# Quantifying the Influences of Epoxide Binding in Epoxide/CO2 Ring Opening Copolymerization Catalysis

## TL;DR

This paper explores how different epoxides affect polymerization rates when using a specific catalyst, revealing a correlation between binding strength and reaction speed.

## Contribution

The study introduces a new linear free energy relationship linking epoxide binding strength to copolymerization rates using UV–vis spectroscopy.

## Key findings

- Epoxide–catalyst binding constants correlate exponentially with copolymerization rates.
- A new linear free energy relationship is established for catalyst performance.
- Structure–activity correlations align with polymerization kinetics and DFT calculations.

## Abstract

Understanding and predicting the effect of epoxide structure
on
the rate of polymerization in epoxide/CO2 ring opening
copolymerization catalysis is a long-standing challenge. Here, a known
highly active Co­(III)­K­(I) catalyst is used to investigate the influences
of six different epoxides' binding strengths on their rates of
copolymerization.
Since calculations and experiments indicate that studying the catalytically
relevant Co­(III)–epoxide adduct directly is experimentally
challenging, epoxide–catalyst binding interactions are quantified
using a Co­(II)­K­(I) complex to model the key catalytic intermediate.
Epoxide–catalyst coordination is investigated using UV–vis
spectroscopy titrations which provide fast and effective determination
of association or binding constants. The epoxide–catalyst equilibrium
constants show a clear exponential correlation with copolymerization
rates and a new catalyst performance linear free energy relationship
is revealed. Epoxides exhibiting stronger catalyst binding constants
show higher copolymerization rates. The structure–activity
correlation is consistent with the polymerization kinetics, mechanism
and DFT calculations. Both the methods to investigate epoxide–catalyst
coordination and the linear free energy relationship are shown to
apply to the series of six epoxides and a second Co­(III)­K­(I) catalyst.
These structure–performance relationships are likely applicable
to other transition metal catalysts and should expedite future epoxide
and catalyst selection to make useful poly­(carbonate) materials.