# Dependence of O2 Depletion on Transition Metal Catalyst in Radical Polymerization of Cross-Linking Alkene Resins

## TL;DR

This study compares how different metal catalysts affect oxygen depletion during the polymerization of cross-linking alkene resins.

## Contribution

The study introduces a method using O2-sensitive spectroscopy to compare the O2 depletion rates of cobalt, iron, and manganese catalysts in resin curing.

## Key findings

- The rate of O2 depletion varies significantly depending on the catalyst used.
- O2 is depleted before the autoacceleration phase of polymerization begins in all cases.
- Cobalt(II), iron(II), and manganese(II) catalysts show distinct behaviors in O2 consumption.

## Abstract

Cobalt(II) carboxylates
show broad reactivity with peroxides
and
O2 and are the industry standard catalyst for the activation
of peroxide initiators for the radical polymerization of alkenes under
ambient conditions. Curing alkene-based resins containing cross-linking
units, i.e., monomers containing two or more alkene units, is important
in forming hard protective coatings and materials. The activation
of peroxide initiators produces the propagating chain end radicals
needed for polymerization. Since polymerization progress depends on
the rate of initiator activation and the concentration of propagating
radicals, interception of radicals by O2 can inhibit curing.
Cobalt(II) carboxylates are used due to their reactivity in the presence
of oxygen, even in resin coatings. Alternative catalysts based on
manganese and iron are desirable. Hence, the impact of O2 on their performance in resin curing is of interest. Here, we use
NIR emission and time-resolved spectroscopy, employing the O2-sensitive probe [Ru(ph2phen)3]2+, to determine the concentration of dissolved [O2] in
alkene resins during curing with three representative catalysts, Co(II)(2-ethylhexanoate)2, Fe(II)-bispidine, and Mn(II)(neodecanoate)2.
The rate of depletion of O2 is highly dependent on the
catalyst used, but in all cases, it is well before the onset of the
autoacceleration of polymerization in cross-linking resins.

In this study, we use NIR emission and
time-resolved spectroscopy,
employing the O2-sensitive probe [Ru(ph2phen)3]2+, to determine the concentration of dissolved
O2 in alkene resins during curing with three representative
catalysts, Co(II)(2-ethylhexanoate)2, Fe(II)-bispidine,
and Mn(II)(neodecanoate)2. The rate at depletion of O2 is highly dependent on the catalyst used, but in all cases,
it is well before the onset of the autoacceleration of polymerization
in cross-linking resins.