Bifunctional Peroxides Research Articles

Base induced synthesis of isochroman spiropyrazolones via bifunctional peroxides

Isochroman is one of the powerful scaffolds which demonstrated various important biologically activities. Herein we represented the novel and versatile method for the synthesis of valuable isochroman spiropyrazolones of difunctional peroxides and pyrazolones via [1+5] annulation. This process represents a novel spiroisocchroman synthesis protocol and is featured by good functional group compatibility, mild conditions and readily available substrates.

Frontal polymerisation of acrylic acid tuned by micellar aggregates in a deep eutectic solvent

A frontal polymerisation (FP) is obtained when a polymerisation creates a spatial front of the reaction. Because of the heat of the reaction associated, a temperature spatial front is also observed. In this paper, the usual chain polymerisation of acrylic acid (AA) is studied when the monomer forms a deep eutectic solvent (DES), i.e. a liquid similar to an ionic liquid. In this DES, AA behaves as a hydrogen donor and ethylammonium chloride as a hydrogen acceptor. The use of a DES is convenient as an effective polymerisation media because the heat of the reaction can be controlled. We study the rate and the heat of polymerisation during the formation of a front using micellar structures where a bifunctional peroxide hydrophobic initiator, abbreviated Luperox, dissolves successfully. Our experiments follow the FP using infrared images and rheology. We found that micellar aggregates of different sizes are interesting modulators of the polymerisation rate and heat of the reaction. Our results show that smaller aggregates produce higher rates of reaction with a decoupled increment of temperature; in contrast to what is observed with bigger aggregates: a slow reaction rate with a coupled moderate heat of reaction.

A formal (3 + 2) annulation–Cannizzaro cascade of bifunctional peroxides for the synthesis of dihydrofurans

Tunable tandem processes of bifunctional peroxides allow the divergent construction of functionalized dihydrofurans and epoxides by simply changing the basic conditions.

Tunable Reaction Mode of Bifunctional Peroxides with Ketones to Access α-Oxacyclic Ketones and Enals.

A new annulation reaction between allylic/benzylic peroxides and ketones has been developed to provide the α-oxacyclic ketones in moderate yields under the KOtBu basic conditions. Mechanistic studies reveal that these peroxides undergo the Kornblum-DeLaMare rearrangement to release the aldehyde intermediates and subsequently initiate the aldol/etherification tandem process to deliver the final products. Accordingly, these peroxides serving as "masked" enals have also been utilized to prepare the previously hard-to-achieve α-enal-tethered ketones in one step.

Annulation-retro-Claisen cascade of bifunctional peroxides for the synthesis of lactone natural products.

A new and highly efficient annulation-retro-Claisen cascade, which involves the [4 + 1] or [5 + 1] annulation of α-benzoylacetates with bielectrophilic peroxides and a subsequent debenzoylation process under mild basic conditions, has been developed for the rapid construction of valuable tetrahydrofuran- and dihydropyran-2-carboxylates in good yields. By employing the new reaction, the unified total synthesis of γ- and δ-lactone natural products such as (±)-tanikolide, (±)-goniothalamins, (±)-7-epi-goniodiol, and (±)-plakolide A has been accomplished in 4-7 steps.

A Unified Catalytic Asymmetric (4+1) and (5+1) Annulation Strategy to Access Chiral Spirooxindole‐Fused Oxacycles

AbstractA unified catalytic asymmetric (N+1) (N=4, 5) annulation reaction of oxindoles with bifunctional peroxides has been achieved in the presence of a chiral phase‐transfer catalyst (PTC). This general strategy utilizes peroxides as unique bielectrophilic four‐ or five‐atom synthons to participate in the C−C and the subsequent umpolung C−O bond‐forming reactions with one‐carbon unit nucleophiles, thus providing a distinct method to access the valuable chiral spirooxindole‐tetrahydrofurans and ‐tetrahydropyrans with good yields and high enantioselectivities under mild conditions. DFT calculations were performed to rationalize the origin of high enantioselectivity. The gram‐scale syntheses and synthetic utility of the resultant products were also demonstrated.

Mathematical Modeling of Free Radical Solution Terpolymerization Reactions in a Batch and Continuous Flow Stirred Tank Reactors

AbstractA mathematical model that describes a free radical solution terpolymerization is applied to styrene (St), methyl methacrylate (MMA), and maleic anhydride (MAh) polymerization system. This terpolymerization model allows for the use of either monofunctional or bifunctional peroxide initiators, and it is applied to batch and continuous reactions. The key model outputs are global monomer conversion, terpolymer composition, terpolymer average molecular weights, and terpolymer monomer sequence distributions. A few kinetic parameters are estimated such that global conversion is properly predicted by the model including initiator efficiency and two termination rate constants. Molecular weights are shown to be dominated by chain transfer reactions. Experimental trends of conversion, terpolymer molar masses (molecular weights), and composition are reasonably well predicted by the model.

Study of the Addition of a Thermoplastic Vulcanizate to a HDPE Composite Highly Filled with Magnesium Hydroxide and Its Effect on the Tensile and Flame Retardant Properties

A work was carried out in order to obtain a TPV based on HDPE and EPDM, studying the effect of three different peroxides. The effect of one mono- and two bifunctional peroxides was studied. In general, at equal wt% of peroxide, the bifunctional peroxides produced greater gel content, higher tensile stress, and higher elongation at break. Thereafter, the work was focused on studying the effect of this TPV, as well as a commercial TPO, on the tensile and flame retardant properties of composites based on blends of HDPE and a thermoplastic elastomer (either TPV or TPO), plus 130 phr of magnesium hydroxide (MH). The composites without the rubbery phase, but with 130 phr of MH, were highly brittle and fragile. The composites with the rubbery phase, on the other hand, (either TPO or TPV), were tougher and presented relatively much higher tensile properties. With regard to flame retardancy, the formulations containing the TPV showed better flame retardancy and passed as V-1 in the UL-94V. With respect to the cone calorimeter, those with TPO or TPV all generated a total of 80 MJ of heat energy. The compositions with TPV, however, generated this amount of heat over a larger period of time, i.e., showing less heat generated per second. In addition, the compositions with TPV presented a markedly lower pHRR, by an average of 15%. Thermogravimetric analysis (TGA) showed that the MH in the samples with a 40 wt% rubbery phase starts decomposing at 315°C. However, as the temperature increases, the MH in the TPV composite apparently decomposes at a slower rate than that in the TPO composite.

General [4 + 1] Cyclization Approach To Access 2,2-Disubstituted Tetrahydrofurans Enabled by Electrophilic Bifunctional Peroxides.

A general [4 + 1] cyclization reaction of carbonyl nucleophiles with 2-iodomethylallyl peroxides, which function as unique electrophilic oxygen synthons, for the synthesis of a broad range of 2,2-disubstituted tetrahydrofurans is achieved under operationally simple conditions. The unprecedented asymmetric version of such reaction is also realized via chiral auxiliary-assisted cyclization, thus providing a distinct approach to access chiral tetrahydrofurans with high diastereoselectivities. The new method can be applied to the synthesis of core structure of posaconazole drug.

Modeling of ethylene copolymerization in nonisothermal high‐pressure reactors using bifunctional initiators

Enhancing the performance of high‐pressure LDPE process is valuable for polymer industry. However, the severe thermodynamics requirement of high pressure and temperature hinders the reaction process from getting simultaneously high monomer conversion and polymer molecular weights. Bifunctional peroxides used as initiators can boost the polymerization rate and alter rheological polymer properties. This article proposes a new kinetics model of ethylene/butyl acrylate copolymerization with bifunctional initiators in a high‐pressure nonisothermal tubular reactor. Model predictions are compared with available data. A SQP optimization scheme is employed to determine a suitable wall temperature for each zone along the nonisothermal tubular reactor. In comparison with the monofunctional TBPPI peroxide, a lower amount of the bifunctional DHBPPI peroxide is needed to get a higher conversion in shorter residence time, but at the expense of higher thermal energy. The results also showed that polymers produced with bifunctional peroxides are significantly more branched. POLYM. ENG. SCI., 59:74–85, 2019. © 2018 Society of Plastics Engineers

Real time monitoring of the quiescent suspension copolymerization of vinyl chloride with methyl methacrylate in microreactors – Part 3. A kinetic study by raman spectroscopy and evolution of droplet size

The present work presents results on the copolymerization kinetics of methyl methacrylate (MMA) and vinyl chloride (VCM) monitored by Raman spectroscopy and on the evolution of droplets as captured by charge-coupled device (CCD) camera in a microcapillary reactor. Different experimental recipes were proposed using commercial initiators in order to compare the system performance when initiated with monofunctional and bifunctional peroxides. The experimental setup was able to capture the distinct stages of the copolymerization within a microreactor up to high conversions (>90%) in quiescent state. It is shown that the copolymerization of MMA with VCM leads to distinct morphological structures, when compared to VCM homopolymerization, forming a core and a shell after a certain critical conversion. A new mechanism is proposed for the copolymerization based on the results from both video camera and Raman spectroscopy.

Real time monitoring of the quiescent suspension polymerization of vinyl chloride in microreactors – Part 2. A kinetic study by Raman spectroscopy and evolution of droplet size

This paper regards the experimental study on the polymerization of vinyl chloride droplets in quiescent state using microreactors. As presented in a previous work performed with methyl methacrylate monomer, this work presents results on the reaction kinetics of vinyl chloride (VCM) polymerization monitored by Raman spectroscopy and on the evolution of VCM droplets as captured by charge-coupled device (CCD) camera in a microcapillary. Different experimental recipes were proposed using commercial initiators in order to compare the system performance when initiated with monofunctional and bifunctional peroxides. For the first time in the open literature the evolution of VCM droplets is shown up to high conversions (>90%) in quiescent state. It is also shown how the pressure drop can modify the PVC particle morphology at the end of polymerization. Finally, it is shown that the Raman technique is able to monitor the reaction kinetics at different conditions, being possible to identify four different characteristic stages during the vinyl chloride polymerization reactions.

Real time monitoring of the quiescent suspension polymerization of methyl methacrylate in microreactors—Part 1. A kinetic study by Raman spectroscopy and evolution of droplet size

This paper presents an experimental study on the polymerization of droplets of methyl methacrylate (MMA) in quiescent state using microreactors. The reaction kinetics was monitored by Raman spectroscopy, while the images of MMA droplets image were captured by CCD (charge-coupled device) camera within a microcapillary. Different experimental recipes were proposed with commercial initiators in order to compare the system performance with two types of initiators: monofunctional and bifunctional peroxides. It is shown in this paper that the Raman technique is able to monitor the reaction kinetics at different conditions. For the first time in the open literature it was possible to identify the evolution of the monomer droplets during polymerization to high conversions (>90%) in quiescent state. In addition, it was possible to identify three different stages during the polymerization reactions of MMA. Finally, it is shown that the dispersities (M¯w/M¯n) obtained with the bifunctional initiator were lower than 2, while the dispersities obtained with the monofunctional initiator were greater than 2.

Production and Application Properties of Dispersive Viscosity Index Improvers

Polymeric dispersive viscosity index improvers of lubricating mineral oils based on styrene, dodecyl-methacrylate, octadecyl methacrylate, and N,N-dimethylaminoethyl methacrylate (d-PSAMA) were produced by performing copolymerizations isothermally up to the high conversion in mineral base oil solution, using monofunctional or bifunctional peroxide initiator. The obtained kinetics results reveal the benefits of the usage of a bifunctional peroxide initiator over a monofunctional, because complete conversion of monomers was accomplished in the shorter reaction time, performing the process in a full batchwise mode. When the bifunctional initiator was applied, the required polymerization temperature was slightly higher (105 °C), and copolymers of higher average molecular weight values (Mw = 60–120 kg mol–1) were obtained, while in case of the monofunctional peroxide initiator, the reaction temperature was 100 °C, and average molecular weight values of copolymers were Mw = 30–100 kg/mol. Investigated applicati...

Terpolymerization kinetics of methyl methacrylate or styrene/dodecyl methacrylate/octadecyl methacrylate systems

AbstractThis study describes low‐conversion terpolymerization kinetic investigations of methyl methacrylate/dodecyl methacrylate/octadecyl methacrylate (MMA/DDMA/ODMA) and styrene/dodecyl methacrylate/octadecyl methacrylate (ST/DDMA/ODMA) systems. Terpolymerizations were performed isothermally (70–105 °C), in 1 mol dm−3 xylene solutions, using 0.01 mol dm−3 of bifunctional peroxide initiator 1,1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane or monofunctional tert‐butylperoxy‐2‐ethylhexanoate. Synthesized terpolymers were characterized with respect to composition and molar mass distribution. Initial polymerization reaction rates as well as terpolymer average molar masses decreased with increasing MMA or ST content in the monomer mixture, for both initiators and all investigated temperatures. Overall reaction rates were found to be significantly larger for the MMA/DDMA/ODMA system. In the MMA/DDMA/ODMA system, experimental terpolymer compositions were found to be similar to the initial monomer feed compositions—all the experimental monomer feed mixtures were close to the azeotropic composition. The Alfrey–Goldfinger terpolymerization equation was successfully used for the description of MMA/DDMA/ODMA terpolymerization kinetics, where the existence of the true azeotropic ternary point was established. The same equation did not perform as well for the ST/DDMA/ODMA terpolymerization system. Copyright © 2006 Society of Chemical Industry

NEURAL NETWORK IDENTIFICATION OF STYRENE FREE RADICAL POLYMERIZATION

In this study, a one-hidden-layer Artificial Neural Network (ANN) using a back-propagation structure has been trained on experimental data for the identification of styrene conversion and polymer average molecular weight produced in a bulk polymerization initiated by bifunctional peroxides. Two identification schemes, a leave-N-out and black-box with constant and adaptive step-size, are presented. Both schemes gave good predictions of monomer conversion and molecular weight averages. Neural networks for nonlinear identification of monomer conversion and average molecular weights can be used along with other approaches to improve modeling of polymerization reactions, especially when the kinetic mechanism is not well established.

Simulation of Free Radical Bulk/Solution Homopolymerization Using Mono- and Bi-functional Initiators

Monofunctional and bifunctional peroxides are extensively utilized in the production of polystyrene. However, their decomposition kinetics is still an important area to investigate. A computer package developed previously by Gao and Penlidis (1996), which was based on mono-fimctionally initiated polymerization, is extended in this study to cover homopolymerization of styrene using bifunctional initiators. A database of a wide variety of bifimctional peroxides used in polystyrene production is developed along with a database for twelve new monofimctional initiators. The package handles several different scenarios of styrene polymerization, whether it is in bulk / solution or isothermal / non-isothermal medium. The model is tested with a wide range of conversion and average molecular weight data either from the literature or available from industry. Simulation results agree with the data trends, which makes the simulator a very powerful tool in aid of initiator selection and evaluation. At the end of the paper, results on homopolymerizations of acrylates and methacrylates are also discussed.

ESR spin-trap study of the radicals present during the thermolysis of some novel alkyl peroxy esters

The thermolysis of four alkylperoxy esters was undertaken at various temperatures between 300 and 353 K and the radicals generated were trapped employing DMPO, DEPMPO, PBN-d14 and TTBNB. The adducts of a range of second-generation carbon-centred radicals, formed via decarboxylation of the acyloxyl moiety, including those of the 2,4,4-trimethylpentyl and hept-3-yl radicals, were also observed. The co-generated tert-alkoxyl radicals, released during the thermolysis of tert-butylperoxy-3,3,5-trimethylhexanoate, tert-amylperoxy-2-ethylhexanoate and the bifunctional peroxide 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, were all successfully trapped, as were a range of second-generation carbon-centred radicals formed following -scission of these tert-alkoxyl radicals.

Asymmetrical Bifunctional Organic Peroxides as Initiators for the High-Pressure Polymerization of Ethylene

Abstract As a follow-up to earlier investigations into the high-pressure polymerization of ethylene with symmetrically substituted bifunctional peroxides, the suitability of 2,5-dimethylhexane-2-t-butylperoxy-5-perpivalate, a peroxide with different substituents on both O—O groups, has been tested. The polymerization tests were carried out in continuous operation in a stirred autoclave at 1700 bar, 240–285°C, a residence time of 60 s, and an initiator concentration of 3–25 mol ppm in the feed. Conversions of up to 30% were achieved. The specific initiator consumption was 0.2–1 g initiator per kg polyethylene. The density of the polymers obtained was 0.915–0.925 g/mL, their average molecular weight was 40 × 103 to 60 × 103, and their melt flow index was 0.001–100 g/10 min. On the basis of the molecular weight distribution, polydispersities of 4–7 were obtained.

The Decomposition of 2,2-Bis(tert-Butylperoxy)-butane under High Pressure

Abstract The thermal decomposition of the bifunctional peroxide 2,2-bis(tertbuty1 peroxy)butane was investigated in a flow reactor at temperatures of 135 to 212°C and pressures of up to 2000 bar. The concentration of the peroxide in isododecane was varied between 1 and 22% by weight. The rate of decomposition measured was used to determine the energy of activation (EA = 151.1 ± 3 kJ/mol) and the activation volume (Δv” = 22.3 mL/mol). Up to a peroxide concentration of 5% by weight, the decomposition takes place according to a firat-order rate equation. Above this concentration, induced decomposition takes effect. Gas chromatographic analysis showed that the liquid decomposition products consisted mainly of acetone and tert-butyl alcohol apart from methyl ethyl ketone, propionic acid methyl ester, acetic acid ethyl ester, tert-butyl methyl ether, and oligomers of the solvent. The gaseous decomposition products consisted of methane and carbon dioxide as well as small quantities of ethane, propane, and ethyle...