Mechanism Of Ring-opening Polymerization Research Articles

A theoretical exploration of monomer activation mechanisms in bis-lithium N[sbnd]heterocyclic carbenes complexes for enhanced understanding of charge distribution in ring-opening polymerization of ε-caprolactone

A comprehensive examination was conducted on the ring-opening polymerization (ROP) mechanism of ε-caprolactone (ε-CL) employing bis-lithium N-heterocyclic carbene complexes (bisLiNHCs) in a theoretical framework. The modeled reactions were carried out utilizing density functional theory at B3LYP level. An activated-monomer mechanism was observed, characterized by occurrence of two distinct transition states. Initiating with activation of ε-CL via two lithium atoms from bisLiNHCs catalysts, the ensuing step involved nucleophilic addition of carbonyl group stemming from the lithium benzoxide (LiBnO) initiator. The ring opening ε-CL was accomplished via classical cleavage of acyl-oxygen bond. The determination of reaction barrier heights for ε-caprolactone with bisLiNHCs catalysts involved the examination of potential energy profiles. The computed energy profiles revealed exothermic characteristics for each ROP reaction, with the identification of a rate-determining step occurring at the second transition state, which entailed cleavage of acyl-oxygen bond from monomer. Furthermore, through comparisons catalytic capabilities of bisLiNHCs derivatives and energy barrier heights, it was observed that the length and flexibility of linker chain as well as steric effects from substituent groups, significantly influenced the geometric configuration. These specific variations induce alterations in both distance and angular orientation, which are pivotal aspects influencing the chelation dynamics between lithium and oxygen atoms.

A Mechanism-Based Reaction-Diffusion Model for Accelerated Discovery of Thermoset Resins Frontally Polymerized by Olefin Metathesis.

Frontal ring-opening metathesis polymerization (FROMP) involves a self-perpetuating exothermic reaction, which enables the rapid and energy-efficient manufacturing of thermoset polymers and composites. Current state-of-the-art reaction-diffusion FROMP models rely on a phenomenological description of the olefin metathesis kinetics, limiting their ability to model the governing thermo-chemical FROMP processes. Furthermore, the existing models are unable to predict the variations in FROMP kinetics with changes in the resin composition and as a result are of limited utility toward accelerated discovery of new resin formulations. In this work, we formulate a chemically meaningful model grounded in the established mechanism of ring-opening metathesis polymerization (ROMP). Our study aims to validate the hypothesis that the ROMP mechanism, applicable to monomer-initiator solutions below 100 °C, remains valid under the nonideal conditions encountered in FROMP, including ambient to >200 °C temperatures, sharp temperature gradients, and neat monomer environments. Through extensive simulations, we demonstrate that our mechanism-based model accurately predicts the FROMP behavior across various resin compositions, including polymerization front velocities and thermal characteristics (e.g., Tmax). Additionally, we introduce a semi-inverse workflow that predicts FROMP behavior from a single experimental data point. Notably, the physiochemical parameters utilized in our model can be obtained through DFT calculations and minimal experiments, highlighting the model's potential for rapid screening of new FROMP chemistries in pursuit of thermoset polymers with superior thermo-chemo-mechanical properties.

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.

Microstructural Analysis of Benzoxazine Cationic Ring-Opening Polymerization Pathways.

Herein, an evaluation of the initial step of benzoxazine polymerization is presented by mass spectrometry, with a focus on differentiating the phenoxy and phenolic products formed by distinct pathways of the cationic ring opening polymerization (ROP) mechanism of polybenzoxazine formation. The use of infrared multiple photon dissociation (IRMPD) and ion mobility spectrometry (IMS) techniques allows for differentiation of the two pathways and provides valuable insights into the ROP mechanism. The results suggest that type I pathway is favored in the initial stages of the reaction yielding the phenoxy product, while type II product should be observed at later stages when the phenoxy product would interconvert to the most stable type II phenolic product. Overall, the findings presented here provide important information on the initial step of the benzoxazine polymerization, allowing the development of optimal polymerization conditions and represents a way to evaluate other multifunctional polymerization processes.

Design, synthesis and curing mechanism of two novel photothermal dual-curing adhesives for propellants and explosives

Photothermal dual-curing adhesive is not only required to realize the basic curing function, but also has the characteristics of rapid setting and strong curing, which possesses a vital role in the molding speed, stability and structure integrity for 3D-printed propellants and explosives. Herein, the acrylate hydroxyl terminated polybutadiene, as novel photothermal dual-curing binders, were designed and synthesized utilizing cationic ring opening polymerization and active monomer mechanism as the strategy of photothermal dual-curing reaction. The mechanical properties and thermal stability of the photothermal dual-curing elastomers were systematically investigated. The results suggested that the target MAHTPB(Acrylate hydroxy‑terminated polybutadiene)-based adhesives could be cured rapidly within 5 s under UV light irradiation and completely cured in 1.5 h under heating conditions. Specifically, the elastomer film formed by MAHTPB-based photothermal dual-curing has a tensile strength of 4.63 MPa and an elongation of 386%, which exhibits stronger mechanical properties than the elastomer film formed by single photo- or thermal-curing. As a result, the synthesized photothermally cured adhesives have performed 3D printing experiments and achieved relatively satisfactory printing effects. Our study aims to solve the problems of short photocuring time, slow curing rate and incomplete curing for traditional photocuring, which lays a solid foundation to achieve rapid prototyping and precise performance control in 3D printing of propellants and explosives.

Catalytic Living ROMP: Synthesis of Degradable Star Polymers.

Star polymers have attracted considerable attention over the past few years due to their distinctive physical and chemical attributes that are different from conventional linear polymers. Here, we present a one-pot synthesis of narrowly dispersed and degradable homoarm and miktoarm star polymers exploiting the catalytic living ring-opening metathesis polymerization (ROMP) mechanism. Several complex polymeric architectures (such as A3-, A4-, A6-, A2B-, A3B-, and AB2-type star polymers) were synthesized quite straightforwardly by using appropriate vinyl ether chain transfer agents. SEC, 1H NMR, and DOSY NMR spectroscopy were employed to analyze and characterize all of the synthesized polymers. We believe that this sustainable and environmentally friendly synthesis of star polymers could become an important synthetic tool for polymer engineers working on supramolecular, industrial or biomedical applications.

Design of advanced and highly effective partially bio-energetic polybenzoxazines as the next generation of reactive structure materials

ABSTRACT In this study, a new class of energetic green benzoxazine polymers is introduced based on vanillin, as a renewable reactant. The newly developed monomers were afforded by the reaction of vanillin with exploshores groups bearing compounds, namely the 2,4 dinitrophenylhydrazine and the para-nitroaniline, respectively, following the typical Mannich reaction. The chemical structure and the formation of the oxazine ring of both monomers were confirmed by 1H and 13C NMR, FTIR, and elemental analysis. The ring opening polymerization mechanism was investigated by FTIR and DSC-TGA analyses. The energetic performances, as well as the physicochemical properties, were studied by a bomb calorimeter, deflagration tester, and electronic densimeter. Overall, both polymers showed promising energetic performances with deflagration temperatures of about 275 and 261°C for the 2,4 dinitrophenylhydrazine and para-nitroaniline-based polybenzoxazines, respectively. The thermal analysis results highlighted that these polymers can be effectively used as reactive structure materials (RSMs) owing to their combination of high thermal stability above operational temperatures and remarkable energetic performances.

A mechanistic study on homo- and copolymerization of L-Lactide and ε-caprolactone catalyzed by an aluminum complex bearing a Bis(phenoxy)amine ligand: A DFT study

Polymerization of biodegradable lactide and lactone has been the subject of intense research during the past decade. We used density functional theory (DFT) calculations to investigate the initiation and first propagation for ring-opening polymerization (ROP) mechanisms of L-lactide (LA) and ε-caprolactone (CL) on aluminum complexes bearing the bis(phenoxy)-amine ligand with pyridine (Catalyst I) and diethylamine (Catalyst II) sidearm. Here, the ROP mechanisms of LA and CL on both catalysts were classified into 3 parts: (1) LA homopolymerization, (2) CL homopolymerization, and (3) LA and CL copolymerization. For homopolymerization, Catalyst I shows a greater performance than Catalyst II on both LA and CL due to its less bulky sidearm. However, CL homopolymerization on Catalyst I is more favorable than that of LA, which is caused by the stronger CL coordination on the catalyst. For LA and CL copolymerization, the amine sidearm variation and the vdW interactions of monomers on Catalysts I and II provide different copolymer products, the tapered and random copolymers, respectively. These calculated results are in good agreement with our previous experimental reports. The understanding gained in the current study might be helpful in the development of high-performance catalysts for the ROP reaction of biodegradable lactide and lactone.

The influence and mechanism of ligand steric hindrance and electronic effects on the ring-opening metathesis polymerization of polycyclopentene under tungsten complex

Polycyclopentene rubber has attracted attention due to its unique ring-opening metathesis polymerization (ROMP) mechanism, which endows it with a range of excellent properties, including recyclability and structural controllability. In order to facilitate the production of polycyclopentene, a tungsten olefin metathesis catalytic system was developed. The influence of ligand steric hindrance and electronic effects on the reaction was investigated through kinetic experiments and density functional theory (DFT) calculations. The results show that increased ligand steric hindrance enhances reaction stability, while the electro-withdrawing group on the ligand accelerates catalyst activation. Additionally, a ligand “release-return” mechanism for polymerization initiation was proposed. The polycyclopentene's thermal properties and stereoregularity were explored.

Phosphaphenanthrene-Functionalized Benzoxazines Bearing Intramolecularly Hydrogen-Bonded Phenolic Hydroxyl: Synthesis, Structural Characterization, Polymerization Mechanism, and Property Investigation

Hydrogen bonding in thermosetting resins can have a significant influence on the polymerization processes and the properties of corresponding thermosets, but its role in the polymerization of benzoxazine resins remains unclear. Here, we synthesized two novel phosphaphenanthrene-functionalized benzoxazine monomers from 2-6-oxido-6H-dibenz-[c,e][1,2]oxaphosphorin-1,4-dihydroxy phenylene, aniline/furfurylamine, and paraformaldehyde and investigated the structures by 1H, 13C, and 31P NMR, Fourier transform infrared (FT-IR), elemental analysis, and high-resolution mass spectrometry. Ring-opening polymerizations of both monomers were then studied by differential scanning calorimetry (DSC) and in situ FT-IR spectroscopy, and the resulting thermosets exhibited high thermal stability and low flammability. Density functional theory (DFT) calculations suggested that intramolecular hydrogen bonds are preferably formed between the phenolic −OH and the P═O in the phosphaphenanthrene functionality for both monomers, which is in line with the experimental results. We proposed a cation-activated ring-opening polymerization mechanism where intramolecular hydrogen bonding plays a pivotal role. The combination of experimental and computational effort provides molecular-level insights into intramolecular hydrogen bonding and its role in polymerization mechanisms in benzoxazine chemistry as well as a new angle for the design of high-performance thermoset polymers.

Ring-Opening Oligomerization Mechanism of a Vanillin-Furfurylamine-Based Benzoxazine and a Mono-Azomethine Derivative.

Exploring the ring-opening polymerization (ROP) mechanism of benzoxazines is a fundamental issue in benzoxazine chemistry. Though some research papers on the topic have been reported, the ROP mechanism of mono-benzoxazines is still elusive. The key point for mechanistic studies is to determine and characterize the structure and formation pathways of the products generated in ROP. In this paper, the ROP of a vanillin-furfurylamine-based benzoxazine and a mono-azomethine derivative is studied with differential scanning calorimetry, fourier transform infrared spectroscopy, nuclear magnetic resonance, and electrospray ionization mass spectrometry, respectively. The results show that the products consist of a range of cationic species, zwitterions, fragments, and series of cyclic and linear oligomers of varying molecular sizes. It is proposed that both mono-benzoxazines undergo thermally activated cationic ring-opening oligomerization via zwitterion intermediates. Upon thermal induction, multi-bond-cleavage takes place to form various zwitterionic intermediates, which react with a monomer, a fragment, or a second zwitterion by several pathways to generate cyclic and linear oligomers.

Experimental and computational investigations on ring-opening polymerization mechanisms of amide-functional benzoxazines

Experimental and computational investigations on ring-opening polymerization mechanisms of amide-functional benzoxazines

Isothermal Crystallization of Poly(ε–Caprolactone) PCL in Three‐Armed Copolymers

AbstractBranched copolymers are a special class of polymeric materials in which are reflected the combined effects of polymer segments and architectural constraints of the branched architecture. In this work, three‐armed graft copolymers, poly (hydroxyethyl methacrylate‐graft‐poly(caprolactone), [P(HEMA‐g‐PCL)]3, are synthesized by combination of reversible addition‐fragmentation chain‐transfer (RAFT) and ring opening polymerization (ROP) mechanisms in a one‐pot/one‐step protocol. The resulting macromolecules are characterized by 1H Nuclear Magnetic Resonance (NMR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The preliminary results indicate the success of the methodology and are in agreement with literature reports. In addition, DSC isothermal crystallization are performed, and Avrami's theory is employed in order to obtain kinetics parameters of interest, such as the half‐life for the crystallization process (t1/2), the bulk crystallization constant (k), and the Avrami's exponent (n). Thermal analysis evidences a noticeable reduction in the melting temperature compared with linear PCL homopolymer. However, the presence of branches does not modify the values of the maximum degradation temperatures significantly. Finally, the synthesized copolymers adopt a two‐dimensional crystallization type (disk and cylindrical).

Scalable and Room-Temperature Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Active Lithium Tetramethylene-Tethered Bis[N-(N'-butylimidazol-2-ylidene)] N-Heterocyclic Carbene as a Lewis Acid Organocatalyst.

The Lewis acid organocatalytic system of lithium tetramethylene-tethered bis[N-(N'-butylimidazol-2-ylidene)] N-heterocyclic carbene (1,4-bisNHC) including lithium benzyloxide and benzyl alcohol has been successfully utilized in the ring-opening polymerization (ROP) of ε-caprolactone (CL) for the first time. The catalytic performance of this organic catalyst in the synthesis of high-molecular-weight polymers was investigated via bulk polymerization using different combinations of tetramethylene-tethered bis[N-(N'-butylimidazolium)] hexafluorophosphate (1,4-bis[Bim][PF6]), benzyl alcohol (BnOH), and n-butyl lithium (nBuLi) ([1,4-bis[Bim][PF6]]/[BnOH]/[nBuLi]) with the molar ratios of 0:2:2, 1:1:3, 1:2:3, and 1:2:4. The results showed that the molar ratio of 1:2:3 efficiently and rapidly initiated the bulk ROP of CL at room temperature with a high molar ratio of CL to 1,4-bis[Bim][PF6] of 3000/1 and produced the highest number of average-molecular-weight (Mn) poly(ε-caprolactone) (103,057 g mol-1) with the dispersity (D̵) and %conversion of 1.73 and 98% in a short period of time (152 s). From comparative studies, the relative polymerization rates of the bulk ROP of CL with different [1,4-bis[Bim][PF6]]/[BnOH]/[nBuLi] molar ratios was determined in the following order: 1:2:4 > 1:1:3 > 1:2:3 > 0:2:2. For mechanistic investigation, the bulk ROP mechanism of CL with our organic catalyst was proposed through the intramolecular bis-lithium-carbene interaction pathway for 1,4-bisNHC1,1,3, 1,4-bisNHC1,2,3, and 1,4-bisNHC1,2,4 systems.

Ring-Opening Polymerization (ROP) and Catalytic Rearrangement as a Way to Obtain Siloxane Mono- and Telechelics, as Well as Well-Organized Branching Centers: History and Prospects.

PDMS telechelics are important both in industry and in academic research. They are used both in the free state and as part of copolymers and cross-linked materials. At present, the most important, practically used, and well-studied method for the preparation of such PDMS is diorganosiloxane ring-opening polymerization (ROP) in the presence of nucleophilic or electrophilic initiators. In our brief review, we reviewed the current advances in the field of obtaining polydiorganosiloxane telechelics and monofunctional PDMS, as well as well-organized branching centers by the ROP mechanism and catalytic rearrangement, one of the first and most important reactions in the polymer chemistry of silicones, which remains so at the present time.

Investigation of initiator metal efficiency in the ring‐opening polymerization of lactones: an experimental and computational study

AbstractPoly(δ‐valerolactone) (PVL) was synthesized by ring‐opening polymerization (ROP), employing tin(II) acetate (SnAcet2), lead(II) acetate trihydrate (PbAcet2·3H2O) and cadmium(II) acetate dihydrate (CdAcet2·2H2O) complexes as initiators without any co‐initiator. The highest molecular weight PVL (45 438 g mol−1, 91% yield) was obtained with CdAcet2·2H2O. Characterization of the synthesized products was performed by FTIR, 1H NMR, 13C NMR, gel permeation chromatography (GPC), matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF/TOF MS), TGA and DSC. Electrostatic data (natural bond orbital and Hirshfeld) and lowest unoccupied molecular orbital (LUMO) of the initiators were obtained by using several density functional theory methods (B3LYP, ωB97X‐D, PBEPBE, BPV86, HSEH1PBE, MPW1PW91, M06 and M062X). In addition, the initiation stage of the ROP mechanism of δ‐valerolactone with these metal acetate complexes was investigated at the ωB97X‐D level with a mixed basis set. It was computationally determined that the most effective initiator was also CdAcet2. The molecular weight variation of PVLs synthesized with these initiators can be associated with the combined evaluation of atomic charge, LUMO and orbital overlap analyses. The computationally obtained reaction barriers for the initiators support this idea, also. In addition, toxicity tests carried out for PVLs synthesized with acetate complexes containing Sn, Cd and Pb revealed that the Sn and Cd complexes do not have a toxic effect on cell viability at some dilution rates. © 2021 Society of Industrial Chemistry.

Ring-Opening Polymerization of CO2-Based Disubstituted δ-Valerolactone toward Sustainable Functional Polyesters.

3-Ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVL) is a disubstituent δ-lactone derived from CO2 and 1,3-butadiene. In this contribution, we report the ring-opening polymerization (ROP) of EVL with β-butyrolactone (BBL) as the comonomer catalyzed by scandium triflate [Sc(OTf)3]. The obtained polyester bearing active unsaturated bonds has the weight-average molecular weight (Mw) of 4.1 kg/mol, in which the EVL content is 38 mol % in accordance with the initial ratio of 40 mol %. The copolymers are characterized in detail and the cationic ROP mechanism has been confirmed by kinetic study, chain end analysis and density functional theory (DFT) calculation. The modification of the unsaturated bonds in EVL repeating units via the thio-ene click reaction with mercapto-ended polysarcosine polysarcosine yields the amphiphilic grafting polymers. It is a CO2 fixation approach toward the functional poly(EVL-r-BBL) that is promising as a degradable polyester precursor for adhesive or surface-coating materials.

Alternating Copolymerization Realized with Alternating Transformation of Anion-Migrated Ring-Opening Polymerization and Anionic Polymerization Mechanisms

Alternating Copolymerization Realized with Alternating Transformation of Anion-Migrated Ring-Opening Polymerization and Anionic Polymerization Mechanisms

The Reaction Mechanism of Ring-opening Polymerization of ε-Caprolactone Using Bis(benzoylacetonato)zirconium(IV) Catalyst With PM3 Semi-Empirical Method

Acknowledged that polycaprolactone (PCL) is one of the prospective polymer category. This is due to PCL has a great mechanical properties, biodegradability, and excellent mixing ability with various other polymers. The effective technique to get PCL is through the ring opening polymerization (ROP) of caprolactone (ε-CL) using metal catalyst. The aims of this research was to determine a reasonable reaction mechanism of the ROP of ε-CL using bis(benzoylacetonato)zirconium(IV) chloride catalyst. In this investigation the PM3 semi-empirical method was assigned to calculate the monomer, intermediate structures, and polymer structure. Then, to compute and visualize geometry structure was employed by using the HyperChem 8.0 program. This software operates on the Windows 07 system. The calculation results imply that to get PCL using bis(benzoylacetonato)zirconium(IV) catalyst required a few steps i.e. coordination ε-CL in metal center, χ-CL deprotonation, the insertion of ε–CL, and propagation of the chain.

Synthesis of Well-defined Poly(tetrahydrofuran)-b-Poly(a-amino acid)s via Cationic Ring-opening Polymerization (ROP) of Tetrahydrofuran and Nucleophilic ROP of N-thiocarboxyanhydrides

The synthesis of block copolymers of poly(tetrahydrofuran)-b-poly(α-amino acid) (PTHF-b-PAA) is challenging since it is difficult to combine the two blocks produced via different/conflicting ring-opening polymerization (ROP) mechanisms. In this contribution, the cationic ROP of THF is catalyzed by rare-earth triflate [RE(OTf)3] and terminated by 2-(t-butyloxycarbonyl-amino) ethanol (BAE). After the deprotection of t-butyloxycarbonyl (Boc) group, the chain end of PTHF is quantitatively changed to amino group which thereafter initiates the nucleophilic ROP of α-amino acid N-thiocarboxyanhydrides (NTAs). Both polymerizations are well controlled, generating PTHF and PAA segments with designable molecular weights (MWs). PTHF-b-polylysine (PTHF-b-PLys) and PTHF-b-polysarcosine (PTHF-b-PSar) are obtained with MWs between 8.6 and 28.7 kg/mol. The above amphiphilic diblock copolymers form micelles in water. PTHF40-b-PSar32 acts as a surfactant to stabilize oil-in-water emulsions. Both segments of PTHF-b-PAA are biocompatible and promising in the biomedical application.