On the toughness of photopolymerizable (meth)acrylate networks for biomedical applications

Photopolymerizable networks are being explored for a variety of biomedical applications because they can be formed in situ, rendering them useful in minimally invasive procedures. The purpose of this study was to establish fundamental relationships between toughness, network chemical structure, and testing temperature of photopolymerizable (meth)acrylate networks deformed in air and under hydrated conditions. Networks were formed by combining at least one monofunctional (meth)acrylate with a difunctional methacrylate, and weight ratios were adjusted to vary the degree of crosslinking, elastic modulus, and glass transition temperature (T_g). Stress–strain behavior and toughness were determined by performing tensile strain to failure tests at temperatures spanning the glassy and rubbery regimes of each network both in air and phosphate‐buffered saline. In air, all of the networks demonstrated a peak in toughness below the network's T_g. At an “equivalent” test temperature relative to T_g, crosslinking concentration and monomer chemistry influenced the toughness of each network. Apparent toughness is significantly altered in an aqueous environment, an effect driven by water absorption into the network causing the T_g to decrease. The results from this study provide the fundamental knowledge required to guide the development of tougher photopolymerizable networks for mechanically strenuous biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure–property relationships in photopolymerizable polymer networks: Effect of composition on the crosslinked structure and resulting thermomechanical properties of a (meth)acrylate‐based system

Photoinitiated polymer networks were formed by copolymerization of tert‐butyl acrylate with di(ethylene glycol) dimethacrylate (DEGDMA) or poly(ethylene glycol) dimethacrylate (PEGDMA). The degree of crosslinking was systematically varied by modifying the weight fraction and molecular weight of the dimethacrylate crosslinking agent. An increase in effective crosslink density with increasing crosslinking agent concentrations was confirmed by decreasing equilibrium swelling ratios (q) and increasing rubbery moduli (E_R). Glass transition temperatures (T_g) varied from ?22 to 124°C, increasing with increasing DEGDMA content and decreasing with increasing PEGDMA content. Tensile deformation behavior (at T_g) ranged from an elastomeric‐like large‐strain response for lightly crosslinked materials to a small‐strain brittle response for highly crosslinked networks. At low crosslinking levels, the strain‐to‐failure of the network polymers decreased quickly with increasing crosslinking agent concentration. The stress at failure demonstrated a more complex relationship with crosslinking agent concentration. The effect of composition on network structure and resulting properties (q, E_R, strain‐to‐failure) decreased as the crosslinking agent concentration increased. The results reveal trade‐offs in T_g, E_R, strain‐to‐failure, and failure stress with composition and network structure, and are discussed in light of the wide range of potential applications suggested in the literature for (meth)acrylate‐based photopolymerizable polymer networks including biomaterials and shape‐memory polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Partially constrained recovery of (meth)acrylate shape‐memory polymer networks

The purpose of this study was to characterize the partial strain recovery of a thermoset shape‐memory polymer under a constraining stress. Three polymer networks were synthesized from tert‐butyl acrylate and poly(ethylene glycol) dimethacrylate (PEGDMA) solutions. The molecular weight and the weight fraction of the PEGDMA crosslinking monomer was altered systematically to maintain a constant glass transition temperature (T_g = 54°C) but tailorable rubbery moduli, which varied by almost an order of magnitude for the three polymer networks (E = 1.8–11.3°MPa). The shape‐recovery behavior of the polymers under a constraining stress was characterized for programming temperature below (20°C) and above (70°C) the T_g. The experiments revealed a peak in the recovered strain for samples programmed at 20°C. Recovered strain scaled linearly with the constraining stress by the rubbery modulus. The work performed by the shape‐memory polymer networks was observed to be primarily a function of constraining stress and crosslinking density, while programming temperature had a relatively mild influence; however, the efficiency of the shape‐memory effect was shown to be a function of constraining stress and programming temperature, but was independent of crosslinking density. Maximum work efficiencies (up to 45%) were observed for programming temperature of 70°C. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Viscoelastic characteristics of shape memory polymers

Shape memory polymers (SMPs) can keep a temporary state and subsequently recover to the original shape through a prescribed thermomechanical process. Although different theoretical models have been presented, the viscous effects were seldom considered. This article aims to provide an insight into the viscoelastic property of SMPs and its effect on the functional realization. Systematic thermomechanical experiments were performed. Special considerations were focused on the viscoelastic response of SMPs in the vicinity of the glass transition temperature T_g. The relations between shape switching transition temperature T_tran and T_g were also discussed. The results confirm that T_tran departs from T_g due to the viscoelastic effect and does not keep a constant value during heating and cooling processes. The viscoelastic effect reaches to maximum value at T_g, then decreases slowly at cooling and quickly at heating. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Removal of heavy metal ions from aqueous solutions by radiation‐induced chitosan/(acrylamidoglycolic acid‐co‐acrylic acid) magnetic nanopolymer

An effective method was developed to isolate toxic heavy metal ions from the aqueous solution by the magnetic nanopolymers. The magnetic sorbent was prepared with radiation‐induced crosslinking polymerization of chitosan (CS), 2‐acrylamido‐glycolic acid (AMGA), and acrylic acid (AAc), which stabilized by magnetite (Fe₃O₄) as nanoparticles. The formation of magnetic nanoparticles (MNPs) into the hydrogel networks was confirmed by Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, and Scanning electron microscopy, which revealed the formation of MNPs throughout the hydrogel networks. The swelling behavior of the hydrogels and magnetic ones was evaluated at different pH values. The adsorption activity for heavy metals such as Cu²⁺ and Co²⁺ by nonmagnetic and magnetic hydrogels, Fe₃O₄/CS/(AMGA‐co‐AAc), in terms of adsorption amount was studied. It was revealed that hydrogel networks with magnetic properties can effectively be used in the removal of heavy metal ions pollutants and provide advantageous over conventional ones. POLYM. ENG. SCI., 55:1441–1449, 2015. © 2015 Society of Plastics Engineers     

Synthesis and characterization of novel core‐shell magnetic nanogels based on 2‐acrylamido‐2‐methylpropane sulfonic acid in aqueous media

Ultrafine well‐dispersed Fe₃O₄ magnetic nanoparticles were directly prepared in aqueous solution using controlled coprecipitation method. The synthesis of Fe₃O₄/poly (2‐acrylamido‐2‐methylpropane sulfonic acid) (PAMPS), Fe₃O₄/poly (acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) poly(AM‐co‐AMPS) and Fe₃O₄/poly (acrylic acid‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) poly(AA‐co‐AMPS) ‐core/shell nanogels are reported. The nanogels were prepared via crosslinking copolymerization of 2‐acrylamido‐2‐methylpropane sulfonic acid, acrylamide and acrylic acid monomers in the presence of Fe₃O₄ nanoparticles, N,N′‐methylenebisacrylamide (MBA) as a crosslinker, N,N,N′,N′‐tetramethylethylenediamine (TEMED) and potassium peroxydisulfate (KPS) as redox initiator system. The results of FTIR and ¹H‐NMR spectra indicated that the compositions of the prepared nanogels are consistent with the designed structure. X‐ray powder diffraction (XRD) and transmission electron microscope (TEM) measurements were used to determine the size of both magnetite and stabilized polymer coated magnetite nanoparticles. The data showed that the mean particle size of synthesized magnetite (Fe₃O₄) nanoparticles was about 10 nm. The diameter of the stabilized polymer coated Fe₃O₄ nanogels ranged from 50 to 250 nm based on polymer type. TEM micrographs proved that nanogels possess the spherical morphology before and after swelling. These nanogels exhibited pH‐induced phase transition due to protonation of AMPS copolymer chains. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Properties of electropolymerized polycarboxyphenylmethacrylamide matrices/graphite fiber composites: Crosslinking effect

Imide formation from -CONH and -COOH functional groups of 2-carboxyphenylmethacrylamide (2-CPM), 4-carboxyphenylmethacrylamide (4-CPM), 4-carboxyphenyl methacrylamide/methylmethacrylate (4-CPM/MMA) and 4-carboxyphenylmethacrylamide/N-phenylmalemide (4-CPM/NPMI) electropolymerized matrices was investigated. It was found that 2-CPM polymers undergo intramolecular imidization and anhydride formation, which result in a small amount of crosslinked network. On the other hand, the thermally cured 4-CPM polymer demonstrates a significant increase in gel fraction. T_g and dynamic storage modulus, owing to crosslinked network formation. T_gs of 4-CPM/MMA and 4-CPM/NPMI composites measured by thermomechanical analysis after thermal heating were increased and were correlated very well with the preheating time. The 4-CPM/MMA composites with a particle crosslinking (T_g increased to 245°C) maintained a higher Izod impact strength than a typical epoxy composite (200 kJ/m² vs. 100 kJ/m²). Upon heating to promote crosslinking, a lower shear strength (65 MPa) of a 4-CPM/MMA composite increased to a strength of 78 MPa, close to the 80 MPa of an epoxy composite at 67% fiber volume fraction. A lower water absorption of around 1% was associated with the increased crosslinking. The mechanical properties of the 4-CPM/NPMI composites showed a similar trend upon preheating.     

Effect of the filler size and content on the thermomechanical properties of particulate aluminum nitride filled epoxy composites

Polymer matrix composites based on brominated epoxy as the matrix and aluminum nitride (AlN) particles as the filler were prepared. The influences of the size, content, and size distribution of AlN on the thermomechanical properties, including the glass‐transition temperature (T_g), coefficient of thermal expansion (CTE), dynamic storage modulus (E′), dynamic loss modulus (E″), and loss factor (tan δ), of the composites were investigated by thermomechanical analysis and dynamic mechanical analysis. There was a total change trend for T_g; that is, T_g of the composites containing nano‐aluminum nitride (nano‐AlN; 50 nm) was lower than that of the micro‐aluminum nitride (micro‐AlN; 2.3 μm) filled composites, especially at high nano‐AlN contents. The T_g depression of the composites containing nano‐AlN was related to the aggregation of nano‐AlN and voids in the composites. On the other hand, the crosslink density of the epoxy matrix decreased for nano‐AlN‐filled composites, which also resulted in a T_g depression. The results also show that E′ and E″ increased, whereas tan δ and CTE of the composites decreased, with increasing the AlN content or increasing nano‐AlN fraction at the same AlN content. These results indicate that increasing the interfacial areas between AlN and the epoxy matrix effectively enhanced the dynamic modulus and decreased CTE. In addition, at a fixed AlN content of 10 wt %, a low E′ of pre‐T_g (before T_g temperature) and high T_g were observed at the smaller weight ratio of nano‐AlN when combinations of nano‐AlN plus micro‐AlN were used as the filler. This may have been related to the best packing efficiency at that weight ratio when the bimodal filler was used. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Interpolyelectrolyte complexes of maleic acid copolymers and chitosan for stabilization and functionalization of magnetite nano‐ and microparticles

A facile method of preparation of stabilized and functionalized nano‐ and microparticles of magnetite by successive application of oppositely charged polymers with a regular structure of macromolecular chains (chitosan and maleic acid copolymers) onto Fe₃O₄ core are developed. This approach makes it possible to create two types of magnetite interpolyelectrolyte shells, containing carboxylic or amino groups in outer layer of shell. Composition and magnetic properties of composite particles depend on nature of the copolymer of maleic acid, reaction conditions and size of obtained particles. The carboxylic groups of copolymer in outer layer of interpolyelectrolyte shell were converted into reactive anhydride groups by heating. Thermal treatment also leads to covalent crosslinking of shell and improves stability of composites both in acidic and alkaline media. Horseradish peroxidase was successfully immobilized onto covalently crosslinked and activated microparticles of Fe₃O₄ in aqueous medium without of condensing agents. The proposed reproducible and low‐cost technique does not use toxic reagents or solvents at all stages, including preparation of Fe₃O₄, formation, activation and crosslinking, of magnetite shell, modification of activated surface of composite particles. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39663.     

Stabilized electrospinning of heat stimuli/in situ crosslinkable nanofibers and their self‐same nanocomposites

We present a strategy for stabilizing the morphological integrity of electrospun polymeric nanofibers by heat stimuli in situ crosslinking. Amorphous polymer nanofibers, such as polystyrene (PS) and its co‐polymers tend to lose their fiber morphology during processing at temperatures above their glass transition temperature (T_g) typically bound to happen in nanocomposite/structural composite applications. As an answer to this problem, incorporation of the crosslinking agents, phthalic anhydride (PA) and tributylamine (TBA), into the electrospinning polymer solution functionalized by glycidylmethacrylate (GMA) copolymerization, namely P(St‐co‐GMA), is demonstrated. Despite the presence of the crosslinker molecules, the electrospinning polymer solution is stable and its viscosity remains unaffected below 60 °C. Crosslinking reaction stands‐by and can be thermally stimulated during post‐processing of the electrospun P(St‐co‐GMA)/PA‐TBA fiber mat at intermediate temperatures (below the T_g). This strategy enables the preservation of the nanofiber morphology during subsequent high temperature processing. The crosslinking event leads to an increase in T_g of the base polymer by 30 °C depending on degree of crosslinking. Crosslinked nanofibers are able to maintain their nanofibrous morphology above the T_g and upon exposure to organic solvents. In situ crosslinking in epoxy matrix is also reported as an example of high temperature demanding application/processing. Finally, a self‐same fibrous nanocomposite is demonstrated by dual electrospinning of P(St‐co‐GMA) and stabilized P(St‐co‐GMA)/PA‐TBA, forming an intermingled nanofibrous mat, followed by a heating cycle. The product is a composite of crosslinked P(St‐co‐GMA)/PA‐TBA fibers fused by P(St‐co‐GMA) matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44090.     

Influence of nanosilica particles on the cure and physical properties of an epoxy thermoset resin

Measurements are reported on the cure and physical properties of an epoxy resin created using a functionalised nanosilica filler. The filled bisphenol A epoxy (Nanopox A410) contained 40 wt% silica nanoparticles and was blended with two bisphenol A resins of molecular weights of 355 and 1075 g mol^?1, respectively. Cure was achieved using 3,3‐diaminodiphenylsulfone. The functionality of the mixture containing the epoxy nanoparticles was determined using NMR analysis. Cure times showed a progressive decrease with increasing silica level. Dynamic mechanical thermal analysis showed a decrease in the value of the glass transition temperature (T_g) with increasing silica level. T_g was further studied using differential scanning calorimetry. The ability of the nanosilica to create a stable network structure was demonstrated by the variation of the high‐temperature modulus with silica composition. Thermomechanical analysis carried out below and above T_g showed a progressive decrease in the expansion coefficients with increasing silica level, indicating the effectiveness of the functionalised silica nanoparticles in forming a network. The network formed during cure in the nano‐modified epoxy is unable to undergo the densification possible in the pure resin material and explains the observed lowering of T_g with increasing nanosilica content. Copyright © 2009 Society of Chemical Industry     

Evaluation of new 3‐mercaptopropionate thiols for thiol‐ene photopolymerization coatings using experimental design

Three 3‐mercaptopropionate thiols, 1,6‐Hexane bis(3‐mercaptopropionate) (HD‐SH), trans‐1,4‐Cyclohexanedimethyl bis(3‐mercaptopropionate) (CHDM‐SH), and 4,4′‐Isopropylidenedicyclohexane bis(3‐mercaptopropionate) (HBPA‐SH) were formulated with 1,3,5‐triallyl‐1,3,5‐triazine‐2,4,6(1H,3H,5H)‐trione (TATATO) and photoinitiator. The formulations were photopolymerized via thiol‐ene photopolymerization. A ternary experimental design was employed to elucidate the influence the three thiols on the thermomechanical and coatings properties of thiol‐ene photopolymerizable materials. Tensile strength, tensile modulus, elongation‐to‐break, glass transition temperature (T_g), and crosslink density (XLD) were investigated. Coating properties including pencil hardness, pull‐off adhesion, MEK double rubs, and gloss were also investigated. Relative reaction conversion was determined by photo differential scanning calorimeter (PDSC). Thiol‐ene photopolymerizable materials containing HBPA‐SH resulted in improving tensile strength, tensile modulus, T_g, and pencil hardness but lowering of crosslink density and relative conversion. This was attributed to steric and rigidity of the double cycloaliphatic structure. The inclusion of CHDM‐SH into the systems resulted in the synergistic effect on elongation‐to‐break and pull‐off adhesion. The HD‐SH generally resulted in a diminution of thermomechanical and coating properties, but improved the crosslink density. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Use of lignin strengthened with modified wheat gluten in biodegradable composites

In this study, composites from alkali lignin and wheat gluten, modified with different percentages of sodium silicate, were prepared and characterized. Moreover, the addition of silica to the aforementioned composites was studied with the aim of improving the thermal and mechanical properties. The effect of wheat gluten percent and the extent of its modification on the blends properties were investigated via diametric tensile strength, thermomechanical analysis (TMA), scanning electron microscope (SEM), thickness swelling and thermogravimetric analysis (TGA). The results showed significant improvement in the diametric tensile strength, thickness swelling, uniformity in the fracture surface, and the shift of glass transition temperature (T_g) toward higher values with increasing wheat gluten percent and its modification extent. These results reflect the enhancement of interaction between alkali lignin and wheat gluten. Alkali lignin/wheat gluten blends filled with silica possessed distinguishable characteristics and improved diametric tensile strength, low thermal expansion, and high T_g. Interestingly, TMA results showed that high dimensional stability against heating (thermal expansion percent) could be obtained using 60% wheat gluten modified with 15% sodium silicate and filled with 10% silica. This sample showed the highest T_g and the lowest thickness swelling in addition to smooth, uniform, and glossy surface as shown from the SEM images and TMA charts. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Controlled release of protein from magnetite–chitosan nanoparticles exposed to an alternating magnetic field

In this research, the controlled release of proteins from magnetite (Fe₃O₄)–chitosan (CS) nanoparticles exposed to an alternating magnetic field is reported. Fe₃O₄–CS nanoparticles were synthesized with sodium tripolyphosphate (TPP) molecules as a crosslinking reagent. Bovine serum albumin (BSA) was used as a model protein, and its controlled release studied through the variation of the frequency of an alternating magnetic field. The results show the successful coating of CS and BSA on the Fe₃O₄ nanoparticles with an average diameter of 50 nm. Intermolecular interactions of TPP with CS and BSA were confirmed by Fourier transform infrared spectroscopy. The application of low‐frequency alternating magnetic fields to such magnetic CS nanoparticles enhanced the protein release properties, in which the external magnetic fields could switch on the unloading of these nanoparticles. We concluded that enhanced BSA release from nanoparticles exposed to an alternating magnetic field is a promising method for achieving both the targeted delivery and controlled release of proteins. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43335.     

Characterization of stabilized porous magnetite core–shell nanogel composites based on crosslinked acrylamide/sodium acrylate copolymers

Stabilized and dispersed superparamagnetic porous nanogels based on sodium acrylate (AA‐Na) and acrylamide (AM) in a surfactant‐free aqueous system were synthesized via solution polymerization at room temperature. The formation of magnetite nanoparticles was confirmed and their properties characterized using Fourier transform infrared spectroscopy. Extensive characterization of the magnetic polymer particles using transmission electron microscopy (TEM), dynamic light scattering and zeta potential measurements revealed that Fe₃O₄ nanoparticles were incorporated into the shells of poly(AM/AA‐Na). The average particle size was 5–8 nm as determined from TEM. AM/AA‐Na nanoparticles with a diameter of about 11 nm were effectively assembled onto the negatively charged surface of the as‐synthesized Fe₃O₄ nanoparticles via electrostatic interaction. Crosslinked magnetite nanocomposites were prepared by in situ development of surface‐modified magnetite nanoparticles in an AM/AA‐Na hydrogel. Scanning electron microscopy was used to study the surface morphology of the prepared composites. The morphology, phase composition and crystallinity of the prepared nanocomposites were characterized. Atomic force microscopy and argon adsorption–desorption measurements of Fe₃O₄.AM/AA indicated that the architecture of the polymer network can be a hollow porous sphere or a solid phase, depending on the AA‐Na content. © 2013 Society of Chemical Industry     

Synthesis and characterization of (Fe3O4/MWCNTs)/ epoxy nanocomposites

A sonochemical technique is used for in situ coating of iron oxide (Fe₃O₄) nanoparticles on outer surface of MWCNTs. These Fe₃O₄/MWCNTs were characterized using a high‐resolution transmission electron microscope (HRTEM), X‐ray diffraction, and thermogravimetric analysis. The as‐prepared Fe₃O₄/MWCNTs composite nanoparticles were further used as reinforcing fillers in epoxy‐based resin (Epon‐828). The nanocomposites of epoxy were prepared by infusion of (0.5 and 1.0 wt %) pristine MWCNTs and Fe₃O₄/MWCNTs composite nanoparticles. For comparison purposes, the neat epoxy resin was also prepared in the same procedure as the nanocomposites, only without nanoparticles. The thermal, mechanical, and morphological tests were carried out for neat and nanocomposites. The compression test results show that the highest improvements in compressive modulus (38%) and strength (8%) were observed for 0.5 wt % loading of Fe₃O₄/MWCNTs. HRTEM results show the uniform dispersion of Fe₃O₄/MWCNTs nanoparticles in epoxy when compared with the dispersion of MWCNTs. These Fe₃O₄/MWCNTs nanoparticles‐infused epoxy nanocomposite shows an increase in glass transition (T_g) temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of molecular weight on shape memory behavior in polyurethane films

Understanding the relationship between the number‐average molecular weight (M_n) and the shape memory behavior of polymers is crucial for a complete picture of their thermomechanical properties, and hence for the development of smart materials, and, in particular, in textile technology. We report here on the study of shape memory properties as a function of M_n of polymers. Shape memory polyurethanes (SMPUs) of different M_n were synthesized, with various catalyst contents or molar ratio(r = NCO/OH) in the composition. In particular, two types of SMPU, namely T_m and T_g types according to their switch temperature type, were synthesized to compare the influence of M_n on their shape memory behavior. X‐ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and shape memory behavior results for the SMPUs are presented. The results indicate that the melting temperature (T_m), the glass transition temperature (T_g), the crystallinity, and the crystallizability of the soft segment in SMPUs are influenced significantly by M_n, before reaching a critical limit around 200 000 g mol^?1. Characterization of the shape memory effect in PU films suggests that the T_m‐type films generally show higher shape fixities than the T_g‐type films. In addition, this shape fixity decreases with increasing M_n in the T_g‐type SMPU, but the shape recovery increases with M_n in both types of SMPU. The shape recovery temperature, in contrast, decreases with M_n as suggested by the result of their thermal strain recovery. It is concluded that a higher molecular weight (M_n > 200 000 g mol^?1) is a prerequisite for SMPUs to exhibit higher shape recovery at a particular temperature. Copyright © 2007 Society of Chemical Industry     

Shape memory epoxy nanocomposites with carbonaceous fillers and in‐situ generated silver nanoparticles

Aim of this work is to develop a novel epoxy based nanocomposite and to analyse its shape memory behavior. In particular, silver nanoparticles are in‐situ generated within an epoxy resin subsequently filled with both carbon black (CB) and carbon nanofibers (NFs) at different ratios and at a total amount of 4 wt%. Differential scanning calorimetry shows how the introduction of both CB and NF induces a slight decrease of the glass transition temperature (T_g) of the samples. The T_g drop due to nanofiller addition determines a decrease of both flexural modulus and stress at yield with respect to the neat resin, especially at elevated CB concentrations, while the presence of Ag nanoparticles plays a positive effect on the flexural properties. The best mechanical properties can be detected at a CF/NF ratio of 50%, coupled with a noticeable decrease of the electrical resistivity down to 10² Ω·cm and an interesting heating capability through Joule effect. The electro‐mechanical shape‐memory characterization under bending configuration demonstrates how it is possible to obtain an almost complete shape recovery after 60 s under an applied voltage of 220 V. POLYM. ENG. SCI., 59:694–703, 2019. © 2018 Society of Plastics Engineers     

Facile control of high temperature shape memory polymers

Glass transition temperature (T_g) is crucial in determining application areas of high temperature shape memory polymers (SMPs), but some T_gs are difficult or uneconomic to be obtained. Here we introduce a facile way to prepare high temperature SMPs with controllable T_gs from 183 to 230 °C by copolymerization of polyimides, and relationships between T_gs and diamine components of the shape memory copolyimides agree with Fox Equation. These copolyimides can fix temporary shape and return to original shape nicely, and the possible mechanisms of their high shape fixity and shape recovery are analyzed on the basis of thermomechanical properties and molecular structures. The copolymerization of shape memory polyimides has offered an effective way to obtain high temperature SMPs with desired properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44902.     

Preparation of chitosan‐coated magnetite nanoparticles and application for immobilization of laccase

In this study, immobilization of laccase (L) enzyme on magnetite (Fe₃O₄) nanoparticles was achieved, so that the immobilized enzyme could be used repeatedly. For this purpose, Fe₃O₄ nanoparticles were coated and functionalized with chitosan (CS) and laccase from Trametes versicolor was immobilized onto chitosan‐coated magnetic nanoparticles (Fe₃O₄‐CS) by adsorption or covalent binding after activating the hydroxyl groups of chitosan with carbodiimide (EDAC) or cyanuric chloride (CC). For chitosan‐coated magnetic nanoparticles, the thickness of CS layer was estimated as 1.0–4.8 nm by TEM, isoelectric point was detected as 6.86 by zeta (ζ)‐potential measurements, and the saturation magnetization was determined as 25.2 emu g^?1 by VSM, indicating that these nanoparticles were almost superparamagnetic. For free laccase and immobilized laccase systems, the optimum pH, temperature, and kinetic parameters were investigated; and the change of the activity against repeated use of the immobilized systems were examined. The results indicated that all immobilized systems retained more than 71% of their initial activity at the end of 30 batch uses. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011