# Cyclic polyglycolide by means of metal acetylacetonates

## TL;DR

This paper explores the use of metal acetylacetonates to polymerize glycolide, producing cyclic poly(glycolic acid) efficiently with zirconium acetylacetonate as the best catalyst.

## Contribution

The study introduces zirconium acetylacetonate as a highly effective catalyst for low-temperature, rapid synthesis of cyclic PGA.

## Key findings

- Zirconium acetylacetonate enabled efficient polymerization at lower temperatures (130 °C).
- Cyclic PGA was confirmed via MALDI-TOF and showed similar crystal lattices to linear PGA.
- Molecular weights of 2000–3500 g mol−1 were achieved with dispersities below 2.0.

## Abstract

Glycolide was polymerized in bulk at 160 °C using various metal acetylacetonates as catalysts. Zirconium acetylacetonate was particularly efficient, enabling rapid polymerization even at 130 °C. The formation of cyclic poly(glycolic acid) (PGA), most likely via a ring-expansion polymerization (REP) mechanism, was proven by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Depending on the polymerization conditions, the formation of even-numbered cycles was favored to varying degrees. Number-average molecular weights (Mn) in the range of 2000–3500 g mol−1 were achieved with dispersities below 2.0. Wide-angle X-ray scattering (WAXS) powder patterns showed that the crystal lattice was the same as that of known linear PGAs, regardless of the Mn values. These patterns enabled a comparison of crystallinities with values derived from DSC measurements.

Polymerizations of glycolide with various metal acetylacetonates showed that Zr(acac)4 is the most reactive catalyst, yielding low-molecular-weight cyclic poly(glycolide). The combination of WAXS and DSC measurements confirmed a ΔH0m of 206 J g−1.