JOURNAL OF MATERIALS SCIENCE 37 (2 0 0 2 ) 4677 – 4682 Structure vs release-rate relationships in polymeric esters of plant growth regulators M. I. SHTILMAN Mendeleev University of Chemical Technology, Miusskaya 9., Moscow, 125047 Russia A. M. TSATSAKIS ∗ , A. K. ALEGAKIS University of Crete, Department of Medicine, Heraklion, Voutes 71409, Greece E-mail: aris@med.uoc.gr P. S. VOSKANYAN, I. M. SHASHKOVA Mendeleev University of Chemical Technology, Miusskaya 9., Moscow, 125047 Russia A. K. RIZOS University of Crete, Department of Chemistry, Heraklion, 71409, Greece E. KRAMBOVITIS Institute of Molecular Biology and Biotechnology, Heraklion, 71100, Greece Polymeric derivatives of plant growth regulators (phytoactive polymers) demonstrate their biological activity after releasing the low-molecular-weight bioactive substances by hydrolysis. In the present work the release rates for a series of polymeric esters of carboxyl-containing plant growth regulators of the auxin group (2,4-dichlorophenoxy acetic acid, 1-naphthylacetic acid, 2-naphthoxyacetic acid, and 2-naphthylthioacetic acid) were studied. The effective rate constants in experiments of alkaline hydrolysis decreased as the molecular mass of the polymer increased, the content of acid hydrophobic residues in polymer increased, and the acidity of the acid decreased. Data on the elucidation of stucture versus release-rate relationships in polymeric esters of plant growth regulators will further aid the preparation of novel delivery systems with optimal biological activity. C  2002 Kluwer Academic Publishers 1. Introduction Phytoactive polymers, polymeric derivatives of plant growth regulators (PGRs), are biologically active after releasing the low-molecular regulator as a result of the hydrolysis of the chemical bond linking the regulator to the polymer carrier [1–10]. In spite of the series of works in this direction, the effect the chemical structure of phytoactive polymers on their ability for hydrolysis was not sufficiently studied [11–14]. At the same time such knowledge may prove useful in the development of novel highly efficient preparations for plant growing. The aim of the present study is to reveal how the rate of hydrolysis is correlated with structure of water soluble polymeric esters of the above mentioned aryl- containing carboxylic acids of the auxin type, contain- ing various side groups (lyophilizing groups) imparting to the polymer solubility in water on hydrophilicity. To address these questions we studied polymeric esters of 2,4-dichlorophenoxy acetic acid (2,4-D), 1-naphthylacetic acid (NAA), 2-naphthoxyacetic acid (NOAA) and 2-naphthylthioacetic acid (NTAA) (Fig. 1A–C). The polymeric esters of PGRs were prepared by the reaction of the acrylamide-vinyl-2- chloroethyl ether (90.5 : 9.5) with the potassium salts of ∗ Author to whom all the correspondence should be addressed. the acids 2,4-D, NAA, NOAA, and NTAA (Method A); by co-polymerization of the allylic ester of 2,4-D (AE 2,4-D) with acrylamide, vinylpyrrolidone or acrylic acid (Method B); and by acylation of polyvinyl alco- hol of different molecular weight with acyl chlorides of 2,4-D and NAA (Method C). The selection of these polymeric derivatives of PGR’s enabled us to examine the effect of different side groups of their structure (e.g., the type of the side lyophilizing groups, the amount of the PGR residues in the polymer, the molecular weight of the carrier poly- mer, and the structure of PGR) on their hydrolysis. 2. Materials and methods 2.1. Starting compounds 2.1.1. Method A Copolymers of acrylamide with 2-chloroethyl-vinyl ether (CEVE) containing 9.5% CEVE units, of 24 × 10 3 M w , were prepared by polymerization of the monomers in isopropanol in the presence of azodiisobutironitrile (AIBN) [15]. The synthesis of polymeric esters of 2,4-D, NAA, NOAA and NTAA was carried out by the reaction of acrylamide-CEVE copolymer with the 0022–2461 C  2002 Kluwer Academic Publishers 4677