Rare Earth Complex Initiated Ring-Opening Polymerization of 2,2-Dimethyltrimethylene Carbonate

Aliphatic polycarbonate is a series of useful biodegradable materials attracting more interests recently. Poly(2,2-dimethyltrimethylene carbonate) (polyDTC) has been studied for a long time. Polymerization of DTC can be catalyzed by alkyl metals1, trifluoromethanesulfonic acid and its esters2, alcohol/methylaluminum diphenolate system3 and etc. Herein tris(2,6-di-tert-butyl-4-methylphenoxo) lanthanides (Ln(OAr)3, Ln=La, Nd) are firstly applied to initiate the polymerization of DTC. Ln(O…     

Kinetic Study of Cationic Polymerization of α-Methylstyrene Initiated by BuOTICl3 In Dlchloromethane Solution

The cationic polymerization of α-methylstyrene Initiated by n-BuOTiCl₃ has been studied at -70° C in dlchloromethane solution by using a calorlmetric technique. Polymerizations were performed under high vacuum either in dry conditions for which low monomer conversions were observed (4-12%), or In the presence of added cocatalyst (H₂O or HCl). In these last cases, yields were quantitative, and it was shown that polymerization rate was proportional to added water concentration and first order with respect to catalyst and to monomer. A kinetic scheme is proposed, based on a monomer-Independent initiation step and on a unimolecular termination process. At -70° C, the initiation rate is higher than termination rate during the whole course of the polymerization, and the concentration of active centers increases continuously. The following rate constants were found at -70°C: k_i. = 17 ± 6, k = 2.2 ± 1.1 ± 10⁴,k_trm = 30 ± 15 liter/mole-Sec, and k_t =0 54 ± 0 05 sec^?1. At -50 and -30° C, the concentration of active centers goes through a maximum during the polymerization and incomplete monomer conversions were observed, showing that all the catalyst is consumed. The different rate constants were tentatively estimated at these temperatures by using a simulation method, and this led to a negative value of ca. -7 kcal/mole for the apparent activation energy for propagation, and to a value of ～ 5 kcal/ mole for E_i. The observation of a negative (E_p)_app might be explained either by a shift of the dissociation equilibrium of the growing ends or by a solvation process of these growing ends by monomer prior to the propagation step.     

Kinetic Study of the Al-Schiff's Base Initiated Polymerization of ε-caprolactone and Synthesis of Graft Poly(methylmethacrylate-g-caprolactone)

Graft copolymers of polycaprolactone (PCL) on polymethacrylate (PMMA) backbone have been successfully synthesized and characterized by SEC, ¹H and ¹³C NMR spectroscopy. The strategy used consisted of polymerizing ε-CL, followed by end-functionalization of the resulting PCL using methacryloyl chloride. Free radical polymerization of the methacryl double bond lead to the C-C polymer backbone and an overall graft copolymer. The polymerization of ε-caprolactone was achieved using Al-Schiff's base isopropoxide (HAPENAlOⁱPr) in DCM at ambient temperature. SEC and MALDI analysis of the polymers confirmed that mostly linear chains were obtained with the Al initiator, up until high monomer conversion. The low molar mass PCL was then end-capped with a methacryloyl group, in a quantitative manner, as evidenced by ¹H NMR. The macromonomer thus obtained was copolymerized in small proportions with methyl methacrylate by conventional free radical polymerization and atom transfer radical polymerization (ATRP). Analysis of the products by NMR and SEC showed the presence of true graft copolymers and the absence of homopolymers.     

β-Myrcene Coordination Polymerization: Experimental and Kinetic Modeling Study

The present work presents phenomenological models to describe the coordination polymerization of β-myrcene using the Ziegler–Natta catalyst system composed by neodymium versatate (NdV₃), diisobutylaluminum hydride (DIBAH), and dimethyldichlorosilane. The kinetic parameters required to simulate the reactions are estimated, and the amount of DIBAH used as a chain transfer agent (CTA) is obtained by a data reconciliation strategy since it can participate in side reactions. Several experiments are performed at different conditions to evaluate the impact of key operation variables on the control of monomer conversion and average molar masses. It is shown that the initial NdV₃, β-myrcene, and DIBAH concentrations exert strong influences on the course of the polymerization. The kinetic mechanism of Coordinative Chain Transfer Polymerization (CCTP) fits well with the data of final average molar masses and monomer conversion, while the dynamic trajectories of these variables are fitted better by kinetic mechanisms of more conventional coordination polymerizations, considering site deactivation and termination by chain transfer. In all cases, the proposed models are able to predict the experimental data well after successful parameter estimation and reconciliation of CTA concentrations, indicating that the kinetic mechanism can be characterized by different kinetic regimes.     

Ring-Opening Metathesis Polymerization Kinetics of Cyclooctene with Second Generation Grubbs’ Catalyst

A kinetic study of the ring-opening metathesis polymerization (ROMP) of cis-cyclooctene using the ruthenium initiator benzylidene [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene]-dichloro-(tricyclohexylphosphine) (second generation Grubbs’ catalyst) was carried out by ¹H-NMR. The dependence on the reaction rate with the temperature and the influence of the addition of a chain transfer agent were evaluated. Some kinetic constants are also reported for this system.     

Recent Developments in the Ring-Opening Polymerization of ϵ-Caprolactone and Derivatives Initiated by Tin(IV) Alkoxides

The macromolecular engineering of aliphatic polyesters by ring-opening polymerization (ROP) initiated by aluminum alkoxides is now well established. Tin (IV) alkoxides are less popular, mainly because of a poorer control of the chain growth. This paper discusses some recent examples from CERM, showing that tin (IV) alkoxides can advantageously replace the aluminum counterparts as ROP initiators. For instance, they can initiate successfully the Ring-Opening Polymerization of α-chloro-ϵ-caprolactone and dioxepane-2-one. They are also very promising initiators for ROP in supercritical CO₂ and for the synthesis of clay/aliphatic polyester nanocomposites.     

Kinetics of D,L–Lactide Polymerization Initiated with Zirconium Acetylacetonate

The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol⁻¹. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy E_a=44.51±5.35 kJ mol⁻¹, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol⁻¹ K⁻¹. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.     

Binuclear Aluminum Complexes Supported by Linked Bis(β-diketiminate) Ligands for Ring-Opening Polymerization of Cyclic Esters

Binuclear aluminum alkyl complexes 2a–4g supported by linked bis(β-diketiminate) ligands were synthesized via the reaction of AlEt_3 or AlMe_3 and the corresponding proligand in a 2:1 molar ratio with moderate yields. The isolated complexes were well-characterized by ~1H-NMR, ~(13)C-NMR and elemental analysis. The binuclear nature of aluminum complex 2b was further confirmed by an X-ray diffraction study. All complexes 2a–4g could efficiently initiate the ring-opening polymerization(ROP) of ε-caprolactone in toluene. The substituents at the aromatic rings and the linker unit in the auxiliary ligands exerted significant influence on the catalytic behavior of the investigated aluminum complexes. Complex 4g(R~1 = R~2 = Cl) containing propylenyl bridging unit exhibited the highest catalytic activity among these complexes, which might be attributed to the increased electrophilicity of the metal center as well as more opened coordination sphere. The molecular weights of obtained poly(ε-caprolactone)s deviating considerably from the theoretical values indicated that the ROP of ε-caprolactone by complexes 2a–4g was not well-controlled, which was also judged from the broad molecular weight distributions(MWD = 1.47-2.47) of produced poly(ε-caprolactone)s. These complexes proved to be inactive toward the polymerization of rac-lactide alone. In the presence of alcohol the polymerization occurred, which was actually initiated by the decomposition species of the aluminum complex upon the treatment with isopropanol.     

Kinetic Study of Radical Polymerization VI. Copolymer Composition and Kinetic Parameters for Coplymerization of Styrene‐Itaconic Acid by On‐Line 1H‐NMR

Free radical solution copolymerization of styrene (St) and itaconic acid (IA) in dimethylsulfoxide‐d₆ (DMSO‐d₆) as the solvent and the use of 2,2′‐azobisisobutyronitrile (AIBN) as the initiator at 78°C was investigated by an on‐line ¹H‐NMR spectroscopy technique. Individual monomer conversion vs. reaction time, which was calculated from the ¹H‐NMR spectra data, was used to study the drift in monomer mixture composition vs. conversion. It was found that in general, both monomers were incorporated almost equally into the copolymer. However, when the mole fraction of IA was low, the tendency of IA toward incorporation into the copolymer chain was somewhat higher than St and by increasing the mole fraction of IA in the reaction mixture, the inverse tendency was observed. Overall monomer conversion as a function of time was calculated from individual monomer conversion data and used for the estimation of k_p /k_t ^0.5 for various monomer mixture compositions. This ratio was decreased with increasing the amount of IA in the initial feed, indicating a decrease in the rate of copolymerization. Changes in the copolymer composition vs. overall monomer conversion were investigated experimentally from the NMR spectra. This was in good agreement with the changes in monomer mixture composition vs. reaction progress. Plotting the copolymer composition vs. initial monomer feed showed tendency of the system toward alternating copolymerization.     

Studies on the Polymerization of Methyl Methacrylate Initiated with Organic Hydroperoxide-Aromatic Tertiary Amine Systems

Radical polymerization of methyl methacrylate(MMA) initiated with organic hydro-peroxide-amine system was studied.t-Butyl hydroperoxide(TBH) and cumene hydroper-oxide(CHP) were used as organic hydroperoxide components,and aromatic tertiary amines,such as N.N-dimethyl aniline(DMA) and its p-substituted derivatives,i.e.N.N-di-me(hyl-p-toluidine(DMT),p-nitro-N,N-dimethyl aniline(NDMA) and p-dimelhyla-mino benzaldehyde(DMAB),were used as amine components.It was found that although the aromaic amine with electron-donating group would enhance,while electron-withdrawing group would reduce,the polymerization rate Rp ane their differences were not so great and all the Rp values were in the same order of magnitude.The values of overall activation enegry,Ea,of MMA polymerization initiated with TBH-amine and CHP-amine systems were determined in the range of 50-57kJ/mole for TBH-amine systems and of 39-62kJ/mole for CHP-amine systems,respectively.Furthemore,the reaction mechanism and kinetics of polymerization of MM     

Unsymmetrical N-Heterocyclic Carbene: 1-Isopropyl-3-benzylimidazol-2-ylidene as Catalyst for Ring-Opening Polymerization of ϵ-Caprolactone

An unsymmetrical N-heterocyclic carbene, namely 1-isopropyl-3-benzylimidazol-2-ylidene, is a highly active catalyst for ring-opening polymerization of ?-caprolactone (CL) to give polycaprolactone (PCL) with number average molecular weight (Mn) as high as 2.66 × 10⁴ at 0°C in 100 min in tetrahydrofuran (THF). The effects of monomer/initiator molar ratio ([M]/[I]), catalyst/initiator molar ratio ([C]/[I]), monomer concentration, as well as polymerization temperature and time have been investigated. The kinetic studies of CL polymerization have indicated that the polymerization rate is first-order with respect to both monomer and catalyst concentrations. The apparent activation energy amounts to 56.04 kJ/mol. The proposed mechanism is a monomer-activated process.     

An Approximate Kinetic Treatment of Slow‐Initiated Living Polymerization. I. First‐Order Initiation and Propagation

A new method for deriving the initiation rate constant for a slowinitiated living polymerization process in which all reactions are first order with respect to all participants is presented. The method is based upon an approximate analytical solution of the set of differential equations modeling this class of processes. The solution is found by asymptotic expansion of the unknown functions, using a dimensionless parameter which characterizes the process.     

Kinetic Study of Radical Polymerization VIII. A Comprehensive Study of Solution Copolymerization of Vinyl Acetate and Methyl Acrylate by 1H‐NMR Spectroscopy

Radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) was performed in a solution of benzene‐d₆ using benzoyl peroxide (BPO) as the initiator at 60°C. Kinetic studies of this copolymerization reaction were investigated by on‐line ¹H‐NMR spectroscopy. Individual monomer conversions vs. reaction time, which was followed by this technique, were used to calculate the overall monomer conversion, as well as the monomer mixture and the copolymer compositions as a function of time. Monomer reactivity ratios were calculated by various linear and nonlinear terminal models and also by simplified penultimate model with r _2(VA)=0 at low and medium/high conversions. Overall rate coefficient of copolymerization was calculated from the overall monomer conversion vs. time data and k _p  . k _t ^?0.5 was then estimated. It was observed that k _p  . k _t ^?0.5 increases with increasing the mole fraction of MA in the initial feed, indicating the increase in the polymerization rate with increasing MA concentration in the initial monomer mixture. The effect of mole fraction of MA in the initial monomer mixture on the drifts in the monomer mixture and copolymer compositions with reaction progress was also evaluated experimentally and theoretically.     

Ab initio Calculation and Kinetic Study for the Abstraction Reaction of H with Sihcl3

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Emulsion Polymerization Pathway for Preparation of Polyaniline‐Sulfate Salt,using Non Ionic Surfactant

In this work, aniline was polymerized directly to the polyaniline‐sulfate salt without using a protonic acid. The polyaniline‐sulfate salt was prepared by emulsion polymerization, using a non ionic surfactant such as poly(ethylene glycol)–block poly(propylene glycol)‐block poly(ethylene glycol). In the aniline oxidation process, to give the polyaniline salt by ammonium persulfate, the sulfate ion is generated from ammonium persulfate and doped on to the polyaniline. Ammonium persulfate acts both as an oxidizing agent, as well as the protonating agent in the aniline polymerization process, to give the polyaniline salt. This result indicates that the effect of sulfate ion, generated by ammonium persulfate during oxidation of aniline to the polyaniline salt, may be taken into consideration in the polymerization process of aniline.     

Kinetic Study of Radical Polymerization v. Determination of Reactivity Ratio in Copolymerization of Acrylonitrile and Itaconic Acid by 1H‐NMR

Many reports exist in the literature about the application of ¹H and ¹³C‐NMR techniques to analyze the copolymer structure and composition and also determination of reactivity ratios. In this work, on‐line ¹H‐NMR spectroscopy has been applied to identify reactivity ratios of itaconic acid and acrylonitrile in the solution phase (DMSO as the solvent) and in the presence of AIBN as the radical initiator. All the peaks corresponding to the existing protons were assigned quietly. Therefore, the kinetics of the copolymerization reaction was investigated by studying the variation of integral of two characteristic peaks regarding each monomer. The obtained data were used to find the reactivity ratios of acrylonitrile and itaconic acid by linear least‐squares methods such as Finemann‐Ross, inverted Finemann‐Ross, Mayo‐Lewis, Kelen‐Tudos, extended Kelen‐Tudos and Mao‐Huglin. In addition, a non‐linear least‐square method (Tidwell‐ Mortimer) was used at low conversions. Extended Kelen‐ Tudos and Mao‐Huglin were applied to determine reactivity ratio values at high conversions as well.     

An Efficient Preparation of Alkyl α-Bromomethylacrylates by Dehydrobromination of Alkyl β,β′-Dibromoisobutyrates with Potassium Fluoride

1° and 2° alkyl esters of β,β′-dibromoisobutyric acid are efficiently dehydrobrominated to alkyl α-bromomethylacrylates by anhydrous potassium fluoride (2.5 equiv) in refluxing acetonitrile/DMF (85:15). 3° isobutyrates give reduced yields of acrylates due to accompanying cleavage of the ester by the HF produced.     

The Use of Principal Component Analysis for the Study of the Interaction of Anionic Surfactants with Hydroxypropyl-β- Cyclodextrin

The interaction of 11 sulfosuccinic acid ester anionic surfactants with hydroxypropyl--cyclodextrin (HPCD) were determined with reversed-phase thin-layer chromatography and the relative strength of interaction was calculated. The relationship between the strength of interaction and the physicochemical parameters of anionic surfactants was elucidated with principal component analysis (PCA). HPCD interacted with the anionic surfactants decreasing their hydrophobicity. The distribution of the points of the strength of interaction and physicochemical parameters on the two dimensional nonlinear map of PC loadings suggested that the strength of interaction between the anionic surfactants and HPCD is of mixed steric character, with hydrophobic and electronic forces being involved in the interaction.     

Infrared Kinetic Study of the Catalyzed and Uncatalyzed Reaction of Butanol-1 with α-NaphthyIisocyanate in Various Solvents

The condensation reaction of α-naphthylisocyanate with n-butanol has been studied in toluene and in bis(2-methoxyethyl) ether (diglyme) by IR spectroscopy at different temperatures (20–60°C). A kinetic study shows that it is first order with respect to each reactant even when the reaction is catalyzed by tin octoate. A general mathematical treatment indicates that secondary reactions may occur in some conditions of temperature, solvent and catalyst, but do not take place in our system. The activation enthalpy and entropy have been determined.     

Radical Polymerization of N,N″-Methylenebisacrylamide by Peroxidiphosphate-Ag+ Redox System: A Kinetic Study

Abstract

The kinetics of aqueous polymerization of N,N′-methylenebisacrylamide (N,N′ -MBA) was studied under an inert atmosphere within the 20-40°C temperature range. The rate of polymerization was found to be proportional to N,N′ -MBA and square-root dependent to the concentration of Ag⁺ and peroxidiphosphate. An intramolecular cyclization prior to propagation is proposed in the mechanism to explain the kinetic data. The overall energy of activation has been found to be 30.2 ± 0.1 kJ · mol^?1. On the basis of experimental results, a suitable scheme has been proposed and a rate expression has been derived.