Free Radical Polymerization Process Research Articles

Hybrid membranes of nanostructrual copolymer and ionic liquid for carbon dioxide capture

Efficient CO2 capture membranes were prepared using a hybrid comprising the poly(styrene-block-butadiene-block-styrene)-graft-poly(oxyethylene methacrylate) (SBS-g-POEM) nanostructural copolymer and the ionic liquid (IL) 1-ethyl-3-methylimidazolium dicyanamide (EMIMDCA). The SBS-g-POEM copolymer was synthesized via a mass-producible, cheap, free-radical polymerization process. The specific interaction of SBS-g-POEM with EMIMDCA and the good miscibility of these species were confirmed by Fourier transform infrared spectroscopy (FT–IR) and wide angle X-ray scattering (WAXS) and by using a universal testing machine (UTM). The microphase-separated nanostructure of the membranes and uniform distribution of EMIMDCA were also observed using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The neat SBS membrane exhibited a CO2 permeability of 372 Barrer (1 Barrer=10−10cm3(STP)·cm/(cm2·s·cmHg) and CO2/N2 selectivity of 16.4; these values increased to 407 Barrer and 21.6, respectively, for the SBS-g-POEM membrane due to the high CO2 affinity of the polar POEM side chains. Upon incorporation of EMIMDCA, the CO2 permeability increased to 514 Barrer without a large sacrifice of the selectivity. In contrast, the blend of neat SBS and EMIMDCA did not show any gas separation ability due to the inhomogeneity and poor mechanical properties, indicating the importance of grafting POEM to the SBS main chains.

Preparation of Quantum Dots Hydrogel Nanocomposites with Improved Cytotoxicity.

Nanocomposites are materials with unique properties and a wide range of applications. The combination of different nanostructures with traditional materials gives a variety of possibilities that should be analyzed. Especially, functional fluorescent semiconductor quantum dots (QDs) embedded in polymeric matrices have shown promising fluorescence and biocompatibility properties. These hybrid materials can be used in medical applications such as biodiagnostic and bioimaging. In this study, two hydrogels, one of polyethylene glycol diacrylate (PEGDA) and other of polyacrylamide (PAAm), were prepared with quantum dots of CdTe (4 nm of diameter) and characterized. The aim of this research was to analyze the optical properties of the nanocomposites and their cell viability. QDs nanocomposites were fabricated by a free radical polymerization process. The optical studies showed that the nanocomposites have well defined properties of fluorescence. To study the biocompatibility of the nanocomposites, metastatic B16f10 cell line were used and MTT assay was performed. The nanocomposites had a significant improved cell viability compared with QDs solutions.

Graft Copolymerization of N-Isopropylacrylamide and Acrylic Acid on Bentonite Colloids for In-Depth Fluid Diversion

A new cost-effective in-depth fluid diversion has been developed and reported. In this paper, the diverting agent is prepared successfully from natural bentonite particles that were modified with N-isopropylacrylamide (NIPAM) and acrylic acid (AA) copolymers. First, bentonite particles were intercalated with small precursor molecules that contained functional groups. These precursors were used to reduce the bentonite particle size and introduce a vinyl group for subsequent polymerization. Then, poly(NIPAM-co-AA) was grafted onto hydrophilic bentonite through a free radical polymerization process. The grafted bentonite morphology, microstructure, and thermal stability were investigated using FTIR spectroscopy, dynamic light scattering, XRD, and TGA measurements. The particle dispersion stability and rheological properties have been investigated by using a turbidimeter and rheometer. Sand packs and core flooding tests were conducted to investigate the injectivity and determine permeability reductions. Exper...

Removal of dye by carboxymethyl cellulose, acrylamide and graphene oxide via a free radical polymerization process

Carboxymethyl cellulose has been used for the design of novel engineered hydrogels in order to obtain effective three-dimensional structures for industrial applications. In this work, dye removal carboxymethyl cellulose-acrylamide-graphene oxide (CMC-AM-GO) hydrogels were prepared by a free-radical polymerization method. The GO was developed by the modified Hummers method. The CMC-AM-GO and GO were characterized by FTIR, XRD and SEM. The swelling and swelling kinetics were calculated using gravimetric process. The kinetic parameter, swelling exponent values [n=0.59–0.7507] explained the fact that the CMC-AM-GO hydrogles have super Case II diffusion transport mechanism. CMCx-AM-GO (x=1–4) and CMC-AM hydrogels were used for removal of Acid Blue-133. The result explains that composite hydrogels significantly removed the acid blue when compared to the neat hydrogel. The maximum AB absorption (185.45mg/g) capacity was found in the case of CMC2-AM-GO hydrogel. Therefore, cellulose-based GO hydrogels can be termed as smart systems for the abstraction of dye in water purification applications.

Fabrication of magnetic nanoparticles armed with quaternarized N-halamine polymers as recyclable antibacterial agents

Magnetic recyclable bactericidal nanocomposites (Fe3O4@PDMC) were well-designed and prepared by coating of Fe3O4 nanoparticles with quaternarized N-halamine polymers via the free radical polymerization process. In which, 5,5-dimethylhydantoinyl-(3-ethyl-methacrylamine)propyl dimethylammonium bromide (DEMPA), a new monomeric N-halamine precursor, was used as a coating material as well as the dual-functional bactericidal agent. The developed Fe3O4@PDMC nanocomposites exhibited suitable size and super-paramagnetic responsibility. The antibacterial results showed that the Fe3O4@PDMC nanocomposites had excellent biocidal abilities against Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative). Furthermore, the TTC (Triphenyl Tetrazolium Chloride)–dehydrogenase activity assay confirmed that the reductions of the bacteria were mainly attributed to powerful biocidal effects of the coating polymer instead of bacteria capture by the cationic surface. Interestingly, due to the magnetic responsive performance of Fe3O4, the as-prepared Fe3O4@PDMC nanocomposites can be recycled by a magnet and reused for antibacterium through the quenching/rechlorination procedure. All the results presented in this study show that the proposed Fe3O4@PDMC nanocomposites could be a competitive candidate for water purification systems and household sanitation.

Synthesis by In Situ‐Free Radical Polymerization, Characterization, and Properties of Poly (n‐butyl methacrylate)/Samarium‐Doped Titanium Dioxide Nanoparticles Composites

AbstractUsing free radical polymerization process a series of samarium‐doped titanium dioxide (Sm3+‐doped TiO2) nanoparticles containing poly (n‐butyl methacrylate) (PBMA) composites were synthesized. The fabricated samples were characterized by XPS, FTIR, UV, XRD, DSC, TGA, flame retardancy studies, and impedance analyser. The shift in FTIR peak of the nanocomposites to higher wavenumber indicates the interfacial interaction between nanoparticles and PBMA. The UV spectra indicated that the metal oxide nanoparticles could enhances the interfacial interaction in the polymer composites. SEM images showed the uniform dispersion of nanoparticles into the macromolecular chain of PBMA. XRD patterns of the composites indicated the ordered arrangement of nanoparticles within the polymer and the regularity of the chain improved by the increase in concentration of nanoparticles. Better flame resistance and thermal stability were attained by the addition of nanoparticles. The flame retardancy and thermal stability of the composites were improved with the increase in concentration of Sm3+‐doped TiO2. The glass transition temperatures of the composites were much enhanced by the increase in weight percentage of nano‐filler. The AC conductivity, dielectric constant and dielectric loss tangent of the composites were higher than the pure PBMA and these properties enhanced with the loading of nanoparticles up to 7 wt.% and thereafter the values decreases.

Modification of Microelectrode Surface with Hydrogel Layers and Determination of Pore Size in Layers

Hydrogels are three dimensional networks filled with water. Some of the gels can undergo fast, reversible volume phase transition (VPT) in response to a change in environmental conditions. During the transition the gels transform from one state to another (swollen/ shrunken) by changing content of water in the network. Interestingly, the gels have properties of both: solids and liquids. In the macroscopic scale the structure of the network is responsible for the mechanical energy storage. In the microscopic scale the gels exhibit the properties of water: their density is similar and diffusion processes occur in the network [1]. Pores and channels of nanometer size are employed to separate the analytes by size and to control their transport. The size of the pores could be easily changed in the hydrogel matrix by involving the shrinking and swelling process especially in the gels with continuous volume phase transition. The main aim of this paper was to develop an electrochemical method of obtaining the NIPA- and NIPA-co-AA hydrogel films on the microelectrode surface without previous surface functionalization. Another aim was to determine the size of pores/channels in NIPA- and NIPA-co-%AA gels and to evaluate porosity of the gels. The hydrogel films were anchored to the microelectrode surface via electrochemically induced free radical polymerization (EIFRP) process with utilizing the chronoamperometric method. We found that cyclic voltammetry could be also successfully applied to obtain thin hydrogel layers. The electrochemical studies of the discontinuous volume phase transition and the determination of the channel size were done using the ferrocene molecules modified with polyethylene glycol units (PEG) of various length. Figure 1. Woltamperograms obtained during the electrochemically induced free radical polymerization on platinum microelectrode This work was supported by a grant from the National Science Centre of Poland, Preludium 8, 2014/15/ST5/01980 [1] A. B. Imran, T. Seki, Y. Takeok, Polymer Journal, 2010, 42, 839–851 Figure 1

Quartz Crystal Microbalance Electrode Modified with Thermoresponsive Crosslinked and Non-Crosslinked N- Isopropylacrylamide Polymers. Response to Changes in Temperature

Electrochemical quartz crystal microbalance (EQCM) electrode was modified with environmentally sensitive polymers. The polymer layers on the electrode were composed of either crosslinked or non-crosslinked thermoresponsive poly(N-isopropylacrylamide). For anchoring thin gel films on the electrode surface the electrochemically induced free-radical polymerization (EIFRP) was employed. The electroreduction of the peroxydisulfate anion led to generation of free radical. This radical initiated the free radical polymerization process that led to the formation of a thin gel layer attached to the electrode surface. To monitor in situ the growth of the polymer film the changes in resonant frequency of the quartz-crystal were recorded. A significant decrease in the frequency (growth of the layer) was seen in the potential range where the reduction of peroxydisulfate anion took place. The morphology of the layers was examined with a scanning electron microscopy (SEM). The phenomenon of volume phase transition (shrinking/swelling process) in the gel layers initiated by a change in temperature was investigated. Unexpected big, sharp and of negative sign minima appeared at the change-in-frequency vs. temperature plots. These minima were not seen in the plots obtained for the polymers without linker. That situation should be useful in the investigation of chemical interactions proceeding under the conditions of volume phase transition. The influence of volume phase transition on the transport of a member of a model red-ox system, ferro- and ferricyanide couple, and therefore on height of its voltammetric response was examined. The changes in electrochemical properties of the layers induced by volume phase transition were monitored with electrochemical impedance spectroscopy.

3D Printing of Micropatterned Anion Exchange Membranes.

Micropatterned anion exchange membranes (AEMs) have been 3D printed via a photoinitiated free radical polymerization and quaternization process. The photocurable formulation, consisting of diurethane dimethacrylate (DUDA), poly(ethylene glycol) diacrylate (PEGDA), dipentaerythritol penta-/hexa- acrylate, and 4-vinylbenzyl chloride (VBC), was directly cured into patterned films using a custom 3D photolithographic printing process similar to stereolithography. Measurements of water uptake, permselectivity, and ionic resistance were conducted on the quaternized poly(DUDA-co-PEGDA-co-VBC) sample series to determine their suitability as ion exchange membranes. The water uptake of the polymers increased as the ion exchange capacity (IEC) increased due to greater quaternized VBC content. Samples with IEC values between 0.98 to 1.63 mequiv/g were synthesized by varying the VBC content from 15 to 25 wt %. The water uptake was sensitive to the PEGDA content in the network resulting in water uptake values ranging from 85 to 410 wt % by varying the PEGDA fractions from 0 to 60 wt %. The permselectivity of the AEM samples decreased from 0.91 (168 wt %, 1.63 mequiv/g) to 0.85 (410 wt %, 1.63 mequiv/g) with increasing water uptake and to 0.88 (162 wt %, 0.98 mequiv/g) with decreasing IEC. Permselectivity results were relatively consistent with the general understanding of the correlation between permselectivity, water uptake, and ion content of the membrane. Lastly, it was revealed that the ionic resistance of patterned membranes was lower than that of flat membranes with the same material volume or equivalent thickness. A parallel resistance model was used to explain the influence of patterning on the overall measured ionic resistance. This model may provide a way to maximize ion exchange membrane performance by optimizing surface patterns without chemical modification to the membrane.

Quartz crystal microbalance electrode modified with thermoresponsive crosslinked and non-crosslinked N-isopropylacrylamide polymers. Response to changes in temperature

Electrochemical quartz crystal microbalance (EQCM) electrode was modified with environmentally sensitive polymers. The polymer layers on the electrode were composed of either crosslinked or non-crosslinked thermoresponsive poly(N-isopropylacrylamide). For anchoring thin gel films on the electrode surface, the electrochemically induced free radical polymerization (EIFRP) was employed. The electroreduction of the peroxydisulfate anion led to generation of free radical. This radical initiated the free radical polymerization process that led to the formation of a thin gel layer attached to the electrode surface. To monitor in situ the growth of the polymer film the changes in resonant frequency of the quartz crystal were recorded. A significant decrease in the frequency (growth of the layer) was seen in the potential range where the reduction of peroxydisulfate anion took place. The morphology of the layers was examined with a scanning electron microscopy (SEM). The phenomenon of volume phase transition (shrinking/swelling process) in the gel layers initiated by a change in temperature was investigated. Unexpected big, sharp, and of negative sign minima appeared at the change-in-frequency vs. temperature plots. These minima were not seen in the plots obtained for the polymers without linker. That situation should be useful in the investigation of chemical interactions proceeding under the conditions of volume phase transition. The influence of volume phase transition on the transport of a member of a model red-ox system, ferro- and ferricyanide couple, and therefore on height of its voltammetric response was examined. The changes in electrochemical properties of the layers induced by volume phase transition were monitored with electrochemical impedance spectroscopy.

Study of the morphology and the adsorption behavior of molecularly imprinted polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization process based on two functionalized β-cyclodextrin as monomers

The adsorption behavior of molecularly imprinted polymers (MIPs) prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization process through the effect of polymer morphologies was described. In this study, two kinds of RAFT-MIPs were synthesized based on methacrylic acid functionalized β-cyclodextrin (MAA-β-CD) and 2-hydroxyethyl methacrylate functionalized β-cyclodextrin (HEMA-β-CD) monomers, represented as RAFT-MMIP and RAFT-HMIP, respectively. The results of RAFT-MIPs were respectively compared with MMIP and HMIP prepared by free radical polymerization (FRP) process (without RAFT agent). The Field Emission Scanning Electron Microscope (FESEM) images showed that the RAFT-MMIP had slightly spherical and spongy-porous structure, and the MMIP had rough surface structure. Besides, the surface area of RAFT-MMIP was larger than MMIP. In contrast, the RAFT-HMIP formed non-porous particles with a smooth surface structure, while the HMIP formed a porous structure with a large surface area size. Through their physical characteristics, it proved that the morphological properties played an important factor which affected the adsorption behavior properties of MIPs, including kinetic, isotherm and thermodynamic studies. The superior physical characteristics of RAFT-MMIP demonstrated the greater equilibrium contact time, fast kinetic adsorption, higher adsorption rate, enhanced adsorption capacity and higher binding affinity. However, the non-porous RAFT-HMIP structure was poor in the adsorption behavior system. The RAFT polymerization successfully worked depending on the monomer used to generate potential MIPs.

Determining Free‐Radical Propagation Rate Coefficients with High‐Frequency Lasers: Current Status and Future Perspectives

Detailed knowledge of the polymerization mechanisms and kinetics of academically and industrially relevant monomers is mandatory for the precision synthesis of tailor-made polymers. The IUPAC-recommended pulsed-laser polymerization-size exclusion chromatography (PLP-SEC) approach is the method of choice for the determination of propagation rate coefficients and the associated Arrhenius parameters for free radical polymerization processes. With regard to specific monomer classes-such as acrylate-type monomers, which are very important from a materials point of view-high laser frequencies of up to 500 Hz are mandatory to prevent the formation of mid-chain radicals and the occurrence of chain-breaking events by chain transfer, if industrially relevant temperatures are to be reached and wide temperature ranges are to be explored (up to 70 °C). Herein the progress and state-of-the-art of high-frequency PLP-SEC with pulse repetition rates of 500 Hz is reported, with a critical collection of to-date investigated 500 Hz data as well as future perspectives for the field.

Rationally designed gibbous stimuli-responsive colloidal nanoparticles.

Multiphase colloidal copolymer nanoparticles, if properly designed, offer a number of unique properties and well-documented technological opportunities for drug delivery, nanolithography, high surface area colloidal crystals, or hollow nanoparticles, to name just a few. Using a simple free radical polymerization process, we synthesized copolymer nanoparticles with controlled stimuli-responsive phase-separated gibbosities. The topography of the gibbous phase can be controlled by the copolymer composition and polymerization conditions. When pH-sensitive monomers were copolymerized onto surface bulges, pH changes resulted in localized gibbous phase dimensional changes. Facilitated by monomer diffusion into interfacial particle seed solution regions, localized polymerization near the surface is responsible for the formation of phase-separated gibbous topographies. This general approach may offer a number of possibilities for controllable design of ordered heterogeneous copolymer morphologies for a variety of applications.

Rapid Fabrication of Periodic Patterns on Poly(styrene-co-acrylonitrile) Surfaces Using Direct Laser Interference Patterning

Periodic microstructures in styrene-acrylonitrile (SAN) copolymers are fabricated by two-beam direct laser interference patterning using a nanosecond pulsed laser operating at a wavelength of 266 nm. The SAN copolymers are synthesized using different molar ratios (styrene to acrylonitrile) by a free radical polymerization process. The chemical composition of the copolymers and their properties are determined using Fourier transformed infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Depending on the composition of the irradiated copolymer films, with weight ratios ranging from 58 to 96.5% of styrene to acrylonitrile, different ablation behaviors are observed. The laser fluence necessary to locally ablate the copolymer is found to be dependent on the copolymer composition. Unlike other dielectric polymers, the laser irradiation produced both direct ablation of the irradiated material and collapse of the surface. It is shown that, by varying the laser fluence and the copolymer composition, the surface structure can be changed from a periodic pattern with a swelled topography to an ablated-like structure. The number of holes does not depend monotonically on the amount of PS or PAN units but shows a more complex behavior which depends on the copolymer composition and the laser fluence.

Multi-objective nonlinear predictive control of process systems: A dual-mode tracking control approach

There typically exist different and often conflicting control objectives, e.g., reference tracking, robustness and economic performance, in many chemical processes. The current work considers the multi-objective control problems of continuous-time nonlinear systems subject to state and input constraints and multiple conflicting objectives. We propose a new multi-objective nonlinear model predictive control (NMPC) design within the dual-mode paradigm, which guarantees stability and constraint satisfaction. The notions of utopia point and compromise solution are used to reconcile the confliction of the multiple objectives. The designed controller minimizes the distance of its cost vector to a vector of independently minimized objectives, i.e., the steady-state utopia point. Recursive feasibility is established via a particular terminal region formulation while stabilizing the closed-loop system to the compromise solution via the dual-mode control principle. In order to derive the terminal region as large as possible, a terminal control law with free-parameters is constructed by using the control Lyapunov functions (CLFs) technique. Two examples of multi-objective control of a CSTR and a free-radical polymerization process are used to illustrate the effectiveness of the new multi-objective NMPC and to compare their performance.

Influence of nanoparticle morphology on reaction kinetics, particle size and rheology in acrylic latex

ABSTRACTOrganic/inorganic (O/I) composite latexes combine the best attributes of inorganic solids with the processability, lightweight and handling advantages of organic polymers. There are common methods to produce polymer nanocomposites: melt compounding, in-situ polymerization and solution mixing. Emulsion polymerization is an unique chemical process widely used to produce waterborne resins with various colloidal and physicochemical properties. This free radical polymerization process involves emulsification of the relatively hydrophobic monomer in water by an oil-in-water emulsifier, followed by the initiation reaction with a water insoluble initiator. This research focuses on the synthesis and reactions kinetics of polyacrylic latex with the incorporation of various nanospheres (SiO2, TiO2, Al2O3 and Fe2O3), and layered silicate (Bentonite nanoclay) nanoparticles via emulsion polymerization. The influence of nanoparticle concentration on reaction kinetics was also investigated. The results showed that the concentration of nanoparticles has significant influence on the monomer conversion, particle size, coagulum content and viscosity of the emulsion. Furthermore, the nanostructured emulsions were shear thinning, exhibiting a power-law behavior, and the viscosity was influenced by the nanoparticle morphology.

Oligomer-salt derived 3D, heavily nitrogen doped, porous carbon for Li-ion hybrid electrochemical capacitors application

3D high surface area porous carbon is seen to form via self assembly of porous graphene sheets by direct pyrolysis of an oligomer salt tailored for the realization of molecular level activation. The oligomer salt was derived from 4-amino benzoic acid as the monomer by a facile free radical polymerization process. Incorporation of the functional groups (COONa) eliminate the need for any external activating agents (KOH, ZnCl2, etc.) and also render high degree of sub-nanoscale homogeneity. This oligomer derived carbon (ODC) exhibits efficient performance in non-aqueous charge storage application namely Li-ion hybrid electrochemical capacitor (Li-HEC) owing to its high surface area, 3D interconnectivity and an appropriate pore size distribution. The Li-HEC fabricated with ODC based electrodes delivered a maximum energy density of ∼63Whkg−1 with spinel Li4Ti5O12 as the anode.

PH-Sensitive Nanocapsules with Barrier Properties: Fragrance Encapsulation and Controlled Release

A facile synthesis method for polymer nanocapsules with high diffusion barrier and stimuli-responsive release properties is presented. The highly volatile fragrance α-pinene was used as hydrophobic model compound for the encapsulation process, which is based on a miniemulsion-analogous free radical polymerization process. The copolymer composition was systematically varied, and increasing contents of methacrylic acid as functional monomer in combination with high glass transition temperatures enabled unusually high encapsulation efficiencies of ≥90% for capsules with z-average diameters of <200 nm. Temperature and pH change can be used as trigger to open the capsules, and the release kinetics can be tailored depending on the polymer shell composition. In contrast to more frequently applied barrier microcapsules the nanocapsules provide drastically improved colloidal stabilities. Furthermore, the barrier nanocapsule approach is principally not restricted to fragrances and is expected to be compatible with other hydrophobic actives.

Quantum Mechanical Investigation on Bimolecular Hydrogen Abstractions in Butyl Acrylate-Based Free Radical Polymerization Processes

The present computational study focuses on the investigation of bimolecular hydrogen abstractions that can occur during free radical polymerization (FRP) processes. In particular, several hydrogen abstractions from four monomers (butyl acrylate, BA; styrene, ST; butyl methacrylate, BMA; vinyl acetate, VA) and three different backbone chains (poly-BA, poly-BA-co-VA, and poly-BA-co-ST) have been studied. The aim is to provide an overview of the kinetics for all possible intermolecular hydrogen abstraction reactions from all chemical species present in a bulk FRP as well as to support the understanding of the influence of chemical environment on hydrogen abstractions. All simulations were performed using density functional theory (DFT) with quantum tunneling factors estimated using the Eckart model. This study provides proof that the presence of an electron donating group in the chemical environment of the abstracted hydrogen atoms can lead to lower activation energies and higher rate coefficients for abstraction whereas the presence of an electron withdrawing group leads to opposite effects.

Optimal Grade Transition for Quality Control of Continuous Free Radical Polymerization Process

Optimal Grade Transition for Quality Control of Continuous Free Radical Polymerization Process