# Influence of the Substitution Pattern of Terpene‐Based Seven‐Membered Lactones on Yttrium‐Mediated Ring‐Opening Polymerization: A Kinetic and Mechanistic Investigation

## TL;DR

This paper studies how the structure of two terpene-based lactones affects their polymerization speed and control when using a yttrium catalyst.

## Contribution

The study reveals how substituent positions in terpene lactones influence polymerization kinetics and energy barriers using experimental and computational methods.

## Key findings

- (+)‐Carvomenthide polymerizes faster than (‐)‐menthide, with lower activation energy.
- (‐)‐Menthide shows more controlled polymerization despite higher energy barriers.
- DFT calculations confirm experimental trends and highlight mechanistic differences in chain propagation.

## Abstract

Terpenes exhibit a wide range of structures, thus enabling diverse applications. Herein, (‐)‐menthide and trans (+)‐carvomenthide were synthesized from terpenoids (‐)‐menthone and (+)‐dihydrocarvone, differing solely in their substitution pattern. (‐)‐Menthide features a methyl group at position 4 and an isopropyl group at position 7, whereas (+)‐carvomenthide shows the inverse arrangement. Both lactones were transformed into polyesters via ring‐opening polymerization (ROP) using an amino‐alkoxy‐bis(phenolate) yttrium catalyst. Polymerization kinetics revealed first‐order behavior, with (+)‐carvomenthide polymerizing significantly faster than (‐)‐menthide, while (‐)‐menthide demonstrated a more controlled polymerization. Activation energies were 36.3 kJ mol−1 for (+)‐carvomenthide and 40.8 kJ mol−1 for (‐)‐menthide. The Gibbs free energy of activation confirmed the lower energy barrier for (+)‐carvomenthide polymerization, with experimental values of 81.9 kJ mol−1 compared to 89.1 kJ mol−1 for (‐)‐menthide. Density functional theory (DFT) calculations supported the experimental results, with computed Gibbs free energy barriers of 84.5 kJ mol−1 for trans (+)‐carvomenthide and 82.3 kJ mol−1 for (‐)‐menthide and mechanistic differences. Refined free energy barriers were determined to be 102.1 kJ mol⁻1 for (‐)‐menthide and 84.9 kJ mol⁻1 for trans (+)‐carvomenthide, agreeing with the experimental trend. These findings highlight the critical role of molecular structure and substituent position on polymerization kinetics and energy barriers in metal‐catalyzed polymerization.

(‐)‐Menthide and trans (+)‐carvomenthide, differing only in substitution pattern, were polymerized via ROP using a bis(phenolate) yttrium catalyst. Kinetic studies showed faster polymerization of (+)‐carvomenthide but greater control with (‐)‐menthide. Experimental and DFT analyses revealed mechanistic differences in chain propagation, highlighting how molecular structure influences reactivity and polymerization control.