Hydrogel–type Polymers in the Controlled Release of Phytodrugs R. Solaro 1 , S. D’Antone 1 , E. Chiellini 1 , A. Rehab 2 , A. Akelah 2 and R. Issa 2 1 Department of Chemistry and Industrial Chemistry, University of Pisa, via Risorgimento 35, 56100 Pisa, Italy 2 Department of Chemistry, University of Tanta, Tanta, Egypt The preparation and structural characterization of polymeric herbicides consisting of 2,4-dichlorophenoxyacetic acid and 4-chloro-2-methyl– phenoxyacetic acid either covalently or ionically bound to linear and crosslinked polymers are described. Poly(styrene/divinylbenzene) resins, crosslinked polysaccharides, and homo and copolymers of oligo(oxy- ethylene) monomethacrylates were used as polymeric supports Herbicide binding was attained by nucleophilic displacement, esterification and ion- exchange reactions. Herbicide release from polymer beads was monitored in water solution buffered at pH 4, 7 and 9. The observed release profiles are discussed in terms of polymer inherent structural features. The release kinetics did not fit simple diffusional schemes while could be satisfac- torily reproduced by the contemporary occurrence of two exponential decay processes, differing by two orders of magnitude in their rates. Utilization of chemicals in agriculture, as administered by conventional routes, is often wasteful and moreover can cause serious environmental problems, harmful to wildlife and even to humans. Delivery of agrochemicals by controlled release formulation is more than a promising concept offering advantages of ecological and economical relevance (1–4). The replacement of conventional herbicide application by controlled release techniques would avoid spreading an excess of toxic substances and at the same time could increase the efficiency of administration. Synthetic and naturally occurring polymers are the cornerstone of this technique. Hydrophilic polymers and polymeric hydrogels have been largely studied and applied in several fields and they appear to deserve attention for the formulation of controlled release systems to be specifically used in sandy soils (5–10). Indeed systems displaying the capability of retaining a fairly large amount of water might help to dimin- ish the pressure for frequent irrigation and hence washing out of any applied phytodrug to that kind of soils. In this connection and within the framework of an international cooperation pur- posely established, we have undertaken a research project focused on the preparation of