Mechanism Of Polymerization Reaction Research Articles

Wood consolidation through an epoxy‐acrylic gamma‐crosslinked three‐dimensional system

AbstractEmerging technologies based on polymeric materials are progressively developed in order to preserve and consolidate cultural heritage artifacts. In this study, we aimed to obtain a hybrid polymer reliant on two types of thermosets that undergo irreversible crosslinking via ionizing radiation‐induced polymerization, the polymer's structure and characteristics being tailored using specific dose rates, doses, linear energy transfer and monomers ratio, in order to achieve the established performance requirements. Here, we demonstrate a covalently bonded 3D hybrid diepoxy‐triacrylic polymer that is chemically and dimensionally stable, intending to use it as a consolidant of highly degraded wooden artifacts in order to mitigate oxygen inhibition from radical chain reactions, to increase chemical and thermal stability, as well as to obtain a stiffer consolidated artifact, therefore more resistant to deformation. Various types of analytical techniques such as Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy, Mass Spectrometry or Thermal analysis were performed in order to support our strategy and predictions regarding the synergistic effect given by gamma irradiation‐driven crosslinking through simultaneous cationic and radical chain growth polymerization reaction mechanisms. We achieved a homogenous polymeric formulation and wood‐polymer composite materials with high modulus of elasticity, therefore providing up to a twofold increase in Young's modulus in the consolidated wood, a good chemical resistance to various solvents and outstanding thermal resistance up to 381°C. Consequently, the consolidation methodology, as well as mechanical testing, analytical and morphological characterization of the resulted composite will be discussed. Apart from consolidating cultural heritage wooden artifacts, this synthetic route and impregnation methodology provide opportunities for wood‐polymer composites in a wealth of applications as reinforced wood‐based materials.

Study on polymerization kinetics of copolymerized flame-retardant polyamide 66: Apparent rate constant and reaction activation energy

The research of polymerization kinetics and reaction mechanism on flame-retardant polyamide 66 (FRPA66) is of great significance for its industrial production. Here, FRPA66 is prepared by one-step melt polycondensation of nylon 66 salt and a reactive flame retardant DPDA. By exploring the relationship of viscosity-average molecular weight versus reaction time at different polymerization stages, the apparent rate constant of FRPA66 is calculated to be 41.8 dL g−1s−1. Besides, molecular simulation analysis demonstrates that the reaction activation energy of DPDA and nylon 66 salt in pre-polymerization stage is 312.04 kcal/mol, indicating that the pre-polymerization time can be extended to make up for the lack of pre-polymerization power of FRPA66. In the final polymerization stage, reasonable control of releasing pressure and polymerization time can promote the self-condensation of a small part of DPDA, thus improving the molecular weight of FRPA66. Finally, based on the polymerization kinetic and reaction mechanism, FRPA66 containing 5% DPDA can reach V-0 level.

Strength development and polymerization reaction mechanism of sulfur-tailings-based geopolymer produced with CaO and Na2SiO3 composite activator

Mining and beneficiation processes are accompanied by the discharge of large quantities of tailings, which occupy large areas of land and cause environmental pollution, which is a significant concern. This study prepared an environmentally friendly geopolymer using sulfur tailings and granulated blast furnace slag (GBFS) and characterized its performance and mechanism analysis. A low-cost and efficient CaO-Na2SiO3 composite activator and comprehensive utilization method for sulfur tailings have been proposed. The experimental results showed that the CaO-Na2SiO3 composite activator can improve the strength of STBG, especially the early strength. The highest 28d compressive strength of STBG can reach 32.2 MPa when the CaO content in the composite activators was 10%. However, when the CaO content in the activators was greater than 10%, the cumulative pore volume and harmful pore volumes of the STBG increased to 0.17 mg/L and 0.07 mg/L respectively, and the compressive strength developed slowly in the later period. In addition, the highest immobilization efficiency of STBG for Cu, Pb, and Mn can reach 99.9%, 93.9%, 91.6% respectively. The STBG can effectively immobilize heavy metals.

Direct observation of radiation-induced graft polymerization on a polyethylene film

Radiation-induced graft polymerization is widely used in the synthesis of polymeric materials with various functionalities; however, the details of the reaction mechanism are still unresolved. Herein, the initial stage of the graft polymerization reaction was investigated through atomic force microscopy (AFM). We used glycidyl methacrylate (GMA) in methanol (monomer solution) and a high-density polyethylene (HDPE) film with a well-ordered lamellar structure as the substrate. Using polymer film surfaces with a maximum grafting degree of 0.5%, AFM can distinguish between crystalline and amorphous polyethylene (PE) phases as well as a grafted polymer GMA (PGMA) phase. The graft polymerization reaction started from the interface between the crystalline and amorphous PE phases. As the reaction proceeded, the PGMA covered the crystalline PE phase: i.e., the entire surface of the PE film were covered by the PGMA. Further, the crystalline lamellae of the PE film eventually became a scaffold for the formation of aggregates comprising grafted polymer chains alone. The graft polymerization reaction mechanism was explained by comparing the solubility parameters of the monomer solution, substrate, and grafted polymer chains. Understanding the reaction mechanism at a low grafting degree obtained in this study may contribute to enhancing the efficiency of the graft polymerization reaction on any polymeric material.

Stereoselective Polymerization of Aromatic Vinyl Polar Monomers

AbstractPolar vinyl polymers, a class of polymers with polar groups as side chains, have significant advantages over conventional nonpolar polyolefin materials in terms of viscosity, toughness, interfacial properties (dyeability and printability), and compatibility with solvents or other polymers. Among them, aromatic polar vinyl polymers are of interest because of their good heat resistance properties. In addition, stereoselective polymerization of aromatic polar vinyl monomers has been rapidly developed because the steric structure of the polymer has a significant impact on its physical properties. In this paper, we review the research progress of stereoselective polymerization catalysts for aromatic polar vinyl monomers in recent years, discuss in detail the influence of ligand structure, electronic effect of substituents, spatial site resistance effect, central rare earth metal species and polymerization solvents on the activity and stereoselectivity of polymerization reactions, and explore the possible mechanism of polymerization reaction.

Controlled polymerization and side reaction mechanism of bio-sourced pentanediamine-derived semi-aromatic copolyamides

Based on new findings, the mechanism underlying the difficulty in increasing the molecular weight of pentanediamine-based PA was revealed.

C 1-Symmetric {cyclopentadienyl/indenyl}-metallocene catalysts: synthesis, structure, isospecific polymerization of propylene and stereocontrol mechanism.

A series of new Me2Si-bridged cyclopentadiene/indene proligands {Me2Si(R2',5'2-R3',4'2-Cp)(R2,R4,R5,R6-Ind)H2} (1a-j) with various substitutions both on the indene and cyclopentadiene moieties was prepared. The corresponding C1-symmetric group 4 ansa-metallocene complexes (M = Zr, Hf), namely, {Me2Si(Me4Cp)(Ind)}ZrCl2 (2a-Zr), {Me2Si(Me4Cp)(2-Me,4-Ph-Ind)}MCl2 (2b-M), {Me2Si(Me4Cp)(2-Me,4-Ph,6-tBu-Ind)}ZrCl2 (2c-Zr), {Me2Si(Me4Cp)(2-Me,4-Ph,5-OMe,6-tBu-Ind)}MCl2 (2d-M), {Me2Si(Me4Cp)(2-R',4-(3',5'-tBu2,4'-OMe-C6H2),5-OMe,6-tBu-Ind)}ZrCl2, R' = Me (2e-Zr), R' = Et (2f-Zr), {Me2Si(2,5-Ph2-3,4-Me2-Cp)(2-Me,4-(3',5'-tBu2,4'-OMe-C6H2),5-OMe,6-tBu-Ind)}ZrCl2 (2g-Zr), {Me2Si(Me4Cp)(2-Me,4-(3',6'-tBu2-carbazol-4'-yl)-Ind)}ZrCl2 (2h-Zr), {Me2Si(2,5-Me2,3,4-iPr2-Cp)(2-Me,4-Ph-Ind)}ZrCl2 (2i-Zr), {Me2Si(2,5-Me2,3,4-iPr2-Cp)(2-Me,4-Ph,6-tBu-Ind)}ZrCl2 (2j-Zr) and {Me2Si(Me4Cp)(2-Me-4,5-[a]anthracene-Ind)}MCl2 (2k-Zr) were synthesized and characterized by NMR spectroscopy and mass spectrometry. The solid-state molecular structures of 2b-Zr, 2d-Zr, 2e-Zr, 2f-Zr, 2j-Zr and 2k-Zr were determined by X-ray crystallography. The zirconocene complexes, once activated with MAO in toluene solution, exhibited propylene polymerization activities at 60 °C up to 161 000 kg(PP) mol(Zr)-1 h-1, affording highly isotactic polypropylenes (iPP) with [m]4 up to 96.5% and Tm up to 157 °C. Also, metallocene complexes 2b-e-Zr were supported on SiO2-MAO and evaluated in slurry bulk propylene polymerization at 70 °C, producing iPPs with [m]4 = 91.7-96.6 mol% and low regiodefects (0.2-0.3 mol%) content, with productivities up to 636 000 kg(PP) mol(Zr)-1 h-1. DFT calculations allowed rationalizing a polymerization reaction mechanism occurring through "chain-stationary" enchainment with preference for 1,2-insertions.

Synthesis of Modified Polycarboxylate and Its Application in Ultra-High Performance Concrete

Modified polyurethane prepolymer was prepared using the segmental synthesis method. Then, pectiniform polycarboxylate was synthesized at normal temperature in the complex initiation system of H2O2, APS, sodium bisulfite, Vc, and Rongalit according to the free radical polymerization reaction mechanism, using TPEG, AA, and PEG as raw materials and TGA as the chain transfer agent. Compared with commercial Sika polycarboxylate, its flowability, strength, drying shrinkage, and auto-shrinkage were studied. The experimental results show that the synthesized polycarboxylate could be better dispersed. Adding silica fume can enhance the compressive strength of ultra-high performance concrete (UHPC), while slag may decline its strength. By incorporating slag and silica fume, the drying shrinkage of UHPC was reduced, but its auto-shrinkage was increased.

Isocyanate-crosslinked silica aerogel monolith with low thermal conductivity and much enhanced mechanical properties: Fabrication and analysis of forming mechanisms

The applications of silica aerogels are restricted due to their intrinsic fragile property. Polymerization of di-isocyanates can be templated onto the mesoporous surface of the –NH2 group modified silica clusters, resulting in the conformal crosslinked coating on surface of silica clusters. Aminopropyltriethoxysilane (APTES), as the silica co-precursor and amine group modification agent, is involved containing tetramethyl orthosilicate (TMOS) silica precursor, while hexamethylene diisocyanate (HDI) is incorporated as the polymer crosslinking agent. The effects of different amounts of APTES on the physicochemical properties of the resulting crosslinked aerogels are investigated. The results show that the optimized APTES/TMOS volume ratio can be determined at 0.5:1. The resulting optimal crosslinked silica aerogel possesses large BET specific surface area of 150.9 m2/g, low thermal conductivity of 0.037 W/(m·K), and the Young's modulus is as large as 18 MPa under strain of 4.2%, much higher than that in the previously published works. The polymerization reaction mechanism forming the polyurethane chains has also been proposed. In addition, the interactions between silica clusters and polymer chains are studied by molecular mechanics and molecular dynamics. The interactions are mainly dependent on non-bonding energy, and the electrostatic energy has decisive impact on the combination of silica clusters and polymer chains. The density field of C, H, N, O, and Si elements overlaps with each other, indicating that the polymer crosslinked silica aerogel maintains typical three-dimensional porous structure. The N element enriches in the region between silica clusters, further verifying the formation –CONH–(CH2)6–CONH- polyurethane chains, which is actually responsible for the much enhanced mechanical property.

Theoretical Studies of Reaction Mechanisms for Half-Titanocene-Catalyzed Styrene Polymerization, Ethylene Polymerization, and Styrene–Ethylene Copolymerization: Roles of the Neutral Ti(III) and the Cationic Ti(IV) Species

Reaction mechanisms of styrene polymerization, ethylene polymerization, and styrene–ethylene copolymerization catalyzed by the half-titanocene [(Me5C5)TiCl2(OAr)] complex were studied based on dens...

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.

Simulation approaches for the mechanisms of thermoset polymerization reactions

Abstract Detailed modeling and simulation of the reaction of alcohol and isocyanate moieties to form urethane have provided a reason to question conventional opinions that this is a step-growth polymerization process. In particular, industrial formulations are dominated by catalytic mechanisms, and these chain mechanisms can change the polymer growth mechanism. This paper's research evaluates experimental data of reaction temperature and resin viscosity of urethane gel reactions that substantiate a chain-growth mechanism. One of the artifacts of a chain-growth mechanism is the rapid appearance of relatively large molecules that reduce gel point times earlier with step-growth mechanisms.

Ring-opening Polymerization Reaction Mechanism of ε-Caprolactone Catalyzed by Bis(dibenzoylmethanato) zirconium(IV) Using PM3 Semi-Empirical Method

Polycaprolactone (PCL) is a semi-crystalline polymer and belongs to a biodegradable plastic. PCL also can naturally degraded, has a high degree of adjustment with other polymer, and has great mechanical and thermal properties. By using the Lewis acid catalyst, PCL can be yielded through the ring opening polymerization (ROP) of caprolactone (ε-CL). The objective of this study was to explore the most likely reaction mechanism of the ROP of ε-CL using bis(dibenzoylmethanato) zirconium(IV) chloride as a catalyst. Here, the Hyper Chem 8.0 program was performed to compute the monomer molecule, intermediate molecules, and polymer molecule. The program can be launch on the Windows 07 systems. The method used was the PM3 semi-empirical method. This program also used to show the results of optimized structures. The calculation results show that to generate PCL required bis(dibenzoylmethanato) zirconium (IV) catalyst. The ROP reaction mechanism of ε-CL can be occurs through direct coordination ε-CL on the Zr complex. After that, deprotonation and insertion monomer. Last step was chain propagation of the χ–CL.

Reaction mechanism and kinetics of Criegee intermediate and hydroperoxymethyl formate

The reaction mechanism and kinetics of the simplest Criegee intermediate CH2OO reaction with hydroperoxymethyl formate (HPMF) was investigated at high-level quantum chemistry calculations. HPMF has two reactive functional groups, -C(O)OH and -OOH. The calculated results of thermodynamic data and rate constants indicated that the insertion reactions of CH2OO with –OOH group of HPMF were more favorable than the reactions of CH2OO with -C(O)OH group. The calculated overall rate constant was 2.33 × 10−13 cm3/(molecule⋅sec) at 298 K and the rate constants decreased as the temperature increased from 200 to 480 K. In addition, we also proved the polymerization reaction mechanism between CH2OO and -OOH of HPMF. This theoretical study interpreted the previous experimental results, and supplied the structures of the intermediate products that couldn't be detected during the experiment.

Kinetics and mechanisms of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with cyanuric acid

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with cyanuric acid (CA) were investigated. Competitive free radical polymerization and aza-Michael addition reaction mechanisms involved in the BMI/CA reaction system were characterized by using DSC, 1H-NMR, electron spin resonance (ESR) and gel permeation chromatography (GPC). Free radical polymerization mechanism predominated in the BMI/CA reaction system. Both model-free and model-fitting methods were used to determine the isoconversional activation energy (Eα) and pre-exponential factor (Aα). The values of Eα and Aα for aza-Michael addition reaction evaluated at α = 0.1 were 86 kJ mol−1 and 2.42 × 1010 min−1, respectively, and the reaction model was f(α) = 1.73(1 - α)α0.11. By contrast, Eα gradually decreased with increasing α (decreased from 88 to 48 kJ mol−1) in the α range 0.15−0.9, which was attributed to the inherent multi-step kinetics in free radical polymerization.

Comparison of the Reactivity and Structures for the Neutral and Cationic Bis(imino)pyridyl Iron and Cobalt Species by DFT Calculations

Density Functional Theory (DFT) method was adopted to investigate and compare the reaction mechanisms of ethylene polymerization catalyzed by neutral, cationic bis(imino)pyridyl (PDI) iron and cobalt derivatives. The electronic structure and the oxidation states of the metal center and the PDI ligand were analyzed by taking spin states, natural bond orbital (NBO) charge distribution, etc. into consideration, revealing that the reactivity is closely related to the valence electron numbers instead of the charge numbers. The neutral Co(0) had the lowest reactivity as it possessed the most electrons. During the formation of the cationic Co(+)/Fe(+), one electron was mainly lost from PDI ligand rather than the metal center while the metal center maintained +II valence state through the process. Moreover, a special unsymmetrically bidentate N^N coordination manner was found to provide the deficient metal surroundings with 14e, which may initiate the reactivity of some unsymmetrical species with rich electrons. Finally, an anion [AlMe4]− participating process was proposed to explain the presence of the experimentally observed LCo(+)B(C2H4). A special intermediate, Co(+)B(C2H4) [AlMe4]− with Co in +I and absence of Co–C σ bond, was obtained. These calculation results may provide fundamental information for further understanding and designing the ethylene polymerization catalysts.

The Synthesis and Characterization of Polyacrolein through Radical Polymerization

AbstractA radical polymerization reaction of acrolein is reported in this article. The free radical initiator which can effectively promote the free radical polymerization of acrolein is screened out. The optimal conditions of the reaction are investigated and the yield could be up to 93.67%, in which the ratio of initiator to monomer is 1:50, monomer concentration is 7.5 mol L−1, reaction temperature is 50 °C, and the reaction time is 6 h. The structure characterizations of the obtained polymers are performed using hydrogen nuclear magnetic resonance spectroscopy, fouriertransform infrared spectroscopy, and matrix‐assisted laser desorption ionization time of fligh mass spectroscopy. The results show that the structure of the polymer contains fragments generated by decomposition of the initiator, aldehyde groups, and vinyl groups. The reaction mechanism of acrolein polymerization in the presence of free radical initiator is proposed. Thus, a novel method for the preparation of polyacrolein via radical polymerization is provided in this article.

Autopolymerization of 2-bromo-3-methoxythiophene, analysis of reaction products and estimation of polymer structure

The study concerning the physical and chemical properties of thiophene derivatives has received much attention because they are incorporated in natural products, medicines, functional materials, and photoresponsive dyes. The autopolymerization reaction is one of the synthesis methods of polythiophenes using halogenated thiophene derivatives. In this paper, we analyzed the products and reaction mechanism of the polymerization reaction of 2-bromo-3-methoxythiophene by investigating the gas, liquid, and solid states using UV-Vis, electron spin resonance (ESR), gas chromatography/mass spectrometry (GC/MS), elemental analysis, NMR, and FT-IR spectroscopy. Consequently, we found a side reaction of the autopolymerization reaction and estimated that the polymerization reaction mechanism occurred in multiple steps. When we employed the brominated alkoxythiophene as a monomer, hydrogen bromide gas was generated to act not only as a catalyst of the polymerization reaction but also as an acid to cleave the alkoxyl group. The results provide useful information for the design of monomers via autopolymerization. The mechanism of intense autopolymerization reaction of 2-bromo-3-methoxythiophenes spewing brownish gas was clarified from UV-Vis, ESR, GC/MS, elemental analysis, NMR, and FT-IR spectroscopy. The reaction contained the formation of the hydrogen bromide gas during the autopolymerization. The gas induced the cleavage of the methoxy group on the thiophene ring to form the methyl bromide gas as the side reaction. This work provides an important guide for the application of the autopolymerization of thiophene derivatives to design new polymer materials.

Synthesis and Properties of Cellulose-based Superabsorbent Hydrogel by a New Crosslinker

Cellulose-based superabsorbent hydrogel (SAH) has been successfully prepared by the grafting method with cellulose and sodium acrylate as well as aluminum hydroxide as a novel crosslinker. The factors influencing water absorption such as the neutralization degree of acrylic acid (AA), the amount of initiator ammonium persulfate (APS) and crosslinker, and the proportion of cellulose to AA were investigated. The chemical structure and thermal behavior of the SAH were analyzed by fourier-transform infrared spectrometry, field-emission scanning electron microscopy, and thermal gravimetry, respectively. Results showed that the water absorbency of the SAH in distilled water and 0.9 wt% NaCl solution reached 922 and 118 g/g when the mass ratio of cellulose to AA, APS to AA, Al(OH) to AA, and the neutralization degree of AA was 39 wt%, 0.67 wt%, 0.89 %, and 76 %, respectively. Under the same condition, the hydrogel synthesized by traditional crosslinker N,N-methylenebisacrylamide was only 530 and 84 g/g in distilled water and 0.9 wt% NaCl solution, respectively. The mechanism of polymerization reaction was analyzed. And the cost and feasibility for the mass-producing the hydrogel were analyzed.

Exploring the Nature of the Energy Barriers on the Mechanism of the Zirconocene-Catalyzed Ethylene Polymerization: A Quantitative Study from Reaction Force Analysis

Ethylene polymerization mediated by methyl-bis(cyclopentadienyl)-zirconium or zirconocene catalyst, [ZrCp₂CH₃]⁺, is one of the most popular catalytic reaction for polyethylene production. Rationalizing the major effects that control the polymer growth result in a challenge for computational studies. Through quantum chemical calculations, we characterized the zirconocene ethylene polymerization reaction mechanism: chain initiation (I; first ethylene insertion) [ZrCp₂CH₂CH₂CH₃]⁺, chain propagation (P; from second (P₁) to ninth (P₉) ethylene insertion) [ZrCp₂ (CH₂)₂₀CH₃]⁺, and chain termination processes (T; β-hydrogen elimination from P₅ or P₉) [ZrHCp₂ (H₂C═CH(CH₂)₁₈CH₃]⁺ are analyzed through the potential energy surface (PES) and reaction force analysis (RFA). The RFA approach involves pulling out the portion of an activation barrier that corresponds to distorting reactants into the geometries they adopt in a transition state structure until it reaches the structural relaxation toward the equilibrium geometry of the product. Because the interactions between the zirconocene and the ethylene molecule are influenced by a combination of several kinds of steric and electronic effects, it is indispensable to understanding these interactions in order to rationalize and predict in a quantitative manner the reaction barrier heights and the concomitant polymer growth. In the present work, we employ a simple procedure within the framework of the RFA and the density functional steric energy decomposition analysis (EDA) approach to quantitatively separate the different types of interactions; steric (ΔE_s), electrostatic (ΔE_e), and quantum (ΔE_q) effects in order to predict the impact of each factor on the course of the polymerization process as well as for the polymer control and design.