Effect of Polymer Matrix on Kinetics and Mechanism of Carbene Reactions

Abstract

The features of kinetics and mechanism of the cage radical reactions initiated by carbenes in solid polymers has been considered. The peculiar low temperature reaction of arylcarbenes is their interaction in clusters with formation of biradicals (BR). The yield of BR is a measure of the distribution non-homogeneity of the carbene precursors in polymers. The reaction of BR formation allows us to study the molecular dynamics at cryogenic temperatures. The main factor determining the kinetic non-equivalence of triplet carbenes in low temperature reaction of the hydrogen atom abstraction is the dispersion of the cage distances between carbenes and C-H bonds of macromolecules. The strong effect of structural modifications in filled polymers on the thermal decay of carbenes has been established. The matrix effect on the mechanism of the product formation in the carbene reactions, associated with the relaxation processes, has been recognized by the example of the polyvinylalcohol cross-linkage. The advantage of polyisoprene stabilization against thermoxidation by the phenol grafting in carbene synthesis has been shown.

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

“…Numerous literature data (see, e.g., Refs 70 ± 72) demonstrate the possibility of using this effect for the establishment of a detailed mechanism of processes involving RP. The application of a magnetic field was shown 46,67,69 to influence noticeably the rate of low-temperature decay of BCHC in PMMA and CTA (Fig. 2); however, the character of this influence is different.…”

“…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.…”

“…90 Despite different contents of Aerosil, the kinetics of low-temperature BCHC decay in PMMA and CTA is characterised by the parameter n which is constant at a given temperature. 69,89 Figure 5 shows the dependence of k 0 on the distance l between the filler particles. One can see from the graphs presented in Fig.…”