New mechanism for autoxidation of polyolefins: kinetic Monte Carlo modelling of the role of short-chain branches, molecular oxygen and unsaturated moieties

Abstract

In this work, a bivariate kinetic Monte Carlo (kMC) model is constructed to study autoxidation, which is the degradation of polymers in the presence of oxygen. The use of computational...

Elucidating the Role of Alkoxy Radicals in Polyethylene Radio-Oxidation Kinetics

“…A recent work featuring a kinetic model based on ab initio results for molecules stresses the importance of this pathway, and also previous studies have shown that taking into account reaction 1b is important for reproducing experimentally some observed autoacceleration effects in the oxidation process. In particular, this reaction was introduced in kinetic models of radio-oxidation in order to correctly predict the radio-chemical yields of oxidation products and chain scission and to account for the non-Arrhenius behavior of the oxidation induction time and of the oxidation rate …”

“…Some of these mechanisms were investigated in a recent paper 19 of which we became aware during the review process. The outcome, for PE, relying on a careful kinetic model based on reaction rates from the literature and from ab initio calculations globally support our conclusions.…”

“…Another point that has been rarely addressed is how the various reaction rates are affected by the local environment (crystalline, amorphous, or at the interface between the two). Most theoretical approaches, including the recent paper by De Keer et al, consider reactions for molecules in the gas phase, ,− others recently have considered crystalline or surface environments; , this issue is a relevant one to understand the actual reaction pathways, also because frequently the crystallinity ratio can evolve during the oxidation processes . Given the complex microstructure of PE, featuring crystalline lamellae typically 10 nm thick, , separated by amorphous regions, the dominant oxidation reaction pathways could be different according to the local environment (i.e., amorphous phase, inside crystalline lamellae, or at their surface).…”

Observation and Modeling of a Sharp Oxygen Threshold in Aqueous Free Radical and RAFT Polymerization

“…The majority of groups working to address O 2 effects in reaction kinetics is focused on photopolymerization. − There are reports of very small amounts of O 2 affecting solution RAFT polymerization by permeation through a continuous flow microreactor wall and of modeling of particle size distribution during emulsion vinyl chloride polymerization, and kinetic Monte Carlo was used to study autoxidation of polyolefins . Nonetheless, there are few studies quantitatively investigating how O 2 affects reaction kinetics, through continuous reaction monitoring, as done in this work.…”

Macromolecular Photoediting Using Single-Electron Logic

“…As this was much lower than what was observed during our reactivity study, O 2 seemed to be the more likely origin of the enhanced degradation. Pyrillium catalysts are known to sensitize 1 O 2 , which can form reactive peroxide species that promote polymer cracking. ,− To investigate the possibility of analogous reactivity under our conditions, samples of 1 (25.1 mg; 0.27 mmol), 2 (5.5 mg; 0.014 mmol), and (PhS) 2 (15.2 mg; 0.07 mmol) were dried over P 2 O 5 for 16 h. The dried reagents were dissolved in anhydrous DCM (0.075 M) in a glovebox and irradiated with blue light under a balloon of anhydrous O 2 . After irradiation for 1 h, SEC analysis revealed a 96% reduction in M n relative to 1 (Δ M n = −113 kDa; Figure S10), which mirrored the enhanced activity we originally observed under ambient conditions (Table ).…”