Copolymers of Acrylic Acid with 2-Acryloyloxyethyl 2,4-Dichlorophenoxyacetate: Synthesis and Herbicide Release Marta Ferna ´ndez-Garcı ´a, Manuel Sa ´nchez-Chaves Instituto de Ciencia y Tecnologı ´a de Polı ´meros (C.S.I.C.), Juan de la Cierva 3, Madrid 28006, Spain Received 22 September 2005; accepted 9 April 2006 DOI 10.1002/app.24701 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Free-radical copolymerization of acrylic acid with 2-acryloyloxyethyl 2,4-dichlorophenoxyacetate using 1.0 mol/L 1,4-dioxane solution and 1.5  10 2 mol/L of 2,2 0 azobisisobutyronitrile as initiator has been carried out at 508C. In addition to low conversion solution experiments performed to estimate the monomer reactivity ratios, three different copolymerizations over the whole range of conversions have been made. Theoretical values of cumulative copolymer com- position, determined by the Mayo-Lewis terminal model, have been correlated with those experimentally obtained. Finally, the herbicide release in three different aqueous pH buffer solu- tions has been evaluated in heterogeneous phase. Ó 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4238–4244, 2006 Key words: free radical copolymerization; 2,4-dichlorophe- noxyacetic acid; acrylic acid; 2-acryloyloxyethyl 2,4-dichloro- phenoxyacetate; reactivity ratios; copolymer composition; herbicide release INTRODUCTION Controlled-release technology has emerged as one promising approach to solve the problems that accom- pany the use of biologically active agents, whether pharmaceutical or agrochemical. These systems find good application in agriculture because of environ- mental concerns that impose severe restrictions on uses of mobile herbicides with high activity. 1–6 In most controlled-release formulations, the bio- logically active agent is dispersed in, or combined with, polymeric matrices, 1,7 i.e., (a) physical mixing of an active agent with a polymer to yield a rate con- trolling device; or (b) chemical binding of the active agent to the polymer matrix to act as carrier and consequent release of the active ingredient is con- trolled by the chemical cleavage of polymer-active agent bond or by environmentally induced depoly- merization. The macromolecular nature of these for- mulations allows to control mobility and effective- ness period of the active agent. The selection of either method for achieving controlled-release in a particular application depends on the release rate required, properties of the active agent, and the cost. In addition, controlled-release administration of agrochemicals has certain advantages over conven- tional methods of agrochemicals use. 1 The latter pro- vides an initial concentration far in excess of that required for immediate results to ensure the pres- ence of sufficient chemical for a practical period of time; such overdosing wastes much of the chemical potential, and all too often causes toxicity problems for nontarget organisms and produces undesirable side effect in the environmental. To overcome this problem, the principle of dual application of poly- mer-supported herbicides based on combinations of either herbicide-fertilizer 8,9 or herbicide-water con- servation (hydrogels) has also been introduced in an attempt to eliminate the disadvantages of using excessive amount of inert polymers as carriers for herbicides. 10,11 The herbicide 2,4-dichlorophenoxyacetic acid (2,4- D), a growth regulator herbicide, has been used widely in agriculture, forestry, home and garden ap- plications and to control weeds in parks and rights- of-way for over 50 years. Because of its wide employ and recent concerns over its safety, it is also one of the most studied herbicides in use today. It has been attached to monomers, synthetic and natural poly- mers, 7–9,12–16 which allow to prevent toxic and harm- ful effects. On the other hand, the copolymerization of herbicide-containing monomers let the possibility of changes in the polymer structure using another comonomer and therefore, the ability to control the molecular design of the herbicide/polymer ratio. Therefore, in this work, the free-radical copoly- merization of acrylic acid (AA) with a vinyl ester derived of 2,4-D is presented. The herbicide contain- Correspondence to: M. Ferna ´ndez-Garcı ´a (martafg@ictp. csic.es). Contract grant sponsor: Comunidad Auto ´ noma de Madrid; contract grant number: 07G/0031/2003. Journal of Applied Polymer Science, Vol. 102, 4238–4244 (2006) V V C 2006 Wiley Periodicals, Inc.