Polymers

3837 KiB

Open AccessArticle

Smart Homopolymer Microgels: Influence of the Monomer Structure on the Particle Properties

by Bastian Wedel, Yvonne Hertle, Oliver Wrede, Johannes Bookhold and Thomas Hellweg

Polymers 2016, 8(4), 162; https://doi.org/10.3390/polym8040162 - 23 Apr 2016

Cited by 52 | Viewed by 11260

In this work, we compare the properties of smart homopolymer microgels based on N-n-propylacrylamide (NNPAM), N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM) synthesized under identical conditions. The particles are studied with respect to size, morphology, and swelling behavior using scanning electron and [...] Read more.

In this work, we compare the properties of smart homopolymer microgels based on N-n-propylacrylamide (NNPAM), N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM) synthesized under identical conditions. The particles are studied with respect to size, morphology, and swelling behavior using scanning electron and scanning force microscopy. In addition, light scattering techniques and fluorescent probes are employed to follow the swelling/de-swelling of the particles. Significant differences are found and discussed. Poly(N-n-propylacrylamide) (PNNPAM) microgels stand out due to their very sharp volume phase transition, whereas Poly(N-isopropylmethacrylamide) (PNIPMAM) particles are found to exhibit a more homogeneous network structure compared to the other two systems. Full article

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5270 KiB

Open AccessArticle

Stereocomplex-Reinforced PEGylated Polylactide Micelle for Optimized Drug Delivery

by Chunsheng Feng, Meihua Piao and Di Li

Polymers 2016, 8(4), 165; https://doi.org/10.3390/polym8040165 - 22 Apr 2016

Cited by 18 | Viewed by 6812

Abstract

The instability of PEGylated polylactide micelles is a challenge for drug delivery. Stereocomplex interaction between racemic polylactide chains with different configurations provides an effective strategy to enhance the stability of micelles as the nanocarriers of drugs. In this work, a stereocomplex micelle (SCM) [...] Read more.

The instability of PEGylated polylactide micelles is a challenge for drug delivery. Stereocomplex interaction between racemic polylactide chains with different configurations provides an effective strategy to enhance the stability of micelles as the nanocarriers of drugs. In this work, a stereocomplex micelle (SCM) self-assembled from the amphiphilic triblock copolymers comprising poly(ethylene glycol) (PEG), and dextrorotatory and levorotatory polylactides (PDLA and PLLA) was applied for efficient drug delivery. The spherical SCM showed the smallest scale and the lowest critical micelle concentration (CMC) than the micelles with single components attributed to the stereocomplex interaction between PDLA and PLLA. 10-Hydroxycamptothecin (HCPT) as a model antitumor drug was loaded into micelles. Compared with the loading micelles from individual PDLA and PLLA, the HCPT-loaded SCM exhibited the highest drug loading efficiency (DLE) and the slowest drug release in phosphate-buffered saline (PBS) at pH 7.4, indicating its enhanced stability in circulation. More fascinatingly, the laden SCM was demonstrated to have the highest cellular uptake of HCPT and suppress malignant cells most effectively in comparison to the HCPT-loaded micelles from single copolymer. In summary, the stereocomplex-enhanced PLA–PEG–PLA micelle may be promising for optimized drug delivery in the clinic. Full article

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

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5061 KiB

Open AccessArticle

Modelling and Validation of Synthesis of Poly Lactic Acid Using an Alternative Energy Source through a Continuous Reactive Extrusion Process

by Satya P. Dubey, Hrushikesh A. Abhyankar, Veronica Marchante, James L. Brighton, Kim Blackburn, Clive Temple, Björn Bergmann, Giang Trinh and Chantal David

Polymers 2016, 8(4), 164; https://doi.org/10.3390/polym8040164 - 22 Apr 2016

Cited by 23 | Viewed by 8155

Abstract

PLA is one of the most promising bio-compostable and bio-degradable thermoplastic polymers made from renewable sources. PLA is generally produced by ring opening polymerization (ROP) of lactide using the metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts in a suitable solvent. [...] Read more.

PLA is one of the most promising bio-compostable and bio-degradable thermoplastic polymers made from renewable sources. PLA is generally produced by ring opening polymerization (ROP) of lactide using the metallic/bimetallic catalyst (Sn, Zn, and Al) or other organic catalysts in a suitable solvent. In this work, reactive extrusion experiments using stannous octoate Sn(Oct)₂ and tri-phenyl phosphine (PPh)₃ were considered to perform ROP of lactide. Ultrasound energy source was used for activating and/or boosting the polymerization as an alternative energy (AE) source. Ludovic^® software, designed for simulation of the extrusion process, had to be modified in order to simulate the reactive extrusion of lactide and for the application of an AE source in an extruder. A mathematical model for the ROP of lactide reaction was developed to estimate the kinetics of the polymerization process. The isothermal curves generated through this model were then used by Ludovic software to simulate the “reactive” extrusion process of ROP of lactide. Results from the experiments and simulations were compared to validate the simulation methodology. It was observed that the application of an AE source boosts the polymerization of lactide monomers. However, it was also observed that the predicted residence time was shorter than the experimental one. There is potentially a case for reducing the residence time distribution (RTD) in Ludovic^® due to the ‘liquid’ monomer flow in the extruder. Although this change in parameters resulted in validation of the simulation, it was concluded that further research is needed to validate this assumption. Full article

(This article belongs to the Special Issue Computational Modeling and Simulation in Polymer)

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2588 KiB

Open AccessArticle

Biodegradable Polyphosphazene Based Peptide-Polymer Hybrids

by Anne Linhardt, Michael König, Wolfgang Schöfberger, Oliver Brüggemann, Alexander K. Andrianov and Ian Teasdale

Polymers 2016, 8(4), 161; https://doi.org/10.3390/polym8040161 - 22 Apr 2016

Cited by 30 | Viewed by 10289

Abstract

A novel series of peptide based hybrid polymers designed to undergo enzymatic degradation is presented, via macrosubstitution of a polyphosphazene backbone with the tetrapeptide Gly-Phe-Leu-Gly. Further co-substitution of the hybrid polymers with hydrophilic polyalkylene oxide Jeffamine M-1000 leads to water soluble and biodegradable [...] Read more.

A novel series of peptide based hybrid polymers designed to undergo enzymatic degradation is presented, via macrosubstitution of a polyphosphazene backbone with the tetrapeptide Gly-Phe-Leu-Gly. Further co-substitution of the hybrid polymers with hydrophilic polyalkylene oxide Jeffamine M-1000 leads to water soluble and biodegradable hybrid polymers. Detailed degradation studies, via ³¹P NMR spectroscopy, dynamic light scattering and field flow fractionation show the polymers degrade via a combination of enzymatic, as well as hydrolytic pathways. The peptide sequence was chosen due to its known property to undergo lysosomal degradation; hence, these degradable, water soluble polymers could be of significant interest for the use as polymer therapeutics. In this context, we investigated conjugation of the immune response modifier imiquimod to the polymers via the tetrapeptide and report the self-assembly behavior of the conjugate, as well as its enzymatically triggered drug release behavior. Full article

(This article belongs to the Special Issue Biodegradable Polymers)

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2476 KiB

Open AccessArticle

Synthesis of Highly Branched Polyolefins Using Phenyl Substituted α-Diimine Ni(II) Catalysts

by Fuzhou Wang, Ryo Tanaka, Zhengguo Cai, Yuushou Nakayama and Takeshi Shiono

Polymers 2016, 8(4), 160; https://doi.org/10.3390/polym8040160 - 22 Apr 2016

Cited by 39 | Viewed by 9948

Abstract

A series of α-diimine Ni(II) complexes containing bulky phenyl groups, [ArN = C(Naphth)C = NAr]NiBr₂ (Naphth: 1,8-naphthdiyl, Ar = 2,6-Me₂-4-PhC₆H₂ (C1); Ar = 2,4-Me₂-6-PhC₆H₂ (C2); Ar = 2-Me-4,6-Ph₂C₆H [...] Read more.

A series of α-diimine Ni(II) complexes containing bulky phenyl groups, [ArN = C(Naphth)C = NAr]NiBr₂ (Naphth: 1,8-naphthdiyl, Ar = 2,6-Me₂-4-PhC₆H₂ (C1); Ar = 2,4-Me₂-6-PhC₆H₂ (C2); Ar = 2-Me-4,6-Ph₂C₆H₂ (C3); Ar = 4-Me-2,6-Ph₂C₆H₂ (C4); Ar = 4-Me-2-PhC₆H₃ (C5); Ar = 2,4,6-Ph₃C₆H₂ (C6)), were synthesized and characterized. Upon activation with either diethylaluminum chloride (Et₂AlCl) or modified methylaluminoxane (MMAO), all Ni(II) complexes showed high activities in ethylene polymerization and produced highly branched amorphous polyethylene (up to 145 branches/1000 carbons). Interestingly, the sec-butyl branches were observed in polyethylene depending on polymerization temperature. Polymerization of 1-alkene (1-hexene, 1-octene, 1-decene and 1-hexadecene) with C1-MMAO at room temperature resulted in branched polyolefins with narrow M_w/M_n values (ca. 1.2), which suggested a living polymerization. The polymerization results indicated the possibility of precise microstructure control, depending on the polymerization temperature and types of monomers. Full article

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2073 KiB

Open AccessArticle

The Effects of in Situ-Formed Silver Nanoparticles on the Electrical Properties of Epoxy Resin Filled with Silver Nanowires

by Gwang-Seok Song, Dai Soo Lee and Ilho Kang

Polymers 2016, 8(4), 157; https://doi.org/10.3390/polym8040157 - 21 Apr 2016

Cited by 10 | Viewed by 6738

Abstract

A novel method for preparing epoxy/silver nanocomposites was developed via the in situ formation of silver nanoparticles (AgNPs) within the epoxy resin matrix while using silver nanowires (AgNWs) as a conductive filler. The silver–imidazole complex was synthesized from silver acetate (AgAc) and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole [...] Read more.

A novel method for preparing epoxy/silver nanocomposites was developed via the in situ formation of silver nanoparticles (AgNPs) within the epoxy resin matrix while using silver nanowires (AgNWs) as a conductive filler. The silver–imidazole complex was synthesized from silver acetate (AgAc) and 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole (imidazole). AgNPs were generated in situ during the curing of the epoxy resin through the thermal decomposition of the AgAc–imidazole complex, which was capable of reducing Ag⁺ to Ag by itself. The released imidazole acted as a catalyst to cure the epoxy. Additionally, after the curing process, the in situ-generated AgNPs were stabilized by the formed epoxy network. Therefore, by using the thermal decomposition method, uniformly dispersed AgNPs of approximately 100 nm were formed in situ in the epoxy matrix filled with AgNWs. It was observed that the nanocomposites containing in situ-formed AgNPs exhibited isotropic electrical properties in the epoxy resins in the presence of AgNWs. Full article

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

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7028 KiB

Open AccessFeature PaperReview

Design and Utility of Metal/Metal Oxide Nanoparticles Mediated by Thioether End-Functionalized Polymeric Ligands

by Shumaila Razzaque, Syed Zajif Hussain, Irshad Hussain and Bien Tan

Polymers 2016, 8(4), 156; https://doi.org/10.3390/polym8040156 - 21 Apr 2016

Cited by 48 | Viewed by 12671

Abstract

The past few decades have witnessed significant advances in the development of functionalized metal/metal oxide nanoparticles including those of inorganic noble metals and magnetic materials stabilized by various polymeric ligands. Recent applications of such functionalized nanoparticles, including those in bio-imaging, sensing, catalysis, drug [...] Read more.

The past few decades have witnessed significant advances in the development of functionalized metal/metal oxide nanoparticles including those of inorganic noble metals and magnetic materials stabilized by various polymeric ligands. Recent applications of such functionalized nanoparticles, including those in bio-imaging, sensing, catalysis, drug delivery, and other biomedical applications have triggered the need for their facile and reproducible preparation with a better control over their size, shape, and surface chemistry. In this perspective, the multidentate polymer ligands containing functional groups like thiol, thioether, and ester are important surface ligands for designing and synthesizing stable nanoparticles (NPs) of metals or their oxides with reproducibility and high yield. These ligands have offered an unprecedented control over the particle size of both nanoparticles and nanoclusters with enhanced colloidal stability, having tunable solubility in aqueous and organic media, and tunable optical, magnetic, and fluorescent properties. This review summarizes the synthetic methodologies and stability of nanoparticles and fluorescent nanoclusters of metals (Au, Ag, Cu, Pt, and other transition metal oxides) prepared by using thioether based ligands and highlights their applications in bio-imaging, sensing, drug delivery, magnetic resonance imaging (MRI), and catalysis. The future applications of fluorescent metal NPs like thermal gradient optical imaging, single molecule optoelectronics, sensors, and optical components of the detector are also envisaged. Full article

(This article belongs to the Collection Featured Mini Reviews in Polymer Science)

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2456 KiB

Open AccessArticle

Effect of Small Reaction Locus in Free-Radical Polymerization: Conventional and Reversible-Deactivation Radical Polymerization

by Hidetaka Tobita

Polymers 2016, 8(4), 155; https://doi.org/10.3390/polym8040155 - 20 Apr 2016

Cited by 8 | Viewed by 5376

Abstract

When the size of a polymerization locus is smaller than a few hundred nanometers, such as in miniemulsion polymerization, each locus may contain no more than one key-component molecule, and the concentration may become much larger than the corresponding bulk polymerization, leading to [...] Read more.

When the size of a polymerization locus is smaller than a few hundred nanometers, such as in miniemulsion polymerization, each locus may contain no more than one key-component molecule, and the concentration may become much larger than the corresponding bulk polymerization, leading to a significantly different rate of polymerization. By focusing attention on the component having the lowest concentration within the species involved in the polymerization rate expression, a simple formula can predict the particle diameter below which the polymerization rate changes significantly from the bulk polymerization. The key component in the conventional free-radical polymerization is the active radical and the polymerization rate becomes larger than the corresponding bulk polymerization when the particle size is smaller than the predicted diameter. The key component in reversible-addition-fragmentation chain-transfer (RAFT) polymerization is the intermediate species, and it can be used to predict the particle diameter below which the polymerization rate starts to increase. On the other hand, the key component is the trapping agent in stable-radical-mediated polymerization (SRMP) and atom-transfer radical polymerization (ATRP), and the polymerization rate decreases as the particle size becomes smaller than the predicted diameter. Full article

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

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3008 KiB

Open AccessArticle

Poly-Lactide/Exfoliated C30B Interactions and Influence on Thermo-Mechanical Properties Due to Artificial Weathering

by Wendy Margarita Chávez-Montes, Guillermo González-Sánchez and Sergio Gabriel Flores-Gallardo

Polymers 2016, 8(4), 154; https://doi.org/10.3390/polym8040154 - 20 Apr 2016

Cited by 6 | Viewed by 7251

Abstract

Thermal stability as well as enhanced mechanical properties of poly-lactide (PLA) can increase PLA applications for short-use products. The conjunction of adequate molecular weight (M_W) as well as satisfactory thermo-mechanical properties, together, can lead to the achievement of suitable properties. [...] Read more.

Thermal stability as well as enhanced mechanical properties of poly-lactide (PLA) can increase PLA applications for short-use products. The conjunction of adequate molecular weight (M_W) as well as satisfactory thermo-mechanical properties, together, can lead to the achievement of suitable properties. However, PLA is susceptible to thermal degradation and thus an undesired decay of M_W and a decrease of its mechanical properties during processing. To avoid this PLA degradation, nanofiller is incorporated as reinforcement to increase its thermo-mechanical properties. There are many papers focusing on filler effects on the thermal stability and mechanical properties of PLA/nanocomposites; however, these investigations lack an explanation of polymer/filler interactions. We propose interactions between PLA and Cloisite30B (C30B) as nanofiller. We also study the effects on the thermal and mechanical properties due to molecular weight decay after exposure to artificial weathering. PLA blank and nanocomposites were subjected to three time treatments (0, 176, and 360 h) of exposure to artificial weathering in order to achieve comparable materials with different M_W. M_W was acquired by means of Gel Permeation Chromatography (GPC). Thermo-mechanical properties were investigated through Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Dynamic Mechanical Thermal Analysis (DMTA) and Fourier Transform Infrared Spectroscopy (FTIR). Full article

(This article belongs to the Special Issue Biodegradable Polymers)

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1882 KiB

Open AccessArticle

Physical and Mechanical Evaluation of Five Suture Materials on Three Knot Configurations: An in Vitro Study

by Desire Abellán, José Nart, Andrés Pascual, Robert E. Cohen and Javier D. Sanz-Moliner

Polymers 2016, 8(4), 147; https://doi.org/10.3390/polym8040147 - 20 Apr 2016

Cited by 36 | Viewed by 9707

Abstract

The aim of this study was to evaluate and compare the mechanical properties of five suture materials on three knot configurations when subjected to different physical conditions. Five 5-0 (silk, polyamide 6/66, polyglycolic acid, glycolide-e-caprolactone copolymer, polytetrafluoroethylene) suture materials were used. Ten samples [...] Read more.

The aim of this study was to evaluate and compare the mechanical properties of five suture materials on three knot configurations when subjected to different physical conditions. Five 5-0 (silk, polyamide 6/66, polyglycolic acid, glycolide-e-caprolactone copolymer, polytetrafluoroethylene) suture materials were used. Ten samples per group of each material were used. Three knot configurations were compared A.2=1=1 (forward–forward–reverse), B.2=1=1 (forward–reverse–forward), C.1=2=1 (forward–forward–reverse). Mechanical properties (failure load, elongation, knot slippage/breakage) were measured using a universal testing machine. Samples were immersed in three different pH concentrations (4,7,9) at room temperature for 7 and 14 days. For the thermal cycle process, sutures were immersed in two water tanks at different temperatures (5 and 55 °C). Elongation and failure load were directly dependent on the suture material. Polyglycolic acid followed by glycolide-e-caprolactone copolymer showed the most knot failure load, while polytetrafluoroethylene showed the lowest (P < 0.001). Physical conditions had no effect on knot failure load (P = 0.494). Statistically significant differences were observed between knot configurations (P = 0.008). Additionally, individual assessment of suture material showed statistically significant results for combinations of particular knot configurations. Physical conditions, such as pH concentration and thermal cycle process, have no influence on suture mechanical properties. However, knot failure load depends on the suture material and knot configuration used. Consequently, specific suturing protocols might be recommended to obtain higher results of knot security. Full article

(This article belongs to the Special Issue Biodegradable Polymers)

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4080 KiB

Open AccessArticle

Bio-Based Resin Reinforced with Flax Fiber as Thermorheologically Complex Materials

by Ali Amiri, Arvin Yu, Dean Webster and Chad Ulven

Polymers 2016, 8(4), 153; https://doi.org/10.3390/polym8040153 - 19 Apr 2016

Cited by 30 | Viewed by 7879

Abstract

With the increase in structural applications of bio-based composites, the study of long-term creep behavior of these materials turns into a significant issue. Because of their bond type and structure, natural fibers and thermoset resins exhibit nonlinear viscoelastic behavior. Time-temperature superposition (TTS) provides [...] Read more.

With the increase in structural applications of bio-based composites, the study of long-term creep behavior of these materials turns into a significant issue. Because of their bond type and structure, natural fibers and thermoset resins exhibit nonlinear viscoelastic behavior. Time-temperature superposition (TTS) provides a useful tool to overcome the challenge of the long time required to perform the tests. The TTS principle assumes that the effect of temperature and time are equivalent when considering the creep behavior, therefore creep tests performed at elevated temperatures may be converted to tests performed at longer times. In this study, flax fiber composites were processed with a novel liquid molding methacrylated epoxidized sucrose soyate (MESS) resin. Frequency scans of flax/MESS composites were obtained at different temperatures and storage modulus and loss modulus were recorded and the application of horizontal and vertical shift factors to these viscoelastic functions were studied. In addition, short-term strain creep at different temperatures was measured and curves were shifted with solely horizontal, and with both horizontal and vertical shift factors. The resulting master curves were compared with a 24-h creep test and two extrapolated creep models. The findings revealed that use of both horizontal and vertical shift factors will result in a smoother master curves for loss modulus and storage modulus, while use of only horizontal shift factors for creep data provides acceptable creep strain master curves. Based on the findings of this study, flax/MESS composites can be considered as thermorheologically complex materials. Full article

(This article belongs to the Special Issue Renewable Polymeric Adhesives)

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1746 KiB

Open AccessArticle

Opening New Gates for the Modification of PVC or Other PVC Derivatives: Synthetic Strategies for the Covalent Binding of Molecules to PVC

by Rodrigo Navarro, Mónica Pérez Perrino, Carolina García, Carlos Elvira, Alberto Gallardo and Helmut Reinecke

Polymers 2016, 8(4), 152; https://doi.org/10.3390/polym8040152 - 19 Apr 2016

Cited by 36 | Viewed by 9425

Abstract

Several synthetic strategies based on the use of substituted aromatic and hetero-aromatic thiols for the covalent binding of modifier compounds to PVC are described. A variety of aliphatic alcohols and amines are linked to the aromatic or heteroaromatic rings via highly active functionalities [...] Read more.

Several synthetic strategies based on the use of substituted aromatic and hetero-aromatic thiols for the covalent binding of modifier compounds to PVC are described. A variety of aliphatic alcohols and amines are linked to the aromatic or heteroaromatic rings via highly active functionalities as the isocyanate, acidchloride, or chlorosulfonyl group, and the three chlorine atoms of trichlorotriazine. The first three pathways lead to protected aromatic disulfides obtaining the substituted aromatic thiols by reduction as a final step of an unprecedented synthetic route. The second approach, in a novel, extremely efficient, and scalable process, uses the particular selectivity of trichlorotriazine to connect aliphatic amines, alcohols, and thiols to the ring and creates the thiol via nucleophilic substitution of a heteroaromatic halogen by thiourea and subsequent hydrolysis. Most of the modifier compounds were linked to the polymer chains with high degrees of anchorage. The presented approaches are highly versatile as different activations of aromatic and heteroaromatic rings are used. Therefore, many types of tailored functional nucleophiles may be anchored to PVC providing non-migrating materials with a broad range of applications and properties. Full article

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10111 KiB

Open AccessFeature PaperArticle

The in Vitro and in Vivo Degradation of Cross-Linked Poly(trimethylene carbonate)-Based Networks

by Liqun Yang, Jianxin Li, Miao Li and Zhongwei Gu

Polymers 2016, 8(4), 151; https://doi.org/10.3390/polym8040151 - 19 Apr 2016

Cited by 31 | Viewed by 8152

Abstract

The degradation of the poly(trimethylene carbonate) (PTMC) and poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-co-CL)) networks cross-linked by 0.01 and 0.02 mol % 2,2′-bis(trimethylene carbonate-5-yl)-butylether (BTB) was carried out in the conditions of hydrolysis and enzymes in vitro and subcutaneous implantation in vivo [...] Read more.

The degradation of the poly(trimethylene carbonate) (PTMC) and poly(trimethylene carbonate-co-ε-caprolactone) (P(TMC-co-CL)) networks cross-linked by 0.01 and 0.02 mol % 2,2′-bis(trimethylene carbonate-5-yl)-butylether (BTB) was carried out in the conditions of hydrolysis and enzymes in vitro and subcutaneous implantation in vivo. The results showed that the cross-linked PTMC networks exhibited much faster degradation in enzymatic conditions in vitro and in vivo versus in a hydrolysis case due to the catalyst effect of enzymes; the weight loss and physical properties of the degraded networks were dependent on the BTB amount. The morphology observation in lipase and in vivo illustrated that enzymes played an important role in the surface erosion of cross-linked PTMC. The hydrolytic degradation rate of the cross-linked P(TMC-co-CL) networks increased with increasing ε-caprolactone (CL) content in composition due to the preferential cleavage of ester bonds. Cross-linking is an effective strategy to lower the degradation rate and enhance the form-stability of PTMC-based materials. Full article

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

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5857 KiB

Open AccessArticle

Processing of Polysulfone to Free Flowing Powder by Mechanical Milling and Spray Drying Techniques for Use in Selective Laser Sintering

by Nicolas Mys, Ruben Van De Sande, An Verberckmoes and Ludwig Cardon

Polymers 2016, 8(4), 150; https://doi.org/10.3390/polym8040150 - 19 Apr 2016

Cited by 34 | Viewed by 10954

Abstract

Polysulfone (PSU) has been processed into powder form by ball milling, rotor milling, and spray drying technique in an attempt to produce new materials for Selective Laser Sintering purposes. Both rotor milling and spray drying were adept to make spherical particles that can [...] Read more.

Polysulfone (PSU) has been processed into powder form by ball milling, rotor milling, and spray drying technique in an attempt to produce new materials for Selective Laser Sintering purposes. Both rotor milling and spray drying were adept to make spherical particles that can be used for this aim. Processing PSU pellets by rotor milling in a three-step process resulted in particles of 51.8 μm mean diameter, whereas spray drying could only manage a mean diameter of 26.1 μm. The resulting powders were characterized using Differential Scanning Calorimetry (DSC), Gel Permeation Chromatography (GPC) and X-ray Diffraction measurements (XRD). DSC measurements revealed an influence of all processing techniques on the thermal behavior of the material. Glass transitions remained unaffected by spray drying and rotor milling, yet a clear shift was observed for ball milling, along with a large endothermic peak in the high temperature region. This was ascribed to the imparting of an orientation into the polymer chains due to the processing method and was confirmed by XRD measurements. Of all processed powder samples, the ball milled sample was unable to dissolve for GPC measurements, suggesting degradation by chain scission and subsequent crosslinking. Spray drying and rotor milling did not cause significant degradation. Full article

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2762 KiB

Open AccessArticle

²H Solid-State NMR Analysis of the Dynamics and Organization of Water in Hydrated Chitosan

by Fenfen Wang, Rongchun Zhang, Tiehong Chen and Pingchuan Sun

Polymers 2016, 8(4), 149; https://doi.org/10.3390/polym8040149 - 19 Apr 2016

Cited by 12 | Viewed by 6855

Abstract

Understanding water–biopolymer interactions, which strongly affect the function and properties of biopolymer-based tissue engineering and drug delivery materials, remains a challenge. Chitosan, which is an important biopolymer for the construction of artificial tissue grafts and for drug delivery, has attracted extensive attention in [...] Read more.

Understanding water–biopolymer interactions, which strongly affect the function and properties of biopolymer-based tissue engineering and drug delivery materials, remains a challenge. Chitosan, which is an important biopolymer for the construction of artificial tissue grafts and for drug delivery, has attracted extensive attention in recent decades, where neutralization with an alkali solution can substantially enhance the final properties of chitosan films cast from an acidic solution. In this work, to elucidate the effect of water on the properties of chitosan films, we investigated the dynamics and different states of water in non-neutralized (CTS-A) and neutralized (CTS-N) hydrated chitosan by mobility selective variable-temperature (VT) ²H solid-state NMR spectroscopy. Four distinct types of water exist in all of the samples with regards to dynamic behavior. First, non-freezable, rigid and strongly bound water was found in the crystalline domain at low temperatures. The second component consists of weakly bound water, which is highly mobile and exhibits isotropic motion, even below 260 K. Another type of water undergoes well-defined 180° flips around their bisector axis. Moreover, free water is also present in the films. For the CTS-A sample in particular, another special water species were bounded to acetic acid molecules via strong hydrogen bonding. In the case of CTS-N, the onset of motions of the weakly bound water molecules at 260 K was revealed by ²H-NMR spectroscopy. This water is not crystalline, even below 260 K, which is also the major contribution to the flexibility of chitosan chains and thus toughness of materials. By contrast, such motion was not observed in CTS-A. On the basis of the ²H solid-state NMR results, it is concluded that the unique toughness of CTS-N mainly originates from the weakly bound water as well as the interactions between water and the chitosan chains. Full article

(This article belongs to the Collection Polysaccharides)

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1564 KiB

Open AccessArticle

Mesogenic Polyelectrolyte Gels Absorb Organic Solvents and Liquid Crystalline Molecules

by Yusuke Nishikori, Kazuya Iseda, Kenta Kokado and Kazuki Sada

Polymers 2016, 8(4), 148; https://doi.org/10.3390/polym8040148 - 19 Apr 2016

Cited by 9 | Viewed by 6120

Abstract

In this paper, mesogenic polyelectrolyte gels (MPEgels) tethering mesogenic groups on the side chains were synthesized from a mesogenic monomer and ionic monomer via a conventional radical polymerization process. The obtained MPEgels absorbed various organic solvents in a wide range of dielectric constants [...] Read more.

In this paper, mesogenic polyelectrolyte gels (MPEgels) tethering mesogenic groups on the side chains were synthesized from a mesogenic monomer and ionic monomer via a conventional radical polymerization process. The obtained MPEgels absorbed various organic solvents in a wide range of dielectric constants from chloroform (ε = 7.6) to DMSO (ε = 46.5). The electrostatic repulsion among the polymer chains and the osmotic pressure between the interior and exterior of the MPEgel is responsible for the high swelling ability, revealed by the common ion effect using tetra(n-hexyl)ammonium tetra(3,5-bis(trifluoromethyl)phenylborate (THATFPB). The obtained MPEgels could also absorb liquid crystalline molecules such as 4-cyano-4’-pentylbiphenyl (5CB), analogously caused by the above-mentioned polyelectrolyte characteristic. The MPEgels exhibited liquid crystal transition temperature (T_NI) on differential scanning calorimetry (DSC) measurement, and the increase of the ionic group content lowered T_NI. The MPEgels absorbing liquid crystalline molecules exhibited differing T_NI, dependent on the compatibility of the mesogenic group on the side chain to the liquid crystalline molecule. Full article

(This article belongs to the Collection Polyelectrolytes)

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1985 KiB

Open AccessArticle

Synthesis of Monodisperse Silica Particles Grafted with Concentrated Ionic Liquid-Type Polymer Brushes by Surface-Initiated Atom Transfer Radical Polymerization for Use as a Solid State Polymer Electrolyte

by Takashi Morinaga, Saika Honma, Takeo Ishizuka, Toshio Kamijo, Takaya Sato and Yoshinobu Tsujii

Polymers 2016, 8(4), 146; https://doi.org/10.3390/polym8040146 - 16 Apr 2016

Cited by 17 | Viewed by 9281

Abstract

A polymerizable ionic liquid, N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEMM-TFSI), was polymerized via copper-mediated atom transfer radical polymerization (ATRP). The polymerization proceeded in a living manner producing well-defined poly(DEMM-TFSI) of target molecular weight up to about 400 K (including [...] Read more.

A polymerizable ionic liquid, N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEMM-TFSI), was polymerized via copper-mediated atom transfer radical polymerization (ATRP). The polymerization proceeded in a living manner producing well-defined poly(DEMM-TFSI) of target molecular weight up to about 400 K (including a polycation and an counter anion). The accurate molecular weight as determined by a GPC analysis combined with a light scattering measurement, and the molecular weight values obtained exhibited good agreement with the theoretical values calculated from the initial molar ratio of DEMM-TFSI and the monomer conversion. Surface-initiated ATRP on the surface of monodisperse silica particles (SiPs) with various diameters was successfully performed, producing SiPs grafted with well-defined poly(DEMM-TFSI) with a graft density as high as 0.15 chains/nm². Since the composite film made from the silica-particle-decorated polymer brush and ionic liquid shows a relatively high ionic conductivity, we have evaluated the relationship between the grafted brush chain length and the ionic conductivity. Full article

(This article belongs to the Collection Silicon-Containing Polymeric Materials)

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4109 KiB

Open AccessArticle

Modification of Spherical Polyelectrolyte Brushes by Layer-by-Layer Self-Assembly as Observed by Small Angle X-ray Scattering

by Yuchuan Tian, Li Li, Haoya Han, Weihua Wang, Yunwei Wang, Zhishuang Ye and Xuhong Guo

Polymers 2016, 8(4), 145; https://doi.org/10.3390/polym8040145 - 15 Apr 2016

Cited by 16 | Viewed by 6978

Abstract

Multilayer modified spherical polyelectrolyte brushes were prepared through alternate deposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly-l-aspartic acid (PAsp) onto negatively charged spherical poly(acrylic acid) (PAA) brushes (SPBs) on a poly(styrene) core. The charge reversal determined by the [...] Read more.

Multilayer modified spherical polyelectrolyte brushes were prepared through alternate deposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly-l-aspartic acid (PAsp) onto negatively charged spherical poly(acrylic acid) (PAA) brushes (SPBs) on a poly(styrene) core. The charge reversal determined by the zeta potential indicated the success of layer-by-layer (LBL) deposition. The change of the structure during the construction of multilayer modified SPBs was observed by small-angle X-ray scattering (SAXS). SAXS results indicated that some PAH chains were able to penetrate into the PAA brush for the PAA-PAH double-layer modified SPBs whereas part of the PAH moved towards the outer layer when the PAsp layer was loaded to form a PAA-PAH-PAsp triple-layer system. The multilayer modified SPBs were stable upon changing the pH (5 to 9) and ionic strength (1 to 100 mM). The triple-layer modified SPBs were more tolerated to high pH (even at 11) compared to the double-layer ones. SAXS is proved to be a powerful tool for studying the inner structure of multilayer modified SPBs, which can establish guidelines for the a range of potential applications of multilayer modified SPBs. Full article

(This article belongs to the Collection Polyelectrolytes)

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11107 KiB

Open AccessArticle

Rapid Hydrophilization of Model Polyurethane/Urea (PURPEG) Polymer Scaffolds Using Oxygen Plasma Treatment

by Rok Zaplotnik, Alenka Vesel, Gregor Primc, Xiangyu Liu, Kevin C. Chen, Chiju Wei, Kaitian Xu and Miran Mozetic

Polymers 2016, 8(4), 144; https://doi.org/10.3390/polym8040144 - 15 Apr 2016

Cited by 3 | Viewed by 6998

Abstract

Polyurethane/urea copolymers based on poly(ethylene glycol) (PURPEG) were exposed to weakly ionized, highly reactive low-pressure oxygen plasma to improve their sorption kinetics. The plasma was sustained with an inductively coupled radiofrequency generator operating at various power levels in either E-mode (up to the [...] Read more.

Polyurethane/urea copolymers based on poly(ethylene glycol) (PURPEG) were exposed to weakly ionized, highly reactive low-pressure oxygen plasma to improve their sorption kinetics. The plasma was sustained with an inductively coupled radiofrequency generator operating at various power levels in either E-mode (up to the forward power of 300 W) or H-mode (above 500 W). The treatments that used H-mode caused nearly instant thermal degradation of the polymer samples. The density of the charged particles in E-mode was on the order of 10¹⁶ m⁻³, which prevented material destruction upon plasma treatment, but the density of neutral O-atoms in the ground state was on the order of 10²¹ m⁻³. The evolution of plasma characteristics during sample treatment in E-mode was determined by optical emission spectroscopy; surface modifications were determined by water adsorption kinetics and X-ray photoelectron spectroscopy; and etching intensity was determined by residual gas analysis. The results showed moderate surface functionalization with hydroxyl and carboxyl/ester groups, weak etching at a rate of several nm/s, rather slow activation down to a water contact angle of 30° and an ability to rapidly absorb water. Full article

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

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3760 KiB

Open AccessArticle

Analysis and Testing of Bisphenol A—Free Bio-Based Tannin Epoxy-Acrylic Adhesives

by Shayesteh Jahanshahi, Antonio Pizzi, Ali Abdulkhani and Alireza Shakeri

Polymers 2016, 8(4), 143; https://doi.org/10.3390/polym8040143 - 15 Apr 2016

Cited by 37 | Viewed by 12250

Abstract

A tannin-based epoxy acrylate resin was prepared from glycidyl ether tannin (GET) and acrylic acid. The influence of the reaction condition for producing tannin epoxy acrylate was studied by FT-MIR, ¹³C-NMR, MALDI-TOF spectroscopy and shear strength. The best reaction conditions for producing [...] Read more.

A tannin-based epoxy acrylate resin was prepared from glycidyl ether tannin (GET) and acrylic acid. The influence of the reaction condition for producing tannin epoxy acrylate was studied by FT-MIR, ¹³C-NMR, MALDI-TOF spectroscopy and shear strength. The best reaction conditions for producing tannin epoxy acrylate resin without bisphenol A was by reaction between GET and acrylic acid in the presence of a catalyst and hydroquinone at 95 °C for 12 h. FT-MIR, ¹³C-NMR and MALDI-TOF analysis have confirmed that the resin has been prepared under these conditions. The joints bonded with this resin were tested for block shear strength. The results obtained indicated that the best strength performance was obtained by the bioepoxy-acrylate adhesive resin prepared at 95 °C for a 12-h reaction. Full article

(This article belongs to the Special Issue Renewable Polymeric Adhesives)

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3960 KiB

Open AccessArticle

Effect of Rubber Nanoparticle Agglomeration on Properties of Thermoplastic Vulcanizates during Dynamic Vulcanization

by Hanguang Wu, Ming Tian, Liqun Zhang, Hongchi Tian, Youping Wu, Nanying Ning and Guo-Hua Hu

Polymers 2016, 8(4), 127; https://doi.org/10.3390/polym8040127 - 15 Apr 2016

Cited by 37 | Viewed by 8037

Abstract

We previously reported that the dispersed rubber microparticles in ethylene-propylene-diene monomer (EPDM)/polypropylene (PP) thermoplastic vulcanizates (TPVs) are actually agglomerates of rubber nanoparticles. In this study, based on this new understanding of the microstructure of TPV, we further revealed the microstructure-properties relationship of EPDM/PP [...] Read more.

We previously reported that the dispersed rubber microparticles in ethylene-propylene-diene monomer (EPDM)/polypropylene (PP) thermoplastic vulcanizates (TPVs) are actually agglomerates of rubber nanoparticles. In this study, based on this new understanding of the microstructure of TPV, we further revealed the microstructure-properties relationship of EPDM/PP TPV during dynamic vulcanization, especially the effect of the size of rubber nanoparticle agglomerates (d_n), the thicknesses of PP ligaments (ID_poly) and the rubber network on the properties of EPDM/PP TPV. We were able to simultaneously obtain a high tensile strength, elongation at break, elastic modulus, and elasticity for the EPDM/PP TPV by the achievement of a smaller d_n, a thinner ID_poly and a denser rubber network. Interestingly, the effect of d_n and ID_poly on the elastic modulus of EPDM/PP TPV composed of rubber nanoparticle agglomerates is different from that of EPDM/PP TPVs composed of rubber microparticles reported previously. The deformation behavior of the TPVs during stretching was studied to understand the mechanism for the achievement of good mechanical properties. Interestingly, the rubber nanoparticle agglomerates are oriented along the tensile direction during stretching. The TPV samples with smaller and more numerous rubber nanoparticle agglomerates can slow down the development of voids and cracks more effectively, thus leading to increase in tensile strength and elongation at break of the EPDM/PP TPV. Full article

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Open AccessArticle

Density Functional Theory of Polymer Structure and Conformations

by Zhaoyang Wei, Nanying Ning, Liqun Zhang, Ming Tian and Jianguo Mi

Polymers 2016, 8(4), 121; https://doi.org/10.3390/polym8040121 - 15 Apr 2016

Cited by 12 | Viewed by 8512

Abstract

We present a density functional approach to quantitatively evaluate the microscopic conformations of polymer chains with consideration of the effects of chain stiffness, polymer concentration, and short chain molecules. For polystyrene (PS), poly(ethylene oxide) (PEO), and poly(methyl methacrylate) (PMMA) melts with low-polymerization degree, [...] Read more.

We present a density functional approach to quantitatively evaluate the microscopic conformations of polymer chains with consideration of the effects of chain stiffness, polymer concentration, and short chain molecules. For polystyrene (PS), poly(ethylene oxide) (PEO), and poly(methyl methacrylate) (PMMA) melts with low-polymerization degree, as chain length increases, they display different stretching ratios and show non-universal scaling exponents due to their different chain stiffnesses. In good solvent, increase of PS concentration induces the decline of gyration radius. For PS blends containing short (m₁ = 1 − 100) and long (m = 100) chains, the expansion of long chains becomes unobvious once m 1 is larger than 40, which is also different to the scaling properties of ideal chain blends. Full article

(This article belongs to the Special Issue Computational Modeling and Simulation in Polymer)

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3322 KiB

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pH-Triggered Sheddable Shielding System for Polycationic Gene Carriers

by Jialiang Xia, Huayu Tian, Jie Chen, Lin Lin, Zhaopei Guo, Bing Han, Hongyan Yang and Zongcai Feng

Polymers 2016, 8(4), 141; https://doi.org/10.3390/polym8040141 - 14 Apr 2016

Cited by 5 | Viewed by 5662

Abstract

For improving the therapeutic efficiency of tumors and decreasing undesirable side effects, ternary complexes were developed by coating pH-sensitive PEG-b-PLL-g-succinylsulfathiazole (hereafter abbreviated as PPSD) with DNA/PEI polyplexes via electrostatic interaction. PPSD can efficiently shield the surface charge of DNA/PEI. [...] Read more.

For improving the therapeutic efficiency of tumors and decreasing undesirable side effects, ternary complexes were developed by coating pH-sensitive PEG-b-PLL-g-succinylsulfathiazole (hereafter abbreviated as PPSD) with DNA/PEI polyplexes via electrostatic interaction. PPSD can efficiently shield the surface charge of DNA/PEI. The gene transfection efficiency of ternary complexes was lower than that of DNA/PEI at pH 7.4; however, it recovered to the same level as that of DNA/PEI at pH 6.0, attributed to the pH-triggered release of DNA/PEI from ternary complexes. Cell uptake results also exhibited the same trend as transfection at different pH values. The suitable ability for pH-triggered shielding/deshielding estimated that PPSD demonstrates potential as a shielding system for use in in vivo gene delivery. Full article

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

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3043 KiB

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Transparent Blend of Poly(Methylmethacrylate)/Cellulose Acetate Butyrate for the Protection from Ultraviolet

by Raouf Mahmood Raouf, Zaidan Abdul Wahab, Nor Azowa Ibrahim, Zainal Abidin Talib and Buong Woei Chieng

Polymers 2016, 8(4), 128; https://doi.org/10.3390/polym8040128 - 14 Apr 2016

Cited by 17 | Viewed by 7594

Abstract

The use of transparent polymers as an alternative to glass has become widespread. However, the direct exposure of these materials to climatic conditions of sunlight and heat decrease the lifetime cost of these products. The aim of this study was to minimize the [...] Read more.

The use of transparent polymers as an alternative to glass has become widespread. However, the direct exposure of these materials to climatic conditions of sunlight and heat decrease the lifetime cost of these products. The aim of this study was to minimize the harm caused by ultraviolet (UV) radiation exposure to transparent poly(methylmethacrylate) (PMMA), which usually leads to changes in the physical and chemical properties of these materials and reduced performance. This was achieved using environmentally friendly cellulose acetate butyrate (CAB). The optical, morphological, and thermal properties of CAB blended with transparent PMMA was studied using UV-VIS spectrophotometry, scanning electron microscopy, X-ray diffraction, dynamic mechanical analysis, and thermal gravimetric analysis. The results show that CAB was able to reduce the effects of UV radiation by making PMMA more transparent to UV light, thereby preventing the negative effects of trapped radiation within the compositional structure, while maintaining the amorphous structure of the blend. The results also show that CAB blended with PMMA led to some properties commensurate with the requirements of research in terms of a slight increase in the value of the modulus and the glass transition temperature for the PMMA/CAB blend. Full article

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1166 KiB

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Enzyme-Catalyzed Synthesis of Water-Soluble Conjugated Poly[2-(3-thienyl)-Ethoxy-4-Butylsulfonate]

by Yun Zhao, Hongyan Zhu, Xinyang Wang, Yingying Liu, Xiang Wu, Heyuan Zhou and Zhonghai Ni

Polymers 2016, 8(4), 139; https://doi.org/10.3390/polym8040139 - 13 Apr 2016

Cited by 6 | Viewed by 6601

Abstract

An environmentally friendly water-soluble conjugated polythiophene poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] (PTEBS) has been found to be effective for making hybrid solar cells. In this work, we first report the enzyme-catalyzed polymerization of (3-thienyl)-ethoxy-4-butylsulfonate (TEBS) using horseradish peroxidase (HRP) enzyme as a catalyst and hydrogen peroxide (H [...] Read more.

An environmentally friendly water-soluble conjugated polythiophene poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] (PTEBS) has been found to be effective for making hybrid solar cells. In this work, we first report the enzyme-catalyzed polymerization of (3-thienyl)-ethoxy-4-butylsulfonate (TEBS) using horseradish peroxidase (HRP) enzyme as a catalyst and hydrogen peroxide (H₂O₂) as an oxidant in an aqueous buffer. This enzyme-catalyzed polymerization is a “green synthesis process” for the synthesis of water-soluble conjugated PTEBS, the benefits of which include a simple setting, high yields, and an environmentally friendly route. Fourier transform infrared spectra (FTIR) and UV–Vis absorption spectra confirm the successful enzyme-catalyzed polymerization of TEBS. The thermo gravimetric (TG) data show the obtained PTEBS is stable over a fairly high range of temperatures. The present PTEBS has a good solubility in water and ethanol, and photoluminescence quenching of PTEBS/titanium dioxide (TiO₂) composite implies that the excitons dissociate and separate successfully at the interface of PTEBS and TiO₂, which help to build solar cells using green processing methods. Full article

(This article belongs to the Special Issue Enzymatic Polymer Synthesis)

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3983 KiB

Open AccessFeature PaperReview

Supported Catalysts Useful in Ring-Closing Metathesis, Cross Metathesis, and Ring-Opening Metathesis Polymerization

by Jakkrit Suriboot, Hassan S. Bazzi and David E. Bergbreiter

Polymers 2016, 8(4), 140; https://doi.org/10.3390/polym8040140 - 12 Apr 2016

Cited by 31 | Viewed by 9455

Abstract

Ruthenium and molybdenum catalysts are widely used in synthesis of both small molecules and macromolecules. While major developments have led to new increasingly active catalysts that have high functional group compatibility and stereoselectivity, catalyst/product separation, catalyst recycling, and/or catalyst residue/product separation remain an [...] Read more.

Ruthenium and molybdenum catalysts are widely used in synthesis of both small molecules and macromolecules. While major developments have led to new increasingly active catalysts that have high functional group compatibility and stereoselectivity, catalyst/product separation, catalyst recycling, and/or catalyst residue/product separation remain an issue in some applications of these catalysts. This review highlights some of the history of efforts to address these problems, first discussing the problem in the context of reactions like ring-closing metathesis and cross metathesis catalysis used in the synthesis of low molecular weight compounds. It then discusses in more detail progress in dealing with these issues in ring opening metathesis polymerization chemistry. Such approaches depend on a biphasic solid/liquid or liquid separation and can use either always biphasic or sometimes biphasic systems and approaches to this problem using insoluble inorganic supports, insoluble crosslinked polymeric organic supports, soluble polymeric supports, ionic liquids and fluorous phases are discussed. Full article

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3287 KiB

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A Hyper-Viscoelastic Constitutive Model for Polyurea under Uniaxial Compressive Loading

by Yang Bai, Chunmei Liu, Guangyan Huang, Wei Li and Shunshan Feng

Polymers 2016, 8(4), 133; https://doi.org/10.3390/polym8040133 - 12 Apr 2016

Cited by 44 | Viewed by 8219

Abstract

A hyper-viscoelastic constitutive model for polyurea by separating hyperelastic and viscoelastic behaviors has been put forward. Hyperelasticity represents the rate-independent responses at low strain rates, described by a three-parameter Mooney-Rivlin model and a third Ogden model. By fitting the quasi-static experimental data, the [...] Read more.

A hyper-viscoelastic constitutive model for polyurea by separating hyperelastic and viscoelastic behaviors has been put forward. Hyperelasticity represents the rate-independent responses at low strain rates, described by a three-parameter Mooney-Rivlin model and a third Ogden model. By fitting the quasi-static experimental data, the Ogden model is more appropriate to describe the hyperelastic behaviors for its better agreement at strain over 0.3. Meanwhile, viscoelasticity represents the rate-dependent responses at high strain rates, described by the Standard Linear Solids (SLS) model and the K-BKZ model. By fitting the experimental data of split Hopkinson pressure bar (SHPB), the SLS model is more appropriate to describe the viscoelastic behaviors at strain rates below 1600 s⁻¹, but the K-BKZ model performs better at strain rates over 2100 s⁻¹ because of the substantial increase of Young’s modulus and the state of polyurea transforming from rubbery to glassy. The K-BKZ model is chosen to describe the viscoelastic behavior, for its low Root Mean Square Error (RMSE) at strain rates below 1600 s⁻¹. From the discussion above, the hyper-viscoelastic constitutive model is chosen to be the combination of the Ogden model and the K-BKZ model. Full article

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5687 KiB

Open AccessArticle

Preparation of Esterified Bacterial Cellulose for Improved Mechanical Properties and the Microstructure of Isotactic Polypropylene/Bacterial Cellulose Composites

by Bo Wang, Dan Yang, Hai-rong Zhang, Chao Huang, Lian Xiong, Jun Luo and Xin-de Chen

Polymers 2016, 8(4), 129; https://doi.org/10.3390/polym8040129 - 12 Apr 2016

Cited by 27 | Viewed by 6856

Abstract

Bacterial cellulose (BC) has great potential to be used as a new filler to reinforce isotactic polypropylene (iPP) due to its high crystallinity, biodegradability, and efficient mechanical properties. In this study, esterification was used to modify BC, which improved the surface compatibility of [...] Read more.

Bacterial cellulose (BC) has great potential to be used as a new filler to reinforce isotactic polypropylene (iPP) due to its high crystallinity, biodegradability, and efficient mechanical properties. In this study, esterification was used to modify BC, which improved the surface compatibility of the iPP and BC. The results indicated that the cellulose octoate (CO) changed the surface properties from hydrophilic to lipophilic. Compared to the pure iPP, the tensile strength, charpy notched impact strength, and tensile modulus of the iPP/BC composites increased by 9.9%, 7.77%, and 15.64%, respectively. However, the addition of CO reinforced the iPP/CO composites. The tensile strength, charpy notched impact strength, and tensile modulus of the iPP/CO composites increased by 14.23%, 14.08%, and 17.82% compared to the pure iPP. However, the elongation at break of both the composites is decreased. The SEM photographs and particle size distribution of the composites showed improvements when the change of polarity of the BC surface, interface compatibility, and dispersion of iPP improved. Full article

(This article belongs to the Collection Polysaccharides)

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Open AccessReview

Precision Synthesis of Functional Polysaccharide Materials by Phosphorylase-Catalyzed Enzymatic Reactions

by Jun-ichi Kadokawa

Polymers 2016, 8(4), 138; https://doi.org/10.3390/polym8040138 - 11 Apr 2016

Cited by 42 | Viewed by 10311

Abstract

In this review article, the precise synthesis of functional polysaccharide materials using phosphorylase-catalyzed enzymatic reactions is presented. This particular enzymatic approach has been identified as a powerful tool in preparing well-defined polysaccharide materials. Phosphorylase is an enzyme that has been employed in the [...] Read more.

In this review article, the precise synthesis of functional polysaccharide materials using phosphorylase-catalyzed enzymatic reactions is presented. This particular enzymatic approach has been identified as a powerful tool in preparing well-defined polysaccharide materials. Phosphorylase is an enzyme that has been employed in the synthesis of pure amylose with a precisely controlled structure. Similarly, using a phosphorylase-catalyzed enzymatic polymerization, the chemoenzymatic synthesis of amylose-grafted heteropolysaccharides containing different main-chain polysaccharide structures (e.g., chitin/chitosan, cellulose, alginate, xanthan gum, and carboxymethyl cellulose) was achieved. Amylose-based block, star, and branched polymeric materials have also been prepared using this enzymatic polymerization. Since phosphorylase shows a loose specificity for the recognition of substrates, different sugar residues have been introduced to the non-reducing ends of maltooligosaccharides by phosphorylase-catalyzed glycosylations using analog substrates such as α-d-glucuronic acid and α-d-glucosamine 1-phosphates. By means of such reactions, an amphoteric glycogen and its corresponding hydrogel were successfully prepared. Thermostable phosphorylase was able to tolerate a greater variance in the substrate structures with respect to recognition than potato phosphorylase, and as a result, the enzymatic polymerization of α-d-glucosamine 1-phosphate to produce a chitosan stereoisomer was carried out using this enzyme catalyst, which was then subsequently converted to the chitin stereoisomer by N-acetylation. Amylose supramolecular inclusion complexes with polymeric guests were obtained when the phosphorylase-catalyzed enzymatic polymerization was conducted in the presence of the guest polymers. Since the structure of this polymeric system is similar to the way that a plant vine twines around a rod, this polymerization system has been named “vine-twining polymerization”. Through this approach, amylose supramolecular network materials were fabricated using designed graft copolymers. Furthermore, supramolecular inclusion polymers were formed by vine-twining polymerization using primer–guest conjugates. Full article

(This article belongs to the Special Issue Enzymatic Polymer Synthesis)

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3905 KiB

Open AccessArticle

Hg(II) Coordination Polymers Based on N,N’-bis(pyridine-4-yl)formamidine

by Wayne Hsu, Xiang-Kai Yang, Pradhumna Mahat Chhetri and Jhy-Der Chen

Polymers 2016, 8(4), 137; https://doi.org/10.3390/polym8040137 - 11 Apr 2016

Cited by 11 | Viewed by 5955

Abstract

Reactions of N,N’-bis(pyridine-4-yl)formamidine (4-Hpyf) with HgX₂ (X = Cl, Br, and I) afforded the formamidinate complex {[Hg(4-pyf)₂]·(THF)}_n, 1, and the formamidine complexes {[HgX₂(4-Hpyf)]·(MeCN)}_n (X = Br, 2; I, 3), which have been structurally characterized [...] Read more.

Reactions of N,N’-bis(pyridine-4-yl)formamidine (4-Hpyf) with HgX₂ (X = Cl, Br, and I) afforded the formamidinate complex {[Hg(4-pyf)₂]·(THF)}_n, 1, and the formamidine complexes {[HgX₂(4-Hpyf)]·(MeCN)}_n (X = Br, 2; I, 3), which have been structurally characterized by X-ray crystallography. Complex 1 is a 2D layer with the {4⁴·6²}-sql topology and complexes 2 and 3 are helical chains. While the helical chains of 2 are linked through N–H···Br hydrogen bonds, those of 3 are linked through self-complementary double N–H···N hydrogen bonds, resulting in 2D supramolecular structures. The 4-pyf- ligands of 1 coordinate to the Hg(II) ions through one pyridyl and one adjacent amine nitrogen atoms and the 4-Hpyf ligands of 2 and 3 coordinate to the Hg(II) ions through two pyridyl nitrogen atoms, resulting in new bidentate binding modes. Complexes 1–3 provide a unique opportunity to envisage the effect of the halide anions of the starting Hg(II) salts on folding and unfolding the Hg(II) coordination polymers. Density function theory (DFT) calculation indicates that the emission of 1 is due to intraligand π→π * charge transfer between two different 4-pyf- ligands, whereas those of 2 and 3 can be ascribed to the charge transfer from non-bonding p-type orbitals of the halide anions to π * orbitals of the 4-pyf- ligands (n→π *). The gas sorption properties of the desolvated product of 1 are compared with the Cu analogues to show that the nature of the counteranion and the solvent-accessible volume are important in determining their adsorption capability. Full article

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

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Polymers, Volume 8, Issue 4 (April 2016) – 65 articles

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