Mechanical properties of transparent poly(methyl methacrylate) nanocomposites reinforced with core–shell polyacrylonitrile/poly(methyl methacrylate) nanofibers

Having considered the mechanical and optical properties related to microstructure, the authors of the present work did a study of the in situ interface formation between polyacrylonitrile/poly(methyl methacrylate) (PAN/PMMA) core–shell nanofibers and PMMA resin so as to prepare reinforced PMMA nanocomposites (NCs). The NCs were produced using the dip-coating method. The core–shell nanofibers were generated via phase separation of PAN/PMMA solution during the conventional electrospinning. The results of attenuated total reflection-Fourier transform infrared spectroscopy, transmission electron microscope, and energy dispersive X-ray spectrometer confirmed the formation of core–shell structure of the PAN/PMMA nanofibers. According to the findings of the study, the NCs reinforced with 1.7% volume fractions (v _f) of the core–shell nanofibers, having the composition of 50/50 (PAN/PMMA), had the highest tensile and bending properties. The obtained results showed that by increasing the v _f of nanofibers from 1.7 to 2.9%, the tensile and bending moduli increased by 29.9 and 44.2%, respectively. Increasing v _f to 5.7% decreased the just-mentioned properties. Moreover, the transparency of NCs decreased by less than 1, 10, and 18%, respectively, when the aforementioned volume fractions were applied. The theoretical values for the tensile modulus were calculated using the models proposed by Manera, Pan, and Halpin–Tsai–Nielsen. The best prediction was made when the model proposed by Halpin–Tsai–Nielsen was applied.     

The preparation and characteristics of poly(methyl methacrylate–methylacrylate acid)/nano-ZnO composite latex particles

In this work, poly(methyl methacrylate-co-methylacrylate acid)/ZnO (poly(MMA–MAA)/ZnO) composite latex particle was synthesized by three steps The first step was to synthesize poly(MMA–MAA) copolymer latex particles by soapless emulsion polymerization. Following the first step, the second step was to polymerize MMA, MAA and 3,3-(trimethoxysilyl) propyl methacrylate (MPS) in the presence of poly(MMA–MAA) seed latex particles to form the poly(MMA–MAA)/poly(MMA–MAA–MPS) core–shell latex particles. In the third step, the poly(MMA–MAA)/poly(MMA–MAA–MPS) latex particles reacted with ZnO nanoparticles, which were synthesized by a traditional sol gel method, to form the polymer/inorganic poly(MMA–MAA)/poly(MMA–MAA–MPS)/ZnO composite latex. In this study, MPS with silanol groups essentially was used as the coupling agent to couple with ZnO nanoparticles, while the results of the study showed that there was not covalent bond existed between ZnO particles and polymer latex. The ZnO particles were adsorbed on the surface of polymer latex by electrostatic interaction. Besides, the linear poly(MMA–MAA)/crosslinking poly(MMA–MAA–MPS) core–shell latex particles which were synthesized in the second step were heated in the presence of ammonia to form the hollow poly(MMA–MAA–MPS) latex particles. The factors of heating time and concentration of crosslinking agent significantly influenced the morphology of hollow poly(MMA–MAA–MPS) latex particles.     

Thermodynamic and kinetic studies of crystal violet dye adsorption with poly(methyl methacrylate)–graphene oxide and poly(methyl methacrylate)–graphene oxide–zinc oxide nanocomposites

We successfully prepared poly(methyl methacrylate) (PMMA)–graphene oxide (GO) and PMMA–GO–zinc oxide (ZnO) nanocomposites and characterized them using different techniques. The adsorption performances of the as-prepared composites were investigated for crystal violet (CV) dye removal. The contact time as a main factor affecting the adsorption process by adsorbents was studied. Because the adsorption capacity value for CV was found to show no extensive changes after 35 min, 35 min was selected as the best contact time for our system. The adsorption results revealed that the best capacity of CV adsorption onto the PMMA–GO and PMMA–GO–ZnO nanocomposites occurred at pH 12 and 298 K. The respective entropies (−0.208 and −0.168 kJ mol⁻¹ K⁻¹) and enthalpies (−72.86 kJ/mol, and −55.54 kJ/mol) for PMMA–GO and PMMA–GO–ZnO and Gibbs energy revealed that the process of adsorption was exothermic. In addition, the Elovich, pseudo-first-order, intraparticle diffusion, and pseudo-second-order (four types) models were applied to our kinetic study. Our results indicate that CV adsorption onto PMMA–GO and PMMA–GO–ZnO was good with the pseudo-second-order (type 1) and pseudo-first-order models because of the low χ² value and the high correlation coefficient value. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47495.     

Modeling of interdiffusion in poly(vinyl acetate)–poly(methyl methacrylate)–toluene multicomponent systems

Work on interdiffusion has been mainly carried out in binary systems in the past, and this work has focused on polymer–solvent (S) systems and polymer blends. To understand and predict the interdiffusion of two solids in the presence of one S, we present a new mathematical model based on the Onsager approach. Within our model, interdiffusion kinetics are described with a modification of the reptation model for long polymer chains, and the chemical potential gradient is used as the driving force behind mass transfer. The chemical potential is calculated with a Flory–Huggins approach. The model was validated with 29 Raman spectroscopy experiments in poly(vinyl acetate)–poly(methyl methacrylate)–toluene systems at 20 °C. Monomer mobilities (L _i,0s) were determined for both polymers to show the independence of L _i,0 from the chain length. The L _i,0s were found to be strongly dependent on the S content. With the knowledge of phase equilibria and L _i,0s, interdiffusion in the ternary polymer–polymer–S system could be predicted by the introduced model. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47092.     

Rubber toughening of unsaturated polyester with core–shell poly(siloxane)-epoxy microspheres

In this paper, we have explored the potential of core–shell poly(siloxane)-epoxy microspheres towards improving the dynamic properties of a conventional unsaturated polyester (USP). Micro-sized poly(siloxane) beads were prepared by suspension polymerisation route, where the particle dimensions could be tailored by varying the operating parameters, particularly stirring speed and feed concentration. The core was subsequently coated with epoxy to form an external layer compatible with the USP resin, with an aim to aid its homogeneous dispersion in the thermosetting resin. Toughened USP composites containing varying amounts of both coated and uncoated microspheres (3–10 % w/w) were prepared by curing under ambient conditions, and their mechanical properties were evaluated under both quasi-static and dynamic loading conditions. The introduction of epoxy-coated poly(siloxane) led to a proportional decrease in the tensile strength and modulus, which were found to compare well with the predictions based on Halpin–Tsai and Lewis–Nielson empirical models. Significant improvements in the impact strength of USP could be achieved, and under optimised conditions, 101 % increase in the impact strength was observed, which corroborated with significant increase in mean critical stress intensity factor (76 %). Morphological investigations of the fractured surface revealed the presence of characteristic features which were used to establish the underlying routes responsible for the toughened nature of the USP composites.     

One-step synthesis of pH-sensitive poly(Acrylamide-co-Sodium Acrylate) beads with core–shell structure

This work describes a novel one-step method to prepare poly(AMm-co-AAcNa) pH-sensitive hydrogel beads with core–shell structure induced by a spontaneous phase separation process during polymerization. In virtue of the phase separation process, polymers with high molecular weight separate to the core phase whereas monomers are left in the shell. This redistribution inside the droplets enables the polymerization environment change sharply to endow the beads with different network structure in core and shell. FTIR spectrum and EDS show that core and shell share identical composition; yet GPC exhibits a bimodal molecular weight distribution which lead to a conventional network in core but a rich-in-branch network in shell. This difference in structure results in mainly three discrepancies in performance. The level of volume change that the beads exhibit at about pH = 4 is much more intense for shell than for core; the swelling/shrinking kinetics of the core and shell indicates that shell responses about 30 times faster than core does; fitting of the absorbency capacity exhibited that the ones of the core and shell are about 67 g/g and 2126 g/g, respectively. A microfluidic device with co-axial channel structure is introduced in this fabrication. The hydrogel beads exhibited narrow size distribution and the diameter of core and shell could be freely controlled by the high controllability of microfluidic technology and by manipulating the phase separation process. In sum, this method impart us an easy and fast-running way to obtain hydrogel beads with core–shell structure, which has potential in various applications like optical material, lenses and sensors.     

Synthesis of cyclic poly(methyl methacrylate) by the intramolecular cyclization of α-amino, ω-carboxyl heterodifunctional poly(methyl methacrylate)

Summary α-Amino, ω-carboxyl heterodifunctional poly(methyl methacrylate) was prepared by a living anionic polymerization of methyl methacrylate using N,N'-diphenylethylenediamine monolithium amide and succinic anhydride as an initiator and terminator, respectively. Its intramolecular cyclization was carried out to obtain a well-defined cyclic poly(methyl methacrylate). Received: 27 June 2001/Accepted: 16 July 2001     

Effects of liquid–liquid phase separation on crystallization of poly(ethylene glycol) in blends with isotactic poly(methyl methacrylate)

To analyze the interplay between crystallization and liquid–liquid phase separation (LLPS), isothermal crystallization behavior of poly(ethylene glycol) (PEG) in blends with isotactic poly(methyl methacrylate) (i-PMMA) was investigated by differential scanning calorimetry (DSC). The blend system had an upper critical solution temperature (UCST) type phase diagram. When the crystallization occurred simultaneously with LLPS, the overall crystallization rate was enhanced at high crystallization temperatures T_c, relatively compared with that of neat PEG. This behavior was interpreted by the combination of the effects of spinodal quench depth ?T_s and usual supercooling degree ?T_c, according to the theory of Mitra and Muthukumar, namely, the crystallization rate is enhanced by the concentration fluctuation-assisted nucleation at high T_c. In the crystallization after LLPS proceeded, on the other hand, the overall crystallization rate was slow and less dependent on the blend composition. In addition, it was revealed by small-angle X-ray scattering measurements that amorphous i-PMMA was excluded from the interlamellar region of PEG crystals in SQ as well as WQ.     

Preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures

In this article, we report an original and feasible protocol for the preparation of superparamagnetic β-cyclodextrin-functionalized composite nanoparticles with core–shell structures via cross linking reaction on the surface of carboxymethyl β-cyclodextrin-modified magnetite (Fe₃O₄) nanoparticles by using epichlorohydrin as a crosslinking agent. The structure and morphology of the prepared composite nanoparticles were studied by Fourier transform infrared spectrometry, X-ray diffraction measurement, transmission electron microscopy and the thermogravimetric analysis. The results show that the prepared roughly spherical composite nanoparticles (diameter about 10–20 nm) with core–shell structures turned out to be magnetite nanoparticles surface-surrounded by a layer of cross-linked CM-β-cyclodextrin polymer. Results of vibrating sample magnetometry testing and inclusive behaviour studying confirmed the superparamagnetism with saturation magnetization value of 52.0 emu/g in an external applied magnetic field of 20000 Oe and inclusion functionality of the composite nanoparticles consisting of magnetite cores and β-cyclodextrin moiety, which implies very important applications in targeting drug delivery technology and separation for specific substances.     

Preparation of clay–poly(glycidyl methacrylate) composite support for immobilization of cellulase

A composite material was synthesized by grafting of glycidyl methacrylate onto clay using surface initiation atom transfer radical polymerization (SI-ATRP) technique. Epoxy group of the grafted p(GMA) chains was reacted with hexamethylenediamine (HMDA). The composite material was characterized using scanning electron microscopy (SEM) and FTIR. Cellulase from Trichoderma reesei was immobilized on the aminated composite particles via adsorption and covalent binding methods. The amounts of adsorbed enzyme on the aminated composite particles were 43.4 mg/g. The recovered activities of the adsorbed and covalently immobilized cellulase were found to be 87.7% and 73.2% for the substrate, carboxymethyl cellulose (CMC, 1.0 g/L). The pH stabilities and thermo-stabilities, repeated use and storage stabilities of both immobilized cellulase preparations were evaluated. The immobilized cellulase preparations have better stabilities and higher retained activities with respect to pH, temperature and storage than those of the free enzyme. Operational stability of the covalently immobilized cellulase was tested in a continuous flow system, and the activity loss was about 4% at the end of 48 h operation period.     

Preparation of poly[(vinyl alcohol)-co-(methyl methacrylate)] by oxidative transformation of C–Si bond in poly[di(isobutoxy)phenylvinylsilane-co-(methyl methacrylate)]

Radical copolymerization of di(isobutoxy)methylvinylsilane 1 and di(isobutoxy)phenylvinylsilane 2 with methyl methacrylate (MMA) and n-butyl acrylate (n-BA) was carried out, and the oxidative cleavage of Si–C bonds in the resulting copolymers was examined to prepare copolymers having repeating units of vinyl alcohol (VA). Although the incorporation of 1 and 2 in the copolymerization of these alkoxyvinylsilanes with MMA was not so effective (1 or 2 content < 18 mol%), MCPBA-induced oxidative transformation of a poly(2-co-MMA) with 9.0 mol% of 2 content proceeded efficiently, giving a poly[(vinyl alcohol)-co-MMA]. On the other hand, whereas poly(1 or 2-co-n-BA)s with relatively higher 1 or 2 contents (up to 45 mol%) can be prepared by the radical copolymerization of 1 or 2 with n-BA, oxidation of the copolymers afforded insoluble products.     

Nanocomposite particles with core–shell morphology III: preparation and characterization of nano Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–poly(styrene–methyl methacrylate) particles via miniemulsion polymerization

Encapsulation of inorganic nanoparticles (as a core) by polymers (as a shell) is one of the interesting research subjects that lead to the synthesis of nanocomposite. These materials include properties of not only the organic polymer (e.g. optical properties, toughness, processability, flexibility, etc.) but also the inorganic nanoparticles (e.g. mechanical strength, thermal stability, etc.). Some of the applied preparative methods are dry-spray, dispersion, suspension, emulsion and miniemulsion polymerization techniques. Here, miniemulsion polymerization technique was used in order to obtain white-color nanocomposite latex particles containing nano-alumina (40–47 nm) encapsulated by copoly [styrene (St)–methyl methacrylate (MMA)] under high-shear ultrasonic irradiation. At first, bare nano-alumina was encapsulated with the copolymer to obtain latex particles. In another attempt and in order to investigate the effect of compatiblizing system, alumina nanoparticles were coated with oleic acid in order to form modified alumina core. Then miniemulsion polymerization was performed in the minidroplets including modified alumina, St and MMA for obtaining core/shell nanocomposite particles. The progress of encapsulation polymerization was followed by different instrumental techniques such as FT-IR spectra, thermal gravimetric analysis, dynamic light scattering, induced-coupled plasma, TEM and SEM.     

Poly(methyl methacrylate)-functionalized reduced graphene oxide-based core–shell structured beads for thermally conductive epoxy composites

Thermally conductive epoxy nanocomposite with core–shell structured filler beads has been prepared. The core represents plasma-treated poly(methyl methacrylate) bead, and the shell, amine-functionalized reduced graphene oxide (frGO) sheets. The negatively charged core and the positively charged shell form core–shell unified structure through electrostatic attraction and the conductive bridges are formed among neighboring filler particles in the composite mass. The epoxy composite prepared with these core–shell structured filler shows a thermal conductivity of 0.72 W m⁻¹ K⁻¹ for an overall frGO concentration of as low as 0.96 wt %. Pal model has been applied to evaluate the effective thermal conductivity of frGO sheets that have been realized in the epoxy composition. Assuming the maximum possible volume packing fraction of the spherical beads for random jamming to be equal to 0.63, the effective thermal conductivity has been estimated as 280 W m⁻¹ K⁻¹. Evaluation of the effective thermal conductivity is a step forward to in-depth study of real contribution of the highly conductive fillers in the polymer composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47377.     

Controlled release of doxycycline within core/shell poly(ε-caprolactone)/poly(ethylene oxide) fibers via coaxial electrospinning

The development of fibers with desired drug release properties has gained a high research interest for water-soluble drugs with controlled drug delivery systems obtained by coaxial electrospinning technique. The objective of this study is to achieve the controlled-release of doxycycline hyclate (DOXH) from the fabricated electrospun fibers. In this case, three different electrospun core/shell fibers have been successfully fabricated using this technique and the model drug, DOXH, has been entrapped in the core layers. The results of the structural properties and in vitro release studies have been compared with electrospun monostructural fibers fabricated by conventional electrospinning technique. Scanning electron microscopy and transmission electron microscopy images have proved that the fabricated electrospun fibers have core/shell structures. Fourier transform infrared spectroscopy has shown convenient interaction and compatibility between polymers and the model drug. X-ray diffraction analysis has revealed that all the encapsulated DOXH are transferred into amorphous physical state and lost its crystalline state in the fibers. Moreover, drug release studies have demonstrated that the electrospun core/shell fibers show a better-controlled release than the monostructural fibers. It can be concluded that the fibers obtained by blending hydrophilic and hydrophobic polymers such as poly(ε-caprolactone) and poly(ethylene oxide) in both shell and core sides are promising candidate for controlled drug release.     

Electrospun biocompatible poly (ε-caprolactonediol)-based polyurethane core/shell nanofibrous scaffold for controlled release of temozolomide

The electrospun biocompatible poly (ε-caprolactonediol)-based polyurethane (PCL-Diol-b-PU) core/shell nanofibrous scaffolds were prepared via the coaxial electrospinning process. Temozolomide (TMZ) as an anticancer drug was loaded into the core of fibers to control the release of TMZ for the treatment of glioblastoma. The properties of nanofibers were characterized using XRD, FTIR, SEM, and TEM analysis. The sustained delivery of TMZ without initial burst release was achieved from all prepared core–shell nanofibrous samples over 30 days. The cytotoxicity results revealed that the TMZ-loaded PCL-Diol-b-PU core–shell nanofibers could be used as a drug delivery implant to deliver TMZ against glioblastoma tumors.     

Preparation in supercritical CO2 of porous poly(methyl methacrylate)–poly(l-lactic acid) (PMMA–PLA) scaffolds incorporating ibuprofen

Partially biodegradable porous scaffolds incorporating bioactive molecules prepared by clean techniques posses an enormous interest in tissue engineering applications. Poly(methyl methacrylate)–poly(l-lactic acid) (PMMA–PLA) blends were submitted to CO₂ supercritical conditions (P = 160–260 bar, T = 60 °C) after certain time and then rapidly depressurized to obtain porous structures that have been related with the supercritical parameters and to the polymer blend composition. In some cases ibuprofen was also incorporated to the formulations previously to the CO₂ treatment and studied the appropriate conditions for avoiding its extraction in SCCO₂. Scaffolds purity, thermal transitions, swelling and degradation behaviour, and the ibuprofen release were also studied to determine the appropriate scaffolds with a desired porosity for cell seeding. Cell culture was performed on the selected porous scaffolds using human fibroblast examined by scanning electron microscopy (SEM).     

Immobilization of lysozyme on poly(N-isopropyl acrylamide)/2-hydroxyethyl methacrylate copolymer core–shell gel beads

The immobilization of chicken egg white lysozyme (Lyz) molecules on poly(N-isopropyl acrylamide) gel beads containing 2-hydroxyethyl methacrylate (HEMA) (PGBH) was studied as a function of temperature and HEMA content. Using dynamic and static light scattering measurements, nanometer-sized PGBH particles were shown to exhibit thermo-responsive behavior, and aggregate formation occurred during temperature changes from 25 to 40 °C. The radii of PGBH and Lyz-immobilizing PGBH, the amount of immobilized Lyz and the activity of immobilized Lyz depended on both HEMA content and temperature. Moreover, the activity of immobilized Lyz also depended on the molecular size of the substrates, and the Lyz immobilized on PGBH particles with higher HEMA content showed activity toward low molecular weight substrates at 40 °C nearly equal to that of native Lyz, which indicates that no conformational change in the Lyz molecule occurred after immobilization. These results demonstrate that changes in the activity of the immobilized Lyz were due to a balance of an increase in the affinity between the substrate and Lyz resulting from concentration effects and the steric hindrance between the substrate and Lyz incorporated into the PGBH aggregates with increasing HEMA content and temperature. Furthermore, these results demonstrate that PGBH is a useful material as an enzyme immobilization carrier.     

Preparation of core–shell impact modifier particles for PVC with nanometric shell thickness through seeded emulsion polymerization

The improvement in toughness of rigid polymers like poly(vinyl chloride) (PVC) has been of great interest for developing their applications. This could be provided by designing impact modifiers which could be blended with the polymeric matrix. Here, core–shell type impact modifier particles with different glass transition temperatures of the shell and specifically, with nanometric shell thickness were prepared through seeded emulsion polymerization. The core consisted of polybutadiene particles and the shell was made of poly(methylmethacrylate-co-butyl acrylate) that was grafted onto the surface of the seed particles. The polymerization reaction was optimized and the resulting latex particles were well characterized by several techniques such as DSC, DLS, SEM, and TEM. It was found that the core–shell particles have diameters of about 350–360 nm, including the shell with thickness of almost 20–30 nm and glass transition temperatures ranging between 70 and 120 °C. The prepared particles were blended with PVC and the corresponding impact strengths of the moldings were measured by means of Izod impact test. The impact results revealed that by decreasing T _g of the shell in impact modifier particles, the impact resistance of the molded sheets increased remarkably. Also the brittle–ductile transition temperatures (BDTT) of the prepared blends were studied and an increase in BDTT was found with lowering T _g of the shell.     

Preparation of the stable core–shell latex particles containing organic-siloxane in the shell

In this study, the latex particles with a polyacrylate core and a polydimethylsiloxane shell via 3-(methacryloxypropyl)-trimethoxysilane as the space arm to link the core and shell have been prepared by semi continuous seeded emulsion polymerization. And several key polymerization reaction conditions such as the emulsifier concentration, 3-(methacryloxypropyl)-trimethoxysilane dosages, feeding sequence and the acrylates/siloxanes ratio were detailedly discussed. Then, the optimal condition to prepare stable core/shell particles was selected and a proper preparation process has been established. The as-synthesized particles were characterized by TEM and XPS. The clear core/shell structure of the particles could be observed through analysis TEM. In addition, the results of XPS analyses manifested that siloxanes had been grafted on the surface of the polyacrylate particles and they distributed on the outmost layer of the particles. Finally, the surface hydrophobicity of the film formed by latex particles was investigated by the water absorption ratio measurement. The results indicated the developed latex particle provided with a fair water-repellency property.     

Preparation of conducting composite particles of styrene–methyl acrylate copolymer as the core and graphite-incorporated polypyrrole as the shell by surfactant-free mini emulsion polymerization

A series of nearly monodispersed poly(styrene–methyl acrylate) (SMA) copolymer latex particles were coated with polypyrrole having different graphite contents. The composite particles were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The d.c. conductivity and the electrochemical behaviour of the particles were studied by using a standard four-probe method and a cyclic voltameter respectively. The dependence of electrical conductivity of the composites on the concentration of graphite in the polypyrrole shell, the methyl acrylate content in SMA copolymer and the temperature was also investigated. The electrical conductivity of the samples can be tuned by varying the graphite content in the polypyrrole shell phase. The d.c. conductivity decreases with increasing methyl acrylate content in the core particles. Electrochemical study (at a scan rate of 50 mV s⁻¹) reveals that the particles are sufficiently stable under redox potential and should find potential applications in various optoelectronic devices.