Oxidation of unvulcanized, unstabilized polychloroprene: A kinetic study

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. Thermal oxidation in air at atmospheric pressure, in the 80e140 C temperature range and in oxygen at 100 C in the 0.02e3 MPa pressure range, of unvulcanized, unstabilized, unfilled polychloroprene (CR) has been characterized using FTIR and chlorine concentration measurement. The kinetic analysis was focused on double bond consumption. A mechanistic scheme involving unimolecular and bimolecular hydroperoxide decomposition, oxygen addition to alkyl radicals, hydrogen abstraction on allylic methylenes, alkyl and peroxyl additions to double bonds and terminations involving alkyl and peroxy radicals was elaborated. The corresponding rate constants were partly extracted from the literature and partly determined from experimental data using the kinetic model derived from the mechanistic scheme in an inverse approach. Among the specificities of polychloroprene, the following were revealed: The rate of double bond consumption is a hyperbolic function of oxygen pressure that allows a law previously established for the oxidation of saturated substrates to be generalized. CR oxidation is characterized by the absence of an induction period that reveals the instability of hydroperoxides. The kinetic analysis also reveals that peroxyl addition is faster than hydrogen abstraction but slower in CR than in common hydrocarbon polydienes.

Thermal oxidation of Poly(dicyclopentadiene)– kinetic modeling of double bond consumption

“…For summarize, it can be considered as an adaptation of the mechanistic scheme proposed by Tobolski et al [27] for the autoxidation of hydrocarbons (reactions 1u, 1b, 2, 3 and 6), together with some specific reactions for the reactivity of double bonds (reactions (a1) and (a2) [7,12,28]) and the effect of oxygen pressure (or concentration (reactions (4) and (5) [7]). g 1 , g 4 and g 5 are the yields respectively for carbonyls from PO decomposition, crosslinking from P þ P and P þ POO coupling.…”

“…The values of k 6 and k a2 , deduced from this analytical calculation, are compared with values obtained for rubbery polymers (polyisoprene [28], polychloroprene [12]) and model molecules (cyclopentene [30], indene) as shown in Fig. 10.…”

“…For this purpose, we will complete the previously established kinetic model [8] by considering reactions involving the PDCPD double bonds and determining their rate constants. Since crosslinking and double bond consumption can originate from reactions with either P or POO species, our strategy relies on the comparison of the aging behavior under air and under different oxygen pressures [9,10] (which is a way to isolate the specific contribution of some rate constants) following a similar approach to the one used previously for polybutadiene [11] and polychloroprene [12]. Such an experimental approach should help achieve a better separation of the contributions from these two types of reactions.…”

Kinetic analysis of polydicyclopentadiene oxidation

“…Let us recall that the occurrence of termination reactions involving P decreases when increasing oxygen pressure [15]. An increase in oxygen pressure i.e.…”

“…in oxygen concentration in the polymer actually favors the reaction between P and O 2 and thus the decrease in P concentration. Under high oxygen pressure (typically 2.0 MPa of O 2 in polychloroprene [15] or polypropylene [16]), the main termination event is thus "POO þ POO / inactive products". Inversely, under ambient atmosphere, the "P þ P / inactive products" and "P þ POO / inactive products" reactions will predominate.…”