Copolymerization of β-butyrolactones into functionalized polyhydroxyalkanoates using aluminum catalysts: influence of the initiator in the ring-opening polymerization mechanism.

Within bioplastics, natural poly(3-hydroxybutyrate) (PHB) stands out as fully biocompatible and biodegradable, even in marine environments; however, its high isotacticity and crystallinity limits its mechanical properties and hence its applications. PHB can also be synthesized with different tacticities via a catalytic ring-opening polymerization (ROP) of β-butyrolactone (BBL), paving the way to PHB with better thermomechanical and processability properties. In this work, we extend our catalyst family based on aluminum phenoxy-imine methyl catalyst [AlMeL2], that revealed efficient in the ROP of BBL, to the halogeno analogous complex [AlClL2]. As well, we further explore the impact on the ROP mechanism of different initiators with a particular focus in dimethylaminopyridine (DMAP), a hardly studied initiator for the ROP of BBL. A thorough mechanistic study was performed that evidences the presence of two concomitant DMAP-mediated mechanisms, that lead to either a DMAP or a crotonate end-capping group. Besides, in order to increase the possibilities of PHB post-polymerization functionalization, we explore the introduction of a side chain functionality, establishing the copolymerization of BBL with β-allyloxymethylene propiolactone (BPL OAll ), resulting in well-defined P(BBL-co-BPL OAll ) copolymers. This article is protected by copyright. All rights reserved.