Ahmed Akelah

Polymer-clay nanocomposites: Free-radical grafting of polystyrene on to organophilic montmorillonite interlayers

Vinyl monomer-montmorillonite intercalates, which are able to swell and disperse in organic solvents, have been prepared by a cation exchange process by the interaction between the Na+ or Ca2+ cations of montmorillonite and vinylbenzyltrimethylammonium chloride. The resulting vinyl monomer-montmorillonite materials have been identified by X-ray diffraction (XRD), elemental analysis and infrared absorption spectra. Free-radical solution polymerizations of the penetrated styrene between the interlayers of 5, 10, 25 and 50 wt% vinyl monomer-montmorillonite have resulted in grafted polystyrenemontmorillonite materials. The effect of montmorillonite amounts on the formed polystyrene was determined by extraction with organic solvents, which showed an increase in the grafted polymer formed (0.84–2.94 g/g MMT), and a decrease in the external polystyrene with increasing amounts of montmorillonite. The molecular weight of the external polystyrenes was found to be in the range of 22000. The vinyl monomer-montmorillonite and polymer-montmorillonite intercalates have been identified by XRD, elemental analysis and infrared spectroscopy. Examination of the polystyrene-montmorillonite materials by SEM, TEM and XRD showed spherical particles of nanosize about 150–400 nm, and basal spacings of 1.72–2.45 nm.

Polymer-clay nanocomposites: polystyrene grafted onto montmorillonite interlayers

Abstract Vinyl monomer-montmorillonite intercalate which is able to swell and disperse in organic solvents has been prepared by a cation exchange process. Radical polymerization of the penetrated styrene between the interlayers of vinyl monomer-montmorillonite (10 wt%) has resulted in grafted polystyrene-montmorillonite material. This material contains 1.11 g polystyrene/1 g montmorillonite with a basal spacing of 24.5 A. The molecular weight of the external polystyrene was found in the range of 22000. The vinyl monomer-montmorillonite and the polystyrene-montmorillonite intercalates have been identified by XRD, elemental analysis and IR. The SEM and TEM of polystyrene-montmorillonite material showed spherical particles of size about 150–400 nm in diameter.

Recent developments in the application of functionalized polymers in organic synthesis

Abstract Functionalized polymers have continued to find increasing use as supports for reagents, catalysts and protecting groups. Recent applications of these are reviewed along with the use of polymeric species in metal ion separations, in racemate resolutions, as specific adsorbents, in organic synthesis (notably in asymmetric reactions) and in the trapping and identification of reactive intermediates. Some indications of developments in the pipeline and areas of importance for the future are also given.

Organophilic rubber-montmorillonite nanocomposites

Organophilic rubber-montmorillonite intercalates were prepared by a cation exchange process by the interaction between the Na+ ions of montmorillonite and ammonium cations of amine-terminated butadiene acrylonitrile copolymers. The amount of the grafted rubber into montmorillonite layers as determined by the TGA analysis was found to be 0.6 g rubber/1 g rubber-MMT. The resulting rubber-MMT materials were identified by XRD, IR spectra and elemental analysis. The SEM and TEM examinations showed that the clay layers were organized as nanosized clusters whose average size was 60 nm and basal spacings of 15.2 A.

Controlled release of agrochemical molecules chemically bound to polymers

Abstract The widescale use of bioactive agents has brought many advantages, particularly to the agricultural industry. However, there are increasing worries about further escalation of the use of bioactive species, in view of the associated problems, e.g. environmental pollution, accompanying their use. The development and application of controlled release technology has held out the promise of solving many of these problems; this review surveys the current situation regarding those technologies which involve delivery systems in which the agrochemical is chemically bound to a polymer. Since the strategy and chemistry involved in polymeric anti-fouling paints and in polymeric wood preservatives are very similar to those adopted with agrochemicals, short sections on these topics are also included.

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.

Functionalized polymeric materials in agriculture and the food industry

Polymeric Materials: Preparation and Properties.- Part One: Applications of Polymers in Agriculture.- Polymers in Plantation and Plants Protection.- Polymers in Controlled Release of Agrochemicals.- Part Two: Applications of Polymers in Food.- Polymers in Food Processing Industries.- Polymeric Food Additives.- Polymers in Food Packaging and Protection.- Abbreviations.- Index.

Technological applications of functionalized polymers

In most of the major applications of polymeric materials their mechanical properties are often of paramount importance. Even in such applications as electrical insulators their stiffness, cut and abrasion resistance will be of importance as well as their low conductivity. Now, polymers containing specific functional groups are being utilized in analytical and many synthetic organic chemical procedures [1–4], in biologically and pharmacologically active systems, in food additives, and in the field of agricultural chemicals [5]. Following their successful applications in the laboratory and industrial processes, the introduction of active functional groups, other than those previously discussed, into polymers will be discussed in the present article. It is meant only to illustrate selected aspects of more general areas of polymers in the technological uses based on their specific active functional groups, in additon to the advantageous properties of the polymeric material.

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.