ChemInform Abstract: Application of Radical Cage Reactions in Studies of Microstructures of Polymers and Composites

Abstract

Application of Radical Cage Reactions in Studies of Microstructures of Polymers and Composites -[103 refs.]. -(DAVYDOV, E. YA.; VOROTNIKOV, A. P.; PUSTOSHNYI, V. P.; PARIISKII, G. B.; Russ. Chem.

Application of radical cage reactions in studies of microstructures of polymers and composites

“…74 This leads to a higher concentration of diazo compounds in the regions with a decreased packing density of macromolecules, which can result in the formation of clusters. Thus EPR spectroscopy revealed that photolysis (at 77 K) of DDM in common and perdeuterated PMMA, PS and polycarbonate (PC) resulted in carbenes Ph 2 C: formed in the matrix-isolated state and also biradicals 1 75,76 generated in the regions with a decreased packing density of macromolecules due to conversion of DPC dimers (2) in clusters according to the scheme The EPR spectrum of biradicals generated in reaction ( 13) is shown in Fig. 3 a.…”

“…Thus, the effective potential barrier decreases as the temperature increases, and the rate of the process increases accordingly. Vorotnikov et al 61,66,67 determined the values of parameters for the tunnelling of H atom to CHC and DPC in the same polypiperylene matrix. The height U and the width x of the potential barrier as well as the equilibrium distance (R 0 ) between carbon atoms of the active centre of carbene and the C7H groups of polypiperylene in the carbene ± polypiperylene complex were determined from the kinetic data obtained at 77 ± 133 K. The boundary values of these parameters, which correspond to the maximum and minimum rate constants of carbene decay, are presented in Table 1.…”

“…Analysis of KIE in the reaction of BCHC decay in PMMA 66,67 was performed using relations (11), (12) and the condition T& hMO 2 /mo C7H k, under which the linear temperature dependence is transformed into a T 72 dependence. The derived values of characteristic frequencies of intermolecular vibrations (O & 53 cm 71 & 10 13 s 71 ) correlate with the Debye frequencies for molecular crystals.…”

“…68 The difference of distances DR 0 between potential wells in the reaction of H(D) transfer in different kinetic ensembles of carbenes was also determined from the temperature dependence of KIE. 48,66,69 It turned out that the decrease in the rate constant of BCHC decay by one order of magnitude corresponds to DR 0 & 0.006 nm. Such a drastic rate dependence on the distance between reagents is in agreement with the tunnelling mechanism of H atom transfer to triplet carbenes.…”

“…The kinetics of biradical generation in clusters at 77 ± 120 K is well described by the logarithmic dependence on time. Analysis of experimental kinetic dependences performed by Davydov et al 66,75 made it possible to establish the distribution pattern of rate constants as regards the Arrhenius parameters. In general case, the reactivities of carbenes in clusters can be determined from the distribution with respect to both effective activation energies of reaction ( 13) and preexponents.…”