Free-radical Crosslinking Copolymerization Research Articles

Reusable Soft Hydrogels for Gold Recovery from Acidic Environments

In this study, poly((N-(hydroxymethyl) acrylamide)–co-1-allyl-2-thiourea) hydrogels were synthesized by free radical crosslinking copolymerization of N-(hydroxymethyl) acrylamide monomer with the addition of a co-monomer 1-allyl-2-thiourea, and N, N′-methylenebisacrylamide as the crosslinker. The copolymer, poly((N-(hydroxymethyl) acrylamide)–co-1-allyl-2-thiourea), was used as a specific sorbent for the recovery of gold. The characteristics of the hydrogels were examined by elemental analyzer and swelling experiments. The effect of pH on the absorption of gold, and the separation and recovery of gold ions from ore samples were investigated. Measurement of absorbed gold was determined by using F-AAS and GF-AAS.

Rapid pH-dependent phase transition and elasticity of stimuli-responsive cationic poly(N,N-dimethylaminoethyl methacrylate) hydrogels prepared with a dimethacrylate crosslinker

Stimuli-responsive hydrogels prepared from poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and its copolymers have attracted much interest to serve in biomedical and pharmaceutical applications. To investigate pH-dependent swelling and elasticity, a series of cationic hydrogels based on N,N-dimethylaminoethyl methacrylate were prepared by free radical crosslinking copolymerization at 60 °C in the presence of tetraethylene glycol dimethacrylate as the crosslinker. The equilibrium swelling and the mechanical properties of the PDMAEMA hydrogels were investigated as a function of the gel preparation concentration. To explain the effect of pH on the equilibrium swelling of the hydrogels, pH-dependent swelling studies were carried out in solutions of pH ranging from 2.1 to 10.7. It was found that the PDMAEMA hydrogels exhibit a rapid pH-dependent phase transition in aqueous solutions; that is, the gels first remain in the swollen state at acidic pH then collapse in a very narrow range of pH. The results showed that the volume of PDMAEMA hydrogels in acidic conditions is about 10- to 40-fold larger than that in the basic pH region. By using the Flory–Rehner theory, the characteristic network parameters of the PDMAEMA hydrogels were calculated and good agreement obtained between the swelling equilibria of hydrogels and their mechanical properties over the whole range of gel preparation concentration. © 2012 Society of Chemical Industry

A fluorescence study for the critical behavior of polymethylmethacrylate doped by multiwalled carbon nanotube (PMMA–MWNT) composite bulk gel systems

Polymethylmethacrylate (PMMA) doped by multiwalled carbon nanotube (MWNT) bulk gels were prepared with different amounts of MWNTs varying in the range between 1 and 20 wt%. Free-radical cross-linking copolymerization of PMMA–MWNT composite bulk gels was characterized by the steady-state fluorescence technique. Ethylene glycol dimethacrylate (EGDM) and pyrene (P y ) were introduced as cross linker and fluorescence probe, respectively. Changes in the viscosity of the pregel solutions due to glass formation dramatically increased the P y fluorescent intensities, which were used to study the glass transition of PMMA–MWNT composite gels for various MWNT contents. The fluorescence intensity of P y is proportional to the average size of the glassy regions below and to the strength of the infinite network above the glass transition point. Observations around the glass transition point show that there are three regimes for MWNT concentration in which the gel fraction exponent, β, and the weight average degree of polymerization exponent, γ, differ drastically from percolation results, given in three dimensions as β=0.41 and γ=1.80.

Antimicrobial P(HEMA/IA)/PVP semi-interpenetrating network hydrogels

New semi-interpenetrating networks (semi-IPNHs) (P(HEMA/IA)/PVP) were prepared by free radical crosslinking copolymerization of 2-hydroxyethyl methacrylate (HEMA) and itaconic acid (IA, 5 mol%), in the presence of poly(vinyl pyrrolidone) (PVP, 2, 5, and 10 mol%), as an interpenetrating agent. The structure of the semi-IPNHs was confirmed by Fourier transform infrared spectroscopy, and morphology study was performed by scanning electron microscopy, which revealed the characteristic porous morphology. The results obtained by dynamic mechanical analysis showed the improvement of mechanical properties with increasing PVP content in semi-IPNs. The maximum swelling was observed for all studied systems at a slightly acidic media (around pH 6), so it can be said that the content of PVP has no influence on the swelling behavior, in the PVP range investigated. Along with the pH sensitivity, which was expected due to the presence of IA, semi-IPNHs showed temperature-sensitive swelling properties, with the lower critical solution temperature value around 41 °C, which is in the physiologically interesting interval. The antimicrobial activity of the samples was tested using E. coli, S. aureus, and C. albicans pathogens. It was noticed that the antimicrobial potential depends on type of microbes, time of exposure, and PVP content in the samples. Due to their good antimicrobial and mechanical properties these stimuli-sensitive semi-IPNHs have potential to be used as biomaterials for the applications in medicine and pharmacy.

Control of Intermolecular Crosslinking by Long-Chain Alkyl Groups in the Free-Radical Crosslinking Copolymerizations of Alkyl Methacrylates with Trimethylolpropane Trimethacrylate

Control of Intermolecular Crosslinking by Long-Chain Alkyl Groups in the Free-Radical Crosslinking Copolymerizations of Alkyl Methacrylates with Trimethylolpropane Trimethacrylate

Elastic percolation of swollen polyacrylamide (PAAm)–multiwall carbon nanotubes composite

Polyacrylamide (PAAm)–multiwalled carbon nanotube (MWNT) composites were prepared via free radical cross-linking copolymerization with different amounts of MWNTs varying in the range between 0.1 and 50 wt%. The mechanical properties of swollen PAAm–MWNT composites were characterized by the tensile testing technique. A small content of embedded nanotubes dramatically changes the compressive elastic modulus of the composites. Compressive elastic modulus dramatically increases up to 1 wt% MWNT on increasing nanotube content, and then decreases, presenting a critical MWNT value, indicating that there is a sudden change in the material elasticity. The critical exponent, y of elasticity, below the critical MWNT content, 1 wt%, is found to be 0.58, which is consistent with the suggestions of percolation in the superelastic percolation network for PAAm–MWNT composite.

Investigation of Drying of Poly(N-isoproplacrylamide-co-acrylamide) by Fluorescence Technique

The steady-state fluorescence technique was performed on drying of various molar percentages of poly(N-isopropylacrylamide-co- acrylamide) [poly(NIPA-co-AAc)] to elucidate the mechanism of temperature-induced phase separation and the effect of monomer content. Poly(NIPA-co-AAc) copolymers were prepared by free radical cross-linking copolymerization. The fluorescence intensity, I, of pyranine, introduced as a probe, increased as drying time was increased for all samples. The behavior of I was modeled by using the Stern–Volmer equation combined with the moving boundary diffusion model. The desorption coefficient, D, increased as NIPA content was increased at a given temperature. Gravimetric and volumetric experiments also supported the results of the fluorescence technique. The energy, Δ E, values were measured for the drying processes for each molar percentage of NIPA monomer content by using fluorescence, gravimetric, and volumetric methods, respectively. It is understood that Δ E values decrease by increasing NIPA content, until 50% NIPA, and then increase after 50% NIPA, indicating that the phase separation has occurred at 50% NIPA. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E231–E240, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21269

Monitoring of dynamical processes in PAAm–MWNTs composites by fluorescence method

Polyacrylamide (PAAm)–multi walled carbon nanotube (MWNT) composites were prepared by free radical cross-linking copolymerization in water. Ammonium persulfate and N,N’-methylenebis (acrylamide) (BIS) were used as a free radical initiator and a crosslinker, respectively. The drying and swelling processes of disc shaped PAAm–MWNT composites were monitored by the steady-state fluorescence technique at various temperatures. Disc shaped composite gels were prepared with pyranine (P) doped as a fluorescence probe. Scattered, I sc, and emission light, I em, intensities were monitored during drying and swelling of these gels. Since the decrease and increase in I sc corresponds to the decrease and increase in turbidity of the drying and swelling hydrogel, respectively, the corrected fluorescence intensity, I was introduced to analyse the drying and swelling processes. The Stern-Volmer equation combined with moving boundary and Li–Tanaka models were used to explain the behavior of I during drying and swelling processes, respectively. Results indicated that the desorption coefficient, D d decreased by increasing MWNT content, until 1 weight percentage of MWNT is reached and then increased above 1 wt% MWNT for a given temperature during drying. However, cooperative diffusion coefficient, D s behaved opposite to D d during swelling at a given temperature. Supporting gravimetric and volumetric experiments were also carried out during drying and swelling of PAAm–MWNT composite gels.

Efficient immobilization of lipase from Candida rugosa by entrapment into poly(N-isopropylacrylamide-co-itaconic acid) hydrogels under mild conditions

Temperature and pH-sensitive hydrogels, based on N-isopropylacrylamide and itaconic acid, with varying comonomer ratios and crosslinking agent content, were prepared by free radical crosslinking copolymerization. The immobilization of lipase from Candida rugosa was carried out by post-loading entrapment method at different temperatures until equilibrium swelling was achieved. The effects of the hydrogel composition and the immobilization temperature on the hydrogel-binding capacity, immobilized lipase specific activity, as well as the enzyme leakage were studied. It was found that the NiPAAm/IA ratio, crosslinking agent concentration and the temperature at which the entrapment was performed significantly affected the hydrogel-binding capacity. The biocatalysts obtained by entrapment into hydrogel with the highest itaconic acid content at 5 °C exhibited both highest binding capacity and the highest specific activity, but appeared to be less suitable for repeated uses than those obtained at 25 °C.

Bovine serum albumin recognition via thermosensitive molecular imprinted macroporous hydrogels prepared at two different temperatures

A novel temperature-sensitive molecular imprinted hydrogel composed of 2-acrylamido-2-methyl-propanosulfonic acid (AMPS), N-isopropylacrylamide (NIPAm) and acrylamide (AAm) has been prepared by free-radical cross-linking copolymerization in aqueous solution under two different temperatures (25°C and −20°C). Bovine serum albumin (BSA, pI 4.9, MW 66.0kDa) is used as the template protein. The influence of the external temperature stimuli on the affinity of the hydrogels was investigated, and the optimal binding conditions were tested. The adsorption capacity (Qmax) and association constant (K) for the specific interaction between the hydrogel and the template protein were determined by Langmuir isotherm plots. Several types of reference protein, which are different in molecular weights and isoelectric points were chosen to investigate the selectivity of the hydrogels. It was shown that the shape memory and the charge effect were the major factors for the recognition. This imprinted hydrogel was used to specifically adsorb the BSA from the protein mixture and real sample, which demonstrated its potential selectivity.

Investigation on Dynamic Mechanical Properties of Crosslinked Poly(styrene-co-divinylbenzene) Bulk Copolymers: Effect of Divinylbenzene Content

The crosslinked poly(styrene-co-divinylbenzene) (CL-p(St-DVB)) bulk copolymers were fabricated by free-radical bulk crosslinking copolymerization (FCC) with styrene as monomer and divinylbenzene (DVB) as crosslinker. The viscoelastic properties of the crosslinked copolymers were investigated by dynamic mechanical thermal analysis (DMTA) as a function of temperature and frequency. The Arrhenius relationship was employed to calculate the activation energy of the α-relaxation transition for the specimens. The results revealed that the storage modulus (E′) of the copolymer networks enhanced with the rising DVB content. The loss tangent (tanδ) peaks were lower and broader. The dynamic mechanical responses of the CL-p(St-DVB) networks were also strongly depended on the test frequency.

Temperature Effect on Elasticity of Swollen Composite Formed from Polyacrylamide(PAAm) -Multiwall Carbon Nanotubes(MWNTs)

Composites formed from Polyacrylamide (PAAm)-Multiwalled carbon nanotubes (MWNTs) were prepared via free radical crosslinking copolymerization with different amounts of MWNTs varying in the range between 0.1 and 50 wt%. The temperature variations of the elastic modulus, G of the PAAm-MWNT composite due to volume phase transition were measured by using tensile testing technique. The composite preserves the ability to undergo the volume phase transition and its elastic modulus and toughness (T) are found strongly dependent on temperature. It is observed that elastic modulus increased when temperature is increased from 30?C to 60?C. Toughness, however presented the reversed behavior versus temperature compare to the elastic modulus.

Energy needs for drying of PAAm- κC composites prepared with various κC contents

AbstractVarious polyacrylamide (PAAm) - Kappa Carrageenan (κC) composite gels were prepared from acrylamide (AAm), N,N- methylenebisacrylamide (BIS) and different κC contents by free radical crosslinking copolymerization in water. Pyranine (P) was introduced as a fluorescence probe, and scattered light, Isc, and fluorescence intensities, I, from these gels were monitored during drying at different temperature. The fluorescence intensity of pyranine increased as drying time is increased for all samples. The behavior of I was quantified using the Stern-Volmer equation with moving boundary diffusion model. Desorption coefficient, D increased as temperature was increased for a given κC content. Supporting gravimetrical and volumetric experiments were also carried out during drying of PAAm-κC composite gels. The energy, △E values were measured for the drying processes for each κC content gel by using fluorescence, gravimetrical and volumetric methods, respectively. It is understood that △E values increase by increasing κC content, indicating that energy needs for the drying of high κC content gel is larger than low κC content gel.

Synthesis and characterization of poly(2-hydroxyethyl methacrylate/itaconic acid/poly(ethylene glycol) dimethacrylate) hydrogels

Hydrogels based on 2-hydroxyethyl methacrylate (HEMA), different poly(ethylene glycol) dimethacrylates (PEGDMA) and itaconic acid (IA) were prepared by free radical crosslinking copolymerization. The influence of different PEGDMA content and type, with PEG chain length of 550 and 875, on the structure, morphology, biocompatibility, swelling and release properties of P(HEMA/IA/550PEGDMA) and P(HEMA/IA/875PEGDMA) copolymeric hydrogels have been investigated. Preliminary biocompatibility characterization of P(HEMA/IA/PEGDMA) hydrogels, done by the cytotoxicity assays using the HeLa cell line, indicated satisfactory cytocompatibility. Swelling studies were conducted for all samples in a physiological pH and temperature range, showing a noticeable pH sensitivity and temperature dependent equilibrium swelling. The characterization by Fourier transform infrared (FTIR) spectroscopy confirmed the presence of all monomers used in the gel structure, and morphology study, performed by scanning electron microscopy (SEM), revealed no significant differences between the samples with respect to pore size. In order to elucidate the release mechanism, drug release study was carried out in vitro using two forms of vitamin B 3: nicotinamide (NAm) and nicotinic acid (NAc). The dissolution profiles were fitted to various mathematical models and the best fit was obtained for first order kinetics. The favorable swelling and drug release properties of P(HEMA/IA/PEGDMA) hydrogels make them good candidates to be used as biomaterials.

Effect of LCST on the swelling of PAAm-NIPA copolymers: a fluorescence study

Temperature sensitive copolymers were prepared by free radical crosslinking copolymerization in aqueous solution with different molar percentage of N-isopropylacrylamide (NIPA) and acrylamide (AAm) monomers. N,N′-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as a crosslinker and an initiator, respectively. The steady-state fluorescence (SSF) technique was used to determine the low critical phase transition temperature (LCST) for PAAm-NIPA copolymers. Swelling experiments were performed in water at various temperatures by real time monitoring of pyranine (Py) fluorescence intensity, I which decreased as swelling proceeded. The Stern–Volmer equation is modified for low quenching efficiencies to interpret the behavior of pyranine intensity during the swelling of PAAm-NIPA copolymers. The Li–Tanaka equation was used to determine the swelling time constants, τ 1 and the cooperative diffusion coefficients, D 0 from fluorescence intensity, weight and volume variations of the copolymers at various temperatures. It was observed that τ 1 first increased up to LCST, and then decreased; naturally D 0 decreased up to LCST and then increased upon increasing temperature. It was understood that (LCST) increases as PAAm contents increase in the PAAm-NIPA copolymers.

Swelling Kinetics of PAAm–κ-Carrageenan Composites: A Fluorescence Technique

The steady-state fluorescence (SSF) technique was introduced for studying swelling of disc-shaped polyacrylamide (PAAm) gels containing various amount of κ−carrageenan (κC). They were prepared by free-radical cross-linking copolymerization. N,N′-methylenebisacrylamide (BIS) and ammonium persulfate (APS) were added as a cross-linker and an initiator, respectively. Composite gels were prepared at 80°C with pyranine as a fluorescence probe. After drying of these gels, swelling kinetics were performed in water at 60°C by real-time monitoring of the pyranine fluorescence intensity, I, which decreased as swelling proceeded. The Li–Tanaka equation was used to determine the swelling time constants, τ 1, and cooperative diffusion coefficients, D 0, from fluorescence intensity, weight, and volume variations of the gels during the swelling processes in all cases. It was observed that τ 1 decreased and D 0 increased as the κC concentrations in the composites were increased indicating that high κC gels swell faster than low κC gels.

Studies on drying and swelling of PAAm-NIPA composites in various compositions

The steady-state fluorescence technique was introduced for studying the drying and swelling of disc-shaped PAAm-NIPA composites. Disc-shaped gels were formed with various acrylamides (AAm) and N-isopropylacrylamides (NIPA) by free radical crosslinking copolymerization in water. Composites were prepared with pyranine (Py) doped as a fluorescence probe. Scattered light, Isc, and fluorescence intensities, I, were monitored during drying of these gels. The fluorescence intensity of pyranine increased and decreased as drying and swelling time increased respectively for all samples. The Stern-Volmer equation combined with moving boundary and Li-Tanaka models were used to explain the behavior of I during drying and swelling, respectively. It was found that the desorption coefficient, D, increased as NIPA contents were increased for a given temperature during drying. However, the cooperative diffusion coefficient, D0, increased as NIPA contents were decreased during swelling at a given temperature. Supporting gravimetrical and volumetric experiments were also carried out during drying and swelling of PAAm-NIPA composites. It was observed that NIPA contents affect the drying and swelling process. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Drying of Polyacrylamide Composite Gels Formed with Various Kappa- Carrageenan Content

Drying of polyacrylamide (PAAm)-κ-carrageenan (κC) composite gels were monitored by using steady-state fluorescence technique. Disc shaped gels were formed from acrylamide (AAm) and N, N'- methylenebisacrylamide(Bis) with various κ- carrageenan (κC) contents by free radical crosslinking copolymerization in water. Pyranine (P) was doped as a fluorescence probe, and scattered light, I (sc), and fluorescence intensities, I, were monitored during drying of these gels. It is observed that fluorescence intensity of pyranine increased as drying time is increased for all samples. The increase in I was modeled using Stern- Volmer equation and diffusion with moving boundary. It is found that desorption coefficient, D decreased as κC contents were increased. Supporting gravimetrical and volumetric experiments were also carried out during drying of PAAm- κC composite gels.

Gelation, Electrical Conductivity and Elasticity of PAM- MWNT

ABSTRACTPolyacrylamide- Multiwalled carbonnanotube (PAM- MWNT) composites were prepared via free radical crosslinking copolymerization with different amounts of MWNT varying in the range between 0.1 and 15 wt. %. PAM- MWNT composite gels were characterized by fluorescence, dielectric spectroscopy and the tensile testing technique. A small content of doped nanotubes dramatically changed gelation time, conductivity and young modulus, respectively. The gel fraction exponent,βof PAM- MWNT composite gels were measured for various monomer and MWNT concentrations and observed that the gel fraction exponentβagrees best with the percolation theory for various amounts of PAM- MWNT. These polymer systems which are initially of an isolator character are doped with carbon nanotubes of nano dimensions and when the amount of this addition exceeds a critical value (0.3 wt. % MWNT) known as the percolation threshold, then composite gel systems with carbon nanotubes become electrically conducting structures with a critical exponent aroundr=2 which is close to the theoretical prediction of this value in 3D percolated system as known random resistor network. The observed elasticities are decreased above 3 wt. %MWNT with critical exponent aroundy=0.72 which is indicative of a transition from liquid-like to solid-like viscoelastic behavior.

Novel silane based cross-linkers for preparation of methyl methacrylate gels

Abstract(2,2'-(Dimethylsilanediyl)bis(oxy)bis(ethane-1,2-diyl)bis(2-methylacrylate) (Type A cross-linker), (2,2'-(methyl) (phenyl) silanediyl)bis(oxy) bis (ethane-1,2- diyl)bis(2-methylacrylate)) (Type B cross-linker), and (2,2'-(diphenylsilanediyl)bis (oxy)bis(ethane-1,2-diyl)bis(2-methylacrylate)) (Type C cross-linker) three novel cross-linkers, (divinyl monomers), containing silanes and two methacrylates group (Si-DVM) were prepared by the condensation of 2-hydroxyethyl methacrylate (HEMA) with dichlorodimethyl, (DCDM) dichloromethyl phenyl (DCMP) and dichlorodiphenyl silane (DCDPS) in the presence of triethylamine (TEA). With these cross-linkers, methyl methacrylate, (MMA) can copolymerize by free-radical cross-linking copolymerization in toluene at a total monomer concentration of 3 molL-1 and at 70 °C. The experimental results show that increasing of Si-DVM concentration resulted in a decrease in gel point and swelling degree and an increase in conversion percent and weight fraction of the gels. The obtained crosslinkers were characterized by 1H-NMR and 13C-NMR spectroscopy and structural characteristics of the gels were examined by using equilibrium swelling in toluene solvent, gel fraction and Fourier-transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by Scanning electron microscopy (SEM).