Controlled activity polymers .11. Hydrolytic release studies of hydrophilic copolymers with labile esters of model allelopathic phenols

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Polymers and High Performance Materials


The controlled hydrolytic release of phenolic and naphthoic allelopathic compounds from copolymers of acrylic acid (AA), acrylamide (AM) and N-vinylpyrrolidinone with acrylate monomers phenyl acrylate (PA), 2-isopropylphenyl acrylate (IPPA), 2,6-diisopropylphenyl acrylate (DIPPA), 2-acryloxybenzoic acid (2ABA) and 2-acryloxy-1-naphthoic acid (2A1NA) was studied, UV spectroscopy was utilized to monitor the release kinetics of these alleopathic model compounds from well-defined copolymers in (60:40 v/v) aqueous buffer/dioxane solution at five pH conditions. Release behavior of totally soluble copolymers with 2-8 mole % phenolic or naphthoic compound was compared to that of the respective monomers. Hydrolysis rates and extent of hydrolysis depended on the nature of the monomer, comonomer type, copolymer microstructure and pH. Enhanced release rates of 2ABA-AA and 2AlNA-AA polymers were attributed to neighboring group assistance by carboxyl moieties of the pendent allelochemical and polymer chain. Except for 2ABA-AA and 2AlNA-AA, copolymers exhibited a limited extent of hydrolysis dependent upon pH, nature of the monomer and comonomer type. The presence of hydrophobic microdomains in aqueous solutions of these amphiphilic copolymers is likely responsible for the observed behavior. Comparisons of release data from acrylic acid, acrylamide and N-vinylpyrrolidinone copolymers with approximately 40 mole % phenolic ester substitution showed that neighboring ionic groups of PA-AA significantly enhanced release rates. The reduced hydrolysis rates of PA-AM were attributed to a more hydrophobic copolymer microstructure relative to PA-AA.

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Journal of Controlled Release





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