D. Ya. Toptygin

Influence of Structure-Physical Properties of Polymer Matrix on Kinetics of Inside Cell Radical Reactions

Abstract In polymethylmethacrylate and cellulose acetate the kinetics of triplet cyclohexadienone carbenes decay by 77–135 K including a hydrogen atom transfer from C[sbnd]H bonds of macromolecules with the radical pair formation was examined. The kinetics of this process reflects the influence of peculiarities on a level of cells. The influence of external magnetic field on the decay of carbenes was established. The character of the magnetic is different in two polymers. Its determined by the cell recombination efficiency of radicals and the exchanged energy in radical pairs depending on mutual radical configurations. The structure-physical modification of polymers by aerosil filling connected with the formation of interfaces influences strong on the rate of carbenes conversions.

Photosensitivity of methylene chloride, stimulated by free radicals

The direct photolysis of CH2C12 leads to the formation of HC1 and unsaturated compounds with conjugated C=C bonds. These same products are also formed under the influence of light that is not absorbed by CH2C12 (λ > 290 nm) in the presence of initiators of free radical reactions: benzoyl peroxide, benzophenone, anthraquinone, and Fe3+ chlorides.

Peculiarities of the kinetics of the low-temperature formation of peroxide radicals in polypropylene of various structures

1. The kinetics of the Low-temperature reaction of R. + O2 = RO 2 . was studied in polypropylene (PP) of various degrees of crystallinity and supermolecular structures. 2. In atactic PP there is a complete conversion of R. to RO 2 . ; in isotactic samples with a high degree of crystallinity, complete conversion is not observed. The size of the spherulites does not influence the kinetics of the reaction. 3. In the approximation of a rectangular distribution, the Arrhenius parameters of the rate constants of the reaction were determined according to the activation energies of the reaction. The difference in the rates of the reaction in atactic and isotactic PP is due to the four- to fivefold change in the diffusion coefficients of oxygen.

Kinetics of the low-temperature reaction R (radical) + O

1. The kinetics of the low-temperature reaction R. + O2 = RO2. in polystyrene and a glass of its low-temperature analog, cumene, was studied. 2. The limiting step is the migration of dissolved oxygen molecules. The reaction kinetics depends substantially on the inhomogeneity of the matrix. 3. A method is proposed for the determination of the solubility of oxygen, not requiring large quantities of the substance and suitable for various types of samples (films, powders, fibers, etc.). 4. The solubility of oxygen depends substantially on the structure of the sample and influences the rate of oxidation.

sub 2

1. The mechanism of the destruction of solid polycarbonate molecules under the action of benzoate free radicals was studied. Cleavage of the macromolecules occurs at the ester bond and the bond of the quaternary carbon to the benzene ring. 2. The phenomenon of yellowing of solid polycarbonate in the course of destruction is associated with the accumulation of chromophore cyclohexadienone groups.

= RO

The effect of the filler, Aerosil, on the kinetics of quenching of triplet cyclohexadiene carbenes at 100–140 K was detected in polymethyl methacrylate and cellulose triacetate. At a fixed temperature, the average rate constant of the process decreases by one to two orders of magnitude with an increase in the concentration of filler to 65 wt. %. The effect of the filler is due to modification of the physical structure of the polymer in passing into the state of a boundary layer whose thickness was estimated at 15–20 nm based on the kinetic data.

sub 2

Conclusions1.In the photodecomposition of p-benzoquinonediazide in a frozen matrix of piperylene oligomer, the formation of triplet cyclohexadienone carbene has been registered by means of ESR, along with allyl radicals of the matrix and phenoxyl radicals in the isolated state and in the form of radical pairs.2.When the carbene interacts with the matrix, it is inserted at C-H bonds of the macromolecules.3.A tunneling mechanism of H atom transfer has been proposed in the reaction of the carbene with the matrix. Estimates of the height and width of the potential barrier of the reaction are given.

(radical) in solid polystyrene and cumene

Conclusions1.Formation of diphenylcarbene (DPC) and the radical pairs which arise as a result of migration of an H atom from the tertiary C-H bonds of the macromolecules into the DPC was recorded during photodecomposition of diphenyldiazomethane into an oligomer of piperylene by EPR at 77‡K.2.The process of thermal quenching of DPC passes through a stage of formation of radical pairs and is caused by migration of an H atom from the macromolecules of the matrix to the DPC by a tunnel mechanism.3.The kinetic principles of thermal quenching of DPC were explained by the distribution of the distances between the carbenes and C-H bonds in the macromolecules. The characteristics of this distribution of distances were estimated.

The destruction of polycarbonate in the presence of benzoyl peroxide

The decomposition of benzoyl peroxide in solid polycarbonate under UV irradiation is a monomolecular chain process.

Effect of the filler on the kinetics of transformation of triplet carbenes in a polymer matrix

1. The nature of the free radicals formed inβ-D-cellobiose in the photoreduction of ferric chloride was studied by the ESR method at 77°K. 2. The conversions of the primary radicals at increased temperatures were investigated, and processes of their isomerization and dehydration were detected.