Polymers

2532 KiB

Open AccessArticle

Biodegradable Shape Memory Polymeric Material from Epoxidized Soybean Oil and Polycaprolactone

by Takashi Tsujimoto, Takeshi Takayama and Hiroshi Uyama

Polymers 2015, 7(10), 2165-2174; https://doi.org/10.3390/polym7101506 - 27 Oct 2015

Cited by 53 | Viewed by 14462

This article deals with the synthesis of plant oil-based shape memory materials from epoxidized soybean oil (ESO) and polycaprolactone (PCL). PolyESO/PCLs were synthesized by an acid-catalyzed curing in the presence of PCL. During the reaction, PCL scarcely reacted with ESO and the crystallinity [...] Read more.

This article deals with the synthesis of plant oil-based shape memory materials from epoxidized soybean oil (ESO) and polycaprolactone (PCL). PolyESO/PCLs were synthesized by an acid-catalyzed curing in the presence of PCL. During the reaction, PCL scarcely reacted with ESO and the crystallinity of the PCL component decreased to form a semi-interpenetrating network structure. The incorporation of the PCL components improved the maximum stress and strain at break of ESO-based network polymer. The polyESO/PCL was gradually degraded by Pseudomonas cepasia lipase. Furthermore, the polyESO/PCLs exhibited excellent shape memory properties, and the strain fixity depended on the feed ratio of ESO and PCL. The shape memory-recovery behaviors were repeatedly practicable. The resulting materials are expected to contribute to the development of biodegradable intelligent materials. Full article

(This article belongs to the Special Issue Shape-Memory Polymers)

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4963 KiB

Open AccessArticle

Effect of the Network Structure and Programming Temperature on the Shape-Memory Response of Thiol-Epoxy “Click” Systems

by Alberto Belmonte, Dailyn Guzmán, Xavier Fernández-Francos and Silvia De la Flor

Polymers 2015, 7(10), 2146-2164; https://doi.org/10.3390/polym7101505 - 26 Oct 2015

Cited by 42 | Viewed by 8722

Abstract

This paper presents a new methodology to develop “thiol-epoxy” shape-memory polymers (SMPs) with enhanced mechanical properties in a simple and efficient manner via “click” chemistry by using thermal latent initiators. The shape-memory response (SMR), defined by the mechanical capabilities of the SMP (high [...] Read more.

This paper presents a new methodology to develop “thiol-epoxy” shape-memory polymers (SMPs) with enhanced mechanical properties in a simple and efficient manner via “click” chemistry by using thermal latent initiators. The shape-memory response (SMR), defined by the mechanical capabilities of the SMP (high ultimate strength and strain), the shape-fixation and the recovery of the original shape (shape-recovery), was analyzed on thiol-epoxy systems by varying the network structure and programming temperature. The glass transition temperature (Tg) and crosslinking density were modified using 3- or 4- functional thiol curing agents and different amounts of a rigid triglycidyl isocyanurate compound. The relationship between the thermo-mechanical properties, network structure and the SMR was evidenced by means of qualitative and quantitative analysis. The influence of the programming temperature (Tprog) on the SMR was also analyzed in detail. The results demonstrate the possibility of tailoring SMPs with enhanced mechanical capabilities and excellent SMR, and intend to provide a better insight into the relationship between the network structure properties, programming temperature and the SMR of unconstrained (stress-free) systems; thus, making it easier to decide between different SMP and to define the operative parameters in the useful life. Full article

(This article belongs to the Special Issue Shape-Memory Polymers)

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3073 KiB

Open AccessArticle

Maleimide-Functionalized PEI600 Grafted Polyurethane: Synthesis, Nano-Complex Formation with DNA and Thiol-Conjugation of the Complexes for Dual DNA Transfection

by Wei-Chih Hung and Jong-Yuh Cherng

Polymers 2015, 7(10), 2131-2145; https://doi.org/10.3390/polym7101503 - 23 Oct 2015

Cited by 4 | Viewed by 8145

Abstract

A polyurethane (PU) grafted with small molecular weight polyethylenimine (PEI600) was synthesized. This PU-PEI600 can assemble DNA via electrostatic interactions into nano-sized polymer/DNA complexes. The complexes exhibited great transfection efficiency in delivering DNA along with a reduced cell toxicity comparing to commercial PEI25k [...] Read more.

A polyurethane (PU) grafted with small molecular weight polyethylenimine (PEI600) was synthesized. This PU-PEI600 can assemble DNA via electrostatic interactions into nano-sized polymer/DNA complexes. The complexes exhibited great transfection efficiency in delivering DNA along with a reduced cell toxicity comparing to commercial PEI25k (Mw ~25,000). In order to establish a system for concurrently delivering two different DNA or RNA molecules for cell reprogramming (e.g., induced pluripotent stem cells) or the necessity of multi-expression (e.g., double knock down), the PU-PEI600 was further functionalized with maleimide molecules. The novel PU-PEI600-maleimide would still effectively interact with assigned DNA and different functions of PU-PEI600-maleimide/DNA complexes were self-conjugated in presence of a dithiol molecule (1,6-hexanedithiol). In this study, two reporter genes (pEGFP-C2 and pLanRFP-N) were used and evidence of green/red fluorescence co-expression in cells was observed. This article brings a new concept and a practical method for a plurality of different DNA molecules that are more efficient to be concurrently delivered and co-expressed. This method is very helpful in studying cellular multi-regulation or in the treatment of disease with multiple gene defects in vivo. Full article

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

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4446 KiB

Open AccessArticle

PEGylated Fluorescent Nanoparticles from One-Pot Atom Transfer Radical Polymerization and “Click Chemistry”

by Li Qun Xu, Ning Ning Li, Bin Zhang, Jiu Cun Chen and En-Tang Kang

Polymers 2015, 7(10), 2119-2130; https://doi.org/10.3390/polym7101504 - 23 Oct 2015

Cited by 7 | Viewed by 8404

Abstract

The preparation of PEGylated fluorescent nanoparticles (NPs) based on atom transfer radical polymerization (ATRP) and “click chemistry” in one-pot synthesis is presented. First, poly(p-chloromethyl styrene-alt-N-propargylmaleimide) (P(CMS-alt-NPM)) copolymer was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Subsequently, the azido-containing fluorene-based polymer, poly[(9,9-dihexylfluorene)-alt-(9,9-bis-(6-azidohexyl)fluorene)] (PFC6N3), [...] Read more.

The preparation of PEGylated fluorescent nanoparticles (NPs) based on atom transfer radical polymerization (ATRP) and “click chemistry” in one-pot synthesis is presented. First, poly(p-chloromethyl styrene-alt-N-propargylmaleimide) (P(CMS-alt-NPM)) copolymer was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Subsequently, the azido-containing fluorene-based polymer, poly[(9,9-dihexylfluorene)-alt-(9,9-bis-(6-azidohexyl)fluorene)] (PFC6N3), was synthesized via Suzuki coupling polymerization, followed by azidation. Finally, the PEGylated fluorescent NPs were prepared via simultaneous intermolecular “click” cross-linking between P(CMS-alt-NPM) and PFC6N3 and the ATRP of poly(ethylene glycol) methyl ether methacrylate (PEGMMA) using P(CMS-alt-NPM) as the macroinitiator. The low cytotoxicity of the PEGylated fluorescent NPs was revealed by incubation with KB cells, a cell line derived from carcinoma of the nasopharynx, in an in vitro experiment. The biocompatible PEGylated fluorescent NPs were further used as a labeling agent for KB cells. Full article

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

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1198 KiB

Open AccessArticle

Flexural Strengthening of RC Slabs with Prestressed CFRP Strips Using Different Anchorage Systems

by José Sena-Cruz, Julien Michels, Yunus Emre Harmanci and Luís Correia

Polymers 2015, 7(10), 2100-2118; https://doi.org/10.3390/polym7101502 - 23 Oct 2015

Cited by 17 | Viewed by 8328

Abstract

Externally Bonded Reinforcement (EBR) technique has been widely used for flexural strengthening of concrete structures by using carbon fiber-reinforced polymers (CFRP). EBR technique offers several structural advantages when the CFRP material is prestressed. This paper presents an experimental and numerical study on reinforced [...] Read more.

Externally Bonded Reinforcement (EBR) technique has been widely used for flexural strengthening of concrete structures by using carbon fiber-reinforced polymers (CFRP). EBR technique offers several structural advantages when the CFRP material is prestressed. This paper presents an experimental and numerical study on reinforced (RC) slabs strengthened in flexure with prestressed CFRP strips as a structural strengthening system. The strips are applied as an externally bonded reinforcement (EBR) and anchored with either a mechanical or a gradient anchorage. The former foresees metallic anchorage plates fixed to the concrete substrate, while the latter is based on an accelerated epoxy resin curing followed by a segment-wise prestress force decrease at the strip ends. Both anchorage systems, in combination with different CFRP strip geometries, were subjected to static loading tests. It could be demonstrated that the composite strip’s performance is better exploited when prestressing is used, with slightly higher overall load carrying capacities for mechanical anchorages than for the gradient anchorage. The performed investigations by means of a cross-section analysis supported the experimental observation that in case a mechanical anchorage is used, progressive strip debonding changes the fully bonded configuration to an unbonded end-anchored system. The inclusion of defined debonding criteria for both the anchorage zones and free length between the anchorage regions allowed to precisely capture the ultimate loading forces. Full article

(This article belongs to the Special Issue Selected Papers from The 7th International Conference on FRP Composites in Civil Engineering (CICE 2014))

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22849 KiB

Open AccessReview

Carbon Fiber Reinforced Polymer for Cable Structures—A Review

by Yue Liu, Bernd Zwingmann and Mike Schlaich

Polymers 2015, 7(10), 2078-2099; https://doi.org/10.3390/polym7101501 - 22 Oct 2015

Cited by 235 | Viewed by 63954

Abstract

Carbon Fiber Reinforced Polymer (CFRP) is an advanced composite material with the advantages of high strength, lightweight, no corrosion and excellent fatigue resistance. Therefore, unidirectional CFRP has great potential for cables and to replace steel cables in cable structures. However, CFRP is a [...] Read more.

Carbon Fiber Reinforced Polymer (CFRP) is an advanced composite material with the advantages of high strength, lightweight, no corrosion and excellent fatigue resistance. Therefore, unidirectional CFRP has great potential for cables and to replace steel cables in cable structures. However, CFRP is a typical orthotropic material and its strength and modulus perpendicular to the fiber direction are much lower than those in the fiber direction, which brings a challenge for anchoring CFRP cables. This paper presents an overview of application of CFRP cables in cable structures, including historical review, state of the art and prospects for the future. After introducing properties of carbon fibers, mechanical characteristics and structural forms of CFRP cables, existing CFRP cable structures in the world (all of them are cable bridges) are reviewed. Especially, their CFRP cable anchorages are presented in detail. New applications for CFRP cables, i.e., cable roofs and cable facades, are also presented, including the introduction of a prototype CFRP cable roof and the conceptual design of a novel structure—CFRP Continuous Band Winding System. In addition, other challenges that impede widespread application of CFRP cable structures are briefly introduced. Full article

(This article belongs to the Collection Fiber-Reinforced Polymer Composites in Structural Engineering)

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8113 KiB

Open AccessArticle

Comparative Efficacies of a 3D-Printed PCL/PLGA/β-TCP Membrane and a Titanium Membrane for Guided Bone Regeneration in Beagle Dogs

by Jin-Hyung Shim, Joo-Yun Won, Su-Jin Sung, Dong-Hyuk Lim, Won-Soo Yun, Young-Chan Jeon and Jung-Bo Huh

Polymers 2015, 7(10), 2061-2077; https://doi.org/10.3390/polym7101500 - 21 Oct 2015

Cited by 61 | Viewed by 11918

Abstract

This study was conducted to evaluate the effects of a 3D-printed resorbable polycaprolactone/poly(lactic-co-glycolic acid)/β-tricalcium phosphate (PCL/PLGA/β-TCP) membrane on bone regeneration and osseointegration in areas surrounding implants and to compare results with those of a non-resorbable titanium mesh membrane. After preparation of PCL/PLGA/β-TCP membranes [...] Read more.

This study was conducted to evaluate the effects of a 3D-printed resorbable polycaprolactone/poly(lactic-co-glycolic acid)/β-tricalcium phosphate (PCL/PLGA/β-TCP) membrane on bone regeneration and osseointegration in areas surrounding implants and to compare results with those of a non-resorbable titanium mesh membrane. After preparation of PCL/PLGA/β-TCP membranes using extrusion-based 3D printing technology; mechanical tensile testing and in vitro cell proliferation testing were performed. Implant surgery and guided bone regeneration were performed randomly in three groups (a no membrane group, a titanium membrane group, and a PCL/PLGA/β-TCP membrane group (n = 8 per group)). Histological and histometric analyses were conducted to evaluate effects on bone regeneration and osseointegration. Using the results of mechanical testing; a PCL/PLGA/β-TCP ratio of 2:6:2 was selected. The new bone areas (%) in buccal defects around implants were highest in the PCL/PLGA/β-TCP group and significantly higher than in the control group (p < 0.05). Bone-to-implant contact ratios (%) were also significantly higher in the PCL/PLGA/β-TCP and titanium groups than in the control group (p < 0.05). When the guided bone regeneration procedure was performed using the PCL/PLGA/β-TCP membrane; new bone formation around the implant and osseointegration were not inferior to those of the non-resorbable pre-formed titanium mesh membrane. Full article

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

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16074 KiB

Open AccessArticle

RC Columns Strengthened with Novel CFRP Systems: An Experimental Study

by Annalisa Napoli and Roberto Realfonzo

Polymers 2015, 7(10), 2044-2060; https://doi.org/10.3390/polym7101499 - 19 Oct 2015

Cited by 12 | Viewed by 7239

Abstract

This paper presents an experimental study undertaken to investigate the seismic behavior of full scale square (300 mm × 300 mm) reinforced concrete (RC) columns strengthened with novel systems employing carbon fiber-reinforced polymers (CFRP) wraps. Experimental tests were carried out by subjecting specimens [...] Read more.

This paper presents an experimental study undertaken to investigate the seismic behavior of full scale square (300 mm × 300 mm) reinforced concrete (RC) columns strengthened with novel systems employing carbon fiber-reinforced polymers (CFRP) wraps. Experimental tests were carried out by subjecting specimens to a constant axial load and a cyclically reversed horizontal force applied in displacement control. Results have allowed for investigating the influence of the used strengthening systems on the specimens’ performance in terms of flexural strength and ductility as well as on the exhibited failure modes. The effectiveness of the studied techniques is also evaluated by comparing the performance of tested specimens with that of companion columns strengthened with alternative CFRP systems investigated in a previous experimental campaign. Full article

(This article belongs to the Special Issue Selected Papers from The 7th International Conference on FRP Composites in Civil Engineering (CICE 2014))

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3339 KiB

Open AccessArticle

Effect of Palm Oil Bio-Based Plasticizer on the Morphological, Thermal and Mechanical Properties of Poly(Vinyl Chloride)

by Kar Min Lim, Yern Chee Ching and Seng Neon Gan

Polymers 2015, 7(10), 2031-2043; https://doi.org/10.3390/polym7101498 - 19 Oct 2015

Cited by 28 | Viewed by 9503

Abstract

Flexible poly(vinyl chloride) (PVC) was fabricated using a palm oil-based alkyd as a co-plasticizer to di-octyl phthalate (DOP) and di-isononyl phthalate (DiNP). The effects of the incorporation of the palm oil-based alkyd on morphological, thermal and mechanical properties of PVC compounds were studied. [...] Read more.

Flexible poly(vinyl chloride) (PVC) was fabricated using a palm oil-based alkyd as a co-plasticizer to di-octyl phthalate (DOP) and di-isononyl phthalate (DiNP). The effects of the incorporation of the palm oil-based alkyd on morphological, thermal and mechanical properties of PVC compounds were studied. Results showed the incorporation of the alkyd enhanced the mechanical and thermal properties of the PVC compounds. Fourier transform infrared spectroscopy (FTIR) results showed that the polar –OH and –C=O groups of alkyd have good interaction with the –C–Cl group in PVC via polar interaction. The morphological results showed good incorporation of the plasticizers with PVC. Improved tensile strength, elastic modulus, and elongation at break were observed with increasing amount of the alkyd, presumably due to chain entanglement of the alkyd with the PVC molecules. Thermogravimetric analysis results confirmed that the alkyd has improved the thermostability of the PVC compounds. Full article

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2084 KiB

Open AccessArticle

Tailoring Membrane Surface Charges: A Novel Study on Electrostatic Interactions during Membrane Fouling

by Daniel Breite, Marco Went, Andrea Prager and Agnes Schulze

Polymers 2015, 7(10), 2017-2030; https://doi.org/10.3390/polym7101497 - 19 Oct 2015

Cited by 62 | Viewed by 10728

Abstract

In this work we aim to show that the overall surface potential is a key factor to understand and predict anti-fouling characteristics of a polymer membrane. Therefore, polyvinylidene fluoride membranes were modified by electron beam-induced grafting reactions forming neutral, acidic, alkaline or zwitterionic [...] Read more.

In this work we aim to show that the overall surface potential is a key factor to understand and predict anti-fouling characteristics of a polymer membrane. Therefore, polyvinylidene fluoride membranes were modified by electron beam-induced grafting reactions forming neutral, acidic, alkaline or zwitterionic structures on the membrane surface. The differently charged membranes were investigated regarding their surface properties using diverse analytical methods: zeta potential, static and dynamic water contact angle, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Porosimetry measurements proved that there is no pore blocking due to the modifications. Monodisperse suspensions of differently charged polystyrene beads were synthesized by a radical emulsion polymerization reaction and were used as a model fouling reagent, preventing comparability problems known from current literature. To simulate membrane fouling, different bead suspensions were filtered through the membranes. The fouling characteristics were investigated regarding permeation flux decline and concentration of model fouling reagent in filtrate as well as by SEM. By considering electrostatic interactions equal to hydrophobic interactions we developed a novel fouling test system, which enables the prediction of a membrane’s fouling tendency. Electrostatic forces are dominating, especially when charged fouling reagents are present, and can help to explain fouling characteristics that cannot be explained considering the surface wettability. Full article

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

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1095 KiB

Open AccessArticle

Reactivity Comparison of ω-Alkenols and Higher 1-Alkenes in Copolymerization with Propylene Using An Isospecific Zirconocene-MMAO Catalyst

by Benard Oloo Nyangoye, Tianyou Li, Long Chen and Zhengguo Cai

Polymers 2015, 7(10), 2009-2016; https://doi.org/10.3390/polym7101496 - 16 Oct 2015

Cited by 4 | Viewed by 6217

Abstract

Copolymerizations of propylene with ω-alkenols (aluminum-protected 5-hexene-1-ol (AH) and 10-undecene-1-ol (AU)) and non-polar analogues (1-hexene and 1-dodecene) were conducted with a rac-[Me₂Si(2-Me-4-Ph-Ind)₂]ZrCl₂ activated by modified methylaluminoxane. The catalytic system showed high activity for each copolymerization, of which [...] Read more.

Copolymerizations of propylene with ω-alkenols (aluminum-protected 5-hexene-1-ol (AH) and 10-undecene-1-ol (AU)) and non-polar analogues (1-hexene and 1-dodecene) were conducted with a rac-[Me₂Si(2-Me-4-Ph-Ind)₂]ZrCl₂ activated by modified methylaluminoxane. The catalytic system showed high activity for each copolymerization, of which value was independent on the comonomer used and decreased with the increase of the comonomer concentration. The comonomer content of the copolymers obtained also decreased with the increase of the comonomer concentration in each copolymer. The evaluation of the monomer reactivity ratios indicates a preference for the propylene insertion regardless of the last inserted monomer unit in growing polymer chain in all the copolymerizations. The relative reactivity of ω-alkenols was however significantly lower than that of non-polar analogues. These results suggested that the aluminum protection of polar monomer do not affect the activity of copolymerization but significantly decrease the comonomer reactivity. Full article

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

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2175 KiB

Open AccessArticle

Thermal Properties of Methyl Ester-Containing Poly(2-oxazoline)s

by Petra J. M. Bouten, Kathleen Lava, Jan C. M. Van Hest and Richard Hoogenboom

Polymers 2015, 7(10), 1998-2008; https://doi.org/10.3390/polym7101494 - 13 Oct 2015

Cited by 30 | Viewed by 9159

Abstract

This paper describes the synthesis and thermal properties in solution and bulk of poly(2-alkyl-oxazoline)s (PAOx) containing a methyl ester side chain. Homopolymers of 2-methoxycarbonylethyl-2-oxazoline (MestOx) and 2-methoxycarbonylpropyl-2-oxazoline (C3MestOx), as well as copolymers with 2-ethyl-2-oxazoline (EtOx) and 2-n-propyl-2-oxazoline (nPropOx), with systematic variations in composition [...] Read more.

This paper describes the synthesis and thermal properties in solution and bulk of poly(2-alkyl-oxazoline)s (PAOx) containing a methyl ester side chain. Homopolymers of 2-methoxycarbonylethyl-2-oxazoline (MestOx) and 2-methoxycarbonylpropyl-2-oxazoline (C3MestOx), as well as copolymers with 2-ethyl-2-oxazoline (EtOx) and 2-n-propyl-2-oxazoline (nPropOx), with systematic variations in composition were prepared. The investigation of the solution properties of these polymers revealed that the cloud point temperatures (T_CP^s) could be tuned in between 24 °C and 108 °C by variation of the PAOx composition. To the best of our knowledge, the T_CP^sof PMestOx and PC3MestOx are reported for the first time and they closely resemble the TCPs of PEtOx and PnPropOx, respectively, indicating similar hydrophilicity of the methyl ester and alkyl side chains. Furthermore, the thermal transitions and thermal stability of these polymers were investigated by DSC and TGA measurements, respectively, revealing amorphous polymers with glass transition temperatures between -1 °C and 54 °C that are thermally stable up to >300 °C. Full article

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8502 KiB

Open AccessArticle

Modeling the Pyrolysis and Combustion Behaviors of Non-Charring and Intumescent-Protected Polymers Using “FiresCone”

by Long Shi, Michael Yit Lin Chew, Vasily Novozhilov and Paul Joseph

Polymers 2015, 7(10), 1979-1997; https://doi.org/10.3390/polym7101495 - 13 Oct 2015

Cited by 19 | Viewed by 6795

Abstract

A mathematical model, named FiresCone, was developed to simulate the pyrolysis and combustion processes of different types of combustible materials, which also took into account both gas and solid phases. In the present study, some non-charring and intumescent-protected polymer samples were investigated regarding [...] Read more.

A mathematical model, named FiresCone, was developed to simulate the pyrolysis and combustion processes of different types of combustible materials, which also took into account both gas and solid phases. In the present study, some non-charring and intumescent-protected polymer samples were investigated regarding their combustion behaviors in response to pre-determined external heat fluxes. The modeling results were validated against the experimental outcomes obtained from a cone calorimeter. The predicted mass loss rates of the samples were found to fit reasonably well with the experimental data collected under various levels of external irradiation. Both the experimental and modeling results showed that the peak mass loss rate of the non-charring polymer material occurred near the end of burning, whereas for the intumescent-protected polymer it happed shortly after the start of the experiment. “FiresCone” is expected to act as a practical tool for the investigation of fire behavior of combustible materials. It is also expected to model fire scenarios under complicated conditions. Full article

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3003 KiB

Open AccessArticle

Effect of Chemical Treatment of Flax Fiber and Resin Manipulation on Service Life of Their Composites Using Time-Temperature Superposition

by Ali Amiri, Chad A. Ulven and Shanshan Huo

Polymers 2015, 7(10), 1965-1978; https://doi.org/10.3390/polym7101493 - 13 Oct 2015

Cited by 67 | Viewed by 10299

Abstract

In recent years there has been a resurgence of interest in the usage of natural fiber reinforced composites in more advanced structural applications. As a result, the need for improving their mechanical properties, as well as service life modeling and predictions have arisen. [...] Read more.

In recent years there has been a resurgence of interest in the usage of natural fiber reinforced composites in more advanced structural applications. As a result, the need for improving their mechanical properties, as well as service life modeling and predictions have arisen. In this study effect of alkaline treatment of flax fiber as well as addition of 1% acrylic resin to vinyl ester on mechanical properties and long-term creep behavior of flax/vinyl ester composites was investigated. To perform the alkaline treatment, fibers were immersed into 1500 mL of 10 g/L sodium hydroxide/ethanol solution at 78 °C for 2 h. Findings revealed that alkaline treatment was successful in increasing interlaminar shear, tensile and flexural strength of the composite but decreased the tensile and flexural modulus by 10%. Addition of acrylic resin to the vinyl ester resin improved all mechanical properties except the flexural modulus which was decreased by 5%. In order to evaluate the long-term behavior, creep compliance master curves were generated using the time-temperature superposition principle. Results suggests that fiber and matrix treatments delay the creep response and slows the process of creep in flax/vinyl ester composites in the steady state region, respectively. Full article

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988 KiB

Open AccessArticle

Magnesium Pyrazolyl-Indolyl Complexes as Catalysts for Ring-Opening Polymerization of L-Lactide

by Chi-Tien Chen, Deng-Hao Lin and Kuo-Fu Peng

Polymers 2015, 7(10), 1954-1964; https://doi.org/10.3390/polym7101492 - 5 Oct 2015

Cited by 7 | Viewed by 8581

Abstract

A series indole-based ligand precursors, Pz^RIndH (R = H, Pz^HIndH; R = Me, Pz^MeIndH;R = t-Bu, Pz^tBuIndH; and R = Ph, Pz^PhIndH), have been synthesized via copper-catalyzed N-arylation (for Pz^HIndH) [...] Read more.

A series indole-based ligand precursors, Pz^RIndH (R = H, Pz^HIndH; R = Me, Pz^MeIndH;R = t-Bu, Pz^tBuIndH; and R = Ph, Pz^PhIndH), have been synthesized via copper-catalyzed N-arylation (for Pz^HIndH) or the Bartoli indole synthesis (for Pz^MeIndH, Pz^tBuIndH and Pz^PhIndH) reactions with moderate to high yield. Reactions of these ligand precursors with 0.7 equivalentof MgⁿBu₂ in THF (for 1) or hexane (for 2–4) afforded the bis-indolyl magnesium complexes 1–4,respectively. All the ligand precursors and related magnesium complexes have been characterizedby NMR spectroscopy and elemental analyses. The molecular structure is reported for compound 1.These novel magnesium complexes demonstrate efficient catalytic activities for the ring-opening polymerization of L-lactide in the presence of alcohol. Full article

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

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3871 KiB

Open AccessArticle

High Specific Capacitance of Polyaniline/Mesoporous Manganese Dioxide Composite Using KI-H₂SO₄ Electrolyte

by Zhongkai Hu, Lei Zu, Yanhua Jiang, Huiqin Lian, Yang Liu, Zhenzi Li, Fei Chen, Xiaodong Wang and Xiuguo Cui

Polymers 2015, 7(10), 1939-1953; https://doi.org/10.3390/polym7101491 - 30 Sep 2015

Cited by 75 | Viewed by 11665

Abstract

The PANI/Mesoporous MnO₂ composites were prepared through a simple one step method and we introduced the KI-H₂SO₄ solution as the electrolyte of PANI/MnO₂ composites creatively. The characterization of structure, morphology, and composition are obtained by X-ray diffraction, Fourier [...] Read more.

The PANI/Mesoporous MnO₂ composites were prepared through a simple one step method and we introduced the KI-H₂SO₄ solution as the electrolyte of PANI/MnO₂ composites creatively. The characterization of structure, morphology, and composition are obtained by X-ray diffraction, Fourier transform infrared spectroscopy, thermal gravity analysis, Raman spectra, and scanning electron microscope. The electrochemical performances were investigated by constant-current charge–discharge, the voltammetry curve, and alternating current (AC) impedance technique. The specific capacitance of composites is 1405 F/g, which is almost 10 times larger than MnO₂ (158 F/g). We also find that the iodide concentration is closely related to the specific capacitance. Therefore, we explored the specific capacitance at different iodide concentration (0.05, 0.1, 0.2, 0.5, and 1 M), the results indicated that the specific capacitance reached a maximum value (1580 F/g) at 0.5 mol/L. Additionally, the PANI/Mesoporous MnO₂ composites not only exhibited a good ratio discharge property (857 F/g) at high current density, but also revealed an excellent cycling stability after 500 cycles, which retained 90% of the original specific capacitance. Full article

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5039 KiB

Open AccessArticle

The Effect of Allylic Sulfide-Mediated IrreversibleAddition-Fragment Chain Transfer on the EmulsionPolymerization Kinetics of Styrene

by Li An, Zhihui Di, Biaobiao Yu, Jialing Pu and Zhongxiao Li

Polymers 2015, 7(10), 1918-1938; https://doi.org/10.3390/polym7101490 - 29 Sep 2015

Cited by 4 | Viewed by 7985

Abstract

The effect of the irreversible addition-fragment chain transfer agent, butyl(2-phenylallyl)sulfane (BPAS), on the course of the emulsion polymerization of styrene and on the product molecular weight was investigated. The emulsion polymerizations were performed using various amounts of sodium dodecyl sulfate (SDS) as the [...] Read more.

The effect of the irreversible addition-fragment chain transfer agent, butyl(2-phenylallyl)sulfane (BPAS), on the course of the emulsion polymerization of styrene and on the product molecular weight was investigated. The emulsion polymerizations were performed using various amounts of sodium dodecyl sulfate (SDS) as the surfactant and potassium peroxodisulfate (KPS) as the initiator. The relationships between the rates of polymerization (\(R_{p} \)) and the number of particles per volume (\(N_{c} \)) with respect to the concentrations of KPS, SDS, and BPAS were found to be \(R_{p} \propto \left\lbrack KPS \right\rbrack^{0.29} \), \(N_{c} \propto \left\lbrack KPS \right\rbrack^{0.26} \),\(R_{p} \propto \left\lbrack SDS \right\rbrack^{0.68} \), \(N_{c} \propto \left\lbrack SDS \right\rbrack^{0.72} \), and \(R_{p} \propto \left\lbrack BPAS \right\rbrack^{- 0.73} \) . The obtained relationships can be attributed to the exit of the leaving group radicals on BPAS from the polymer particles. The experimental values of the average number of radicals per particle (\(\overset{\_}{n} \)) were strongly dependent on the BPAS concentration and were in good agreement with the theoretical values (\({\overset{\_}{n}}_{theo} \)) from model calculations. The number-average molecular weight (\(\overset{\_}{M_{n}} \)) can be controlled by BPAS over nearly the entire conversion range, which is also in agreement with the mathematical model. In addition, the transfer rate coefficient (\(k_{tr} \)) of BPAS can be estimated as 326 L/mol/s at 70 \(^\circ\)C. Moreover, similar good results were found for the tested redox reactions at 30 \(^\circ\)C. Full article

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

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Open AccessArticle

A Design-Oriented Combined Model (7 MPa to 190 MPa) for FRP-Confined Circular Short Columns

by Zehra Canan Girgin and Konuralp Girgin

Polymers 2015, 7(10), 1905-1917; https://doi.org/10.3390/polym7101489 - 28 Sep 2015

Cited by 20 | Viewed by 8530

Abstract

This study addresses a design oriented combined model to predict the ultimate strengths and ultimate strains in an extensive range of unconfined strength (7 to 190 MPa) for the axially loaded fiber-reinforced polymer (FRP)-wrapped circular short columns. Modified Hoek-Brown strength criterion, which was [...] Read more.

This study addresses a design oriented combined model to predict the ultimate strengths and ultimate strains in an extensive range of unconfined strength (7 to 190 MPa) for the axially loaded fiber-reinforced polymer (FRP)-wrapped circular short columns. Modified Hoek-Brown strength criterion, which was previously extended to FRP-confined concrete from 7 to 108 MPa, is revisited and verified. An empirical strength model beyond 108 MPa encompassing ultra-high strength concrete (UHSC) and ultra-high performance concrete (UHPC) data, as well as empirical strain models, are defined to accomplish the design oriented combined model. This article especially focuses on the verification of the proposed strain models. The assessment performances of those models for carbon FRP (CFRP) and glass FRP (GFRP) confinement are compared with specific models in the current literature. Strength and strain predictions for UHSC and UHPC are integrated into the design oriented combined model as well. The assessments on this model agree with the experimental results in high accuracy. Full article

(This article belongs to the Collection Fiber-Reinforced Polymer Composites in Structural Engineering)

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Polymers, Volume 7, Issue 10 (October 2015) – 18 articles

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