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

Abstract

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.

DFT Modeling of Organocatalytic Ring-Opening Polymerization of Cyclic Esters: A Crucial Role of Proton Exchange and Hydrogen Bonding

“…In line with different types of organocatalysts ( Figure 2), the material that is presented in the review is divided into six main parts bearing in mind the retrospective of the each research topics. This review complements our previous work that was devoted to the DFT modeling of coordination ROP that was recently published in the special issue of Molecules [32].…”

“…The main conclusion of the present review was to recognize that proton exchange and hydrogen bonding [195] play a determining role in organocatalytic ROP of cyclic esters, especially for ROH-initiated processes. This is the difference between coordination ROP [32] and organocatalytic ROP, as discussed in this review, with regard to DFT modeling. Such a difference between coordination and organocatalytic ROP also affects the character of the polymerization: for active coordination catalysts, the polymerization occurs as a living process, the polymerization grade P n is determined by the monomer/catalyst ratio.…”

“…The ROP thermodynamics plays a crucial role for polymerizability of cyclic esters, as mentioned in a number of publications and reviewed in [33]. In our recent review [32], we only mentioned this subject; in the present manuscript we consider the reaction ability of cyclic esters in more detail.…”

Comparative Experimental and Theoretical Study of Mg, Al and Zn Aryloxy Complexes in Copolymerization of Cyclic Esters: The Role of the Metal Coordination in Formation of Random Copolymers

“…Catalytic ring-opening polymerization (ROP) of cyclic esters is the basis for the efficient synthetic approach to actual biodegradable and biocompatible materials [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. Both organocatalysts [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ] and coordination catalysts [ 16 , 17 , 18 , 19 , 20 ] have been efficiently used in ROP. The reaction mechanism of the coordination ROP, catalyzed by metal alkoxy complexes, is traditionally viewed as a repeating sequence of monomer coordination, alkoxy insertion and ring-opening ( Scheme 1 ); these processes are influenced by both the metal nature and ligand environment at the metal center [ 16 , 17 , 18 , 19 , 20 , 21 ].…”

“…Polylactide (PLA) and poly(ε-caprolactone) (PCL), obtained by catalytic ROP of the corresponding cyclic esters, lactide (LA) and ε-caprolactone (εCL) ( Scheme 2 A) [ 1 , 4 , 8 , 15 , 20 , 22 , 23 , 24 ], have currently received great attention in biomedical applications [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Due to the contrasting physical properties of polylactide (PLA) and poly-ε-caprolactone (PCL), random copolymers of LA and εCL have generally proved useful for the development of polymer materials with desired mechanical characteristics and biodegradation rate [ 33 , 34 , 35 , 36 , 37 , 38 ].…”