS), and fluorescence probe techniques. These results indicated that PAMPS–PAaU formed polymer micelles in 0.1 M NaCl aqueous solutions at pH < 9. At pH = 8–9, the polymer formed the micelles intramolecularly due to hydrophobic self-association of the PAaU block within the single polymer chain. On the other hand, at pH < 8, micellization occurred intermolecularly to form polymer micelles comprising hydrophobic PAaU cores and hydrophilic PAMPS shells. Full article

(This article belongs to the Collection Polyelectrolytes)

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2857 KiB

Open AccessArticle

Initiator Systems Effect on Particle Coagulation and Particle Size Distribution in One-Step Emulsion Polymerization of Styrene

by Baijun Liu, Yajun Wang, Mingyao Zhang and Huixuan Zhang

Polymers 2016, 8(2), 55; https://doi.org/10.3390/polym8020055 - 19 Feb 2016

Cited by 40 | Viewed by 14218

Abstract

Particle coagulation is a facile approach to produce large-scale polymer latex particles. This approach has been widely used in academic and industrial research owing to its higher polymerization rate and one-step polymerization process. Our work was motivated to control the extent (or time) [...] Read more.

Particle coagulation is a facile approach to produce large-scale polymer latex particles. This approach has been widely used in academic and industrial research owing to its higher polymerization rate and one-step polymerization process. Our work was motivated to control the extent (or time) of particle coagulation. Depending on reaction parameters, particle coagulation is also able to produce narrowly dispersed latex particles. In this study, a series of experiments were performed to investigate the role of the initiator system in determining particle coagulation and particle size distribution. Under the optimal initiation conditions, such as cationic initiator systems or higher reaction temperature, the time of particle coagulation would be advanced to particle nucleation period, leading to the narrowly dispersed polymer latex particles. By using a combination of the Smoluchowski equation and the electrostatic stability theory, the relationship between the particle size distribution and particle coagulation was established: the earlier the particle coagulation, the narrower the particle size distribution, while the larger the extent of particle coagulation, the larger the average particle size. Combined with the results of previous studies, a systematic method controlling the particle size distribution in the presence of particle coagulation was developed. Full article

(This article belongs to the Special Issue Selected Papers from ASEPFPM2015)

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3952 KiB

Open AccessArticle

Fabrication of Nerve Growth Factor Encapsulated Aligned Poly(ε-Caprolactone) Nanofibers and Their Assessment as a Potential Neural Tissue Engineering Scaffold

by Jue Hu, Lingling Tian, Molamma P. Prabhakaran, Xin Ding and Seeram Ramakrishna

Polymers 2016, 8(2), 54; https://doi.org/10.3390/polym8020054 - 19 Feb 2016

Cited by 78 | Viewed by 8463

Abstract

Peripheral nerve injury is a serious clinical problem to be solved. There has been no breakthrough so far and neural tissue engineering offers a promising approach to promote the regeneration of peripheral neural injuries. In this study, emulsion electrospinning technique was introduced as [...] Read more.

Peripheral nerve injury is a serious clinical problem to be solved. There has been no breakthrough so far and neural tissue engineering offers a promising approach to promote the regeneration of peripheral neural injuries. In this study, emulsion electrospinning technique was introduced as a flexible and promising technique for the fabrication of random (R) and aligned (A) Poly(ε-caprolactone) (PCL)-Nerve Growth Factor (NGF)&Bovine Serum Albumin (BSA) nanofibrous scaffolds [(R/A)-PCL-NGF&BSA], where NGF and BSA were encapsulated in the core while PCL form the shell. Random and aligned pure PCL, PCL-BSA, and PCL-NGF nanofibers were also produced for comparison. The scaffolds were characterized by Field Emission Scanning Electron Microscopy (FESEM) and water contact angle test. Release study showed that, with the addition of stabilizer BSA, a sustained release of NGF from emulsion electrospun PCL nanofibers was observed over 28 days. [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt; MTS] assay revealed that (R/A)-PCL-NGF and (R/A)-PCL-NGF&BSA scaffolds favored cell growth and showed no cytotoxicity to PC12 cells. Laser scanning confocal microscope images exhibited that the A-PCL-NGF&BSA scaffold increased the length of neurites and directed neurites extension along the fiber axis, indicating that the A-PCL-NGF&BSA scaffold has a potential for guiding nerve tissue growth and promoting nerve regeneration. Full article

(This article belongs to the Special Issue Polymers Applied in Tissue Engineering)

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2082 KiB

Open AccessArticle

Functionalized Cellulose Networks for Efficient Oil Removal from Oil–Water Emulsions

by Uttam C. Paul, Despina Fragouli, Ilker S. Bayer and Athanassia Athanassiou

Polymers 2016, 8(2), 52; https://doi.org/10.3390/polym8020052 - 17 Feb 2016

Cited by 47 | Viewed by 7908

Abstract

The separation of oil from water in emulsions is a great environmental challenge, since oily wastewater is industrially produced. Here, we demonstrate a highly efficient method to separate oil from water in non-stabilized emulsions, using functionalized cellulose fiber networks. This is achieved by [...] Read more.

The separation of oil from water in emulsions is a great environmental challenge, since oily wastewater is industrially produced. Here, we demonstrate a highly efficient method to separate oil from water in non-stabilized emulsions, using functionalized cellulose fiber networks. This is achieved by the modification of the wetting properties of the fibers, transforming them from oil- and water-absorbing to water-absorbing and oil-proof. In particular, two diverse layers of polymeric coatings, paraffin wax and poly(dimethylsiloxane)-b-poly(ethylene oxide) (PDMS-b-PEO) diblock copolymer, are applied on the surface of each individual fiber by a two-step dip adsorption process. The resulting cellulose networks exhibit superhydrophilicity and underwater superoleophobicity and they are mechanically reinforced. Therefore, the described treatment makes cellulose fiber networks excellent candidates for the filtration and subsequent removal of oil from oil-in-water non-stabilized emulsions with oil separation efficiency up to 99%. The good selectivity, reproducibility, and cost effectiveness of the preparation process leads to the production of low cost filters that can be used in oil–water separation applications. Full article

(This article belongs to the Collection Polysaccharides)

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3765 KiB

Open AccessArticle

Enhancement of Carbon Nanotube Particle Distribution in PPS/PEEK/Carbon Nanotube Ternary Composites with Sausage-Like Structure

by Lin Cao, Shuling Deng and Zhidan Lin

Polymers 2016, 8(2), 50; https://doi.org/10.3390/polym8020050 - 16 Feb 2016

Cited by 11 | Viewed by 6129

Abstract

Carbon nanomaterial particles were selectively distributed in an incompatible and high-melting-temperature polymer blend interface, or in a particular phase, to obtain conductive composites. The composite products revealed poor morphology stability and mechanical performance due to processing several times. Poly(phenylene sulfide) (PPS) and poly(ether [...] Read more.

Carbon nanomaterial particles were selectively distributed in an incompatible and high-melting-temperature polymer blend interface, or in a particular phase, to obtain conductive composites. The composite products revealed poor morphology stability and mechanical performance due to processing several times. Poly(phenylene sulfide) (PPS) and poly(ether ether ketone) (PEEK) polymers with large differences of processing temperatures were selected as blend components to obtain a compatible blend. PPS/PEEK/multi-walled carbon nanotube (MWCNT) ternary nanocomposites were prepared using a controlled melt blending process. The composite samples with similar sausage-like structures of PEEK, as a dispersed phase, promote MWCNT to maximize concentration distribution in the PPS continuous phase. As a result, the theoretical percolation threshold of the composite reduced to 0.347 wt %. Moreover, the conductivity of the composite remained stable even after processing several times. CNTs revealed a particular effect when distributed selectively in this kind of system: it can enhance the dispersion of phases and also provide conductivity to the blend at small CNT contents, which can provide more useful ideas for the development of high-melting-temperature and antistatic or conductive plastic materials. Full article

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4670 KiB

Open AccessArticle

Dielectric Properties and Energy Storage Densities of Poly(vinylidenefluoride) Nanocomposite with Surface Hydroxylated Cube Shaped Ba_0.6Sr_0.4TiO₃ Nanoparticles

by Shaohui Liu, Shaomei Xiu, Bo Shen, Jiwei Zhai and Ling Bing Kong

Polymers 2016, 8(2), 45; https://doi.org/10.3390/polym8020045 - 16 Feb 2016

Cited by 56 | Viewed by 7315

Abstract

Ceramic-polymer nanocomposites, consisting of surface hydroxylated cube-shaped Ba_0.6Sr_0.4TiO₃ nanoparticles (BST–NPs) as fillers and poly(vinylidenefluoride) (PVDF) as matrix, have been fabricated by using a solution casting method. The nanocomposites exhibited increased dielectric constant and improved breakdown strength. Dielectric constants [...] Read more.

Ceramic-polymer nanocomposites, consisting of surface hydroxylated cube-shaped Ba_0.6Sr_0.4TiO₃ nanoparticles (BST–NPs) as fillers and poly(vinylidenefluoride) (PVDF) as matrix, have been fabricated by using a solution casting method. The nanocomposites exhibited increased dielectric constant and improved breakdown strength. Dielectric constants of the nanocomposite with surface hydroxylated BST–NPs (BST–NPs–OH) were higher as compared with those of their untreated BST–NPs composites. The sample with 40 vol % BST–NPs–OH had a dielectric constant of 36 (1 kHz). Different theoretical models have been employed to predict the dielectric constants of the nanocomposites, in order to compare with the experimental data. The BST–NPs–OH/PVDF composites also exhibited higher breakdown strength than their BST–NP/PVDF counterparts. A maximal energy density of 3.9 J/cm³ was achieved in the composite with 5 vol % BST–NPs–OH. This hydroxylation strategy could be used as a reference to develop ceramic-polymer composite materials with enhanced dielectric properties and energy storage densities. Full article

(This article belongs to the Special Issue Nano- and Microcomposites for Electrical Engineering Applications)

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3480 KiB

Open AccessArticle

Tris(bipyridine)Metal(II)-Templated Assemblies of 3D Alkali-Ruthenium Oxalate Coordination Frameworks: Crystal Structures, Characterization and Photocatalytic Activity in Water Reduction

by Alla Dikhtiarenko, Pedro Villanueva-Delgado, Rafael Valiente, José R. García and José Gimeno

Polymers 2016, 8(2), 48; https://doi.org/10.3390/polym8020048 - 15 Feb 2016

Cited by 19 | Viewed by 8941

Abstract

A series of 3D oxalate-bridged ruthenium-based coordination polymers with the formula of {[Z^II(bpy)₃][M^IRu(C₂O₄)₃]}_n (Z^II = Zn²⁺ (1), Cu²⁺ (3, 4), Ru²⁺ [...] Read more.

A series of 3D oxalate-bridged ruthenium-based coordination polymers with the formula of {[Z^II(bpy)₃][M^IRu(C₂O₄)₃]}_n (Z^II = Zn²⁺ (1), Cu²⁺ (3, 4), Ru²⁺ (5, 6), Os²⁺ (7, 8); M^I = Li⁺, Na⁺; bpy = 2,2’-bipyridine) and {[Zn^II(bpy)₃](H₂O)[LiRu(C₂O₄)₃]}_n (2) has been synthesized at room temperature through a self-assembly reaction in aqueous media and characterized by single-crystal and powder X-ray diffraction, elemental analysis, infrared and diffuse reflectance UV–Vis spectroscopy and thermogravimetric analysis. The crystal structures of all compounds comprise chiral 3D honeycomb-like polymeric nets of the srs-type, which possess triangular anionic cages where [Z^II(bpy)₃]²⁺ cationic templates are selectively embedded. Structural analysis reveals that the electronic configuration of the cationic guests is affected by electrostatic interaction with the anionic framework. Moreover, the MLCT bands gaps values for 1–8 can be tuned in a rational way by judicious choice of [Z^II(bpy)₃]²⁺ guests. The 3D host-guest polymeric architectures can be used as self-supported heterogeneous photocatalysts for the reductive splitting of water, exhibiting photocatalytic activity for the evolution of H₂ under UV light irradiation. Full article

(This article belongs to the Special Issue Coordination Polymers: New Materials for Multiple Applications)

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5164 KiB

Open AccessArticle

Self-Assembly of Discrete Metallocycles versus Coordination Polymers Based on Cu(I) and Ag(I) Ions and Flexible Ligands: Structural Diversification and Luminescent Properties

by Javier Vallejos, Iván Brito, Alejandro Cárdenas, Michael Bolte, Sergio Conejeros, Pere Alemany and Jaime Llanos

Polymers 2016, 8(2), 46; https://doi.org/10.3390/polym8020046 - 15 Feb 2016

Cited by 16 | Viewed by 6467

Abstract

Three new Ag(I) and one Cu(I) coordination compounds with two different positional isomers, propane-1,3-diyl bis(pyridine-4-carboxylate) (L1) and propane-1,3-diyl bis(pyridine-3-carboxylate) (L2), of a bis-(pyridyl-carboxylate) ligand have been synthesized. X-ray diffraction analysis revealed that the self-assembly of L1 with AgCF₃SO₃ and AgClO [...] Read more.

Three new Ag(I) and one Cu(I) coordination compounds with two different positional isomers, propane-1,3-diyl bis(pyridine-4-carboxylate) (L1) and propane-1,3-diyl bis(pyridine-3-carboxylate) (L2), of a bis-(pyridyl-carboxylate) ligand have been synthesized. X-ray diffraction analysis revealed that the self-assembly of L1 with AgCF₃SO₃ and AgClO₄ salts leads to the formation of discrete binuclear metallocycles {Ag(L1)CF₃SO₃}₂ (1) and {Ag(L1)ClO₄}₂ (2), respectively. However, self-assembly of the other ligand, L2, with AgCF₃SO₃ and CuCl salts, results in a 1-D zig-zag chain {Ag(L2)CF₃SO₃}_∞ (3) and a 1-D double-stranded helical chain {Cu₂Cl₂(L2)₂}_∞ (4) coordination polymers, respectively. Solid emission spectra recorded at room temperature show interesting luminescence properties for all four compounds in the range from 438 to 550 nm, especially for compound 4 that was found to change its emission color when the wavelength of the excitation radiation is switched from 332 to 436 nm. Full article

(This article belongs to the Special Issue Coordination Polymers: New Materials for Multiple Applications)

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5057 KiB

Open AccessArticle

SrTiO₃ Nanocube-Doped Polyaniline Nanocomposites with Enhanced Photocatalytic Degradation of Methylene Blue under Visible Light

by Syed Shahabuddin, Norazilawati Muhamad Sarih, Sharifah Mohamad and Juan Joon Ching

Polymers 2016, 8(2), 27; https://doi.org/10.3390/polym8020027 - 15 Feb 2016

Cited by 157 | Viewed by 12495

Abstract

The present study highlights the facile synthesis of polyaniline (PANI)-based nanocomposites doped with SrTiO₃ nanocubes synthesized via the in situ oxidative polymerization technique using ammonium persulfate (APS) as an oxidant in acidic medium for the photocatalytic degradation of methylene blue dye. Field [...] Read more.

The present study highlights the facile synthesis of polyaniline (PANI)-based nanocomposites doped with SrTiO₃ nanocubes synthesized via the in situ oxidative polymerization technique using ammonium persulfate (APS) as an oxidant in acidic medium for the photocatalytic degradation of methylene blue dye. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), UV–Vis spectroscopy, Brunauer–Emmett–Teller analysis (BET) and Fourier transform infrared spectroscopy (FTIR) measurements were used to characterize the prepared nanocomposite photocatalysts. The photocatalytic efficiencies of the photocatalysts were examined by degrading methylene blue (MB) under visible light irradiation. The results showed that the degradation efficiency of the composite photocatalysts that were doped with SrTiO₃ nanocubes was higher than that of the undoped polyaniline. In this study, the effects of the weight ratio of polyaniline to SrTiO₃ on the photocatalytic activities were investigated. The results revealed that the nanocomposite P-Sr500 was found to be an optimum photocatalyst, with a 97% degradation efficiency after 90 min of irradiation under solar light. Full article

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6880 KiB

Open AccessArticle

Conformation and Rheological Properties of Calf-Thymus DNA in Solution

by Lourdes Mónica Bravo-Anaya, Marguerite Rinaudo and Félix Armando Soltero Martínez

Polymers 2016, 8(2), 51; https://doi.org/10.3390/polym8020051 - 11 Feb 2016

Cited by 27 | Viewed by 8704

Abstract

Studies of DNA molecule behavior in aqueous solutions performed through different approaches allow assessment of the solute-solvent interactions and examination of the strong influence of conformation on its physicochemical properties, in the presence of different ionic species and ionic concentrations. Firstly, the conformational [...] Read more.

Studies of DNA molecule behavior in aqueous solutions performed through different approaches allow assessment of the solute-solvent interactions and examination of the strong influence of conformation on its physicochemical properties, in the presence of different ionic species and ionic concentrations. Firstly, the conformational behavior of calf-thymus DNA molecules in TE buffer solution is presented as a function of temperature. Secondly, their rheological behavior is discussed, as well as the evidence of the critical concentrations, i.e., the overlap and the entanglement concentrations (C* and C_e, respectively) from steady state flow and oscillatory dynamic shear experiments. The determination of the viscosity in the Newtonian plateau obtained from flow curves η ( ) allows estimation of the intrinsic viscosity and the specific viscosities at zero shear when C[η] < 40. At end, a generalized master curve is obtained from the variation of the specific viscosity as a function of the overlap parameter C[η]. The variation of the exponent s obtained from the power law η~ ^−s for both flow and dynamic results is discussed in terms of Graessley’s analysis. In the semi-dilute regime with entanglements, a dynamic master curve is obtained as a function of DNA concentration (C_DNA > 2.0 mg/mL) and temperature (10 °C < T < 40 °C). Full article

(This article belongs to the Collection Polyelectrolytes)

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4485 KiB

Open AccessArticle

Developed Hybrid Model for Propylene Polymerisation at Optimum Reaction Conditions

by Mohammad Jakir Hossain Khan, Mohd Azlan Hussain and Iqbal Mohammed Mujtaba

Polymers 2016, 8(2), 47; https://doi.org/10.3390/polym8020047 - 10 Feb 2016

Cited by 15 | Viewed by 6927

Abstract

A statistical model combined with CFD (computational fluid dynamic) method was used to explain the detailed phenomena of the process parameters, and a series of experiments were carried out for propylene polymerisation by varying the feed gas composition, reaction initiation temperature, and system [...] Read more.

A statistical model combined with CFD (computational fluid dynamic) method was used to explain the detailed phenomena of the process parameters, and a series of experiments were carried out for propylene polymerisation by varying the feed gas composition, reaction initiation temperature, and system pressure, in a fluidised bed catalytic reactor. The propylene polymerisation rate per pass was considered the response to the analysis. Response surface methodology (RSM), with a full factorial central composite experimental design, was applied to develop the model. In this study, analysis of variance (ANOVA) indicated an acceptable value for the coefficient of determination and a suitable estimation of a second-order regression model. For better justification, results were also described through a three-dimensional (3D) response surface and a related two-dimensional (2D) contour plot. These 3D and 2D response analyses provided significant and easy to understand findings on the effect of all the considered process variables on expected findings. To diagnose the model adequacy, the mathematical relationship between the process variables and the extent of polymer conversion was established through the combination of CFD with statistical tools. All the tests showed that the model is an excellent fit with the experimental validation. The maximum extent of polymer conversion per pass was 5.98% at the set time period and with consistent catalyst and co-catalyst feed rates. The optimum conditions for maximum polymerisation was found at reaction temperature (RT) 75 °C, system pressure (SP) 25 bar, and 75% monomer concentration (MC). The hydrogen percentage was kept fixed at all times. The coefficient of correlation for reaction temperature, system pressure, and monomer concentration ratio, was found to be 0.932. Thus, the experimental results and model predicted values were a reliable fit at optimum process conditions. Detailed and adaptable CFD results were capable of giving a clear idea of the bed dynamics at optimum process conditions. Full article

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3706 KiB

Open AccessArticle

Development of Poly(ɛ-caprolactone) Scaffold Loaded with Simvastatin and Beta-Cyclodextrin Modified Hydroxyapatite Inclusion Complex for Bone Tissue Engineering

by Jung Bok Lee, Ji Eun Kim, Min Soo Bae, Su A Park, Daniel A. Balikov, Hak-joon Sung, Hoon Bong Jeon, Hun Kuk Park, Soong Ho Um, Kook Sun Lee and Il Keun Kwon

Polymers 2016, 8(2), 49; https://doi.org/10.3390/polym8020049 - 09 Feb 2016

Cited by 18 | Viewed by 7210

Abstract

In this study, we developed poly(ɛ-caprolactone) (PCL) 3D scaffolds using a solid free form fabrication (SFF) technique. β-cyclodextrin (βCD) was grafted to hydroxyapatite (HAp) and this βCD grafted HAp was coated onto the PCL scaffold surface, followed by drug loading through an inclusion [...] Read more.

In this study, we developed poly(ɛ-caprolactone) (PCL) 3D scaffolds using a solid free form fabrication (SFF) technique. β-cyclodextrin (βCD) was grafted to hydroxyapatite (HAp) and this βCD grafted HAp was coated onto the PCL scaffold surface, followed by drug loading through an inclusion complex interaction between the βCD and adamantane (AD) or between βCD and simvastatin (SIM). The scaffold structure was characterized by scanning electron microscopy (SEM). The release profile of simvastatin in the β-CD grafted HAp was also evaluated. Osteogenic differentiation of adipose-derived stromal cells (ADSCs) was examined using an alkaline phosphatase activity (ALP) assay. The results suggest that drug loaded PCL-HAp 3-D scaffolds enhances osteogenic differentiation of ADSCs. Full article

(This article belongs to the Special Issue Polymers Applied in Tissue Engineering)

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6057 KiB

Open AccessArticle

New URJC-1 Material with Remarkable Stability and Acid-Base Catalytic Properties

by Pedro Leo, Fernando Martínez, Guillermo Calleja, David Briones, Lukasz Wojtas and Gisela Orcajo

Polymers 2016, 8(2), 44; https://doi.org/10.3390/polym8020044 - 05 Feb 2016

Cited by 11 | Viewed by 6146

Abstract

Emerging new metal-organic structures with tunable physicochemical properties is an exciting research field for diverse applications. In this work, a novel metal-organic framework Cu(HIT)(DMF)_0.5, named URJC-1, with a three-dimensional non-interpenetrated utp topological network, has been synthesized. This material exhibits a microporous [...] Read more.

Emerging new metal-organic structures with tunable physicochemical properties is an exciting research field for diverse applications. In this work, a novel metal-organic framework Cu(HIT)(DMF)_0.5, named URJC-1, with a three-dimensional non-interpenetrated utp topological network, has been synthesized. This material exhibits a microporous structure with unsaturated copper centers and imidazole–tetrazole linkages that provide accessible Lewis acid/base sites. These features make URJC-1 an exceptional candidate for catalytic application in acid and base reactions of interest in fine chemistry. The URJC-1 material also displays a noteworthy thermal and chemical stability in different organic solvents of different polarity and boiling water. Its catalytic activity was evaluated in acid-catalyzed Friedel–Crafts acylation of anisole with acetyl chloride and base-catalyzed Knoevenagel condensation of benzaldehyde with malononitrile. In both cases, URJC-1 material showed very good performance, better than other metal organic frameworks and conventional catalysts. In addition, a remarkable structural stability was proven after several consecutive reaction cycles. Full article

(This article belongs to the Special Issue Coordination Polymers: New Materials for Multiple Applications)

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1892 KiB

Open AccessArticle

Light Emission Properties of a Cross-Conjugated Fluorene Polymer: Demonstration of Its Use in Electro-Luminescence and Lasing Devices

by Sergio Romero-Servin, Luis-Abraham Lozano-Hernández, José-Luis Maldonado, Ramón Carriles, Gabriel Ramos-Ortíz, Enrique Pérez-Gutiérrez, Ullrich Scherf and Mikhail G. Zolotukhin

Polymers 2016, 8(2), 43; https://doi.org/10.3390/polym8020043 - 05 Feb 2016

Cited by 14 | Viewed by 7648

Abstract

Light emission properties of a fluorene cross-conjugated polymer (PF–1) based on the monomer 4,7-bis[2-(9,9-dimethyl)fluorenyl] benzo[1,2,5]thiadiazole are reported. This polymer exhibits solubility at high concentrations, good processability into thin solid films of good quality and a broad emission band with a fluorescence [...] Read more.

Light emission properties of a fluorene cross-conjugated polymer (PF–1) based on the monomer 4,7-bis[2-(9,9-dimethyl)fluorenyl] benzo[1,2,5]thiadiazole are reported. This polymer exhibits solubility at high concentrations, good processability into thin solid films of good quality and a broad emission band with a fluorescence quantum yield of approximately 1. Based on these features, in this paper we implemented the use of PF–1 as an active layer in polymer light-emitting diodes (PLEDs) and as a laser gain medium in solution. To get insight on the conducting properties of PF–1, two different electron injectors, poly [(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] (PFN) and lithium fluoride (LiF), were used in a simple PLED architecture. PLEDs with the PFN film were found to exhibit better performance with a maximum luminous efficiency of 40 cd/A, a turn-on voltage (V_on) of approximately 4.5 V and a luminance maximum of 878 cd/m² at 5.5 V, with a current density of 20 A/m². For the lasing properties of PF–1, we found a lasing threshold of around 75 μJ and a tunability of 20 nm. These values are comparable with those of rhodamine 6G, a well-known laser dye. Full article

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5319 KiB

Open AccessArticle

Facile Functionalization of Electrospun Poly(ethylene-co-vinyl alcohol) Nanofibers via the Benzoxaborole-Diol Interaction

by Yohei Kotsuchibashi and Mitsuhiro Ebara

Polymers 2016, 8(2), 41; https://doi.org/10.3390/polym8020041 - 05 Feb 2016

Cited by 7 | Viewed by 6757

Abstract

A facile functionalization method of poly(ethylene-co-vinyl alcohol) (EVOH) nanofiber meshes was demonstrated by utilizing the benzoxaborole-diol interaction between EVOH and benzoxaborole-based copolymers (BOP). EVOH and BOP were firstly mixed to prepare the quasi-gel-state solution with enough viscosity for electro-spinning. The fiber [...] Read more.

A facile functionalization method of poly(ethylene-co-vinyl alcohol) (EVOH) nanofiber meshes was demonstrated by utilizing the benzoxaborole-diol interaction between EVOH and benzoxaborole-based copolymers (BOP). EVOH and BOP were firstly mixed to prepare the quasi-gel-state solution with enough viscosity for electro-spinning. The fiber morphology was controlled via changing the mixing ratio of EVOH and BOP. The prepared EVOH/BOP nanofiber mesh showed good stability in aqueous solution. Over 97% of the nanofibers remained after the immersion test for 24 h in acid or alkali aqueous solutions without changing their morphology. Temperature and pH-responsive moieties were copolymerized with BOP, and cationic dye was easily immobilized into the nanofiber mesh via an electrostatic interaction. Therefore, the proposed functionalization technique is possible to perform on multi-functionalized molecule-incorporated nanofibers that enable the fibers to show the environmental stimuli-responsive property for the further applications of the EVOH materials. Full article

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1365 KiB

Open AccessReview

Application of Collagen Scaffold in Tissue Engineering: Recent Advances and New Perspectives

by Chanjuan Dong and Yonggang Lv

Polymers 2016, 8(2), 42; https://doi.org/10.3390/polym8020042 - 04 Feb 2016

Cited by 507 | Viewed by 30461

Abstract

Collagen is the main structural protein of most hard and soft tissues in animals and the human body, which plays an important role in maintaining the biological and structural integrity of the extracellular matrix (ECM) and provides physical support to tissues. Collagen can [...] Read more.

Collagen is the main structural protein of most hard and soft tissues in animals and the human body, which plays an important role in maintaining the biological and structural integrity of the extracellular matrix (ECM) and provides physical support to tissues. Collagen can be extracted and purified from a variety of sources and offers low immunogenicity, a porous structure, good permeability, biocompatibility and biodegradability. Collagen scaffolds have been widely used in tissue engineering due to these excellent properties. However, the poor mechanical property of collagen scaffolds limits their applications to some extent. To overcome this shortcoming, collagen scaffolds can be cross-linked by chemical or physical methods or modified with natural/synthetic polymers or inorganic materials. Biochemical factors can also be introduced to the scaffold to further improve its biological activity. This review will summarize the structure and biological characteristics of collagen and introduce the preparation methods and modification strategies of collagen scaffolds. The typical application of a collagen scaffold in tissue engineering (including nerve, bone, cartilage, tendon, ligament, blood vessel and skin) will be further provided. The prospects and challenges about their future research and application will also be pointed out. Full article

(This article belongs to the Special Issue Polymers Applied in Tissue Engineering)

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6893 KiB

Open AccessArticle

Synthesis of Polyaniline (PANI) in Nano-Reaction Field of Cellulose Nanofiber (CNF), and Carbonization

by Yuki Kaitsuka, Noriko Hayashi, Tomoko Shimokawa, Eiji Togawa and Hiromasa Goto

Polymers 2016, 8(2), 40; https://doi.org/10.3390/polym8020040 - 02 Feb 2016

Cited by 30 | Viewed by 11416

Abstract

Polymerization of aniline in the presence of cellulose nano-fiber (CNF) is carried out. We used dried CNF, CNF suspension, and CNF treated by enzyme and ultra-sonification to obtain polyaniline (PANI)/CNF as a synthetic polymer/natural nano-polymer composite. The polymerization proceeds on the surface of [...] Read more.

Polymerization of aniline in the presence of cellulose nano-fiber (CNF) is carried out. We used dried CNF, CNF suspension, and CNF treated by enzyme and ultra-sonification to obtain polyaniline (PANI)/CNF as a synthetic polymer/natural nano-polymer composite. The polymerization proceeds on the surface of CNF as a nano-reaction field. Resultant composites show extended effective π-conjugation length because CNF as a reaction field in molecular level produced polymer with expanded coil structure with an aid of orientation effect of CNF. Possibility of PANI β-pleats structure in molecular level of PANI on the CNF is also discussed. SEM observation showed that fine structure is easily obtained by combining PANI with CNF. Carbonization of PANI/CNF allows production of nano-fine form with shape preserved carbonization (SPC). Full article

(This article belongs to the Special Issue Conductive Polymers 2016)

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Open AccessArticle

Luminescence and Magnetic Properties of Two Three-Dimensional Terbium and Dysprosium MOFs Based on Azobenzene-4,4′-Dicarboxylic Linker

by Belén Fernández, Itziar Oyarzabal, José M. Seco, Eider San Sebastián, David Fairen-Jiménez, Santiago Gómez-Ruiz, Alfonso Salinas-Castillo, Antonio J. Calahorro and Antonio Rodríguez-Diéguez

Polymers 2016, 8(2), 39; https://doi.org/10.3390/polym8020039 - 02 Feb 2016

Cited by 8 | Viewed by 7252

Abstract

We report the in situ formation of two novel metal-organic frameworks based on terbium and dysprosium ions using azobenzene-4,4′-dicarboxylic acid (H₂abd) as ligand, synthesized by soft hydrothermal routes. Both materials show isostructural three-dimensional networks with channels along a axis [...] Read more.

We report the in situ formation of two novel metal-organic frameworks based on terbium and dysprosium ions using azobenzene-4,4′-dicarboxylic acid (H₂abd) as ligand, synthesized by soft hydrothermal routes. Both materials show isostructural three-dimensional networks with channels along a axis and display intense photoluminescence properties in the solid state at room temperature. Textural properties of the metal-organic frameworks (MOFs) have been fully characterized although no appreciable porosity was obtained. Magnetic properties of these materials were studied, highlighting the dysprosium material displays slightly frequency-dependent out of phase signals when measured under zero external field and under an applied field of 1000 Oe. Full article

(This article belongs to the Special Issue Coordination Polymers: New Materials for Multiple Applications)

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2441 KiB

Open AccessArticle

Comb-Type Grafted Hydrogels of PNIPAM and PDMAEMA with Reversed Network-Graft Architectures from Controlled Radical Polymerizations

by Sheng-Qi Chen, Jia-Min Li, Ting-Ting Pan, Peng-Yun Li and Wei-Dong He

Polymers 2016, 8(2), 38; https://doi.org/10.3390/polym8020038 - 01 Feb 2016

Cited by 13 | Viewed by 11178

Abstract

Dual thermo- and pH-responsive comb-type grafted hydrogels of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(N-isopropylacrylamide) (PNIPAM) with reversed network-graft architectures were synthesized by the combination of atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization and click chemistry. Two [...] Read more.

Dual thermo- and pH-responsive comb-type grafted hydrogels of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(N-isopropylacrylamide) (PNIPAM) with reversed network-graft architectures were synthesized by the combination of atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization and click chemistry. Two kinds of macro-cross-linkers with two azido groups at one chain-end and different chain length [PNIPAM–(N₃)₂ and PDMAEMA–(N₃)₂] were prepared with N,N-di(β-azidoethyl) 2-halocarboxylamide as the ATRP initiator. Through RAFT copolymerization of DMAEMA or NIPAM with propargyl acrylate (ProA) using dibenzyltrithiocarbonate as a chain transfer agent, two network precursors with different content of alkynyl side-groups [P(DMAEMA-co-ProA) and P(NIPAM-co-ProA)] were obtained. The subsequent azido-alkynyl click reaction of macro-cross-linkers and network precursors led to the formation of the network-graft hydrogels. These dual stimulus-sensitive hydrogels exhibited rapid response, high swelling ratio and reproducible swelling/de-swelling cycles under different temperatures and pH values. The influences of cross-linkage density and network-graft architecture on the properties of the hydrogels were investigated. The release of ceftriaxone sodium from these hydrogels showed both thermal- and pH-dependence, suggesting the feasibility of these hydrogels as thermo- and pH-dependent drug release devices. Full article

(This article belongs to the Special Issue Controlled/Living Radical Polymerization)

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1037 KiB

Open AccessArticle

Investigations of the Ligand Electronic Effects on α-Diimine Nickel(II) Catalyzed Ethylene Polymerization

by Lihua Guo, Shengyu Dai and Changle Chen

Polymers 2016, 8(2), 37; https://doi.org/10.3390/polym8020037 - 29 Jan 2016

Cited by 120 | Viewed by 8733

Abstract

The synthesis and characterization of a series of dibenzhydryl-based α-diimine Ni(II) complexes bearing a range of electron-donating or -withdrawing groups are described. Polymerization with ethylene is investigated in detail, involving the activator effect, influence of polymerization conditions on catalyst activity, thermal stability, polymer [...] Read more.

The synthesis and characterization of a series of dibenzhydryl-based α-diimine Ni(II) complexes bearing a range of electron-donating or -withdrawing groups are described. Polymerization with ethylene is investigated in detail, involving the activator effect, influence of polymerization conditions on catalyst activity, thermal stability, polymer molecular weight and melting point. All of these Ni(II) complexes show great activity (up to 6 × 10⁶ g of PE (mol of Ni)⁻¹·h⁻¹), exceptional thermal stability (stable at up to 100 °C) and generate polyethylene with very high molecular weight (M_n up to 1.6 × 10⁶) and very narrow molecular weight distribution. In the dibromo Ni(II) system, the electronic perturbations exhibit little variation on the ethylene polymerization. In the Ni(acac) system, dramatic ligand electronic effects are observed in terms of catalytic activity and polyethylene molecular weight. Full article

(This article belongs to the Special Issue Metal-Mediated Polymer Synthesis)

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1838 KiB

Open AccessFeature PaperArticle

l-Cystine-Crosslinked Polypeptide Nanogel as a Reduction-Responsive Excipient for Prostate Cancer Chemotherapy

by Liang He, Di Li, Zhongtang Wang, Weiguo Xu, Jixue Wang, Hui Guo, Chunxi Wang and Jianxun Ding

Polymers 2016, 8(2), 36; https://doi.org/10.3390/polym8020036 - 29 Jan 2016

Cited by 29 | Viewed by 7138

Abstract

Smart polymer nanogel-assisted drug delivery systems have attracted more and more attention in cancer chemotherapy because of their well-defined morphologies and pleiotropic functions in recent years. In this work, an l-cystine-crosslinked reduction-responsive polypeptide nanogel of methoxy poly(ethylene glycol)-poly(l-phenylalanine-co- [...] Read more.

Smart polymer nanogel-assisted drug delivery systems have attracted more and more attention in cancer chemotherapy because of their well-defined morphologies and pleiotropic functions in recent years. In this work, an l-cystine-crosslinked reduction-responsive polypeptide nanogel of methoxy poly(ethylene glycol)-poly(l-phenylalanine-co-l-cystine) (mPEG-P(LP-co-LC)) was employed as a smart excipient for RM-1 prostate cancer (PCa) chemotherapy. Doxorubicin (DOX), as a regular chemotherapy drug, was embedded in the nanogel. The loading nanogel marked as NG/DOX was shown to exhibit glutathione (GSH)-induced swelling and GSH-accelerated DOX release. Subsequently, NG/DOX showed efficient cellular uptake and proliferation inhibition. Furthermore, NG/DOX presented enhanced antitumor efficacy and security in an RM-1 PCa-grafted mouse model in vivo, indicating its great potential for clinical treatment. Full article

(This article belongs to the Special Issue Functional Polymers for Medical Applications)

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6622 KiB

Open AccessArticle

Artificial Neural Network and Response Surface Methodology Modeling in Ionic Conductivity Predictions of Phthaloylchitosan-Based Gel Polymer Electrolyte

by Ahmad Danial Azzahari, Siti Nor Farhana Yusuf, Vidhya Selvanathan and Rosiyah Yahya

Polymers 2016, 8(2), 22; https://doi.org/10.3390/polym8020022 - 29 Jan 2016

Cited by 17 | Viewed by 5918

Abstract

A gel polymer electrolyte system based on phthaloylchitosan was prepared. The effects of process variables, such as lithium iodide, caesium iodide, and 1-butyl-3-methylimidazolium iodide were investigated using a distance-based ternary mixture experimental design. A comparative approach was made between response surface methodology (RSM) [...] Read more.

A gel polymer electrolyte system based on phthaloylchitosan was prepared. The effects of process variables, such as lithium iodide, caesium iodide, and 1-butyl-3-methylimidazolium iodide were investigated using a distance-based ternary mixture experimental design. A comparative approach was made between response surface methodology (RSM) and artificial neural network (ANN) to predict the ionic conductivity. The predictive capabilities of the two methodologies were compared in terms of coefficient of determination R² based on the validation data set. It was shown that the developed ANN model had better predictive outcome as compared to the RSM model. Full article

(This article belongs to the Collection Polysaccharides)

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3266 KiB

Open AccessArticle

Electrospun Poly(lactide-co-glycolide-co-3(S)-methyl-morpholine-2,5-dione) Nanofibrous Scaffolds for Tissue Engineering

by Yakai Feng, Wei Lu, Xiangkui Ren, Wen Liu, Mengyang Guo, Ihsan Ullah and Wencheng Zhang

Polymers 2016, 8(2), 13; https://doi.org/10.3390/polym8020013 - 29 Jan 2016

Cited by 24 | Viewed by 5833

Abstract

Biomimetic scaffolds have been investigated in vascular tissue engineering for many years. Excellent biodegradable materials are desired as temporary scaffolds to support cell growth and disappear gradually with the progress of guided tissue regeneration. In the present paper, a series of biodegradable copolymers [...] Read more.

Biomimetic scaffolds have been investigated in vascular tissue engineering for many years. Excellent biodegradable materials are desired as temporary scaffolds to support cell growth and disappear gradually with the progress of guided tissue regeneration. In the present paper, a series of biodegradable copolymers were synthesized and used to prepared micro/nanofibrous scaffolds for vascular tissue engineering. Poly(lactide-co-glycolide-co-3(S)-methyl-morpholine-2,5-dione) [P(LA-co-GA-co-MMD)] copolymers with different l-lactide (LA), glycolide (GA), and 3(S)-methyl-2,5-morpholinedione (MMD) contents were synthesized using stannous octoate as a catalyst. Moreover, the P(LA-co-GA-co-MMD) nanofibrous scaffolds were prepared by electrospinning technology. The morphology of scaffolds was analyzed by scanning electron microscopy (SEM), and the results showed that the fibers are smooth, regular, and randomly oriented with diameters of 700 ± 100 nm. The weight loss of scaffolds increased significantly with the increasing content of MMD, indicating good biodegradable property of the scaffolds. In addition, the cytocompatibility of electrospun nanofibrous scaffolds was tested by human umbilical vein endothelial cells. It is demonstrated that the cells could attach and proliferate well on P(LA-co-GA-co-MMD) scaffolds and, consequently, form a cell monolayer fully covering on the scaffold surface. Furthermore, the P(LA-co-GA-co-MMD) scaffolds benefit to excellent cell infiltration after subcutaneous implantation. These results indicated that the P(LA-co-GA-co-MMD) nanofibrous scaffolds could be potential candidates for vascular tissue engineering. Full article

(This article belongs to the Special Issue Polymers Applied in Tissue Engineering)

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729 KiB

Open AccessBrief Report

UV Light Induces Dedoping of Polyaniline

by Yuki Kaitsuka and Hiromasa Goto

Polymers 2016, 8(2), 34; https://doi.org/10.3390/polym8020034 - 28 Jan 2016

Cited by 10 | Viewed by 7038

Abstract

UV (Ultra-Violet) light-driven change in optical absorption of polyaniline (PANI) is reported. Irradiation of UV light to PANI/camphor sulfonic acid prepared by electrochemical polymerization allows dedoping of the PANI. Especially, UV light irradiation in the presence of a radical trap agent effectively reduces [...] Read more.

UV (Ultra-Violet) light-driven change in optical absorption of polyaniline (PANI) is reported. Irradiation of UV light to PANI/camphor sulfonic acid prepared by electrochemical polymerization allows dedoping of the PANI. Especially, UV light irradiation in the presence of a radical trap agent effectively reduces (dedoping) the PANI. The result in this study is quite simple; however, this may be a first report for light-induced dedoping (color change) of a conductive polymer. Full article

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4075 KiB

Open AccessArticle

Reversible Self-Assembly of Backbone-Thermoresponsive Long Chain Hyperbranched Poly(N-Isopropyl Acrylamide)

by Ting-Ting Liu, Wei Tian, Yan-Li Song, Yang Bai, Peng-Li Wei, Hao Yao and Hong-Xia Yan

Polymers 2016, 8(2), 33; https://doi.org/10.3390/polym8020033 - 28 Jan 2016

Cited by 9 | Viewed by 5594

Abstract

In this paper, we mainly described the reversible self-assembly of a backbone-thermoresponsive, long-chain, hyperbranched poly(N-isopropyl acrylamide) (LCHBPNIPAM) in aqueous solution. Here, we revealed a reversible self-assembly behavior of LCHBPNIPAM aqueous solution derived from temperature. By controlling the temperature of LCHBPNIPAM aqueous [...] Read more.

In this paper, we mainly described the reversible self-assembly of a backbone-thermoresponsive, long-chain, hyperbranched poly(N-isopropyl acrylamide) (LCHBPNIPAM) in aqueous solution. Here, we revealed a reversible self-assembly behavior of LCHBPNIPAM aqueous solution derived from temperature. By controlling the temperature of LCHBPNIPAM aqueous solution, we tune the morphology of the LCHBPNIPAM self-assemblies. When the solution temperature increased from the room temperature to the lower critical solution temperature of PNIPAM segments, LCHBPNIPAM self-assembled from multi-compartment vesicles into solid micelles. The morphology of LCHBPNIPAM self-assemblies changed from solid micelles to multi-compartment vesicles again when the temperature decreased back to the room temperature. The size presented, at first, an increase, and then a decrease, tendency in the heating-cooling process. The above thermally-triggered self-assembly behavior of LCHBPNIPAM aqueous solution was investigated by dynamic/static light scattering, transmission electron microscopy, atomic force microscopy, fluorescence spectroscopy, ¹H nuclear magnetic resonance in D₂O, and attenuated total reflectance Fourier transform infrared spectroscopy. These results indicated that LCHBPNIPAM aqueous solution presents a reversible self-assembly process. The controlled release behaviors of doxorubicin from the vesicles and micelles formed by LCHBPNIPAM further proved the feasibility of these self-assemblies as the stimulus-responsive drug delivery system. Full article

(This article belongs to the Special Issue Functional Polymers for Medical Applications)

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10255 KiB

Open AccessArticle

Development of PVDF Membrane Nanocomposites via Various Functionalization Approaches for Environmental Applications

by Douglas M. Davenport, Minghui Gui, Lindell R. Ormsbee and Dibakar Bhattacharyya

Polymers 2016, 8(2), 32; https://doi.org/10.3390/polym8020032 - 27 Jan 2016

Cited by 23 | Viewed by 9423

Abstract

Membranes are finding wide applications in various fields spanning biological, water, and energy areas. Synthesis of membranes to provide tunable flux, metal sorption, and catalysis has been done through pore functionalization of microfiltration (MF) type membranes with responsive behavior. This methodology provides an [...] Read more.

Membranes are finding wide applications in various fields spanning biological, water, and energy areas. Synthesis of membranes to provide tunable flux, metal sorption, and catalysis has been done through pore functionalization of microfiltration (MF) type membranes with responsive behavior. This methodology provides an opportunity to improve synthetic membrane performance via polymer fabrication and surface modification. By optimizing the polymer coagulation conditions in phase inversion fabrication, spongy polyvinylidene fluoride (PVDF) membranes with high porosity and large internal pore volume were created in lab and full scale. This robust membrane shows a promising mechanical strength as well as high capacity for loading of adsorptive and catalytic materials. By applying surface modification techniques, synthetic membranes with different functionality (carboxyl, amine, and nanoparticle-based) were obtained. These functionalities provide an opportunity to fine-tune the membrane surface properties such as charge and reactivity. The incorporation of stimuli-responsive acrylic polymers (polyacrylic acid or sodium polyacrylate) in membrane pores also results in tunable pore size and ion-exchange capacity. This provides the added benefits of adjustable membrane permeability and metal capture efficiency. The equilibrium and dynamic binding capacity of these functionalized spongy membranes were studied via calcium ion-exchange. Iron/palladium catalytic nanoparticles were immobilized in the polymer matrix in order to perform the challenging degradation of the environmental pollutant trichloroethylene (TCE). Full article

(This article belongs to the Special Issue Polymer Thin Films and Membranes 2015)

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Open AccessArticle

Highly Active and Isospecific Styrene Polymerization Catalyzed by Zirconium Complexes Bearing Aryl-substituted [OSSO]-Type Bis(phenolate) Ligands

by Norio Nakata, Tomoyuki Toda, Yusuke Saito, Takanori Watanabe and Akihiko Ishii

Polymers 2016, 8(2), 31; https://doi.org/10.3390/polym8020031 - 26 Jan 2016

Cited by 20 | Viewed by 6272

Abstract

[OSSO]-type dibenzyl zirconium(IV) complexes 9 and 10 possessing aryl substituents ortho to the phenoxide moieties (ortho substituents, phenyl and 2,6-dimethylphenyl (Dmp)) were synthesized and characterized. Upon activation with dMAO (dried methylaluminoxane), complex 9 was found to promote highly isospecific styrene polymerizations ([mm [...] Read more.

[OSSO]-type dibenzyl zirconium(IV) complexes 9 and 10 possessing aryl substituents ortho to the phenoxide moieties (ortho substituents, phenyl and 2,6-dimethylphenyl (Dmp)) were synthesized and characterized. Upon activation with dMAO (dried methylaluminoxane), complex 9 was found to promote highly isospecific styrene polymerizations ([mm] = 97.5%–99%) with high molecular weights M_w up to 181,000 g·mmol⁻¹. When the Dmp-substituted pre-catalyst 10/dMAO system was used, the highest activity, over 7700 g·mmol(10)⁻¹·h⁻¹, was recorded involving the formation of precisely isospecific polystyrenes of [mm] more than 99%. Full article

(This article belongs to the Special Issue Metal-Mediated Polymer Synthesis)

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4090 KiB

Open AccessReview

Seaweed Polysaccharide-Based Nanoparticles: Preparation and Applications for Drug Delivery

by Jayachandran Venkatesan, Sukumaran Anil, Se-Kwon Kim and Min Suk Shim

Polymers 2016, 8(2), 30; https://doi.org/10.3390/polym8020030 - 26 Jan 2016

Cited by 132 | Viewed by 17350

Abstract

In recent years, there have been major advances and increasing amounts of research on the utilization of natural polymeric materials as drug delivery vehicles due to their biocompatibility and biodegradability. Seaweed polysaccharides are abundant resources and have been extensively studied for several biological, [...] Read more.

In recent years, there have been major advances and increasing amounts of research on the utilization of natural polymeric materials as drug delivery vehicles due to their biocompatibility and biodegradability. Seaweed polysaccharides are abundant resources and have been extensively studied for several biological, biomedical, and functional food applications. The exploration of seaweed polysaccharides for drug delivery applications is still in its infancy. Alginate, carrageenan, fucoidan, ulvan, and laminarin are polysaccharides commonly isolated from seaweed. These natural polymers can be converted into nanoparticles (NPs) by different types of methods, such as ionic gelation, emulsion, and polyelectrolyte complexing. Ionic gelation and polyelectrolyte complexing are commonly employed by adding cationic molecules to these anionic polymers to produce NPs of a desired shape, size, and charge. In the present review, we have discussed the preparation of seaweed polysaccharide-based NPs using different types of methods as well as their usage as carriers for the delivery of various therapeutic molecules (e.g., proteins, peptides, anti-cancer drugs, and antibiotics). Seaweed polysaccharide-based NPs exhibit suitable particle size, high drug encapsulation, and sustained drug release with high biocompatibility, thereby demonstrating their high potential for safe and efficient drug delivery. Full article

(This article belongs to the Collection Polysaccharides)

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878 KiB

Open AccessArticle

Iron-Mediated Homogeneous ICAR ATRP of Methyl Methacrylate under ppm Level Organometallic Catalyst Iron(III) Acetylacetonate

by Jian Wu, Xiaowu Jiang, Lifen Zhang, Zhenping Cheng and Xiulin Zhu

Polymers 2016, 8(2), 29; https://doi.org/10.3390/polym8020029 - 26 Jan 2016

Cited by 23 | Viewed by 8207

Abstract

Atom Transfer Radical Polymerization (ATRP) is an important polymerization process in polymer synthesis. However, a typical ATRP system has some drawbacks. For example, it needs a large amount of transition metal catalyst, and it is difficult or expensive to remove the metal catalyst [...] Read more.

Atom Transfer Radical Polymerization (ATRP) is an important polymerization process in polymer synthesis. However, a typical ATRP system has some drawbacks. For example, it needs a large amount of transition metal catalyst, and it is difficult or expensive to remove the metal catalyst residue in products. In order to reduce the amount of catalyst and considering good biocompatibility and low toxicity of the iron catalyst, in this work, we developed a homogeneous polymerization system of initiators for continuous activator regeneration ATRP (ICAR ATRP) with just a ppm level of iron catalyst. Herein, we used oil-soluble iron (III) acetylacetonate (Fe(acac)₃) as the organometallic catalyst, 1,1′-azobis (cyclohexanecarbonitrile) (ACHN) with longer half-life period as the thermal initiator, ethyl 2-bromophenylacetate (EBPA) as the initiator, triphenylphosphine (PPh₃) as the ligand, toluene as the solvent and methyl methacrylate (MMA) as the model monomer. The factors related with the polymerization system, such as concentration of Fe(acac)₃ and ACHN and polymerization kinetics, were investigated in detail at 90 °C. It was found that a polymer with an acceptable molecular weight distribution (M_w/M_n = 1.43 at 45.9% of monomer conversion) could be obtained even with 1 ppm of Fe(acac)₃, making it needless to remove the residual metal in the resultant polymers, which makes such an ICAR ATRP process much more industrially attractive. The “living” features of this polymerization system were further confirmed by chain-extension experiment. Full article

(This article belongs to the Special Issue Controlled/Living Radical Polymerization)

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1801 KiB

Open AccessFeature PaperArticle

Magnetically-Responsive Hydrogels for Modulation of Chondrogenic Commitment of Human Adipose-Derived Stem Cells

by Elena G. Popa, Vítor E. Santo, Márcia T. Rodrigues and Manuela E. Gomes

Polymers 2016, 8(2), 28; https://doi.org/10.3390/polym8020028 - 25 Jan 2016

Cited by 32 | Viewed by 6804

Abstract

Magnetic nanoparticles (MNPs) are attractive tools to overcome limitations of current regenerative medicine strategies, demonstrating potential to integrate therapeutic and diagnostic functionalities in highly controlled systems. In traditional tissue engineering (TE) approaches, the MNPs association with stem cells in a three-dimensional (3D) template [...] Read more.

Magnetic nanoparticles (MNPs) are attractive tools to overcome limitations of current regenerative medicine strategies, demonstrating potential to integrate therapeutic and diagnostic functionalities in highly controlled systems. In traditional tissue engineering (TE) approaches, the MNPs association with stem cells in a three-dimensional (3D) template offers the possibility to achieve a mechano-magnetic responsive system, enabling remote control actuation. Herein, we propose to study the role of MNPs integrated in κ-carrageenan (κC) hydrogels in the cellular response of human adipose-derived stem cells (hASCs) aiming at cartilage TE applications. The results indicated that the concentration of MNPs in the κC hydrogels influences cellular behavior, tuning a positive effect on cell viability, cell content and metabolic activity of hASCs, with the most promising outcomes found in 5% MNP-κC matrices. Although hASCs laden in MNPs-free- and MNPs-κC hydrogels showed similar metabolic and proliferation levels, MNPs κC hydrogels under magnetic actuation evidenced an instructive effect on hASCs, at a gene expression level, towards chondrogenic phenotype even in basic medium cultures. Therefore, the MNPs-based systems developed in this study may contribute to advanced strategies towards cartilage-like engineered substitutes. Full article

(This article belongs to the Special Issue Polymers Applied in Tissue Engineering)

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Polymers, Volume 8, Issue 2 (February 2016) – 31 articles

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