Copolymerization of β‐Butyrolactones into Functionalized Polyhydroxyalkanoates Using Aluminum Catalysts: Influence of the Initiator in the Ring‐Opening Polymerization Mechanism

Abstract

AbstractWithin 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 rac‐β‐butyrolactone (BBL), paving the way to PHB with better thermomechanical and processability properties. In this work, the catalyst family is extended based on aluminum phenoxy‐imine methyl catalyst [AlMeL2], that reveals efficient in the ROP of BBL, to the halogeno analogous complex [AlClL2]. As well, the impact on the ROP mechanism of different initiators is further explored with a particular focus in dimethylaminopyridine (DMAP), a hardly studied initiator for the ROP of BBL. A thorough mechanistic study is 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, the introduction of a side‐chain functionality is explored, establishing the copolymerization of BBL with β‐allyloxymethylene propiolactone (BPLOAll), resulting in well‐defined P(BBL‐co‐BPLOAll) copolymers.