Free Radical Initiator Research Articles

Calcium phosphate mineralization controlled by carboxymethyl cellulose-g-polymethacrylic acid

ABSTRACTCarboxymethyl cellulose-grafted polymethacrylic acid (CMC-g-PMAA) was synthesized by graft copolymerization process onto carboxymethyl cellulose backbone using methacrylic acid as a monomer and ammonium persulfate as a free radical initiator. CMC-g-PMAA was employed as dispersed template for controlling calcium phosphate mineralization from aqueous solutions at different copolymer contents and pHs. Hybrids with different morphologies and particles diameter were investigated by adjusting of preparation conditions. Synthesized hybrids were characterized by FT-IR, SEM, XRD, and particle size analyzer. Such functionalized hybrids with complex morphologies can be manipulated as a novel reinforcing fillers, ceramic precursors, or biomedical implants.

Synthesis of 1-acryloyl-3-phenyl thiourea based pH sensitive hydrogels for removal of samarium and terbium

This paper describes the synthesis of a new chelating poly(acrylamide-co-dimethylaminoethyl methacrylate-co-1-acryloyl-3-phenyl thiourea) (PAPDM) hydrogel. The PAPDM hydrogels were prepared by the simple free radical polymerization of monomers acrylamide, dimethylamino ethyl methacrylate and 1-acryloyl-3-phenyl thiourea. The free radical initiator used for this study was ammonium persulphate and the cross-linker was ethylene glycol di methacrylate. The swelling study of the PAPDM hydrogels were performed in the aqueous environment to calculate the morphological parameters, such as the volume fraction in a swollen gel (v 2m ), polymer-solvent interaction parameter (χ) and molecular weight between the crosslinks (M c ). These hydrogels were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy. Further these chelating hydrogels were investigated for the removal of rare earth metal ions (samarium and terbium) from aqueous environments by varying the adsorption time, adsorbate concentration and monomer ratio. The adsorption time data for samarium and terbium were fitted to two simple kinetic models, pseudo-first and pseudo-second-order, and tested to examine the adsorption mechanisms. The kinetic parameters were calculated. The equilibrium data was fitted well to the Langmuir and Freundlich models.

Structure Elucidation of Poly-Faldaprevir: Polymer Backbone Solved Using Solid-State and Solution Nuclear Magnetic Resonance Spectroscopy

A large-scale synthesis of the hepatitis C virus drug Faldaprevir revealed precipitation of an unknown insoluble solid from methanol solutions of the drug substance. The unknown impurity was determined to be a polymer of Faldaprevir based on analytical methods that included size exclusion chromatography in combination with electrospray ionization mass spectrometry, solution nuclear magnetic resonance (NMR), matrix-assisted laser desorption ionization–time of flight, ultracentrifugation, elemental analysis, and sodium quantitation by atom absorption spectroscopy. Structure elucidation of the polymeric backbone was achieved using solid-state NMR cross-polarization/magic angle spinning (CP/MAS), cross polarization-polarization inversion, and heteronuclear correlation (HETCOR) experiments. The polymerization was found to occur at the vinyl cyclopropane via a likely free radical initiation mechanism. Full proton and carbon chemical shift assignments of the polymer were obtained using solution NMR spectroscopy. The polymer structure was corroborated with chemical synthesis of the polymer and solution NMR analysis.

Low temperature cure-on-command polymerization induced via free radical initiator in an oscillating magnetic field

Three magnetic nanoparticles (Fe3O4, FeCo, Co) were prepared and modified with azo-based free radical initiators via grafting. The resulting magnetic particles underwent a free radical initiation process in an oscillating magnetic field. Three acrylated oligomers, a urethane, epoxide, and polyphosphazene, were used to investigate the curing potential of the magnetic initiators (MI). The curing temperature, Tg, and conversion of the three MI based systems were compared. All three of the MI systems underwent initiation with only a modest temperature increase. The overall conversion and Tg for the MI initiated systems were lower than expected, but with some optimization an ∼80% conversion could be obtained.

Novel thermal and photo curable anti-reflective coatings using fluoroelastomer nanocomposites and self-assembly of nanoparticles

We describe novel optical coatings which require either thermal or photocuring to render them mechanically robust and abrasion resistant. These new coatings are low refractive index fluoroelastomer-nanoparticle composites that form a unique nanostructure during drying of the liquid coating. During drying, the nanoparticles in these liquid coatings migrate towards the substrate. The final, 100-nm-thick anti-reflective coatings are novel and exhibit a unique bilayer structure in which the nanoparticles are ordered and segregated towards the substrate. The coatings are rapidly cured using a new process and exhibit surprising “scratch durability” as measured by aggressively testing with steel wool. Sol gel chemistry is used which involves the reaction of the nanoparticles with an acrylic oxysilane to form nanoparticles which are functionalized with sol gel derived oligomers. The functionalized nanoparticles are combined with a fluoroelastomer containing a free radical initiator and multiolefinic crosslinker, and the composite film is rapidly cured by a thermal or UV process at low temperatures. The final product is a mechanically robust, low refractive index anti-reflective film which is useful for displays and photovoltaic devices. These are unique fluoropolymer nanocomposites which utilize nanoparticle self-assembly to enhance important properties.

Beyond Traditional RAFT: Alternative Activation of Thiocarbonylthio Compounds for Controlled Polymerization.

Recent developments in polymerization reactions utilizing thiocarbonylthio compounds have highlighted the surprising versatility of these unique molecules. The increasing popularity of reversible addition–fragmentation chain transfer (RAFT) radical polymerization as a means of producing well‐defined, ‘controlled’ synthetic polymers is largely due to its simplicity of implementation and the availability of a wide range of compatible reagents. However, novel modes of thiocarbonylthio activation can expand the technique beyond the traditional system (i.e., employing a free radical initiator) pushing the applicability and use of thiocarbonylthio compounds even further than previously assumed. The primary advances seen in recent years are a revival in the direct photoactivation of thiocarbonylthio compounds, their activation via photoredox catalysis, and their use in cationic polymerizations. These synthetic approaches and their implications for the synthesis of controlled polymers represent a significant advance in polymer science, with potentially unforeseen benefits and possibilities for further developments still ahead. This Research News aims to highlight key works in this area while also clarifying the differences and similarities of each system.

Photo Polymerization Of Methyl Methacrylate In Homogeneous Aqueous Medium By Host-Guest Complexation With Β- Cyclodextrin

Photo polymeruization of Methyl Methacrylate (MMA) by host-guest complexation with β-cyclodextrin was investigated in homogeneous aqueous medium. Vinyl monomers like MMA, Styrene etc. become water soluble due to complexation with β-CD and can easily be polymerized in aqueous solution in the presence of free radical initiator. Polymerization was also carried out with uncomplexed monomer and in presence of organic solvent. A systematic study of the kinetics of photosensitized polymerization of MMA with dye (acriflavin) , reducing agent(ascorbic acid) under buffered condition (Na2HPO4 – citric acid) in presence of β-CD in aqueous solution has been made against the different variables like concentration of monomer, dye, ascorbic acid, time and temperature. Presence of β-CD showed obviously effects on the polymerization, so as to increase the rate of polymerization and percentage conversion of monomer, increase of molecular weight of polymer. The mechanism of polymerization and kinetic scheme proposed was examined in the light of the experimental results. Thermal degradation pattern of the polymer sample was studied by thermo gravimetric analysis.

Elastic Light Tunable Tissue Adhesive Dendrimers.

Development of bioadhesive formulations for tissue fixation remains a challenge. The major drawbacks of available bioadhesives are low adhesion strength, toxic byproducts, and complexity of application onto affected tissues. In order to address these problems, this study has developed a hydrogel bioadhesive system based on poly amido amine (PAMAM) dendrimer, grafted (conjugated) with UV-sensitive, 4-[3-(trifluoromethyl)-3H-diazirin-3-yl] benzyl bromide (PAMAM-g-diazirine). This particular diazirine molecule can be grafted to the surface amine groups of PAMAM in a one-pot synthesis. Diazirine functionalities are carbene precursors that form covalent crosslinks with hydrated tissues after low-power UV activation without necessity of free-radical initiators. The rheological properties and adhesion strength to ex vivo tissues are highly controllable depending on diazirine grafting, hydrogel concentration, and UV dose intensity fitting variety types of tissues. Covalent bonds at the tissue/bioadhesive interface provide robust adhesive and mechanical strength in a highly hydrated environment. The free flowing hydrogel conversion to elastic adhesive after UV activation allows intimate contact with the ex vivo swine tissue surfaces with low in vitro cytotoxicity observed, making it a promising bioadhesive formulation toward clinical applications.

Co-polymerized Gellan Gum: A Carrier for Controlled Drug Delivery

Background: Natural polymers have been explored for drug delivery applications since decades, but limited success has been ascribed to their undesired physicochemical properties. Here, we demonstrate the grafting of an anionic and hydrophilic exopolysaccharide ‘gellan gum’with polyacrylamide using microwave irradiation and its potential in controlled delivery of aceclofenac. Methods: Grafting of gellan gum was optimized w.r.t. microwave temperature, exposure time, concentration of free radical initiator and characterized by FTIR, DSC, XRD and SEM analysis. Subsequently, gellan gum and gellan-g-poly(acrylamide) were formulated into aceclofenac tablets and subjected to in vitro drug release, swelling and stability studies. Results: The microwave temperature, exposure time and concentration of free radical initiator had synergistic effect on grafting efficiency up to 80 °C, 120 s and 5 g, respectively. The swelling studies carried out at different pH conditions support the potential of gellan-g-poly(acrylamide). Gellan gum and gellan-g-poly(acrylamide) formulations were compared with commercialized sustained release Zerodol-CR tablets. In vitro release studies revealed the superiority of gellan- g-poly(acrylamide) which was able to sustain the drug release up to 97% over 24 h by zero order kinetics with n value within the range of 1.38-1.80 indicating super case-II (non-Fickian) transport i.e. dominated by diffusion and erosion from polymeric matrix. Interestingly higher drug release was observed in acidic conditions. Conclusion: These findings validate the crucial role of co-polymerization in improving the efficacy of existing natural polymers and support the competence of gellan-g-poly(acrylamide) in the design of highly efficient controlled drug delivery system. Keywords: Acrylamide, co-polymerization, drug delivery, gellan-g-poly(acrylamide), grafted gum, microwave irradiation.

Synthesis and Thermal Stability of Glyoxalated Alkali Lignin-Polyvinylpyrrolidone Resins

Natural, renewable, and non-toxic lignin-based resin was synthesized through copolymerization with monomeric N-vinyl-2-pyrrolidone (VP) in the presence of benzoyl peroxide (BPO) as the free radical initiator. Glyoxalated lignin was used as the feedstock. The mechanism of copolymerization between the glyoxalated alkali lignin and VP monomer was determined through Fourier-transform infrared spectroscopy (FT-IR). The optimum amount of VP monomer used and the reflux time required in the synthesis process were determined through thermogravimetric analysis (TGA). In the presence of BPO, copolymerization between glyoxalated alkali lignin and VP monomer was accomplished via the formation of ether linkages in a condensation reaction at pH 7.0. More ether linkages were formed with higher amounts of VP monomer and longer reflux times. The addition of VP monomer into glyoxalated alkali lignin increased its thermal stability. FT-IR and TGA indicated that 0.012 moles of VP monomer and an 8-h reflux time were optimum conditions for the synthesis of glyoxalated alkali lignin-polyvinylpyrrolidone resins.

Evaluation on the Thermal Stability and Hazards Behaviors of ADVN Using Green Thermal Analysis Approach

ADVN (2,2’-Azobis (2,4-dimethyl) valeronitrile), a free radical initiator, is widely applied for the polymerization reaction of polymers in the chemical industries. When ADVN releases free radical during the decomposition process, it can accompany abundant heat and huge pressure to increase the possibility of thermal runaway and hazard, causing unacceptable thermal explosion or fire accidents. To develop an inherently safer process for ADVN, the thermal stability parameters of ADVN were obtained to investigate thermal decomposition characteristics using a DSC (differential scanning calorimetry) and TG (thermogravimetry). We used various kinetic models to completely depict the kinetic behavior and determine the thermal safety parameters for ADVN. The green thermal analysis approach could be used to substitute for complicated procedures and large-scale experiments of traditional thermal analysis methods, avoiding environmental pollution and energy depletion.

A Solvent and Initiator Free, Low-Modulus, Degradable Polyester Platform with Modular Functionality for Ambient-Temperature 3D Printing

3D printing has enabled the design of biomaterials into intricate and customized scaffolds. However, current 3D printed biomaterial scaffolds have potential drawbacks due to residual monomers, free-radical initiators, solvents, or printing at elevated temperatures. This work describes a solvent, initiator, and monomer-free degradable polyester platform for room temperature 3D printing. Linoleic acid side chains derived from soybean oil lowers the Tg and prevents packing and entanglement, ensuring that G″ > G′ during room temperature printing. Upon printing, cross-linking of pendant functionalized coumarin moieties fixes the viscous filaments to elastomeric solids. Furthermore, the modular design of the polyester platform enables conjugation of ligands, as demonstrated by the conjugation of FITC to surface amines on the 3D printed scaffolds. This low modulus, printable polyester platform addresses several design challenges in 3D printing of functional biomaterials and could potentially be useful in many ti...

PNIPAM-based graft copolymers prepared using potassium persulfate as free-radical initiator: synthesis reproducibility

The use of free radicals has been considered an easy way to get grafted polymers. However, its reproducibility has not yet been evaluated. In this paper, the synthesis reproducibility of copolymers obtained by combining carboxymethylcellulose with N-isopropylacrylamide, in a free-radical copolymerization with potassium persulfate, was investigated. Poly(N-isopropylacrylamide) (PNIPAM) homopolymer and a PNIPAM/CMC blend were also prepared, in order to confirm the success of the synthesis. The polymers were characterized by infrared spectroscopy, thermogravimetry, and rheology. Copolymers and PNIPAM/CMC spectra exhibited characteristic absorptions of the precursor polymers. TGA analyses showed that the copolymers had better thermal stability than CMC and blend. The rheological studies demonstrated that the copolymers exhibited, at low temperatures, an improved thermosensitive performance, higher viscosity, and greater shear thinning behavior, in comparison with PNIPAM and PNIPAM/CMC. The copolymers solutions also exhibited greater thermal stability with increasing temperature. The spectroscopic and rheological properties confirmed the reproducibility of the chemical modification.

Tert‐butyl peroxyacetate initiated semibatch polymerization of 1,1‐difluoroethylene in supercritical carbon dioxide

Due to its inertness and solubility in vinylidene fluoride, (VF2), supercritical carbon dioxide is used as a replacement solvent for producing polyvinylidene fluoride (PVDF). tert‐butyl peroxyacetate (TBPA) was evaluated for the first time as a free radical initiator for radical chain polymerization of VF2 producing PVDF without use of a dispersion agent in a semibatch reactor using supercritical carbon dioxide. Diethyl peroxydicarbonate (DEPDC) at 75°C has been evaluated in many publications as an initiator in batch and continuous reactors for polymerization of VF2 in supercritical carbon dioxide. The effects of monomer and initiator concentration, agitation, and reaction time upon average molecular weight and polydispersity were evaluated using TBPA as an initiator at 104°C and compared with DEPDC initiated polymerization. It was found that as agitation rate, monomer concentration, and reaction time increased, the average molecular weight of PVDF using TBPA as an initiator increased. Lower concentrations of TBPA were needed compared to DEPDC to produce comparable molecular weights of PVDF. Using TBPA as an initiator at the conditions investigated resulted in lower polydispersity at similar monomer concentrations compared to DEPDC. Average molecular weights using TBPA ranged from 49,900 g/mol to 1.3 million g/mol and polydispersity ranged from 1.3 to 5.4. POLYM. ENG. SCI., 56:435–440, 2016. © 2016 Society of Plastics Engineers

Ferulic Acid Regulates the Nrf2/Heme Oxygenase-1 System and Counteracts Trimethyltin-Induced Neuronal Damage in the Human Neuroblastoma Cell Line SH-SY5Y.

Over the past years, several lines of evidence have pointed out the efficacy of ferulic acid (FA) in counteracting oxidative stress elicited by β-amyloid or free radical initiators, based on the ability of this natural antioxidant to up-regulate the heme oxygenase-1 (HO-1) and biliverdin reductase (BVR) system. However, scarce results can be found in literature regarding the cytoprotective effects of FA in case of damage caused by neurotoxicants. The aim of this work is to investigate the mechanisms through which FA exerts neuroprotection in SH-SY5Y neuroblastoma cells exposed to the neurotoxin trimethyltin (TMT). FA (1–10 μM for 6 h) dose-dependently increased both basal and TMT (10 μM for 24 h)-induced HO-1 expression in SH-SY5Y cells by fostering the nuclear translocation of the transcriptional activator Nrf2. In particular, the co-treatment of FA (10 μM) with TMT was also responsible for the nuclear translocation of HO-1 in an attempt to further increase cell stress response in SH-SY5Y cells. In addition to HO-1, FA (1–10 μM for 6 h) dose-dependently increased the basal expression of BVR. The antioxidant and neuroprotective features of FA, through the increase of HO activity, were supported by the evidence that FA inhibited TMT (10 μM)-induced lipid peroxidation (evaluated by detecting 4-hydroxy-nonenal) and DNA fragmentation in SH-SY5Y cells and that this antioxidant effect was reversed by the HO inhibitor Zinc-protoporphyrin-IX (5 μM). Among the by-products of the HO/BVR system, carbon monoxide (CORM-2, 50 nM) and bilirubin (BR, 50 nM) significantly inhibited TMT-induced superoxide anion formation in SH-SY5Y cells. All together, these results corroborate the neuroprotective effect of FA through the up-regulation of the HO-1/BVR system, via carbon monoxide and BR formation, and provide the first evidence on the role of HO-1/Nrf2 axis in FA-related enhancement of cell stress response in human neurons.

2-Acrylamido-2-methyl-1-propanesulfonic Acid Grafted Poly(vinylidene fluoride-co-hexafluoropropylene)-Based Acid-/Oxidative-Resistant Cation Exchange for Membrane Electrolysis.

For developing acid-/oxidative-resistant aliphatic-polymer-based cation-exchange membrane (CEM), macromolecular modification of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) was carried out by controlled chemical grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). To introduce the unsaturation suitable for chemical grafting, dehydrofluorination of commercially available PVDF-co-HFP was achieved under alkaline medium. Sulfonated copolymer (SCP) was prepared by the free radical copolymerization of dehydofluorinated PVDF-co-HFP (DHPVDF-co-HFP) and AMPS in the presence of free radical initiator. Prepared SCP-based CEMs were analyzed for their morphological characteristics, ion-exchange capacity (IEC), water uptake, conductivity, and stabilities (mechanical, chemical, and thermal) in comparison with state-of-art Nafion117 membrane. High bound water content avoids the membrane dehydration, and most optimal (SCP-1.33) membrane exhibited about ∼2.5-fold high bound water content in comparison with that of Nafion117 membrane. Bunsen reaction of iodine-sulfur (I-S) was successfully performed by direct-contact-mode membrane electrolysis in a two-compartment electrolytic cell using different SCP membranes. High current efficiency (83-99%) confirmed absence of any side reaction and 328.05 kJ mol-H2(-1) energy was required for to produce 1 mol of H2 by electrolytic cell with SCP-1.33 membrane. In spite of low conductivity for reported SCP membrane in comparison with that of Nafion117 membrane, SCP-1.33 membrane was assessed as suitable candidate for electrolysis because of its low-cost nature and excellent stabilities in highly acidic environment may be due to partial fluorinated segments in the membrane structure.

Recovery and separation of erythromycin from industrial wastewater by imprinted magnetic nanoparticles that exploit β-cyclodextrin as the functional monomer.

A type of surface imprinting over magnetic Fe3 O4 nanoparticles utilizing erythromycin-A as a template for use in the separation and recovery of erythromycin was developed and investigated. As the intermolecular forces play a key role in the performance of imprinted materials, differential scanning calorimetry, and (1) H NMR spectroscopy was employed to evaluate the interactions between erythromycin and the functional monomer β-cyclodextrin. To synthesize the surface imprinted polymers, magnetic Fe3 O4 nanoparticles, the core materials, were modified with a free radical initiator to initialize polymerization in a "grafting from" manner. Then using acryloyl-modified β-cyclodextrin as the functional monomer and ethyleneglycol dimethacrylate as the cross-linker, thin erythromycin-imprinted films were fabricated by the radical-induced graft copolymerization of monomers on the surface of the Fe3 O4 nanoparticles. Selectivity experiments showed that the erythromycin-A-imprinted materials had recognition ability toward erythromycin derivatives. Finally, these magnetic molecularly imprinted particles were successfully used for the separation and enrichment of erythromycin from the mother liquor. The recovery, detected by high-performance liquid chromatography and differential pulse voltammetry, approached 97%. The combination of the specific selectivity of the imprinted material and the magnetic separation provided a powerful tool that is simple, flexible, and selective for the separation and recovery of erythromycin.

Determination of Homopolymerization Kinetics of 10‐(N‐Methylacrylamido)‐decylphosphonic acid, Its Diethyl ester, and 10‐(Methacryloyloxy)‐decylphosphonic acid, and Their Copolymerization with Methyl methacrylate

Two polymerizable phosphonic acids destined to be constituents of self‐etch adhesives as well as a diethyl phosphonate bearing an N‐methylacrylamide group are examined for their polymerization and copolymerization activity in methanol between 45 and 65 °C. Polymerization proceeds readily through a thermal free radical initiator. The intensity exponents for the monomer and initiator are only slightly over 1 and ≈0.5, respectively, in accordance with the results typically observed for an ideal free radical polymerization with bimolecular termination. The specific feature of this process is the absence of auto‐acceleration during the phosphonic acid monomer polymerization and polymer network formation in case of the phosphonate monomer. The kinetics of copolymerization with methyl methacrylate (MMA) are monitored by online 1H NMR spectroscopy. Two copolymerization reactions for each pair of comonomers are sufficient to evaluate the kinetic data using the Jaacks method, the Fineman–Ross method, and the nonlinear least squares method. All three methods give similar results for particular monomer/MMA couples. image

Healable superhydrophobicity of novel cotton fabrics modified via one-pot mist copolymerization

We describe a simple one-pot mist copolymerization process to fabricate superhydrophobic cotton fabrics. A mixture solution consisting of a free radical initiator, tert-butyl peroxybenzoate (TBPB), and three monomers, lauryl methacrylate (LMA), 2-isocyanatoethyl methacrylate (IEM), and ethylene glycol dimethacrylate (EGD), is atomized to one side of a cotton fabric and polymerized on the surface. SEM images indicate that the copolymer layer on the cotton fiber surface has a randomly wrinkled morphology exhibiting nanoscale roughness. Wetting tests demonstrate that the modified surface possesses a remarkable superhydrophobicity with multiple healing functionalities. A simple ironing treatment at about 200 °C can recover the degraded superhydrophobicity of the modified cotton fabric suffered from 60 cycles of laundries or 2000 cycles of Martindale abrasion. Notably, the mist copolymerization process has no significant impact on the cotton advantages, such as flexibility, water absorptivity, and vapor permeability.

Applications of Fast, Facile, Radiation-Free Radical Polymerization Techniques Enabled by Room Temperature Alkylborane Chemistry

Fast, robust, and scalable techniques for covalent materials assembly are shown to be enabled by variants of a simple mixing-induced free radical initiation scheme broadly termed room-temperature alkylborane (RTA) chemistry. Unique process versatility, speed of reaction, high conversion, and structural control at ambient conditions occur by exploiting air-stable alkylborane-amine complexes that rapidly initiate upon mixing with common amine-reactive decomplexing agents such as carboxylic acid compounds. Three diverse application examples are presented, illustrating facile ambient routes to covalent assembly varying in length scale: (1) copolymers with controllable pressure-sensitive adhesive properties, (2) hydrophilically modified silicone microparticles from heterophase reactions, and (3) UV-free inkjet printable materials suitable for thick-textured patterning and printing, all conducted in open air with no radiation or atmospheric control. These examples demonstrate that this simple "bucket chemistry" can create intriguing degrees of freedom for polymerization, cross-linking and covalent macromolecular assembly with controllable structure and properties, suggesting further opportunities for both fundamental mechanistic investigation and application to a range of old and new materials assembly problems across length scales.