Photo-induced controlled/living copolymerization of styrene and acrylic acid and determination of reactivity ratios

A controlled/living photopolymerization of styrene (St) and acrylic acid (AA) mediated by FeCl₃·6H₂O/tetramethylethylenediamine (TMEDA) was performed in N,N-dimethylformamide using 4-bromomethylbenzophenon (4-BMBP) as photoinitiator at room temperature under UV irradiation. 4-BMBP was first used as ATRP initiator and photoinitiator. A well-defined poly(styrene-co-acrylic acid) with predetermined molecular weight and narrow molecular weight distribution was obtained. The kinetic rule of controlled free radical photopolymerization of St and AA was studied. The kinetic results showed that the obtained random poly(St-co-AA) copolymers produced narrow polydispersity (PDI) within the range of 1.25–1.32 when the conversion was beyond 16.5 %, which was characterized by GPC. The plots of number average molecular weight versus conversion and ln([M]₀/[M]) versus time were linear, indicating a controlled/living photopolymerization process. The system proceeded under mild and environmentally friendly conditions. The effects of initiator, catalyst, ligand, and vitamin C(VC) concentrations on polymerization process were investigated. The copolymers were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR). The methods of Mayo-Lewis (ML), Kelen-Tudos (KT), and Yzrielev-Brokhina Roskin (YBR) were used to calculate the monomer reactivity ratios of controlled/living photopolymerization of St and AA at low conversions under selected conditions. The monomer reactivity ratios of St and AA were calculated to be r _St = 0.82 and r _AA = 0.30, respectively in this system. The living characteristics were demonstrated by chain extension experiment.     

Synthesis and properties of chitosan‐modified poly(acrylic acid)

Potassium persulfate (K₂S₂O₈) was used to initiate the polymerization of acrylic acid (AA) monomer in a chitosan (CS) solution. Both a poly(acrylic acid) (PAA) homopolymer and a CS‐co‐PAA copolymer were produced. When the amount of AA was increased from 5 to 40 g with 5 g of CS, the total monomer conversion was found to increase from 89 to 98% after 2 h of reaction at 70°C. In addition, the percentage of reacted AA monomer being converted to the CS‐co‐PAA copolymer (copolymerization efficiency) and the weight composition of the PAA portion in the copolymer (copolymer composition) both increased with the amount of AA added. The structures and properties of the synthesized CS‐modified PAA polymers were studied. In Fourier transform infrared spectra, the formation of a polyelectrolyte complex between CS chains and PAA chains could be observed. From the thermograms obtained via differential scanning calorimetry, we found that the presence of rigid CS chains increased the glass‐transition temperature of PAA. Thermogravimetric analysis revealed three stages of degradation of the synthesized CS‐modified PAA polymers. The swelling ratio of the CS‐modified PAA polymers depended on the pH value and had a maximum value in a buffer solution at pH 7. This was due to the changes in the morphological structure with the pH value. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

pH‐response superabsorbant hydrogel synthesized by ultraviolet photopolymerization

A new synthesis method of pH‐response superabsorbent hydrogels (SHG) was achieved by direct ultraviolet (UV) photopolymerization, and in particular, the synthesis of SHGs of acrylic acid (AA), sodium acrylate (AANa), and methacrylcholine chloride (MACC) tricomponent copolymer by UV photopolymerization were investigated. The pH value responsive behavior of SHG with different monomer ratios of MACC and AA was researched, and SHG showed large swelling properties at pH value approximately 7. Influences of monomer ratio (mol) of AANa to AA, photoinitiators, crosslinking agents, and exposure time of UV light on the water absorbent properties were studied. The results showed that the water absorbent capacity of SHG based on photoinitiators: Esacure KTO46 or Irgacure 651 can reach comparatively high, N,N′‐Methylene bisacrylamide and diethylene glycol diacrylate (DEGDA) were high efficient crosslinking agents for its crosslinking the molecular chains through attending the copolymerization with monomers. When the exposure time was 10 min, the distilled water absorbency of SHG was 1503 mL/g under the condition: content of MACC, 14.3 wt %; monomer ratio (mol) of AANa to AA: 5.67; content of DEGDA and Irgacure 651, 0.0025 and 0.25 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1847–1852, 2007     

Modification of a nicotinic acid functionalized water‐soluble acrylamide sulfonate copolymer for chemically enhanced oil recovery

N,N‐Diallyl nicotinamide (DANA) and acrylic acid (AA) were used to react with acrylamide (AM) and synthesize a novel nicotinic acid functionalized water‐soluble copolymer AM/AA/DANA by redox free‐radical polymerization. Then, the acrylamide/sodium acrylamido methanesulfonate/acrylic acid/N,N‐diallyl nicotinamide (AM/AMS/AA/DANA) was obtained by the introduction of the ? SO₃^? group into AM/AA/DANA after sulfomethylation. The optimal reaction conditions, such as the monomer ratio, initiator concentration, reaction temperature, and pH of the copolymerization or sulfomethylation, were investigated. Both AM/AA/DANA and AM/AMS/AA/DANA were characterized by IR spectroscopy, ¹H‐NMR, scanning electron microscopy, and intrinsic viscosity testing. We found that the AM/AMS/AA/DANA had a remarkable temperature tolerance (120°C, viscosity retention rate = 39.8%), shear tolerance (1000 s^?1, viscosity retention rate = 23.3%), and salt tolerance (10 g/L NaCl, 1.5 g/L MgCl₂, 1.5 g/L CaCl₂, viscosity retention rates = 37.4, 27.5, and 21.6%). In addition, the result of the core flood test showed that the about 13.1% oil recovery could be enhanced by 2.0 g/L AM/AMS/AA/DANA at 70°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40165.     

Preparation and physical properties of photopolymer/SiO2 nanocomposite for rapid prototyping system

A photopolymer material was applied in liquid rapid prototyping (RP) machine. The prototype fabricated from photopolymer was difficult for storage due to volumetric shrinkage and deformation during curing. The prototype fabricated from photopolymer suffers from the volumetric shrinkage during curing and the continuing deformation for a creeping period after curing. Therefore, we used nano‐SiO₂ as a major additive to modify the physical properties of photopolymer. We also added appropriate dispersant to make nanoparticles distribute uniformly in order to reduce the phase separation in composite material. The experimental results showed that photopolymer/SiO₂ nanocomposite can improve tensile strength and hardness by about 50% and offers better dimensional stability. Photopolymer/SiO₂ nanocomposite can also increase the degradation temperature and shorten manufacturing time for RP processing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of nanocomposite polymers by UV-radiation curing

Clay-based nanocomposite polymers have been synthesized by photoinitiated crosslinking polymerization of acrylate and epoxy functionalized oligomers. The solvent-free resin containing a small amount (3 wt%) of organophilic clay was cured within seconds upon UV irradiation at ambient temperature. The polymerization reaction was followed by infrared spectroscopy and shown to proceed at a great extent in thick samples (2 mm), due to the higher exotherm and the resulting rise in temperature. The organoclay was shown to have no slowing down effect on the photopolymerization of both acrylate and epoxy resins. The addition of clay nanoparticles was found to reduce the gloss of UV-cured coatings due to an enhanced surface roughness. The viscoelastic and tensile properties of the nanocomposite photopolymer were comparable to those of the neat UV-cured polymer, while their resistance to moisture was significantly increased.     

Photocuring and thermomechanical properties of multifunctional amide acrylate compositions derived from castor oil

The photopolymerization of multifunctional acrylate monomers synthesized from castor oil was investigated by photo-DSC. These studies revealed that the extent of photopolymerization depended on the double bond concentration and a greater degree of crosslinking occurred in monomer mixtures with higher difunctional content. The monomer mixtures displayed significantly higher maximum rate of polymerization (R_p^max) and shorter time to reach peak maximum than the pure monomers. DMTA studies of films showed good storage modulus and broad tan δ transitions indicating heterogeneity in the crosslinked networks. The films displayed sub-T_g transitions in the loss modulus curves were possibly due to the side chain motions of the monomer acrylates which increased with increasing triacrylate concentration. Glass transition temperature (T_g) of these networks depended on composition and shifted to higher values with increasing amount of triacrylate.     

Competitive removal of heavy metal ions by cellulose graft copolymers

The effect of composition of graft chains of four types cellulose graft copolymers on the competitive removal of Pb²⁺, Cu²⁺, and Cd²⁺ ions from aqueous solution was investigated. The copolymers used were (1) cellulose‐g‐polyacrylic acid (cellulose‐g‐pAA) with grafting percentages of 7, 18, and 30%; (2) cellulose‐g‐p(AA–NMBA) prepared by grafting of AA onto cellulose in the presence of crosslinking agent of N,N′‐methylene bisacrylamide (NMBA); (3) cellulose‐g‐p(AA–AASO₃H) prepared by grafting of a monomer mixture of acrylic acid (AA) and 2‐acrylamido‐2‐methyl propane sulphonic acid (AASO₃H) containing 10% (in mole) AASO₃H; and (4) cellulose‐g‐pAASO₃H obtained by grafting of AASO₃H onto cellulose. The concentrations of ions which were kept constant at 4 mmol/L in an aqueous solution of pH 4.5 were equal. Metal ion removal capacities and removal percentages of the copolymers was determined. Metal ion removal capacity of cellulose‐g‐pAA did not change with the increase in grafting percentages of the copolymer and determined to be 0.27 mmol metal ion/g_copolymer. Although the metal removal rate of cellulose‐g‐p(AA–NMBA) copolymer was lower than that of cellulose‐g‐pAA, removal capacities of both copolymers were the same which was equal to 0.24 mmol metal ion/g_copolymer. Cellulose did not remove any ion under the same conditions. In addition, cellulose‐g‐pAASO₃H removed practically no ion from the aqueous solution (0.02 mmol metal ion/g_copolymer). The presence of AASO₃H in the graft chains of cellulose‐g‐p(AA–AASO₃H) created a synergistic effect with respect to metal removal and led to a slight increase in metal ion adsorption capability in comparison to that of cellulose‐g‐pAA. All types of cellulose copolymers were found to be selective for the removal of Pb²⁺ over Cu²⁺ and Cd²⁺. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2034–2039, 2003     

Comparison of Selenium Nanoparticles and Sodium Selenite on the Alleviation of Early Atherosclerosis by Inhibiting Endothelial Dysfunction and Inflammation in Apolipoprotein E-Deficient Mice

Atherosclerosis and related cardiovascular diseases represent the greatest threats to human health, worldwide. Previous animal studies showed that selenium nanoparticles (SeNPs) and Na₂SeO₃ might have anti-atherosclerotic activity, but the underlying mechanisms are poorly elucidated. This study compared the anti-atherosclerotic activity of SeNPs stabilized with chitosan (CS-SeNPs) and Na₂SeO₃ and the related mechanism in a high-fat-diet-fed apolipoprotein E-deficient mouse model of atherosclerosis. The results showed that oral administration of both CS-SeNPs and Na₂SeO₃ (40 μg Se/kg/day) for 10 weeks significantly reduced atherosclerotic lesions in mouse aortae. Mechanistically, CS-SeNPs and Na₂SeO₃ not only alleviated vascular endothelial dysfunction, as evidenced by the increase of serum nitric oxide level and the decrease of aortic adhesion molecule expression, but also vascular inflammation, as evidenced by the decrease of macrophage recruitment as well as the expression of proinflammatory molecules. Importantly, these results were replicated within in-vivo experiments on the cultured human endothelial cell line EA.hy926. Overall, CS-SeNPs had a comparable effect with Na₂SeO₃ but might have more potential in atherosclerosis prevention due to its lower toxicity. Together, these results provide more insights into the mechanisms of selenium against atherosclerosis and further highlight the potential of selenium supplementation as a therapeutic strategy for atherosclerosis.     

SELENIUM DIOXIDE AS A CONSTITUENT OF GLASSES1

SeO₂ is added as selenious acid (H₂SeO₃) and as sodium selenite (Na₂SeO₃ to the oxides Na₂O, CaO, BaO, PbO, B₂0₃, and SiO₂ to form glasses and crystalline melts containing apprcciable amounts of SeO₂. The chemical analysis of glasses shows the vaporization of SeOn to be high during the melting stage. Most of these glasses are unstable in air or water. A relatively stable glass contained Na₂O 33.4%, CaO 12.4%, B₂O₃ 37.6%, SiO₂ 5.8%, SeO₂ 10.8%. Melting several compositions in a closed container yielded opaque or crystalline melts, whereas the same compositions melted in air with a partial volatilization of SeO₂ gave clear glasses.     

Synthesis of superabsorbent resin by ultraviolet photopolymerization

Synthesis of superabsorbent resin (SAR) was achieved by a new method, that of direct UV photopolymerization, and in particular the synthesis of a SAR of acrylic acid–potassium acrylate copolymer by UV photopolymerization was investigated. Influences of ratio (mol) of acrylate monomer to acrylic acid monomer, photoinitiators, crosslinking agents, and exposure time of UV light on the water‐absorbent properties were investigated. The results showed that the water absorbency (Q) of SAR based on Irgacure 1700 or Irgacure 1800 was 545–530 mL/g, but under the same conditions Q was 450 mL/g for the SAR based on Irgacure 651. N,N′‐Methylene bisacrylamide, hydroethyl acrylate, and glycerol were used as crosslinking agents, of which N,N′‐methylene bisacrylamide was the most effective. It crosslinked the molecular chains through attending the copolymerization with acrylic acid (AA) and potassium acrylate. When the exposure time was 5 min, the value of Q was 1368 mL/g (the content of N,N′‐methylene bisacrylamide was 100 ppm). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1618–1624, 2004     

Effect of polymer structures on electro-optical properties of polymer stabilized liquid crystal films

The polymer stabilized liquid crystal (PSLC) film is a relatively novel electro-optical material, which is generally obtained by dissolving a small amount of a bifunctional photoreactive monomer in a low molecular mass liquid crystal. In this paper, the PSLC films were prepared with photoreactive biphenyl methacrylate monomers by photopolymerization induced phase separation. The effects of liquid crystal concentration, curing time, monomer structures and alignment layer on the electro-optical properties of PSLC films were investigated. The results show that the transmittance in the OFF state (T _OFF) increased with the liquid crystal concentration, but the driving voltage decreased. T _OFF was also influenced by the curing time. Furthermore, when polyimide was used as alignment layer, the films prepared from the bifunctional monomer shows a higher T _OFF, while those from the single functional monomer exhibited a deformed electro-optical curve due to the unsteady polymer networks. __________ Translated from Polymer Materials Science and Engineering, 2008, 24(1): 63–66 [译自: 高分子材料科学与工程]     

High cell density fermentation of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> GS2 for selenium-enriched yeast production

This paper describes a fed-batch fermentation protocol about production of selenium-enriched yeast. Saccharomyces cerevisiae GS2 was selected because of its high tolerance to selenium. The strain GS2 was tested and 122±0.5 g·l ⁻¹ dry cell weight was obtained after 30 h cultivation through feed back control of feed rate of glucose according to the concentration of ethanol and dissolved oxygen. Furthermore, the optimal pattern of Na₂SeO₃ addition was 9 mg Na₂SeO₃ against 1 g DCW at late exponential phase. With the combination of glucose feeding and Na₂SeO₃ addition, the final dry cell biomass reached 102±0.4 g·l ⁻¹ and a Se uptake level of 2,020±13 mg·Kg⁻¹ was achieved in a 5 l fermentor after 38 h cultivation.     

Crosslinked microparticle preparation in supercritical carbon dioxide with photopolymerization

An antisolvent processing technique by simultaneous compressed antisolvent precipitation and photopolymerization for cross-linked polymer microparticles formation was presented in this paper. In this process, photopolymerization of the homogeneous solution composed of methylene chloride, poly(ethylene glycol)600 diacrylate (PEG600DA) as monomer and diphenyl-(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) or 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator resulted to microparticle when it was sprayed into supercritical carbon dioxide (scCO₂) and simultaneously exposed to initiating light. High miscibility of the solvent in scCO₂ made methylene chloride quickly extracted from the dispersion phase, leaving very high concentrations of monomer (PEG600DA) dispersed in scCO₂. The high monomer concentration combined with photo initiating polymerization facilitates rapid reaction rates and ultimately lead to polymer precipitation. Particle size and morphology were adjustable by changing the processing conditions, such as temperature and pressure. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies on poly(acrylic acid)/attapulgite superabsorbent composite. I. Synthesis and characterization

A novel poly(acrylic acid)/attapulgite superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) on attapulgite micropowder using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator in aqueous solution. The effects on water absorbency of such factors as reaction temperature, initial monomer concentration, degree of neutralization of AA, amount of crosslinker, initiator, and attapulgite were investigated. These crosslinked superabsorbent composites were characterized by thermogravimetetric analysis and scanning electron microscopy. The graft copolymerization reaction of AA on attapulgite micropowder was characterized by FTIR. The water absorbencies for these superabsorbent composites in water and saline solutions were investigated and water‐retention tests were carried out. Results obtained from this study show that the water absorbency of the superabsorbent composite synthesized under optimal synthesis conditions with an attapulgite content of 10% exhibited an absorption of 1017 g H₂O/g sample and 77 g H₂O/g sample in distilled water and in 0.9 wt % NaCl solution, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1596–1603, 2004     

Adhesion performance of UV-cured semi-IPN structure acrylic pressure sensitive adhesives

UV-curable solvent-free pressure sensitive adhesives (PSAs) are gaining importance in the area of adhesives because of increasing environmental concerns and the goal to reduce volatile organic compounds (VOCs) in work areas and consumption places. These PSAs have advantages such as low emission of VOCs, a solvent-free process, a fast producton rate at ambient temperature and only a modest requirement for operating space. In this study, UV-curable PSAs were investigated by measuring their adhesion performance in terms of probe tack, peel strength, shear adhesion failure temperature (SAFT) and holding power. PSAs were synthesized from 2-ethylhexyl acrylate (2-EHA), acrylic acid (AA) and vinyl acetate (VAc), using variations in AA concentration to control the glass transition temperature (T _g) of the prepared PSAs. In addition, two types of trifunctional monomers, trimethylolpropane triacrylate (TMPTA) and trimethylolpropane ethoxylated (6) triacrylate (TMPEOTA), which have different chain lengths, were used to form semi-interpenetrating polymer network (semi-IPN) structures after UV exposure. With increasing AA concentration in the PSAs, both the T _g and viscosity increased. Also, probe tack and SAFT increased, but peel strength decreased. After UV irradiation, probe tack decreased, and SAFT and peel strength increased as AA concentration increased in the PSAs. In most cases, cohesive failure changed to interfacial failure after UV exposure. Also, TMPTA increased the cohesion of PSAs; however, TMPEOTA affected the mobility of PSAs due to the different chain lengths of the two types of trifunctional monomer in a different way. The increase of TMPEOTA content diminished the cohesion of PSAs. Consequently, the adhesion performance of the PSAs was closely related to the T _g of the PSAs, and the two types of trifunctional monomer showed different adhesion performances.     

Synthesis of AA‐based superabsorbent interpenetrated with sodium PVA sulfate

An interpenetrating network of acrylic acid (AA)‐based superabsorbents and sodium PVA sulfate (SPS) were prepared by copolymerizing AA and N,N′‐methylene bisacrylamide as a crosslinking monomer in a solution of SPS with KPS, a radical initiator. The SPS was prepared through the sulfation of the hydroxyl groups of PVA with DMF‐SO₃ complex in DMSO. The AA‐based superabsorbent interpenetrated with SPS (SA‐IP‐SPS) showed superior properties such as higher water and saline absorbency, absorbency under load (AUL), and water retention value (WRV) compared with AA‐based superabsorbent due to the interpenetrated SPS. The maximum water and saline absorbency of SA‐IP‐SPS was 1753 and 125.6 g/g, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2525–2532, 2000     

Photo-DSC cure kinetics of vinyl ester resins II: influence of diluent concentration

The photopolymerization kinetics of two commercial vinyl ester resins (VERs) and a model VER photoinitiated by the camphorquinone/amine photoinitiator system were monitored using isothermal DSC. A decrease in styrene concentration in model VERs was found to raise the rate of photopolymerization. In contrast, when the styrene was replaced by a monomethacrylate diluent, the photopolymerization rate passed through a maximum near 70 wt% diluent monomer. This difference in the variation of the rate of polymerization with decreased monomer concentration was attributed to the competition of the effects of the higher reactivity of the methacrylyl radical relative to the styryl radical and the lower termination rate for divinyl-rich systems (both of which tend to raise the maximum polymerization rate) and the effects of the reduction in the initiation efficiency and decrease in k_p due to increased fraction of pendant double bonds (which lower the polymerization rate) when the concentration of diluent monomer was reduced. Subsequent dark polymerization was observed during a temperature ramp and the onset of polymerization was independent of resin composition due to vitrification effects during the isothermal photocuring stage. The kinetics during the dark polymerization stage was discussed in terms of the radical concentration and the propagation rate constant. Increases in the concentration of either diluent monomer raised the extent of isothermal cure during the isothermal polymerization because vitrification was delayed by the lower crosslink density and the plasticizing effect of the diluent. Higher levels of diluent also raised the maximally attainable conversion due to reduced topological restrictions for reaction in networks of lower crosslink density.     

Reversibly pH-Switchable Anionic-Surfactant-Based Emulsions

To develop a convenient and reversible strategy for phase separation and re-emulsification of surfactant-based emulsions, we established a method for pH switching of emulsions formed from a pH-switchable anionic surfactant, potassium dodecyl seleninate (C₁₂SeO₂K). Upon acidification, C₁₂SeO₂K was protonated to give a precipitate of dodecyl seleninic acid (C₁₂SeO₂H); upon basification, C₁₂SeO₂H was neutralized restore C₁₂SeO₂K. The pH-switchable window of the emulsion thus obtained was a pH range of 7 to 8. Reversible changes in both interfacial tension by ~10.2 mN m^?1, as well as the mechanical, steric, and/or electrical barriers formed by C₁₂SeO₂K at the interface of the oil–aqueous solution account for the fully reversible phase separation and re-emulsification of the C₁₂SeO₂K-based emulsions. A stable emulsion (i.e. the time needed to separate 1 mL of H₂O from 6 mL of emulsion at 25 °C is larger than 1 h) could be cycled at least 25 times when the pH was varied between 7 and 8.     

Photocatalytic degradation of dairy effluent using AgTiO2 nanostructures/polyurethane nanofiber membrane

Dairy effluent (DE) is environmentally toxic and needs special attention. Photocatalytic degradation of DE was studied using novel polyurethane (PU)-based membranes. Typically, silver–titanium dioxide nanofibers (AgTiO₂ NFs) and silver–titanium dioxide nanoparticles (AgTiO₂ NPs) were individually incorporated in PU electrospun nanofibers to overcome the mandatory sophisticated separation of the nanocatalysts, which can create a secondary pollution, after the treatment process. These nanomembranes were characterized in SEM, TEM, XRD and UV studies. The polymeric electrospun nanofibers were smooth and continuous, with an average diameter of about 550 nm, and held their nanofibrous morphology even after more than 2 h of photocatalytic degradation of DE, due to the good stability of PU in the aqueous solutions, which indicates good imprisoning of the functional photocatalysts. The PU–AgTiO₂ NPs and PU–AgTiO₂ NFs were effective materials for degradation of DE, even after two successive cycles. PU–AgTiO₂ NPs and PU–AgTiO₂ NFs showed a maximum degradation of 75% and 95%, respectively after 2 h. The significant enhancement of degradation in the PU–Ag–TiO₂ NPs and PU–Ag–TiO₂ NFs is attributed to the photoactivity of Ag–TiO₂ material under visible light irradiation.