Propagation Of Polymerization Research Articles

Spark discharge-initiated radical polymerization

A new spark discharge initiated radical polymerization (SDRP) was developed. Monomer radicals were generated by spark discharge emitted from a Tesla coil as a resonant transformer generating high frequency and high voltage, and the monomer itself acted as an initiator for propagation in polymerization at the initial stage. Poly(styrene), poly(acrylonitrile), and poly(styrene)/poly(vinyl benzoate) were successfully synthesized by the SDRP. The versatile SDRP was further developed using 2,2,6,6-tetramethylpiperidine 1-oxyl free radical (TEMPO) to create dormant species to perform nitroxide-mediated-radical-polymerization. We employed d-limonene as a solvent for the SDRP because limonene can effectively dissolve the polymers. Furthermore, solitons of polyacetylene were employed as a polymerization initiator. The solutions as a carrier in polyacetylene was generated with spark discharge. This can be referred to as "soliton-initiated polymerization".

Grignard reagents as deprotonation agents for oxazoline-amido-phenolate ligands: structural and catalytic implications with the role of halogen ions.

In this study, various halogen-substituted Grignard reagents were assessed as deprotonating agents for the oxazoline-amido-phenolate ligand, leading to the formation of magnesium complexes. The newly synthesized complexes with halogen substituents displayed three distinct coordinative modes, all extensively characterized through crystallographic methods. The introduction of halogen substituents induced changes in the Lewis acid properties of the complexes, thereby impacting their structural attributes and catalytic behavior during the initiation and propagation of ring polymerization of cyclic esters.

Propagation rate coefficients of 2-(dimethylamino)ethyl methacrylate radical polymerization in bulk, alcohols and alcohol/water solutions determined by PLP-SEC

The pulsed laser polymerization – size exclusion chromatography technique is used to investigate the radical polymerization propagation kinetics of 2-(dimethylamino)ethyl methacrylate in n-butanol and ethanol (EtOH), as well as EtOH/water mixtures.

Why only half of the added ansa-metallocene catalyst active in the E/P/diene polymerization: catalyst evaluation in terms of active center [Zr]/[C*] fraction and polymerization propagation rate constants

To understand how the silyl-bridged metallocene catalysts rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 behave against dienes under the same reaction condition because of its importance as a commercial polymerization catalyst and ethylene propylene diene monomers (EPDM). Adding diene depressed the catalytic activity, especially 5-ethylidene-2-norbornene (ENB) exerted the most substantial deactivation effect. Firstly, we examine the (ENB, vinyl norbornene (VNB) and 4-vinylcyclohexene (VCH)) non-conjugated and conjugated (isoprene (IP), butadiene (BD)) diene and address how polymerization catalysts behave against these dienes. For example, the catalytic activity was enhanced with IP and BD (3–3.3106 gm/mmolMt·h) compared to ENB, VNB and VCH. The VNB incorporation rate was prolonged (5.4 mol%), but with IP and BD, it was relatively moderate. E/P/IP and E/P/BD with higher incorporation of E produced a higher MW, which means that the chain transfer reaction with ethylene is slower than P. Secondly, we address how the dienes exocyclic and exocyclicπ bonds of non-conjugated and conjugated properties of IP and BD affect the kinetic measurements such as active centers [Zr]/[C*] fraction, EPDM chain propagation, termination, and isomerization. Finally, we compare [Zr]/[C*] and kpPE, kpP and kpDienes for different EPDM. After collecting these kinetic parameters, we can describe the mechanism’s intricacy and the existence of considerable catalyst dormancy with dienes under identical reaction conditions.

Ring-Opening Polymerization of L-Lactide Catalyzed by Potassium-Based Complexes: Mechanistic Studies.

Two non-toxic potassium compounds, 1 and 2, with a commercial oximate ligand have been prepared and fully spectroscopically characterized. Their activity as catalysts for the ring-opening polymerization (ROP) process of LLA has been studied, showing that they are extremely active and able to polymerize the monomer in a few minutes. For derivative 2, the presence of a crown ether in the potassium coordination sphere affects the nuclearity of the compound and consequently its solubility, with both aspects having an influence in the polymerization process. Detailed studies of the polymerization mechanism have been performed, and an unusual anionic mechanism was observed in absence of a co-initiator. Indeed, the monomer deprotonation generates a lactide enolate, which initiates the polymerization propagation. On the contrary, when a 1:1 ratio of cat:BnOH is used, a mixture of mechanisms is observed, the anionic mechanism and the activated monomer one, while from a cat:BnOH ratio of 1:2 and over, only the activated monomer mechanism is observed.

Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Dark polymerization of acrylamide induced by tyrosine-containing peptide

We proposed a novel photoinitiation system composed of photosensitizer and tyrosine-containing peptide, which could initiate radical photopolymerization of acrylamide in water in air. And, when the irradiation was extinguished, the formula with purged nitrogen kept polymerizing in the dark for a long time. The highlight of this system stems from the fact that after low-intensity irradiation as brief as 2 or 5 min, the generated radicals have long lifetime, allowing polymerization propagation in the dark to result in high molecular weight and high conversion. The dark polymerization might be ascribed to the protonation and the steric hindrance of polyacrylamide macroradicals, endowed by the tyrosine-containing peptide, preventing the biradical termination. And these behaviors of the investigated peptides were related to the location of the tyrosine residue on polypeptide chain. In addition, this novel photoinitiator can’t initiate dark polymerization of other water-soluble monomers, but can initiate dark copolymerization of acrylamide with these monomers, further indicating that the hydrogen bonding between acrylamide and polypeptide might be the key factor for dark polymerization. This novel system has potential applications in the preparation of biohydrogels.

How to use X-ray diffraction to elucidate 2D polymerization propagation in single crystals.

Covalent long-range ordered (crystalline) sheets called 2D polymers have recently been synthesized by irradiating single crystals of suitably packed monomers. To have such an action proceed successfully, billions of bond formation processes have to be mastered exclusively in two dimensions within 3D crystals. This raises questions as to how to elucidate the mechanism of these unusual polymerizations as well as their entire strain management. The article will show that single crystal X-ray diffraction based on both Bragg and diffuse scattering are powerful techniques to achieve such goal. The very heart of both techniques will be explained and it will be shown what can be safely concluded with their help and what not. Consequently, the reader will understand why some crystals break during polymerization, while others stay intact. This understanding will then be molded into a few guidelines that should help pave the way for future developments of 2D polymers by those interested in joining the effort with this fascinating and emerging class of 2D materials.

Critically evaluated propagation rate coefficients for radical polymerizations: acrylates and vinyl acetate in bulk (IUPAC Technical Report)

Abstract Arrhenius parameters capturing the temperature dependence of radical polymerization propagation rate coefficients, k p, for methyl acrylate, butyl acrylate, and vinyl acetate in bulk are reported, based on the fitting of benchmark data sets compiled from independent laboratories using the pulsed-laser polymerization/size exclusion chromatography method. The reported k p values for acrylates hold for secondary-radical propagation and are needed to calculate effective propagation rate coefficients in situations where there is a significant population of mid-chain acrylate radicals resulting from backbiting, as will be the case at technically relevant temperatures. The results are compared to those previously reported for styrene and methacrylates to highlight the large differences in k p values seen between the major monomer families.

Controlling Polymer Composition in Organocatalyzed Photoredox Radical Ring-Opening Polymerization of Vinylcyclopropanes.

Although radical polymerizations are among the most prevalent methodologies for the synthesis of polymers with diverse compositions and properties, the intrinsic reactivity and selectivity of radical addition challenge the ability to impart control over the polymerization propagation and produce polymers with defined microstructure. Vinylcyclopropanes (VCPs) can be polymerized through radical ring-opening polymerization to produce polymers possessing linear (l) or cyclic (c) repeat units, providing the opportunity to control polymer structure and modify the polymer properties. Herein, we report the first organocatalyzed photoredox radical ring-opening polymerization of a variety of functionalized VCP monomers, where high monomer conversions and spatial and temporal control were achieved to produce poly(VCPs) with predictable molecular weight and low dispersity. Through manipulating polymerization concentration and temperature, tunable l or c content was realized, allowing further investigation of thermal and viscoelastic materials properties associated with these two distinct compositions. Unexpectedly, the photoredox catalysis enables a postpolymerization modification that converts l content into the c content. Combined experimental and computational studies suggested an intramolecular radical cyclization pathway, where cyclopentane and cyclohexane repeat units are likely formed.

From n-butyl acrylate Arrhenius parameters for backbiting and tertiary propagation to β-scission via stepwise pulsed laser polymerization

A stepwise method to estimate the Arrhenius parameters for backbiting, tertiary propagation, and β-scission in acrylate radical polymerization.

Detection of PLP Structure for Accurate Determination of Propagation Rate Coefficients over an Enhanced Range of PLP-SEC Conditions

The factors influencing the periodic structure in molar mass distributions (MMDs) generated in pulsed-laser polymerization (PLP) experiments are investigated to extend the range of operating conditions under which radical polymerization propagation rate coefficients (kp) can be reliably estimated. Specifically, it is shown how kp may be determined well into conditions corresponding to the so-called low and high termination rate limits. A new parameter x is introduced to provide a convenient measure of when PLP pseudostationary conditions approach the low (x ≤ 0.2) and high (x ≥ 5.0) termination rate limits. In addition, a simple transformation is proposed to detect the PLP structure obscured by the background of the distribution under limiting experimental conditions, with simulations confirming that the methodology provides an estimate of kp with reasonable accuracy. The usefulness of the technique is then demonstrated through application to several experimental distributions. The influences of chain tra...

DFT Studies on cis-1,4-Polymerization of Dienes Catalyzed by a Cationic Rare-Earth Metal Complex Bearing an Ancillary PNP Ligand.

Dnsity functional theory (DFT) calculations have been carried out for the highly selective cis-1,4-polymerization of butadiene catalyzed by a cationic rare-earth metal complex bearing an ancillary PNP ligand. It has been found that the chain initiation and propagation of butadiene polymerization occurs via the favorable cis-1,4-insertion route. The trans-1,4 and 1,2-insertion are unfavorable both kinetically and thermodynamically. The chain growth follows the π-allyl-insertion mechanism. The analyses of energy decomposition of transition states indicate that the likelihood of rival insertion pathways is predominantly controlled by the interaction energy of butadiene with a metal center and the deformation energy of butadiene moiety. The electronic factor of the central metal has a decisive influence on the cis- vs. trans-insertion and the regioselectivity (cis-1,4- vs. cis-1,2-insertion) is mainly determined by steric hindrance. Tetrahydrofuran (THF) coordination made monomer insertion less favorable compared with THF-free case and had more noticeable impact on the trans-monomer insertion compared with the cis case. During the chain propagation, cis-insertion of monomer facilitates THF de-coordination and the THF molecule could therefore dissociate from the central metal.

Reaction front propagation of actin polymerization in a comb-reaction system

We develop a theoretical model of anomalous transport with polymerization-reaction dynamics. We are motivated by the experimental problem of actin polymerization occurring in a microfluidic device with a comb-like geometry. Depending on the concentration of reagents, two limiting regimes for the propagation of reaction are recovered: the failure of the reaction front propagation and a finite speed of the reaction front corresponding to the Fisher-Kolmogorov-Petrovskii-Piscounov (FKPP) at the long time asymptotic regime. To predict the relevance of these regimes we obtain an explicit expression for the transient time as a function of geometry and parameters of the experimental setup. Explicit analytical expressions of the reaction front velocity are obtained as functions of the experimental setup.

Dependence of Propagation Rate Coefficients in Radical Polymerization on Solution Properties

The effect of solvents and monomer concentration on rate coefficients of propagation in radical polymerization has received tremendous interest during recent years, but a quantitative explanation and method of prediction of the medium effect is still missing. In this paper, it is shown that the thermodynamic formulation of the transition state theory is able to explain such effects almost quantitatively for a wide variety of monomers and solvents, including not only organic solvents but also less common solvents like ionic liquids or water, and monomers ranging from styrene to water‐soluble monomers like acrylic acid or N‐vinylformamide and also bulky monomers like isobornyl methacrylate. The medium effect is dictated by the activity coefficient of the monomer as well as by the ratio of the activity coefficients of the growing chain and the transition state. The solvent and concentration effects are, thus, a consequence of the degree of nonideality of the system. This interpretation based on the thermodynamics of real solutions offers for the first time a straightforward method to estimate the propagation rate coefficient of a given monomer in various solvents once the corresponding coefficient in bulk monomer is known. image

Unraveling two-dimensional polymerization propagation from diffuse scattering

Unraveling two-dimensional polymerization propagation from diffuse scattering

Cis/trans Isomerization of o-Phosphino-Arenesulfonate Palladium Methyl Complexes

The cis/trans isomerization of (PO-OMe)PdMe(lut) ([PO-OMe]− = 2-{P(2-OMe-Ph)2}-4-Me-benzenesulfonate) was studied to model the proposed isomerization in chain propagation in ethylene polymerization by (o-phosphino-arenesulfonate)PdR(ethylene) species. Nonequilibrium mixtures of cis-P,C- and trans-P,C-(PO-OMe)PdMe(2,6-lutidine) were generated by the reaction of Na[PO-OMe] and {Pd(μ-Cl)Me(2,6-lutidine)}2 in CD2Cl2 at −25 °C. Kinetic studies revealed lutidine-catalyzed and noncatalyzed isomerization pathways. The lutidine-catalyzed pathway involves five-coordinate (PO-OMe)PdMe(lut)2 intermediates that undergo Berry pseudorotation. Kinetic studies, structure–activity relationships, solvent effects, and density functional theory calculations for the noncatalyzed pathway are most consistent with a mechanism, originally proposed by Nozaki, Morokuma, and co-workers, which proceeds through a five-coordinate transition state with κ3-P,O,O coordination of the [PO]− ligand.

Perylene as an Organic Photocatalyst for the Radical Polymerization of Functionalized Vinyl Monomers through Oxidative Quenching with Alkyl Bromides and Visible Light

The generation of carbon-centered radicals from alkyl bromides through an oxidative quenching pathway using perylene as an organic visible-light photocatalyst is described. This methodology is used to initiate the radical polymerization of methyl methacrylate and other functionalized vinyl monomers. The polymers possess bromide chain-end groups that can be used to reinitiate polymerization to produce block copolymers. Control over the polymerization propagation can be achieved through pulsed light sequences while the ability to use natural sunlight to promote carbon–carbon bond formation produces polymers with dispersity as low as 1.29.

A Novel Efficient Ligand in Anionic Polymerization at Elevated Temperature

AbstractThis work confirmed a novel ligand in the anionic polymerization, lithium phenoxide, which helped to improve the controllability of the polymerization. The stability of n‐BuLi against THF at 0°C was effectively improved by adding lithium phenoxide. More than 60% n‐BuLi in THF was alive with the presence of lithium phenoxide after stirring at 0°C for 20 min, compared to 2% under same conditions but without lithium phenoxide. The propagation of polymerization of styrene (St) and methyl methacrylate (MMA) were retarded after adding lithium phenoxide. And by adding more than 10 fold lithium phenoxide, completed conversion was achieved in the polymerization of MMA in THF at 0°C. The lithium phenoxide showed both promoting and inhibiting effects in the polymerization of isoprene (Ip): it promoted the formation of 3,4‐structure, while mitigated the formation of 1,2‐ and 1,4‐structures. In general, the polymerization rate of Ip was promoted by lithium phenoxide.

Spatial Propagation of Protein Polymerization

We consider the spatial dependence of filamentous protein self-assembly. Through studying the cases where the spreading of aggregated material is dominated either by diffusion or by growth, we derive analytical results for the spatial evolution of filamentous protein aggregation, which we validate against Monte Carlo simulations. Moreover, we compare the predictions of our theory with experimental measurements of two systems for which we identify the propagation as either growth or diffusion controlled. Our results connect the macroscopic observables that characterize the spatial propagation of protein self-assembly with the underlying microscopic processes and provide physical limits on spatial propagation and prionlike behavior associated with protein aggregation.