New publication in ACIE online

Iron guanidine complexes have shown exceptional properties as polymerization catalysts in the past years: They have been the first robust, biocompatible catalysts having a higher polymerization activity than the industrially used, but toxic tin octoate and open whole new synthesis routes to block copolymers by polymerizing via ATRP and ROP simultaneously.

In this publication, the way of success is continued by the presentation of a single iron guanidine catalysts being one of the rare examples capable to produce totally different microstructures in copolymers of lactide, glycolide and ε-caprolactone. The catalyst is active under immortal conditions, stable at temperatures as high as 180 °C and polymerizes all three monomers in a controlled manner. By sequential addition of ε-caprolactone followed by glycolide and lactide highly defined block copolymers are accessible with narrow molar mass distributions. Using a bifunctional co-initiator, up to the pentablock copolymer PLA-b-PGA-b-PCL-b-PGA-b-PLA can be synthesized. Random copolymers on the other hand are obtained by polymerizing a monomer mixture and increasing the reaction temperature to 180 °C. Due to the high temperature, transesterifcations are enhanced and scramble the polymer chain to a random copolymer. Mechanistic investigations revealed ε-caprolactone as the driving force for the synthesis of random copolymers since its active chain end rather performs a transesterification with the existing polymer chain than incorporating an available ε-caprolactone monomer.

These findings significantly contribute to the understanding of copolymerization systems and therefore pave the way for the synthesis of bioplastics with tailor-made properties replacing traditional plastics currently causing the environmental crisis.

The article Master of Chaos and Order: Opposite Microstructures of PCL-coPGA-co-PLA Accessible by a Single Catalyst is available on the webpage of the publisher.