Ahmed Rehab

Controlled release of herbicides bound to poly[oligo(oxyethylene) methacrylate] hydrogels

A series of polymeric hydrogels containing different oxyethylene oligomers has been prepared by radical polymerization of oligo(oxyethylene) methacrylate monomers in the presence of different amounts of N,N′-methylenebisacrylamide as crosslinking agent or acrylamide as hydrophilic comonomer. Systemic herbicides, such as 2,4-dichlorophenoxyacetic acid and 4-chloro-2-methylphenoxyacetic acid, were covalently supported on the polymeric hydrogels by esterification of the side chain hydroxyl groups. In the investigated samples, swelling in water depends mainly on the length of the oligo(oxyethylene) side chains, the content of hydrophilic comonomer and, to a minor extent, on the degree of crosslinking. Herbicide loading produces a substantial drop in the water uptake by the polymer. The release of herbicides, investigated at room temperature in water at different pH values, is very much affected by alkalinity and to a lesser extent by the polymer structure.

Controlled Release of Herbicides Supported on Polysaccharide Based Hydrogels

Polymeric hydrogels based on polysaccharides, hydroxyethylcellu lose and dextran, were attained by cross-linking with epichlorohydrin. The cross-linked polymer beads were loaded with 2,4-dichlorophenoxyacetic acid by direct esterification in the presence of carbonyldiimidazole. Loads ranging be tween 0.5 and 2.2 mol of 2,4-dichlorophenoxyacetyloyl groups per glucose unit were obtained. The release of 2,4-D herbicide was investigated in buffered aqueous solution at different pH values (4, 7 and 9) and evaluated with respect to different structural parameters, such as nature of the polymer matrices, cross-linking extent and herbicide loading. A fairly slow release, ranging from 10 to 25% after four months, was recorded under neutral and acid conditions, whereas at pH 9 an initial burst in the release profile, reaching almost 90% release of 2,4-D loading, was observed. In the majority of the cases, the release kinetics are reproduced by the combination of two exponential decay processes, that differ by about three orders of magnitude in their absolute rates.

Synthesis and application of organophilic polystyrene-montmorillonite supported onium salts in organic reactions

Abstract Copolymers of styrene and chloromethylstyrene containing 2% ammonium salt groups have been grafted onto montmorillonite interlayers by cation exchange process. The remaining chloromethyl groups were modified to produce phosphonium salts. The catalytic activities of the phosphonium moieties supported on polystyrene-montmorillonite have been investigated in thiocyanate and nitrite nucleophilic reactions. The effectiveness of these catalysts has been examined under the effects of several factors governing the reactions rates such as the chemical composition of polymers backbone, chemical nature of the active moiety, degree of loading, nature of the solvent, and reaction temperature.

Herbicide containing methacrylates: synthesis, polymerization and release investigation

Abstract The preparation is reported of two series of oligo(oxyethylene) methacrylates containing residues of 2,4-D and CMPA herbicides covalently bound via an ester bond to oligoether side groups having different degree of oligomerization (DPn = 2, 4, 8). The two series of monomers, when submitted to free radical polymerization gave the corresponding homopolymers, that exhibited a water uptake generally lower than 50%. A series of linear and crosslinked polymeric herbicides was also prepared by copoly-merization of the CMPA-containing tetraoxyethylene methacrylate with different comonomers, such as dioxyethylene and octaoxyethylene monomethacrylate, acrylamide, methylene bisacrylamide and 4-vinylpyridine. All the synthesized polymeric herbicides were tested for their release properties in aqueous solution buffered at pH 4, 7 and 9. The herbicide release profiles have been discussed in relation to the polymer inherent structural features and compared with the corresponding polymers obtained by 2,4-D and CMPA binding to preformed poly [oligo(oxyethylene) methacrylate]s. In any case the release kinetics do not fit a simple diffusional scheme and they can be reproduced by the contemporary occurrence of two exponential decay processes, differing by three orders of magnitude in their absolute rates

Ionogenic polymer pro-herbicides based on partially quaternized poly[oligo(oxyethylene) methacrylate]s. synthesis and herbicide release

Abstract The preparation and structural characterization of polymeric proherbicides consisting of 4-chloro-2-methylphenoxyacetic acid (CMPA) ionically bound to linear and crosslinked polymer matrices based on oligo(oxyethylene) monomethacrylates (DPn oligooxyethylene: 2, 4 and 8), containing quaternary onium groups (%-mol: 8–60) are described. CMPA loading was carried out by an ion-exchange procedure and CMPA contents in the range 0.15–0.45 mmol/g of dry polymer were attained. The loaded polymer samples displayed typical moderate to strong hydrogel character. The herbicide release, performed in water medium at controlled pH (4, 7 and 9) and saline content, reached, after three months, a 55% value at best. No definite correlation between structural parameters and release behaviour can be drawn, whereas alkaline conditions seem to favourably affect the herbicide release. The release profiles can be reproduced by a best fit analysis based on the occurrence of two exponential decay processes differing by three orders of magnitude in their absolute rates.

Studies of Photoreactive Poly(Norbornene Derivatives) Bearing Chalcone Units

New photoreactive poly(norbornene derivatives) containing photocrosslinkable pendant units have been prepared via ring opening metathesis polymerization (ROMP) for the first time. The photochemical behavior of these polymers was investigated in dilute solutions. The rates of photocrosslinking were determined under the influence of different factors such as the backbone structure of the polymer, the substituents on the aromatic ring of the photocrosslinkable units, temperature, concentrations of the photocrosslinkable units in the solution, and the solvent. The studies confirmed that all the prepared polymers have higher UV radiation sensitivity in very dilute solutions in different solvents, and at different temperatures.

New catalytic systems based on intercalated polymer-montmorillonite supports

A composite material was prepared by ion exchange between the ammonium salt of the α,ω-diamine-terminated oligo(butadiene-co-acrylonitrile) (ATBN) and the interlamellar cation of the montmorillonite (Na-MMT). Grafted free radical polymerization of both oligo(oxyethylene)methacrylate and chloromethylstyrene supported onto the above composite was prepared. The chloromethyl groups were modified to produce onium salts which are suitable as phase transfer catalysts. The catalytic activities were investigated in nucleophilic reactions of thiocyanate, cyanate and nitrite with alkyl or aryl halides. The effects of the nature and structure of the support, amount of catalyst, solvent, and the temperature on the rate of reactions were studied.

Negative Photoresist Materials Based on Poly(Norbornene Derivatives‐co‐styrene‐co‐maleic Anhydride)

Photosensitive polymers of norbornene‐co‐styrene‐co‐maleic anhydride with different mole ratios were synthesized as a polymer matrix for UV photoresist. These polymers were prepared by radical polymerization under controlled conditions. These polymers have a higher glass transition temperature than polystyrene and are chemically reactive with certain functional groups. The photochemical behaviors of these polymers were investigated in solutions. The rates of photocrosslinking were studied under the influence of different factors such as the backbone structure of the polymer, the substituants on the aromatic ring of the photocrosslinkable units, the temperature, the concentrations of the photocrosslinkable units in the solution, and the solvent. The studies confirmed that all the prepared polymers have higher UV radiation sensitivity in very dilute solutions in different solvents, and at different temperatures.

Synthesis of silver-anchored polyaniline–chitosan magnetic nanocomposite: a smart system for catalysis

A simple route was employed for the fabrication of a polyaniline (PANI)–chitosan (CS)–magnetite (Fe3O4) nanocomposite (PANI–CS–Fe3O4) via the in situ polymerization of aniline in the presence of CS using anhydrous iron(III) chloride as an oxidizing agent. The magnetic character of the nanocomposite results from the presence of iron oxide nanoparticles, which were formed as side products during the synthesis of the PANI–CS nanocomposite. The synthesized PANI–CS–Fe3O4 nanocomposite was fully characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). The reduction of silver nitrate by the synthesized nanocomposite enables the anchoring of silver (Ag) nanoparticles onto its surface. The catalytic properties of the Ag-decorated nanocomposite (Ag@PANI–CS–Fe3O4) toward the reduction of 4-nitrophenol was investigated using sodium borohydride as a reducing agent.

Synthesis and thermal properties of nanocomposites based on exfoliated organoclay polystyrene and poly(methylmethacrylate)

Abstract Exfoliated organoclay-polystyrene (OC-PS) and organoclay-poly(methyl methacrylate) (OC-PMMA) nanocomposites were prepared using novel modified/clay-polymer through both bulk polymerization and solution techniques. The synthesis was achieved by formation of derivative vinylbenzyl ammonium salt intercalated with montmorillonite (MMT) clay. The clay-vinyl/monomer was dispersed in PS or MMA monomers followed by solution polymerization. The clay-PS and clay-PMMA were used as highly compatibilizer organoclay to produce highly exfoliated nanocomposites. Morphological structure of the nanocomposites was investigated by SEM and XRD which confirmed that the clay is homogenously dispersed and exfoliated in the polymer matrixes with interlayer spacing at least of d001-value ≥4 nm for both PS and PMMA. Thermal properties of the nanocomposites show an increase in the decomposition temperature comparing to neat polymer.