Yu. V. Moiseev

Quantitative Foundations of Polymer Biocompatibility and Biodestructibility

Abstract The quantitative aspects of degradation of some polymer used in medical practice as surgical implants are reviewed. The quantitative criteria of biocompatibility of these polymers and their response to the living body are discussed. New experimental data are shown relating the degradation rate of polyesters, polyamides, elastomers in the organism to that in model media. The catalytical activity of biological media (water, salts and enzymes) are also considered in detail.

Definition of terms and classification of processes relating to aging polymers

Abstract The research team of the Institute of Chemical Physics at the Russian Academy of Sciences that has been involved in the investigation of aging of polymers for many years developed a list of terms and definitions associated with the aging process.

NITROSATION OF ASCORBIC ACID BY NITRITE ION IN UNBUFFERED NEUTRAL AND MODERATELY ACIDIC AQUEOUS SOLUTIONS

The kinetics of nitrosation of ascorbic acid by nitrite in unbuffered aqueous solutions was measured in the pH range from 6.7 to 4.0 at 25°C. The reaction order with respect to the proton is reliably lower than 2, especially in a more acidic solution. This means that under the studied conditions unprotonated nitrous acid may be involved directly in nitrosation of ascorbic acid.

Mechanism of nitrosation of ascorbic acid by nitrite in neutral aqueous media

The main issues in nitrosation of ascorbic acid by the nitrite ion in aqueous media are discussed. Possible mechanisms of the reaction in aqueous media with different acidities are analyzed on the basis of available published data. The main kinetic characteristics of nitrosation of ascorbic acid in neutral Tris-HC1 and phosphate buffers were obtained, and they are interpreted with due regard for the possible active participation of buffer components in the reaction.

Kinetics and mechanism of hydrolysis of lactams in aqueous H2S04 solutions

Conclusions1.A study has been made of the kinetic relationships in the hydrolysis ofγ-butyrolactam,δ-valerolactam,ε-caprolactam, and enantholactam in 0.5–65% H2SO4 at 59.5–94°C, and an analysis has been made of the literature data for the hydrolysis ofβ-,γ-, δ-, andε-lactams and N-ethylacetamide in H2SO4, solutions.2.The influence of the medium on the rate constants ofγ-, δ-, ε-, and enantholactams and N-ethylacetamide can be explained quantitatively on the assumption that the hydrolysis proceeds along two pathways. The reaction rates are determined as follows. Along the first pathway, the rate is determined by the product of concentratrations of the un-ionized form of the reagent and H502+ ions. Along the second pathway, the rate is determined by the concentration of the complex BH30+, which consists of the form of the lactam that is protonated at the carbonyl group and a water molecule coordinated on the carbon atom of the carbonyl group.3.Values have been calculated for the rate constants determining the contributions of the individual pathways to the experimentally determined rate constant.4.In the hydrolysis ofβ-propiolactam, the limiting stage is the decomposition of the complex consisting of the un-ionized form of the lactam (B) and the ion pair H30+·H2SO4−. The concentration of such a complex is determined by the product of the concentration of (B) and the thermodynamic activities of the acid and water. Under conditions of hydrolysis, the relative concentration of such a complex is small.

Conversion of polyorganosiloxanes in aggressive media Communication 2. Kinetics of the hydrolysis of octamethylcyclotetrasiloxane in aqueous Eioxane solutions of sulfuric acid

1. The kinetics of the hydrolysis of octamethyleyclotetrasiloxane in aqueous dioxane solutions was studied. 2. In the course of the hydrolysis of octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane is formed, and with increasing water concentration the equilibrium is shifted toward the formation of decamethylcyclopentasiloxane. 3. The rate constants of the forward and reverse reactions and the activation energies of the processes were determined. 4. The dissociation constants of sulfuric acid according to the first step were measured in an aqueous dioxane solution containing 10 M water.

Destruction of polyamides in aggressive media

1. The kinetics of the hydrolysis of cyclic oligomers of polycaproamide was investigated in a broad range of temperatures and H2SO4 concentrations by a spectrophotometric method. 2. The effective rate constant of hydrolysis passes through a maximum with increasing acid concentration. 3. A mechanism of hydrolysis was proposed. 4. The anomalous reactivity of the cyclic dimer of polycaproamide is explained by electrostatic interaction of closely situated amide groups through space.

Destruction of polyamides and polyimides in aggressive media

1. The kinetics of the acid-catalyzed hydrolysis of N-phenylphthalimide and N-phenylphthalamic acid was studied and a mechanism was proposed for the hydrolysis. 2. The “hydrolysis” of N-phenylphthalimide proceeds, without the involvement of water, through the intermediate formation of phthalic anhydride. 3. The rate of hydrolysis of N-phenylphthalimide is two orders of magnitude smaller than that for N-phenylphthalamic acid.

Reaction mechanism for the acid-catalyzed hydrolysis of saccharose

1. A polarimetric study was made of the reaction for the hydrolysis of saccharose in inorganic acid solutions. 2. The A-1 mechanism, on the assumption that saccharose is a base of the type of a Hammett indicator, does not describe the experimental data.

Weak donor-acceptor complexes of o-quinone diazides with phenol-formaldehyde oligomers

SummaryIt has been shown by low-temperature photolysis and ESR that mixtures of o-naphthoquinone diazides with phenol-formaldehyde oligomers in solutions and dry films form weak donor-acceptor complexes in which the intramolecular photoreduction of the o-naphthoquinone diazide can take place.