Acid catalyzed alkylation of phenols with cyclohexene: Comparison between homogeneous and heterogeneous catalysis, influence of cyclohexyl phenyl ether equilibrium and of the substituent on reaction rate and selectivity

The reactivity of several phenols towards liquid phase alkylation with cyclohexene in the presence of heterogeneous and homogeneous acid catalyst at 358 K is studied. The comparison between Amberlyst 15 and CH3SO3H, as examples of heterogeneous and homogeneous systems, shows a higher activity of the former with different behavior of selectivity between the two systems, anyway, in both systems O-alkylation and ring alkylations occur. A remarkable difference in the selectivity of the ring alkylation between heterogeneous and homogeneous systems is observed: Amberlyst 15 shows a constant ortho/para ratio close to 2, while in the presence of CH3SO3H ortho/para is variable from 3 to 5, suggesting an involvement of the cyclohexyl phenyl ether rearrangement. This is proved also by a direct relationship between the ortho/para ratio and the concentration of the cyclohexyl phenyl ether when CH3SO3H is used as a catalyst. The formation of cyclohexyl aril ethers is reversible; on the contrary, ring alkylation appears irreversible. The reactivity of the dimethylphenols shows a strong influence of the steric hindrance of the substituent on the electrophilic attack of the cyclohexyl cation, which is poorly influenced by the inductive effect of the methyl group

Herbicide containing methacrylates: synthesis, polymerization and release investigation

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 rate

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

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

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

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

The preparation and structural characterization are described 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).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 the 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 fitting based on the concurrence of two exponential decay processes differing by three orders of magnitude in their absolute rates