Mechanistic study of transesterification in TBD-catalyzed ring-opening polymerization of methyl ethylene phosphate

Progress in synthesis, modification, characterization and applications of hyperbranched polyphosphate polyesters

Hyperbranched polyphosphate polyesters (HPPs) as a special class of hyperbranched polymers have attracted increased interest and have been intensively studied, because of peculiar structures, excellent biocompatibility, flexibility in physicochemical properties, biodegradability, water soluble, thermal stability, and mechanical properties. HPPs can be divided into phosphates as monomers and phosphates as end groups. In this article, the classification, general synthesis, modifications, and applications of HPP are reviewed. In addition, recent developments in the application of HPP are described, such as modified or functionalized by end capping and hypergrafting to improve the performances in polymer blends, coatings, flame retardant, leather. Furthermore, the modifications and application of HPPs in biomedical materials, such as drug delivery and bone regeneration were discussed. In summary, the hyperbranched polymer enlarges its application range and improves its application performance compared with conventional polymer. In the future, more new HPPs composite materials will be developed through hyperbranched technique. This review of HPPs will provide useful theoretical basis and technical support for the development of new hyperbranched polymer material.

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 1. Polyphosphodiesters

Among natural and synthetic polymers, main-chain phosphorus-containing polyacids (PCPAs) (polyphosphodiesters), stand in a unique position at the intersection of chemistry, physics, biology and medicine. The structural similarity of polyphosphodiesters PCPAs to natural nucleic and teichoic acids, their biocompatibility, mimicking to biomolecules providing the 'stealth effect', high bone mineral affinity of polyphosphodiesters resulting in biomineralization at physiological conditions, and adjustable hydrolytic stability of polyphosphodiesters are the basis for various biomedical, industrial and household applications of this type of polymers. In the present review, we discuss the synthesis, properties and actual applications of polyphosphodiesters.

Cyclic ethylene phosphates with (CH2)nCOOR and CH2CONMe2 substituents: synthesis and mechanistic insights of diverse reactivity in aryloxy-Mg complex-catalyzed (co)polymerization

Herein we present a comparative study of the reactivity of ethylene phosphates with –O(CH2)nCOOMe (n = 1–3, 5), –CH2COOtBu, –OCHMeCOOMe, and –OCH2CONMe2 substituents in BHT-Mg catalyzed ROP.

DBU and TU synergistically induced ring-opening polymerization of phosphate esters: a mechanism study

Biocompatible and biodegradable polyphosphoesters derived from the ring-opening polymerization (ROP) of phosphate esters have drawn increasing attention because of their potential applications in clinical and therapeutic fields.

A New Approach to Developing Long-Acting Injectable Formulations of Anti-HIV Drugs: Poly(Ethylene Phosphoric Acid) Block Copolymers Increase the Efficiency of Tenofovir against HIV-1 in MT-4 Cells

Despite the world’s combined efforts, human immunodeficiency virus (HIV), the causative agent of AIDS, remains one of the world’s most serious public health challenges. High genetic variability of HIV complicates the development of anti-HIV vaccine, and there is an actual clinical need for increasing the efficiency of anti-HIV drugs in terms of targeted delivery and controlled release. Tenofovir (TFV), a nucleotide-analog reverse transcriptase inhibitor, has gained wide acceptance as a drug for pre-exposure prophylaxis or treatment of HIV infection. In our study, we explored the potential of tenofovir disoproxil (TFD) adducts with block copolymers of poly(ethylene glycol) monomethyl ether and poly(ethylene phosphoric acid) (mPEG-b-PEPA) as candidates for developing a long-acting/controlled-release formulation of TFV. Two types of mPEG-b-PEPA with numbers of ethylene phosphoric acid (EPA) fragments of 13 and 49 were synthesized by catalytic ring-opening polymerization, and used for preparing four types of adducts with TFD. Antiviral activity of [mPEG-b-PEPA]TFD or tenofovir disoproxil fumarate (TDF) was evaluated using the model of experimental HIV infection in vitro (MT-4/HIV-1_IIIB). Judging by the values of the selectivity index (SI), TFD exhibited an up to 14-fold higher anti-HIV activity in the form of mPEG-b-PEPA adducts, thus demonstrating significant promise for further development of long-acting/controlled-release injectable TFV formulations.

Versatile Phosphate Diester-Based Flame Retardant Vitrimers via Catalyst-Free Mixed Transesterification

We herein report a new vitrimer system integrated with UV curability, recyclability, and flame retardancy. Energy-efficiency, sustainability, and safety have been required features for next-generation polymer materials. Various attempts have been made to endow thermoset polymers with rapid prototyping capacity, recyclability, and flame retardancy. Thermoset vitrimers based on covalent adaptable networks (CANs) are recyclable and remoldable but are generally not UV curable or flame retardant. Here, we present a conceptually novel option to achieve fast exchange reactions in CANs via catalyst-free mixed transesterification of a UV curable phosphate diester-based acrylate cross-linker. In this system, the phosphate diesters serve as reversible covalent bonds, hydrogen bonding ligands, and flame-retardant structures, while acrylate groups serve as UV curable units as well as transesterification collaborators. After the facile UV curing, an intrinsic flame-retardant and mechanically strong dynamic network was achieved due to abundant hydrogen bonds between P-OH and C═O structures. Additionally, this highly cross-linked network exhibited an attractive recyclability even at temperatures lower than T_g. This phosphate diester-based mixed transesterification concept represents an efficient approach for developing multifunctional vitrimers and can also be generalized into other thermally cured polymer systems.

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

Homogeneity of copolymers is a general problem of catalytic coordination polymerization. In ring-opening polymerization of cyclic esters, the rational design of the catalyst is generally applied to solve this problem by the equalization of the reactivities of comonomers-however, it often leads to a reduction of catalytic activity. In the present paper, we studied the catalytic behavior of BnOH-activated complexes (ВНТ)Mg(THF)2nBu (1), (ВНТ)2AlMe (2) and [(ВНТ)ZnEt]2 (3), based on 2,6-di-tert-butyl-4-methylphenol (BHT-H) in homo- and copolymerization of L-lactide (lLA) and ε-caprolactone (εCL). Even at 1:5 lLA/εCL ratio Mg complex 1 catalyzed homopolymerization of lLA without involving εCL to the formation of the polymer backbone. On the contrary, Zn complex 3 efficiently catalyzed random lLA/εCL copolymerization; the presence of mono-lactate subunits in the copolymer chain clearly pointed to the transesterification mechanism of copolymer formation. Both epimerization and transesterification side processes were analyzed using the density functional theory (DFT) modeling that confirmed the qualitative difference in catalytic behavior of 1 and 3: Mg and Zn complexes demonstrated different types of preferable coordination on the PLA chain (k2 and k3, respectively) with the result that complex 3 catalyzed controlled εCL ROP/PLA transesterification, providing the formation of lLA/εCL copolymers that contain mono-lactate fragments separated by short oligo(εCL) chains. The best results in the synthesis of random lLA/εCL copolymers were obtained during experiments on transesterification of commercially available PLLA, the applicability of 3/BnOH catalyst in the synthesis of random copolymers of εCL with methyl glycolide, ethyl ethylene phosphonate and ethyl ethylene phosphate was also demonstrated.

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

Organocatalysis is highly efficient in the ring-opening polymerization (ROP) of cyclic esters. A variety of initiators broaden the areas of organocatalysis in polymerization of different monomers, such as lactones, cyclic carbonates, lactides or gycolides, ethylene phosphates and phosphonates, and others. The mechanisms of organocatalytic ROP are at least as diverse as the mechanisms of coordination ROP; the study of these mechanisms is critical in ensuring the polymer compositions and architectures. The use of density functional theory (DFT) methods for comparative modeling and visualization of organocatalytic ROP pathways, in line with experimental proof of the structures of the reaction intermediates, make it possible to establish these mechanisms. In the present review, which continues and complements our recent manuscript that focused on DFT modeling of coordination ROP, we summarized the results of DFT modeling of organocatalytic ROP of cyclic esters and some related organocatalytic processes, such as polyester transesterification.

Design of Degradable Polyphosphoester Networks with Tailor-Made Stiffness and Hydrophilicity as Scaffolds for Tissue Engineering

In the recent decades, biodegradable and biocompatible polyphosphoesters (PPEs) have gained wide attention in the biomedical field as relevant substitutes for conventional aliphatic polyesters. These amorphous materials of low glass transition temperature offer promise for the design of soft scaffolds for tissue engineering. Advantageously, the easy variation of the nature of the lateral pendant groups of PPEs allows the insertion of pendent unsaturations valuable for their further cross-linking. In addition, varying the length of the pendent alkyl chains allows tuning their hydrophilicity. The present work aims at synthesizing PPE networks of well-defined hydrophilicity and mechanical properties. More precisely, we aimed at preparing degradable materials exhibiting identical hydrophilicity but different mechanical properties and vice versa. For that purpose, PPE copolymers were synthesized by ring-opening copolymerization of cyclic phosphate monomers bearing different pendent groups (e.g., methyl, butenyl, and butyl). After UV irradiation, a stable and well-defined cross-linked material is obtained with the mechanical property of the corresponding polymer films controlled by the composition of the starting PPE copolymer. The results demonstrate that cross-linking density could be correlated with the mechanical properties, swelling behavior, and degradation rate of the polymers network. The polymers were compatible to human skin fibroblast cells and did not exhibit significant cytotoxicity up to 0.5 mg mL^-1. In addition, degradation products appeared nontoxic to skin fibroblast cells and showed their potential as promising scaffolds for tissue engineering.

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.

DFT Visualization and Experimental Evidence of BHT-Mg-Catalyzed Copolymerization of Lactides, Lactones and Ethylene Phosphates

Catalytic ring-opening polymerization (ROP) of cyclic esters (lactides, lactones) and cyclic ethylene phosphates is an effective way to process materials with regulated hydrophilicity and controlled biodegradability. Random copolymers of cyclic monomers of different chemical nature are highly attractive due to their high variability of characteristics. Aryloxy-alkoxy complexes of non-toxic metals such as derivatives of 2,6-di-tert-butyl-4-methylphenoxy magnesium (BHT-Mg) complexes are effective coordination catalysts for homopolymerization of all types of traditional ROP monomers. In the present paper, we report the results of density functional theory (DFT) modeling of BHT-Mg-catalyzed copolymerization for lactone/lactide, lactone/ethylene phosphate and lactide/ethylene phosphate mixtures. ε-Caprolactone (ε-CL), l-lactide (l-LA) and methyl ethylene phosphate (MeOEP) were used as examples of monomers in DFT simulations by the Gaussian-09 program package with the B3PW91/DGTZVP basis set. Both binuclear and mononuclear reaction mechanistic concepts have been applied for the calculations of the reaction profiles. The results of calculations predict the possibility of the formation of random copolymers based on l-LA/MeOEP, and substantial hindrance of copolymerization for ε-CL/l-LA and ε-CL/MeOEP pairs. From the mechanistic point of view, the formation of highly stable five-membered chelate by the products of l-LA ring-opening and high donor properties of phosphates are the key factors that rule the reactions. The results of DFT modeling have been confirmed by copolymerization experiments.

Data for quantum-chemical modeling of the mechanisms of ring-opening polymerization of methyl ethylene phosphate

The data presented in this paper are related to the research article entitled "Mechanistic study of transesterification in TBD-catalyzed ring-opening polymerization of methyl ethylene phosphate" (Nifant'ev et al., 2019). In this data article, we present 3D molecular information of 76 structures for TBD-catalyzed transformations of methyl ethylene phosphate (MeOEP) and trimethyl phosphate (TMP). We also present 3D molecular information for 24 complexes that model the reaction profile of transesterification of poly(MeOEP) and TMP catalyzed by 2,6-di-tert-butyl-4-methylphenoxy magnezium species, complementing the article "Mechanistic insights of BHT-Mg-catalyzed ethylene phosphate's coordination ring-opening polymerization: DFT modeling and experimental data" (Nifant'ev et al., 2018). The data contains stationary points and transition states (TS) along the first propagation step of MeOEP ring-opening polymerization (ROP) for alternative amide and donor-acceptor mechanisms, initiated by EtOH in the presence of TBD; stationary points and TS for MeOH and HOCH₂CH₂OP(O)(OMe)₂ initiated ROP of MeOEP; and stationary points and TS for transesterification of poly(MeOEP) and TMP. In addition, the data contains stationary points and transition states for the ROP of MeOEP and transesterification of poly(MeOEP) and TMP catalyzed by 2,6-di-tert-butylphenoxy magnesium complex. The data are provided in a PDB format that can be used for further studies.