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 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.

Ring opening copolymerization of δ-valerolactone with 2-methyl-1,3-dioxane-4-one towards poly(3-hydroxypropionate-co-5-hydroxyvalerate) copolyesters

A straightforward strategy of ring-opening copolymerization (ROCOP) toward the synthetic copolyesters is gaining increasing interest. In present work, a novel series of poly(3-hydroxypropionate-co-5-hydroxyvalerate) P(3HP-co-5HV) copolyesters are obtained through ROCOP of...

Synthesis and characterization of guanidinate tin(ii) complexes for ring-opening polymerization of cyclic esters

Novel homoleptic and heteroleptic (guanidinate)tin(ii) complexes were successfully synthesized and structurally characterized. The first heteroleptic (guanidinato)tin(ii) alkoxide complex was synthesized but found to be unstable leading to the corresponding bis(guanidinate)tin(ii) complex. The catalytic activities of bis(guanidinate)tin(ii) complexes having different substituents at the nitrogen atoms (isopropyl (1), cyclohexyl (2), and p-tolyl (3)) were investigated in the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and lactide (LA). The lone-pair electrons of the tin(ii) atom were proposed to act as an initiator similar to N-heterocyclic carbenes. Among the synthesized catalysts, complex 1 having less steric hindrance efficiently catalyzed both homo- and copolymerizations of ε-CL and LA giving high molecular weight cyclic polyesters. Transesterification was found to be the major contributor to the cyclization to cyclic polyesters.

Application of Diethylzinc/propyl Gallate Catalytic System for Ring-Opening Copolymerization of rac-Lactide and ε-Caprolactone

Biodegradable polyesters gain significant attention because of their wide potential biomedical applications. The ring-opening polymerization method is widely used to obtain such polymers, due to high yields and advantageous properties of the obtained material. The preparation of new, effective, and bio-safe catalytic systems for the synthesis of biomedical polymers is one of the main directions of the research in modern medical chemistry. The new diethylzinc/propyl gallate catalytic system was first used in the copolymerization of ε-caprolactone and rac-lactide. In this paper, the activity of the new zinc-based catalytic system in the copolymerization of cyclic esters depending on the reaction conditions was described. The microstructure analysis of the obtained copolyesters and their toxicity studies were performed. Resulted copolyesters were characterized by low toxicity, moderate dispersity (1.19–1.71), varying randomness degree (0.18–0.83), and average molar mass (5300–9800 Da).

Coordination Ring-Opening Polymerization of Cyclic Esters: A Critical Overview of DFT Modeling and Visualization of the Reaction Mechanisms

Ring-opening polymerization (ROP) of cyclic esters (lactones, lactides, cyclic carbonates and phosphates) is an effective tool to synthesize biocompatible and biodegradable polymers. Metal complexes effectively catalyze ROP, a remarkable diversity of the ROP mechanisms prompted the use of density functional theory (DFT) methods for simulation and visualization of the ROP pathways. Optimization of the molecular structures of the key reaction intermediates and transition states has allowed to explain the values of catalytic activities and stereocontrol events. DFT computation data sets might be viewed as a sound basis for the design of novel ROP catalysts and cyclic substrates, for the creation of new types of homo- and copolymers with promising properties. In this review, we summarized the results of DFT modeling of coordination ROP of cyclic esters. The importance to understand the difference between initiation and propagation stages, to consider the possibility of polymer-catalyst coordination, to figure out the key transition states, and other aspects of DFT simulation and visualization of ROP have been also discussed in our review.

Quick construction of a C–N bond from arylsulfonyl hydrazides and Csp2–X compounds promoted by DMAP at room temperature

A mild C–N coupling reaction with arylsulfonyl hydrazides and 2(5H)-furanones shows good yields, excellent reaction regioselectivity and functional group tolerance.