Exposure to ultraviolet (UV) radiation may cause the significant degradation of many materials. UV radiation causes photooxidative degradation which results in breaking of the polymer chains, produces free radical and reduces the molecular weight, causing deterioration of mechanical properties and leading to useless materials, after an unpredictable time. Polystyrene (PS), one of the most important material in the modern plastic industry, has been used all over the world, due to its excellent physical properties and low-cost. When polystyrene is subjected to UV irradiation in the presence of air, it undergoes a rapid yellowing and a gradual embrittlement. The mechanism of PS photolysis in the solid state (film) depends on the mobility of free radicals in the polymer matrix and their bimolecular recombination. Free hydrogen radicals diffuse very easily through the polymer matrix and combine in pairs or abstract hydrogen atoms from polymer molecule. Phenyl radical has limited mobility. They may abstract hydrogen from the near surrounding or combine with a polymer radical or with hydrogen radicals. Almost all synthetic polymers require stabilization against adverse environmental effects. It is necessary to find a means to reduce or prevent damage induced by environmental components such as heat, light or oxygen. The photostabilization of polymers may be achieved in many ways. The following stabilizing systems have been developed, which depend on the action of stabilizer: (1) light screeners, (2) UV absorbers, (3) excited-state quenchers, (4) peroxide decomposers, and (5) free radical scavengers; of these, it is generally believed that excited-state quenchers, peroxide decomposers, and free radical scavengers are the most effective. Research into degradation and ageing of polymers is extremely intensive and new materials are being synthesized with a pre-programmed lifetime. New stabilizers are becoming commercially available although their modes of action are sometimes not thoroughly elucidated. They target the many possible ways of polymer degradation: thermolysis, thermooxidation, photolysis, photooxidation, radiolysis etc. With the goal to increase lifetime of a particular polymeric material, two aspects of degradation are of particular importance: Storage conditions, and Addition of appropriate stabilizers. A profound knowledge of degradation mechanisms is needed to achieve the goal.

/pdf/photodegradation-and-photostabilization-of-polymers-2iaxe4qvtk.pdf

Photodegradation and photostabilization of polymers, especially polystyrene: review

This review is the first to collate and summarize main data on named and unnamed rearrangement reactions of peroxides. It should be noted, that in the chemistry of peroxides two types of processes are considered under the term rearrangements. These are conventional rearrangements occurring with the retention of the molecular weight and transformations of one of the peroxide moieties after O-O-bond cleavage. Detailed information about the Baeyer-Villiger, Criegee, Hock, Kornblum-DeLaMare, Dakin, Elbs, Schenck, Smith, Wieland, and Story reactions is given. Unnamed rearrangements of organic peroxides and related processes are also analyzed. The rearrangements and related processes of important natural and synthetic peroxides are discussed separately.

https://www.beilstein-journals.org/bjoc/content/pdf/1860-5397-12-162.pdf

Rearrangements of organic peroxides and related processes

We have investigated the reactions of H2O2 with Fe2O3, CuO, HfO2, CeO2 and Gd 2O3 in aqueous solution. The reactions rate constants at room temperature were determined. From the temperature depende ...

Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides

Effect of type of peroxide on cross-linking of poly(l-lactide)

Three methods used in the kinetics of liquid-phase radical reactions for estimating the dissociation energies of individual bonds in polyatomic molecules are described. The first approach is based on the study of the equilibrium in radical abstraction reactions involving stable radicals and measurements of the equilibrium constants. The second method is based on the study of the kinetics of homolytic decomposition of molecules. Measuring the activation energy of these reactions makes it possible to estimate the dissociation energies of the weakest bonds, e.g., the O–O bonds in various peroxides. The essence of the third approach developed in the framework of the model of intersecting parabolas is calculations of the bond dissociation energy from the activation energy of a radical reaction involving the molecules under consideration. This method allowed the dissociation energies of the C–H, N–H, O–H and S–H bonds in a large number of organic compounds to be estimated. The scope and the specific features of application of each method are discussed and the bond dissociation energies determined by these methods are given.

http://iopscience.iop.org/article/10.1070/RC2005v074n09ABEH001177/pdf

Estimation of the bond dissociation energies from the kinetic characteristics of liquid-phase radical reactions

Preface. Symbols and Abbreviations. PART I: INITIATORS. Chapter 1. Mechanism of Decomposition of Initiators. 1.1 Introduction. 1.2 Nonconcerted Unimolecular Decomposition. 1.3 Concerted Fragmentation of Initiators. 1.4 Anchimerically Assisted Decomposition of Peroxides. 1.5 Decay of Initiators to Free Radicals and Molecular Products. 1.6 Chain Decomposition of Initiators. References. Chapter 2. Cage Effect. 2.1 Introduction. 2.2 Experimental Evidence for the Cage Effect. 2.3 Mechanistic Schemes of Cage Effect. 2.4 Cage Effect in Solid Polymers. References. Chapter 3. Methods of Study of Initiator Decomposition and Free Radical Generation. 3.1 Kinetic Decay of Initiator (KDI). 3.2 Kinetic Product Formation (KPF). 3.3 Acceptors of Free Radicals (AFR). 3.4 Kinetic Chain Initiated Reaction (KIR). 3.5 Chemiluminescence (CL) Method. References. Chapter 4. Dialkyl Peroxides and Hydroperoxides. 4.1 Dialkyl Peroxides. 4.2 Hydroperoxides and Peracids. References. Chapter 5. Diacyl Peroxides, Peroxy Esters, Polyatomic, and Organometallic Peroxides. 5.1 Diacyl Peroxides. 5.2 Peroxy Esters. 5.3 Decomposition of Polyatomic Peroxides. 5.4 Organometallic Peroxides. References. Chapter 6. Organic Polyoxides. 6.1 Dialkyl Trioxides. 6.2 Hydrotrioxides. 6.3 Tetroxides. References. Chapter 7. Azo Compounds. 7.1 Synthesis and Structure of Azo Compounds. 7.2 Thermochemistry of Azo Compounds. 7.3 Decomposition of Azo Compounds. References. Chapter 8. Compounds with Weak C-C, N-N, C-N and N-O Bonds. 8.1 Polyphenylhydrocarbons. 8.2 Substituted Hydrazines. 8.3 Alkoxyamines. 8.4 Nitro Compounds. 8.5 Nitrates and Nitrites. 8.6 Disulfides and Polysulfides. 8.7 Organometallic Compounds. References. PART II: BIMOLECULAR REACTIONS OF FREE RADICAL GENERATION. Chapter 9. Parabolic Model of Bimolecular Homolytic Reaction. 9.1 Introduction. 9.2 Principles for the Parabolic Model of Bimolecular Homolytic Reaction. 9.3 Parameters of Bimolecular Homolytic Reaction in the Parabolic Model. References. Chapter 10. Bimolecular and Trimolecular Reactions of Free Radical Generation by Dioxygen. 10.1 Reaction of Dioxygen with C-H Bonds of Organic Compounds. 10.2 Reaction of Dioxygen with the Double Bond of Olefins. 10.3 Trimolecular Reaction of Radical Initiation by Dioxygen. References. Chapter 11. Bimolecular Reactions of Free Radical Generation by Ozone. 11.1 Initiation of Radicals by Ozone Reactions. 11.2 Chain Reactions of Ozone Decomposition. References. Chapter 12. Bimolecular Reactions of Hydroperoxides with Free Radical Generation. 12.1 Bimolecular Decomposition of Hydroperoxides. 12.2 Bimolecular Reactions of Hydroperoxides with a pi-Bond to Olefins. 12.3 Bimolecular Reactions of Hydroperoxides with C-H, N-H, and O-H Bonds of Organic Compounds. 12.4 Acid Catalysis for Homolytic Reactions of Hydroperoxides. 12.5 Reaction of Peroxides with Amines. References. Chapter 13. Free Radical Generation by Olefins. 13.1 Reactions of Retrodisproportionation. 13.2 Chain Initiation in Thermal Radical Polymerization. References. Chapter 14. Free Radicals Generation by Haloid Molecules and Nitrogen Dioxide. 14.1 Reactions of Fluorine Compounds. 14.2 Reactions of Dichlorine and Other Chlorine Compounds. 14.3 Initiation by Nitrogen Dioxide. References. Chapter 15. Free Radical Generation by Reactions of Ions with Molecules. 15.1 Decomposition of Hydrogen Peroxide Catalyzed by Transition Metal Ions. 15.2 Catalysis by Ions and Complexes of Transition Metals in Liquid-Phase Oxidation of Organic Compounds. 15.3 Reactions of Free Radicals with Transition Metal Ions. 15.4 Oxidation of Transition Metal Ions by Dioxygen. 15.5 Oxidation of Organic Compounds by Transition Metal Ions. 15.6 Reduction of Peroxides by Radical Anions. References. PART III: REACTIONS OF FREE RADICALS. Chapter 16. Isomerization and Decomposition of Free Radicals. 16.1 Intramolecular Abstraction of Hydrogen Atom. 16.2 Cyclization of Free Radicals. 16.3 Decyclization of Cyclic Radicals. 16.4 Fragmentation of Free Radicals. References. Chapter 17. Free Radical Abstraction Reactions. 17.1 Classification of Radical Abstraction Reactions. 17.2 Enthalpy of Reaction. 17.3 Force Constants of Reacting Bonds. 17.4 Triplet Repulsion. 17.5 Electron Affinity of Atoms in Reaction Center. 17.6 Repulsion of Atoms Forming the Reaction Center. 17.7 Influence of pi-Bonds in the Vicinity of the Reaction Center. 17.8 Steric Effect. 17.9 Polar Effect in Radical Reactions. 17.10 Effect of Multidipole Interaction. 17.11 Solvating Effect. References. Chapter 18. Free Radical Reactions of Hydrogen Transfer and Substitution. 18.1 Reactions of Hydrogen Atom Transfer from a Free Radical to a Molecule. 18.2 Free Radical Substitution Reactions. 18.3 Reaction of Peroxides with Ketyl Radicals. References. Chapter 19. Free Radical Addition. 19.1 Enthalpy and Entropy of Free Radical Addition. 19.2 Empirical Correlation Equations. 19.3 Quantum Chemical Calculations for the Activation Energy. 19.4 Parabolic Model of Radical Addition. 19.5 Contribution of Enthalpy for an Addition Reaction to Its Activation Energy. 19.6 Force Constants of Reacting Bonds. 19.7 Triplet Repulsion in the Transition State of Addition Reactions. 19.8 Influence of Neighboring pi-Bonds on the Activation Energy of Radical Addition. 19.9 Role of the Radius of the Atom Bearing the Free Valence. 19.10 Interaction of Two Polar Groups. 19.11 Multidipole Interaction in Addition Reactions. 19.12 Steric Hindrance. 19.13 Addition of Alkyl Radicals to Dioxygen. References. Chapter 20. Recombination and Disproportionation of Free Radicals. 20.1 Alkyl Radicals. 20.2 Macroradicals. 20.3 Peroxyl Radicals. References. Index.

Handbook of Free Radical Initiators

Decomposition reactions of azo compounds, as studied by quantum chemistry methods and the parabolic model

We have previously shown that the alkylating activit{ of heterofunctional diazoketones is dependent on the intramolecular participation of the heteroatom present in the carrier of the diazocarbonyl function, and an increase in the nucleophilicity of this atom in many instances is associated with an increase in antitumor activity [ii]. The structure of the cyclic transition state (II) in the acidolysis of these heterofunctional ketones is shown below.

T. S. Pokidova

Papers

Handbook of Free Radical Initiators

Decomposition reactions of azo compounds, as studied by quantum chemistry methods and the parabolic model

Synthesis, solvolysis kinetics, and antileukemic activity of 1-diazo-3-(2′-thiohetaryl) alkan-2-ones