ELSEVIER Journal of ControlledRelease 40 (1996) 235-243 journal of controlled release Controlled activity polymers. IX copolymers of acrylic acid and isomeric N-alkylacrylamide monomers with pendent [3-naphthol ester moieties" Hydrolytic release studies C.J. Boudreaux *, W.C. Bunyard, C.L. McCormick Department of Polymer Science. The Universi~ of Southern Mississippi, Hattiesburg. M13940, USA Abstract The hydrolytic release of the allelopathic compound, [3-naphthol, from copolymers of acrylic acid and N-substituted acrylamide monomers [3-naphthyl acrylate, 2-acrylamido([3-naphthyl)isovalerate, 5-acrylamido(13-naphthyl)valerate, 3- acrylamido-3-methyl(f3-naphthyl)butanoate and 6-acrylamido([3-naphthyl)caproate was studied. Reversed-phase liquid chro- matography with ultraviolet spectrophotometric detection was utilized to follow kinetics of naphthol release from series of well-characterized copolymers in aqueous media at three pH conditions. Release profiles of the totally soluble copolymers with 4 to 12 mol% naphthol ester monomers were compared to those of the constituent monomers or model compounds at pH values of 2, 6 and 10. Release rates and the extent of release depended upon the nature of the monomer, the spacing of the naphthol ester moiety from the polymer backbone and pH. The extent of hydrophilicity of the polymer backbone was the major factor as dictated by pH (degree of ionization of the acrylic acid mers) and by the copolymer microstructure. The substituted hydrophobic copolymers exhibited the slowest release rates. At high pH values, a maximum in naphthol ester hydrolysis was observed, apparently due to a thermodynamic limit on charge along the polyelectrolyte. Neighboring group assistance was observed at pH 6 and 2 values for the [3-naphthol acrylate copolymers. The initial hydrolysis rates for all of the other copolymers in water and for the monomers in dioxane/water mixtures followed pseudo-first-order kinetics. The limited extent of hydrolysis, dependent upon pH and composition, was attributed to long-range associative effects in aqueous media. Keywords." Controlledactivity polymers; N-Alkylacrylamide; Acrylic acid; Hydrolyticrelease 1. Introduction In the accompanying paper in this series [1] we detailed synthetic methods for preparing monomers (M1-M5, Fig. 1) containing [3-naphthol ester. We further described the rationale for structural design, synthesis and characterization of series of composi- * Corresponding author. Fax: + 1 601 2665635. 0168-3659/96/$15.00 Publishedby Elsevier Science B.V. SSDI 0168-3659(95)001 90-5 tionally varied acrylic acid copolymers with each of the monomers (P1-P5, Fig. 2). Copolymers from each series were extensively characterized as to com- position, weight average molecular weight and copolymer microstructure, the latter predicted from experimentally derived reactivity ratios. Those poly- mers with complete water-solubility were chosen for controlled release studies reported in this paper. Physical properties are summarized in Table 1. It should be pointed out that copolymers with