Aqueous Free-radical Polymerization Research Articles

Synthesis and solution properties of novel comb-shaped acrylamide copolymers

An amphiphilic macro-monomer of allyl polyoxyethylene-12 ether with butyl-end group (AE12B) was synthesized, and its chemical structure was characterized. AE12B and the other two macro-monomers with different hydrophobic and hydrophilic groups were copolymerized with acrylamide to prepare the novel comb-shaped acrylamide copolymer (CPAM) through aqueous free radical polymerization. The solution properties of CPAM with different side-chain lengths were studied and compared with those of partially hydrolyzed polyacrylamide (HPAM). The experimental results show that the obtained CPAM, compared to HPAM, exhibited a dramatic enhancement in the heat- and salt-resistant properties. In addition, the increase of the side-chain length and the amount of hydrophobic groups in the side-chain improved the thickening properties of CPAM solution under high temperature and high mineralization conditions. Among the investigated macro-monomers, AE12B was optimized for the enhanced thickening properties of the CPAM solution.

Flame retardant finishing of cotton fleece fabric: Part V. Phosphorus‐containing maleic acid oligomers

AbstractThe high flammability of cotton fleece makes it necessary to apply a flame retardant system on cotton fleece so that it can meet the federal regulation ‘Standard for the Flammability of Clothing Textiles’ (16 CFR 1610). The objective of this research was to reduce the flammability of cotton fleece using the phosphorus‐containing maleic acid oligomers (PMAO) synthesized by aqueous free radical polymerization of maleic acid. We found that PMAO can be bound to cotton fleece by esterifying with cotton cellulose with sodium hypophosphite as the catalyst. Both the 45∘ flammability and limiting oxygen index data indicated that the treatment of cotton using PMAO reduced the flammability of cotton fleece. The micro‐scale combustion calorimetric data revealed that PMAO reduced the peak heat release rate and heat release capacity of the treated cotton woven fabric. The cotton fleece treated with PMAO/NaH2PO2 passed the federal flammability test (16 CFR Part 1610) and achieved ‘Class 1’ flammability. The PMAO bound to cotton was durable to multiple home laundering cycles. The treated fleece also showed high strength retention with little change in fabric whiteness. The use of triethanolamine as an additive modestly enhanced the performance of PMAO with no significant changes in fabric physical properties. Copyright © 2009 John Wiley & Sons, Ltd.

Controlled release of theophylline through semi-interpenetrating network microspheres of chitosan-(dextran-g-acrylamide)

Semi-interpenetrating network microspheres of chitosan-(dextran-g-acrylamide) were prepared by emulsion-crosslinking method using glutaraldehyde (GA) as a crosslinking agent. Graft copolymerization of dextran with acrylamide (Dx-g-AAm) was carried out by aqueous free-radical polymerization using ceric ammonium nitrate (CAN) as initiator. The grafting efficiency was found to be 92%. Theophylline (TH), antiasthmatic drug, was successfully encapsulated into semi-INP microspheres by varying the ratio of Dx-g-AAm and amount of GA. The laser light scattering technique shows that the particles size increased with increasing amount of graft copolymer and decrease with increasing amount of GA. The % encapsulation efficiency was found to vary between 50 and 78. MPs were characterized by FTIR spectroscopy and differential scanning calorimetry (DSC) techniques to confirm the graft copolymer, formation of semi-IPN structure of MPs and molecular distribution of the drug molecules in the polymer matrix. In vitro release studies of TH from these matrices have been investigated at Ph 1.2 and 7.4 media and the slow release were extended up to 18 h at 37 degrees C. The release rates were fitted to an empirical equation to estimate the diffusion exponent n, which indicated that the release from the MPs follows non-Fickian type.

Charged Rod‐Like Nanoparticles Assisting Single‐Walled Carbon Nanotube Dispersion in Water

AbstractA new dispersant for stabilization of single wall carbon nanotubes (SWNTs) in water that simultaneously utilizes three different dispersion or stabilization mechanisms: surfactant adsorption, polymeric wrapping, and Coulomb repulsive interaction, has been demonstrated. The new dispersant, a charged rod‐like nanoparticle (cROD), is a cylindrical micelle wrapped by negatively charged polymers which is fabricated by the aqueous free radical polymerization of a polymerizable cationic surfactant, cetyltrimethylammonium 4‐vinylbenzoate (CTVB), in the presence of sodium 4‐styrenesulfonate (NaSS). The surface charge density of the cRODs is controlled by varying the concentration of NaSS. Dispersions of SWNTs are obtained by sonicating a mixture of SWNTs and cROD in water, followed by ultra‐centrifugation and decanting. While the cRODs with neutral or low surface change densities (0 and 5 mol % NaSS) result in very low dispersion power and poor stability, the cRODs with high surface charge densities (15, 25, and 40 mol % NaSS) produce excellent dispersions with SWNT concentration as high as 437 mg L−1 and long term stability. The sharp van Hove transition peaks of the cROD assisted SWNT dispersions indicate the presence of individually isolated SWNTs. Atomic force microscopy and small angle neutron scattering analysis show that the dominant encapsulation structure of the cROD assisted SWNTs is surfactant assisted polymeric wrapping. SWNTs dispersed by the cRODs can be fully dried and easily re‐dispersed in water, providing enhanced processibility of SWNTs.

Introduction of pH‐sensitivity into mechanically strong nanoclay composite hydrogels based on N‐isopropylacrylamide

pH-sensitive nanoclay composite hydrogels based on N-isopropylacrylamide (NIPA) were synthesized by copolymerization with cationic and anionic comonomers. Laponite nanoclay particles served as multifunctional crosslinkers, producing hydrogels with exceptionally high mechanical strengths, as measured by elongation at break. Cationic copolymer gels based on NIPA and dimethylaminoethylmethacrylate were prepared by aqueous free radical polymerization, adopting a procedure reported by Haraguchi (Adv Mater 2002, 14, 1120-1124). Without modification, this technique failed to produce anionic copolymer gels of NIPA and methacrylic acid due to flocculation of clay particles. Three methods were conceived to incorporate acidic MAA into nanoclay hydrogels. First, NIPA was copolymerized with acidic comonomer under dilute conditions, producing hydrogels with good pH-sensitivity but weak mechanical characteristics. Second, NIPA was copolymerized with methyl methacrylate, which was then hydrolyzed to generate acid sidegroups, yielding hydrogels that were much stronger but less pH sensitive. Third, NIPA was copolymerized with an acid comonomer following modification of the nanoclay surface with pyrophosphate ions. The resulting hydrogels exhibited both strong pH-sensitivities at 37 degrees C and excellent tensile properties. Optical transparency changed during polymerization, depending on hydrophobicity of the components. This work increases the diversity and functionality of nanoclay hydrogels, which display certain mechanical advantages over conventionally crosslinked hydrogels.

Microstructure and thermo-responsive behavior of poly( N-isopropylacrylamide) brushes grafted in nanopores of track-etched membranes

We report on the surface-initiated polymerization by aqueous free radical polymerization (FRP) and atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) from nanopore walls of poly(ethyleneterephthalate) (PET) membranes. By combining atomic force microscopy and transmission electron microscopy coupled with an electron energy loss detector, we show that grafting polymers from the walls is an efficient process leading to functional and switchable membranes. The thickness of PNIPAM brushes grafted within small and large nanopores could be measured by a template-based method, indicating that confinement impacts strongly the polymerization process. Finally, the temperature-modulated permeability properties of these responsive polymeric systems are evaluated. Depending on the membrane pore size, two types of permeation control mechanisms are observed. For large pore membranes ( Φ ∼ 330 nm), expanded PNIPAM chains conformations (at T < LCST) result in reduced effective pore size and therefore lower permeabilities relative to collapsed macromolecules chain conformations. In contrast, for narrow pore membranes ( Φ ∼ 80 nm), the PNIPAM layer grafted at the surface of the membrane becomes the rate-controlling factor; the expanded PNIPAM brush represents greater degrees of hydration in the surface layer and therefore gives rise to higher permeabilities than the collapsed conformation. In this situation, the overall permeability is thus comparable to that of a hydrogel membrane.

Janus Microgels Prepared by Surfactant-Free Pickering Emulsion-Based Modification and Their Self-Assembly

We present Janus microgels modified using a Pickering emulsion-based approach and demonstrate their self-assembly. Stimuli-responsive microgels composed of cross-linked poly[N-isopropylacrylamide-co-(acrylic acid)] (pNA) were synthesized by means of aqueous free-radical precipitation polymerization. Using pNA microgels as stabilizers, a Pickering emulsion was formed by simple stirring with pNA dispersion and hexadecane. The amino groups were then introduced by means of a carbodiimide coupling reaction using ethylenediamine and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. These microgels were collected by emulsion collapse. Hemispherical distribution of the amino groups in the modified microgels was confirmed using the Au nanoparticle labeling technique. Interestingly, these microgels were aggregated in string structures at pH 4, whereas they were not at pH 6. Such microgel string structures self-assembled from well-structured microgels by simple stimuli-change have potential use as micro-actuators.

Study on superabsorbent composites. IX: Synthesis, characterization and swelling behaviors of polyacrylamide/clay composites based on various clays

A series of clay-based superabsorbent composite from acrylamide (AM) and various clays, such as attapulgite, kaolinite, mica, vermiculate and Na +-montmorillonite, was prepared by free-radical aqueous polymerization, using N, N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator, and then saponified with sodium hydroxide solution. In this paper, the reaction mechanism and thermal stability of the superabsorbent composites incorporated with various clays were characterized by FTIR, XRD and TGA, respectively. The effects of clay kind and clay content on equilibrium water absorbency of these composites were also investigated and compared. In addition, the influences of clay kind on comprehensive swelling behaviors of the PAM/clay superabsorbent composites were studied. The results indicated that the introduced clays could influence physicochemical properties of obtained superabsorbent composites. Mica could improve thermal stability of corresponding superabsorbent composites to the highest degree comparing with the other clays. The PAM/clay superabsorbent composites incorporated with 10 wt% clay of various kinds were all endowed with equilibrium water absorbency of more than 1300 g g −1. The equilibrium water absorbency decreases with increasing clay content and correlates with the kind of clay. Attapulgite-based superabsorbent composite was endowed with higher water absorbency in univalent cationic saline solution, however, the vermiculite- and the kaolinite-based ones acquired the highest water absorbency in CaCl 2 and FeCl 3 aqueous solution, respectively. Moreover, the superabsorbent composites incorporated with Na +-montmorillonite have higher swelling rate and that of doped with mica was endowed with higher reswelling capability.

Water Uptake Behavior of Poly(methacrylamide‐co‐N‐vinyl‐2‐pyrrolidone‐co‐itaconic acid) as pH‐Sensitive Hydrogels: Part I

Novel hydrogels composed of the three monomers N‐vinyl‐2‐pyrrolidone, methacrylamide and itaconic acid, have been prepared by free radical aqueous polymerization. The gels demonstrated a sharp pH‐dependent swelling. The gel, when transferred from artificial gastric fluid (SGF,pH1.2) to simulated intestinal fluid (SIF, pH 7.4), underwent a sharp swelling transition from 45±4 to 327±12 percent within an hour. The hydrogels also exhibited swelling‐deswelling cycles, within a response time of nearly one hour, while maintaining structural integrity. The increase in monomer acid concentration caused an enhancement in water uptake in SIF while the swelling was observed to decrease in SGF with acid content. For an optimum initiator concentration 0.22 mM, the synthesized gel showed the highest water uptake. On increasing the diameter from 0.21 to 0.92 cm, the initial rate of water uptake decreased from 2.50 to 1.15 percent per minute. The Tanaka‐Fillmore theory was also verified. The activation energy for the swelling of the sample with 7.54 percent mole fraction of itaconic acid was found to be 19.74 kJmol−1.

Formation of Nanostructured Materials via Coalescence of Amphiphilic Hollow Particles

A new, simplified route to amphiphilic core-shell nanotubes, microfibers, and microrods has been developed that does not involve the traditional utilization of well-defined block copolymers. Thus, amphiphilic graft copolymers (PEI-g-PMMA) are prepared by an aqueous free radical polymerization that self-assemble in situ to form uniform core-shell nanoparticles. The hydrophobic homopolymer (PMMA) that is also formed is incorporated in the cores. Slight cross-linking of the shells followed by extraction of the homopolymer results in hollow nanoparticles that coalesce to form nanotubes. When the shells are not cross-linked, the hollow particles coalesce to form microrods and microfibers. The sizes and shapes of the micromaterials can be controlled by varying the experimental conditions.

Synthesis and Swelling Behavior of Acrylamide-Potassium Methacrylate Superabsorbent Copolymers

ABSTRACT A series of acrylamide-potassium methacrylate superabsorbent copolymers were synthesized by simultaneous free radical aqueous polymerization using acrylamide (AAm), potassium methacrylate (KMA), and ammonium persulfate (APS)/ N,N,N′,N′-tetramethylethylenediamine (TMEDA) as initiating system in the presence of a crosslinker. The effects of variables such as concentration of hydrophilic monomer (KMA), crosslinker, initiator and activator, and polymerization temperature on swelling capacity have been investigated in detail. In these polymerizations, two different crosslinking agents, namely 1,4-butanediol diacrylate (BDDA) and ethylene glycol dimethacrylate (EGDMA), were employed to study the effect of crosslinker on swelling properties. The swelling kinetic parameters as well as type of water diffusion into the polymer matrix were evaluated at different temperatures for two series of superabsorbent copolymers. The swelling experiments revealed that EGDMA crosslinked superabsorbents have shown higher swelling capacity for all the compositions of AAm/KMA ratio than BDDA crosslinked analogues. Further, the salt sensitivity and de-swelling capacity of the superabsorbent polymers were studied. The pH effect on the swelling ratio of crosslinked copolymers was also investigated.

Study on superabsorbent composite. III. Swelling behaviors of polyacrylamide/attapulgite composite based on acidified attapulgite and organo-attapulgite

A novel kind of salt-resistant superabsorbent composite, polyacrylamide/attapulgite, from acrylamide (AM) and attapulgite (APT) was prepared by free-radical aqueous polymerization, using N, N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The organification of APT with hexadecyltrimethyl ammonium bromide (HDTMABr) was proved by FTIR and XRD. The effects of acidified APT (H +-APT), organo-APT (HDTMABr-APT) and the content of APT in the superabsorbent composite on the water absorbency and the initial swelling rate for the superabsorbent composite in distilled water and in various saline solutions were studied. The effects of incorporated HDTMABr-APT and H +-APT on the reswelling ability of the superabsorbent composites were investigated. The results indicate that the incorporation of APT had remarkable influence on the improvement of water absorbency and swelling rate of the composites. Comparing with the composite doped with H +-APT, the water absorbency for the composite doped with 10 wt% HDTMABr-APT was enhanced from 2140 g g −1 to 2800 g g −1 in distilled water and from 100 g g −1 to 121 g g −1 in 0.9 wt% NaCl solution, respectively. The water absorbency of the composites in various saline solutions decreased with the increasing concentration, especially for the multivalent cations. In addition, the reswelling ability of the superabsorbent composites is also improved evidently by adding a small amount of HDTMABr-APT into the composite, comparing with that of incorporated with H +-APT.

Hydrogel microparticles as dynamically tunable microlenses.

Tunable micro-optical elements were prepared by aqueous free-radical polymerization and electrostatic self-assembly techniques. Stimuli-responsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-AAc) microgels were used as lenses to generate dynamically tunable optical elements. By using optical microscopy to investigate the micrometer-scale dynamics of the self-assembled microlenses, we demonstrate focal length tuning through modulation of the solution pH and/or temperature.

Preparation of nanoporous SiO x materials via interpenetrating polymer network method

In this letter, polyacrylamide gels with SiO 3 2− and Na + ions in the porous were prepared by using free-radical aqueous polymerization method. Nanoporous SiO x materials were prepared by heating the polyacrylamide gels with colloid of silicic acid in porous to 600 °C and held at this temperature for 24 h. The porous size of nanoporous SiO x materials in the obtained samples was investigated by scanning electron microscopy (SEM) and the average porous size is 50 nm in diameter. From SEM image, we can see the porous size distribution is narrow, but the porous array is irregular. Nanoporous SiO x materials were investigated from the X-ray photoelectron spectra (XPS) spectra and infrared spectrum of the obtained samples. The chemical mechanism for the formation of nanoporous SiO x materials is discussed.

Synthesis of various size CdS nanocrystals in pore of polyacrylamide gels at room temperature

In this letter, polyacrylamide gels were prepared by using free-radical aqueous polymerization method and varying the concentration of the N, N′-methylene-bis-acrylamide from 0.1% to 0.3%, which act as crosslinker. CdS nanocrystals were formed in pore of the polyacrylamide by immersing the gels in 0.1 mol l −1 CdCl 2 and 0.1 mol l −1 Na 2S aqueous solution at room temperature. The effect of pore size of polyacrylamide gels on the size of CdS nanocrystals in the samples was investigated by X-ray powder diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The CdS crystallite structure was investigated from the XRD spectra of the samples and the CdS crystallite average sizes in the pore of polyacrylamide gels were 4.1, 3.4 and 2.2 nm in diameter, respectively. From HRTEM, we can see the size distribution is narrow. The chemical mechanism for the formation of CdS nanocrystals is discussed.

Kinetics of free‐radical graft polymerization of 1‐vinyl‐2‐pyrrolidone onto silica

AbstractThe kinetics of aqueous free‐radical graft polymerization of 1‐vinyl‐2‐pyrrolidone onto silica activated with vinyltrimethoxysilane was studied with a mechanistic polymerization model and experimental data for a temperature range of 70–90 °C. The polymerization was initiated with hydrogen peroxide with initial monomer concentrations ranging from 10 to 40 vol %. The kinetic model, which incorporates the hybrid cage–complex initiation mechanism, describes the experimental polymerization data for which the kinetic order, with respect to the monomer concentration, varies from 1 to . Surface chain growth occurs by both monomer addition and homopolymer grafting, although the latter contribution to the total polymer graft yield is less significant. Increasing the initial monomer concentration enhances both surface polymer density and average grafted chain length. Increasing reaction temperature, however, produces a denser surface layer of shorter polymer chains. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part A: Polym Chem 40: 26–42, 2002

High Pressure Synthesis and Characterization of Acrylonitrile Based Copolymers in Aqueous Free Radical Polymerization Using NMR Spectroscopy

Abstract The influence of reaction pressure on rate of polymerization and intrinsic viscosity in acrylonitrile (AN), methyl acrylate (MA) and itaconic acid (IA) ternary suspension polymerization system has been studied using free radical forming potassium persulphate and sodium metabisulphite water soluble redox initiator pair. The resulting polymers synthesized at various reaction pressures were characterized for tacticity and composition by NMR and other spectroscopic (FT-IR. ESCA) techniques. These polymers were also subjected to differential scanning calorimetric (DSC) analysis and significant change in heat of cyclization were observed with the change in reaction pressure.

Free-radical aqueous slurry polymerizations of acrylonitrile: 2. End-groups and other minor structures in polyacrylonitriles initiated by potassium persulfate/sodium bisulfite

Polyacrylonitriles prepared by aqueous free-radical slurry polymerization using the potassium persulfate/sodium bisulfite redox initiation system have been examined by FT i.r. and high-field 13C and 1H n.m.r. spectroscopy. They have been shown to contain predominantly sulfonate and non-sulfur containing end-groups derived principally from initiation by bisulfite radicals and transfer to the bisulfite ion. Some sulfate end-groups are present also, although in much smaller amounts than the sulfonate end-groups, and are believed to arise from initiation by sulfate radical anions. In these respects, the polymers resemble closely those made by using ammonium persulfate/sodium metabisulfite as the initiator system.

Free-radical aqueous slurry polymerizations of acrylonitrile: 1. End-groups and other minor structures in polyacrylonitriles initiated by ammonium persulfate/sodium metabisulfite

Polyacrylonitriles prepared by aqueous free-radical slurry polymerization at 40°C using ammonium persulfate and sodium metabisulfite as redox initiator have been examined by FTi.r. and by high-field 13C and 1H n.m.r. They have been shown to contain small quantities of acrylamide and acrylic acid units and to possess predominantly sulfonate and non-sulfur containing end-groups derived principally from transfer to bisulfite ion during the polymerization. Other end-groups present in low concentration are sulfate and hydroxyl; the former probably arises from initiation by sulfate radical anions and the latter either from transfer to water or by adventitious hydrolysis of some of the sulfate end-groups. Because they contain few groups capable of initiating intramolecular cyclization, the polyacrylonitriles are white with no sign of discoloration.