Pesticides, controlled release polymers

A. G., and Perkins, B. H., Biodegradable fibers for the controlled release of tetracycline in treatment of peridontal disease, Proc. Int. Symp. Control. Rel. Bioact. Mater., 14, 289, 1987. Dunn, R. L., Lewis, D. H., and Beck, L. R., Fibrous polymer for the delivery of contraceptive steroids to the female reproductive tract, in Controlled Release of Pesticides and Pharmaceuticals (D. H. Lewis, ed.). Plenum Press, New York, 1981, pp. 125-146. 

McCormick, C.L. and M.M. Fooladi, "Synthesis, Characterization, and Release Mechanisms of Polymers Containing Pendant Herbicides," Controlled Release Pesticides, ACS Symposium Series 53, 112-125, H.B. Scher, ed., Washington, D.C., 1977. 

Microencapsulation can be used to provide a temporary barrier between a chemical species and its surrounding environment see also Section 14.3). This permits controlled (slow) release of the active agents following application. Depending on the product and the situation, an active ingredient such as a pesticide may need to be released slowly at low concentration, or slowly at high concentrations. Such controlled release can both reduce the number of crop applications that are required and also help prevent over use and subsequent run-off. The barrier can be provided by a polymer film, in the case of suspensions [867], or a liquid membrane, in the case of single or multiple emulsions [865], Microemulsions have also been used [234,865],... 

Polymers are becoming increasingly important in the area of controlled release, for drugs, flavors, fragrances, fertilizers, and pesticides, to name a few. Often the drug is suspended in a biodegradable polymer that is slowly degraded and metabolized (in other words, is a renewable resource). 

Controlled release formulations are a recent innovation in which the pesticide is incorporated into a carrier, generally a polymeric material (Scher, 1999). The rate of release of the pesticide is determined by the properties of the polymer itself as well as environmental factors. There are mainly two types of CR formulations reservoir devices and monolithic devices. As shown in Figure 2.1, in the reservoir device, the toxicant is enclosed in capsules of thin polymeric material to become microcapsules (1-100 pm in diameter), e.g., Penncap-M microcapsules (methyl parathion). In the monolithic device, the toxicant is uniformly... 

NeogL S. A. N. Polymer Selection for Controlled Release Pesticides. Hi. D. Dissertation, University of Washington, 1970... 

Amylopectins. — The effects of acrylamide graft copolymerization on the solution properties of amylopectin have been discussed. Amylopectin has been dyed with DyAmyl-L and used in this form as a substrate for the assay of a-amylase. Amylopectin has been treated with isocyanate derivatives of 4-amino-( 1,1-dimethyl ethyl)-3-(methylthio)-l,2,4-triazin-5(4/f)-one ( metribuzin ) or acid chloride derivatives of 2,4-dichlorophenoxyacetic acid ( 2,4-D ) and 2,2-dichloropropionic acid ( dalapon ), to produce controlled-release polymeric pesticide systems. The solvent system utilized for these reactions, a lithium chloride or bromide salt in AW-dimethylacetamide, allows dissolution of the reactant salt and facilitates analysis of the polymer product by such techniques as i.r., U.V., and n.m.r. spectroscopies and gel permeation chromatography. Derivatives of other naturally occurring polysaccharides, including amylopectin, cellulose, chitin, and dextran, were also prepared. 

The work presented here constructed a general model of starch-plastic blends as potential controlled release formulations. This model provided a practical method of predicting the kinetics of the starch digestion and product release from starch-plastic blends, thus the kinetics of pesticide release is predictable if the pesticides are either adsorbed or covalently bonded to the starch. The model was developed for starch-plastic blends. It should be adaptable to other blends of incompatible polymers, so long as one of the polymers is susceptible to enzymatic l drolysis. 

Dr. B.R. Ambedkar National Institute of Technology -Jalandhar. Seven students have completed their Ph.D. degree under his supervision. He has a wide experience in the field of natural products, polymers composites, hydrogels, removal of toxic heavy metal ions from waste water, removal of colloidal particles, sustained drug delivery, controlled release of insecticides/pesticides, etc. He has more than 80 research papers in various reputed international journals. He has more than 60 research papers in the proceedings of the international conferences and... 

Because of their unique layered structure and highly tunable chemical composition based on different metal species and interlayer anions, LDHs have many interesting properties, such as unique anion-exchanging ability, easy synthesis, high bond water content, memory effect, nontoxicity, and biocompatibility. Based on these properties, LDHs are considered as very important layered crystals with potential applications in catalysis [6], controlled drugs release [7], gene therapy [8], improvement of heat stability and flame retardancy of polymer composites [9], controlled release or adsorption of pesticides [10], and preparation of novel hybrid materials for specific applications, such as visible luminescence [11], UV/photo stabilization [12], magnetic nanoparticle synthesis [13], or wastewater treatment [14]. 

The field of organic chemistry has seen the most extensive use of polymeric materials as aids in effecting chemical transformation and product isolations. Polymers have been used in other, related areas of chemistry. Applications have been made in analytical chemistry (pH indicators and electrode modifiers), pharmaceutical and agricultural chemistry (controlled-release drugs, pesticides, herbicides, and fertilizers), and biochemistry (enzyme immobilization and affinity chromatography). Applications of polymers to solid-phase enzymo- and radioim-mune assays (Landon, 1977 Chard, 1978) will not be discussed since they are mainly analytical in scope. 

The indiscriminate use of such agricultural chemicals as pesticides, herbicides, and fertilizers is an important source of environmental pollution. A novel application of polymer-bound materials has been made in the controlled release of agricultural chemicals (Allan et al., 1973 Beasley and Collins, 1970 Shambu et al., 1976 Schacht et al., 1977, 1978 reviews of Neogi and Allan, 1974 Scher, 1977). When these chemicals are covalently bound to a polymer from which they can be slowly released into the environment, they not only check pollution but their duration of action is prolonged. The same effect can be obtained by encapsulation of the chemicals in polymeric beads from which they can be released slowly, e.g., 2,4-dichlorophenoxyacetic acid and 4-amino-3,5,6-trichloropicolinic acid have been used in polymer-bound form. 

W.-E. Rudzinski, T. Chipuk, A.-M. Dave, S.-G. Kumbar and T.-M. Aminabhavi, pH-sen-sitive acryhc-based copolymeric hydrogels for the controlled release of a pesticide and a micronutrient,/. Appl. Polym. Sci., 87 (3) 394-403,2003. 

An example of the variety available for controlled release of pesticides from physically bonded polymer materials is found in incorporating aldicarb and dimethoate. The pesticides were generally mixed with preformed polymers and additional additives and the solvents were allowed to evaporate. The efficacy from the release of these two pesticides from such a combination is shown in Table 1. It is clear that various polymer formulations give quite a large range of release times. Release of these two pesticides from plastic formulations into soil have given similar percentages when compared over a 28 day period. 

For the first, diisocyanates, such as 4,4 -diphenyl methane diisocyanate, 1,6-hexamethylene diisocyanate and toluene diisocyanate were allowed, as an example, to react with metribuzin to yield a pesticide-isocyanate adduct. This was then allowed to react with poly(vinyl alcohol) to form a copolymer with controlled release properties. (See Equation 4.) Crosslinked systems were also made by using an excess of the diisocyanate prior to the reaction with polyvinyl alcohol. The metribuzin was released faster from the linear preparation than the crosslinked due to its ability to swell with the hydrophilic polymer hydrolysis and diffusion of the herbicide occurred more easily. Only the hydrolyzed or released metribuzin moved the polymer remained immobile. The commercial formulation of metribuzin was found to be non-toxic after 78 days, but the linear polymer version was found to retain activity even after 112 days. Polymer crosslinking can be varied to provide even longer activity times. 

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