Poly first-order kinetic process

The feasibility of designing polymer-chelator conjugates from which release of the chelator is triggered reversibly by the appearance of the target (toxic) metal in the circulatory system was tested by synthesis and measurement of the rates of metal-catalysis hydrolysis of the ester of poly(vinyl alcohol) and quinaldic acid at pH 7.5. Hydrolysis in 50% aqueous ethanol solution in the presence of the four m.etals, Cu(II), Ni(II), CodI) and Zn(II) at pH 7.5 was first order, with half lives of 67, 71, 172 and 476 min., respectively. The rate of hydrolysis in the absence of metals was not measurable. A double reciprocal plot of kobs vs. [M] for Ni(II) exhibited the expected linearity. For films of the ester, the deviation from first order kinetics was consistent with a contributing diffusion process. 

Kinetics studies have demonstrated that the isomerization is a first-order process, characterized by the activation parameters AH% = 34.5(8) kcal mol-1 and A St = 6(2) e.u. Such rearrangements of poly-(pyrazolyl)borato ligands are not uncommon, and have also been observed for Cu and Co complexes of the tris(3-isopropylpyrazolyl)hydro-borato ligand system, i.e., [T73-HB(3-Pr pz)3]M — [T73-HB(3-Pr1pz)2(5-Pr pz)]M (32). 

The imidization process, either thermally or chemically induced, may be followed by a variety of means. It has been traditionally studied on poly(amic acid)s, as well as with molecular models, by IR and NMR spectroscopy [47,48]. But many other analytical methods have been used, for instance TGA [41,49,50], DSC [42,51], polarizing microscopy [41], gas chromatography [52,53], microdielectrometry [54], or torsional braid analysis [55]. From the numerous contributions on this topic some conclusions can be drawn. Among other features, we remark that a rate reduction of the imidation and the rate constant occurs as the conversion increases, so that it can not be considered as a classical first order reaction. This phenomenon has been explained by considering entropic factors [56]. Since the kinetic data could not be unequivocally assimilated to a determined reaction order, they were interpreted as if the imidization reaetion could be divided into rapid and slow first order cyclization steps. The retardation in... 

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