# Access to Microstructurally Complex Block Copolymers via Switchable Ring-Opening Polymerization of Cyclic Ester Mixtures

## TL;DR

Scientists developed a new method to create complex block copolymers using a switchable catalyst that controls polymerization of different ester monomers.

## Contribution

A highly selective yttrium catalyst enables switchable ring-opening polymerization of multiple cyclic ester monomers to form microstructurally complex block copolymers.

## Key findings

- A yttrium catalyst selectively polymerizes lactide, rac-β-butyrolactone, and ε-caprolactone in a switchable manner.
- Block composition is controlled by the presence or absence of lactide rather than monomer concentration.
- Each block contains two monomers while excluding the third, enabling precise microstructural control.

## Abstract

The synthesis of sequence-controlled block copolymers
from a mixture
of cyclic ester monomers represents a significant challenge. In this
study, we demonstrate the selective and self-switchable ring-opening
polymerization (ROP) of three different cyclic ester monomers (lactide
(LA), rac-β-butyrolactone (rac-β-BL) and ε-caprolactone (ε-CL)) to block copolymers
of the form (AB)
x
(BC)
y
using a highly selective yttrium catalyst. Each block contains
units from two monomers and completely excludes one monomer. The switch
from formation of one block to the next is strictly controlled by
the presence or absence of LA in the reaction mixture rather than
relative concentrations of each monomer. Individual block length and
composition are determined by the initial monomer concentrations.