# Tripartite hydrogen-bonding as a driving force for high-concentration cyclization of poly(l-lactide)

## TL;DR

A new method uses hydrogen bonding to efficiently create large cyclic polylactide molecules under practical conditions.

## Contribution

A tripartite hydrogen-bonding complex enables high-concentration cyclization of poly(l-lactide) with practical synthetic conditions.

## Key findings

- Cyclic PLLA with Mn ≈ 26,000 g mol⁻¹ was achieved at 0.5 M concentration.
- Nanorings with diameters matching expected chain lengths were observed via SPM imaging.
- Intramolecular transesterification at a benzylic ester triggers ring closure efficiently.

## Abstract

A three-step strategy enables efficient cyclization of high-Mn PLLA at 0.5 M. Key to success is a persistent tripartite complex driven by hydrogen bonding and ion pairing. Selective intramolecular transesterification at a benzylic ester triggers ring closure, affording cyclic PLLA (Mn ≈ 26 000 g mol−1) under synthetically practical conditions. SPM imaging reveals nanorings with diameters consistent with the expected contour length of cyclic PLLA chains.

A three-step strategy enables efficient cyclization of high-Mn PLLA at 0.5 M.