Estimation of Rate Constants of Bimolecular Decomposition of Redox Initiators in Radical Polymerization

A rigorous statistical method is established to compute the rate constants of the bimolecular decomposition of redox catalysts used to initiate polymer chains. Results obtained for the systems styrene-dimethylaniline-benzoyl peroxide and acrylamide-thio-glycollic acid-potassium bromate compare favorably with those reported by other workers. The merits of this error-in-variable technique, which outperforms conventional nonlinear least-square analysis and the dead-end polymerization method, are discussed.     

Atom Transfer Radical Polymerization of Styrene Using Multifunctional Iniferter Reagents as Initiators

Summary: Two multifunctional iniferters, 1,4-bis-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (BDCIB) and 1,3,5-tris-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (TDCIB), were successfully synthesized and used as initiators to initiate the polymerization of styrene in the presence of a CuBr/PMDETA complex. The polymerization results demonstrated that the kinetic plots in all cases were first-order to the monomer, the molecular weight of the polymers increased linearly with the monomer conversion; meanwhile, the molecular weight distribution of the polymer was kept to a very low value (M_w/M_n ≤ 1.35). Furthermore, the measured molecular weights were very close to the calculated values, which indicated the high efficiency of the initiator for the polymerization of styrene. The effect of catalyst concentration and initiator concentration was not obvious and the influence of polymerization temperature was apparent, and the polymerization rate increased with the polymerization temperature. The results of chain-extension and ¹H NMR analysis proved that the polymer obtained was capped with diethylthiocarbamoylthiy (DC) group.     

Preparation and Thermal Decomposition of Polyacrylamide and its Derivatives by Plasma-initiated Polymerization

Polyacrylamide (PAM), poly(N,N-dimethylacrylamide) (PDMA) and poly(N,N-diethylacryl-amide) (PDEA) were synthesized by plasma-initiated polymerization. Both wet and dry polymers were prepared. The states of the water absorbed in the wet and dry samples were studied directly by means of TG, and the stabilities of the dry polymers in the process of thermal treatment were investigated by FT-IR. The activation energy of release of the bonded water was calculated by the Kissinger method. The water absorbed in the polymers was found to be in two states, i.e. weakly-bonded water and bonded water, and the absorbed water content varied with the monomer concentration, the plasma duration time and the type of polymer.This revised version was published online in November 2005 with corrections to the Cover Date.     

Preparation of Polystyrenylphosphonous Acid of Low Polymerization Degree and Influence of Initiators upon the Free Radical Reaction Mechanism

Organophosphorus chemistry plays an important role in chemical engineering, pesticide, medicine and catalysis1,2. In recent years, after extensive research and widespread application, synthesis and preparation of new organophosphorus compounds have attracted increasing research interest. Polystyrene is a very important and versatile matrix or precursor of various kinds of functional polymer. Usually, introducing of phosphonic PO3H2 or phosphinic PO2H2 group into polystyrene matrix through…     

Dual Reactivity of Magnesium Compounds as Initiators for Anionic and Cationic Polymerization

Organomagnesium compounds are well known initiators of anionic polymerization of polar monomers. However, we have found recently that in the presence of compounds with labile halogen atoms, e.g., benzyl chloride, they are also active initiators of cationic polymerization of isobutylene and styrene in hydrocarbon media. The tentative scheme of cationic initiation is suggested assuming the formation of benzyl cation connected with Mg₂Cl₅⁻ counter-ion. The scheme is confirmed by quantum-chemical calculations and ¹H NMR analysis of polyisobutylene. On addition of a polar monomer, N,N-dimethylacrylamide or 2-vinylpyridine, to Bu₂Mg-BzCl-isobutylene polymerizing mixture, the former readily polymerizes. The mixture of homopolymers rather than block copolymers is formed in this case, however, this fact proves the co-existence of anionic and cationic centers in the system.     

几种手性原子转移自由基聚合引发剂的合成及其在螺旋选择性聚合中的应用

合成了(S)-2,2'-二(溴甲基)-1,1'-联萘, (S)-2'-甲基-2-溴甲基-1,1'-联萘, α-溴代苯乙酸薄荷酯, N-薄荷基-α-溴代苯乙酰胺和α-溴代苯乙酸胆甾烷醇酯5种旋光的溴代烷并将其用作非手性单体甲基丙烯酸-1-苯基二苯并环庚醇酯 (PDBSMA)的原子转移自由基聚合(ATRP)的手性引发剂. 为了使这些手性引发剂在引发一步生成的初级自由基不发生消旋化, 引发剂中的手性中心都不直接与溴原子相连. 用这5种手性溴代烷做引发剂引发PDBSMA的ATRP所得聚合物可分成四氢呋喃(THF)可溶部分和THF不溶部分. THF可溶部分具有较大的比旋光度. 对THF可溶部分的手性光学性质研究以及比较该部分聚合物和在同样引发条件下得到的甲基丙烯酸甲酯聚合物的比旋光度, 我们得出聚合物大的比旋光度是由聚合物单手性螺旋过量引起的结论, 即合成的手性引发剂对PDBSMA的ATRP均有一定的螺旋选择性, 其中(S)-2,2'-二(溴甲基)-1,1'-联萘、(S)-2'-甲基-2-溴甲基-1,1'-联萘螺旋选择性最好. 引发剂的螺旋诱导能力跟聚合反应的温度有很大关系, 聚合温度上限为70 ℃, 在0～70 ℃之间, 随着温度的升高引发剂的螺旋选择性逐渐增强.     

Controlled Polymerization of Methyl Methacrylate in the Presence of C-Phenyl-N-tert-Butylnitrone and Commercial Radical Initiators

Radical polymerization of methyl methacrylate initiated by dicyclohexyl peroxydicarbonate in the presence of a chain-terminating agent, C-phenyl-N-tert-butylnitrone, as a potential source of stable nitroxyl radicals, was studied.     

A Kinetic Study on the Thermal Decomposition of Three Kinds of Initiators in Styrene

The synthesis of polystyrene plays an important role in the macromolecule industry. In this article, AIBN、BPO and dl-Diethyl-2,3-Dicyano-2,3-Diphenylsuccinate(Ⅰ) were chosen as initiators of styrene. From the curve of conversion(α) and time(t) (chart omitted), we can get the decomposition velocity constant (k_d)、the decomposition activation energy (E_d) of these initiators and the final conversion(α_∞) of styrene.(Table 1).     

Peroxo Salts as Initiators of Vinyl Polymerization. 6. Kinetics of Polymerization of Acrylonitrile Initiated by Potassium Peroxodisulfate in Aqueous Medium-Ag+ Catalysis

The kinetics of polymerization of acrylonitrile initiated by potassium peroxodisulfate in neutral and acid conditions was studied. R_p depended upon [S2O₈ ^2-]^1/2 and [monomer]^3/2 both in neutral and acid solutions. The influence of ionic strength and the cata-lytic effect of Ag⁺ on the System are discussed. Suitable mech-anisms are proposed.     

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

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.     

Charge Transfer Complexes based on Various Amines as Dual Thermal and Photochemical Polymerization Initiators: A Powerful Tool for the Access to Composites

Exploiting highly efficient, environmentally friendly, and economic CTCs (Charger Transfer Complexes) as photo/thermal dual initiators is a huge pursuit of materials practitioners and innovators. To investigate and find out series amines as donors in CTCs, RT-FTIR (Real-Time Fourier Transform Infrared Spectroscopy) was employed to examine the photo initiating efficiency of CTCs based on amines donors and DSC (Differential Scanning Calorimeter) was used to test their thermal initiating ability. The formation of CTCs was investigated and confirmed by molecular orbital (MO) calculations and UV–Vis experimental study. Structure/reactivity/efficiency relationships will be proposed on the base of more than 10 new amine donors. At last, composites based on glass fibers and carbon fibers were fabricated by photo curing and/or photo/thermal dual curing method, which showed excellent mechanical performance in DMA (Dynamic Mechanical Analysis) characterization. This work paves the path toward flexible photo/thermal dual initiators able to react on demand thanks to orthogonal stimuli (light or heat with the same initiating system). It will naturally find use in time and spatially resolved composites manufacturing (were classical simple photoinitiating or thermal systems are inefficient). © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 811–823     

Preparation of Polymer‐Metal Composites via In Situ Decomposition of Metal Salts by Frontal Polymerization

Composites containing powdered zinc, and zinc/lead acetate were prepared via frontal polymerization. In the case of the acetates, elemental metal was formed in an in situ decomposition process. The local area function was used to demonstrate the distribution of fillers, and the uniformity of the area fraction for the quantitative characterization of the distribution. With the use of metal acetates, composites of uniform metal distribution can be produced, unlike in systems with metal powder, where the metal particles are enriched at the margin of the sample. It can be established that the specific direct‐current resistance significantly decreases in AA‐TGDMA composites by the addition of zinc acetate, compared to that of the initial monomer mixture. On heating, the unreacted zinc acetate decomposes further, which results in the further decrease in electrical resistance.

     

Cryoozonolysis of Some Perfluoroolefins and Use of Perfluoro Ozonides as Polymerization Initiators

Low-temperature (77-280 K) ozonolysis of perfluoro-4-methyl-2-pentene and perfluoro-2,4-dimethyl-3-ethyl-2-pentene by direct contact with ozone in the absence of solvents and oxygen was studied. The resulting perfluoro ozonides can be used as initiators of low-temperature polymerization and copolymerization.     

煤油裂解产物/空气与煤油/空气在宽温度范围内点火延迟的对比研究

Kerosene is an ideal endothermic hydrocarbon. Its pyrolysis plays a significant role in the thermal protection for high-speed aircraft. Before it reacts, kerosene experiences thermal decomposition in the heat exchanger and produces cracked products. Thus, to use cracked kerosene instead of pure kerosene, knowledge of their ignition properties is needed. In this study, ignition delay times of cracked kerosene/air and kerosene/air were measured in a heated shock tube at temperatures of 657–1333 K, an equivalence ratio of 1.0, and pressures of 1.01 × 10⁵–10.10 × 10⁵ Pa. Ignition delay time was defined as the time interval between the arrival of the reflected shock and the occurrence of the steepest rise of excited-state CH species (CH*) emission at the sidewall measurement location. Pure helium was used as the driver gas for high-temperature measurements in which test times needed to be shorter than 1.5 ms, and tailored mixtures of He/Ar were used when test times could reach up to 15 ms. Arrhenius-type formulas for the relationship between ignition delay time and ignition conditions (temperature and pressure) were obtained by correlating the measured high-temperature data of both fuels. The results reveal that the ignition delay times of both fuels are close, and an increase in the pressure or temperature causes a decrease in the ignition delay time in the high-temperature region (> 1000 K). Both fuels exhibit similar high-temperature ignition delay properties, because they have close pressure exponents (cracked kerosene: τ_ign∝P^-0.85; kerosene:τ_ign∝P^-0.83) and global activation energies (cracked kerosene: E_a = 143.37 kJ·mol^-1; kerosene: E_a = 144.29 kJ·mol^-1). However, in the low-temperature region (< 1000 K), ignition delay characteristics are quite different. For cracked kerosene/air, while the decrease in the temperature still results in an increase in the ignition delay time, the negative temperature coefficient (NTC) of ignition delay does not occur, and the low-temperature ignition data still can be correlated by an Arrhenius-type formula with a much smaller global activation energy compared to that at high temperatures. However, for kerosene/air, this NTC phenomenon was observed, and the Arrhenius-type formula fails to correlate its low-temperature ignition data. At temperatures ranging from 830 to 1000 K, the cracked kerosene ignites faster than the kerosene; at temperatures below 830 K, kerosene ignition delay times become much shorter than those of cracked kerosene. Surrogates for cracked kerosene and kerosene are proposed based on the H/C ratio and average molecular weight in order to simulate ignition delay times for cracked kerosene/air and kerosene/air. The simulation results are in fairly good agreement with current experimental data for the two fuels at high temperatures (> 1000 K). However, in the low-temperature NTC region, the results are in very good agreement with kerosene ignition delay data but disagree with cracked kerosene ignition delay data. The comparison between experimental data and model predictions indicates that refinement of the reaction mechanisms for cracked kerosene and kerosene is needed. These test results are helpful to understand ignition properties of cracked kerosene in developing regenerative cooling technology for high-speed aircraft.     

离子液体在自由基聚合反应中的应用研究进展

室温离子液体是完全由离子构成的液体,具有几乎没有蒸汽压、溶解度大、溶解范围广、易于回收利用、稳定性好等特点,广泛应用于电化学、有机反应、分离萃取、复合材料等各个领域。近年来已成为各种聚合反应研究的重要课题,且主要集中于自由基聚合反应。作为聚合反应的溶剂,离子液体对聚合反应速率、分子量、聚合物的结构性能都有一定影响。本文根据近几年的文献,归纳分析了离子液体中的常规自由基聚合和活性自由基聚合的反应动力学、反应机理、聚合产物的结构和性能以及离子液体的回收利用等问题。     

Preparation and Thermal Decomposition of Synthetic Bayerite

The formation process of bayerite, from an aqueous solution of sodium aluminate through enforced decomposition of aluminate ions by introducing CO₂ gas and aging with mechanical stirring, was investigated by pH measurements of the mother solution during preparation reaction and characterization of precipitates obtained at various stages of preparation. An amorphous precipitate, produced initially by the reaction of introduced CO₂, transformed to bayerite via pseudoboehmite during aging. It was found that the crystalline particle size and morphology of the crystallized bayerite change depending systematically on the preparation conditions. The reaction pathway of the thermal decomposition of the synthesized bayerite was investigated by using thermoanalytical techniques. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Chaperonin as Protein Nanoreactor for Atom‐Transfer Radical Polymerization

The group II chaperonin thermosome (THS) from the archaea Thermoplasma acidophilum is reported as nanoreactor for atom‐transfer radical polymerization (ATRP). A copper catalyst was entrapped into the THS to confine the polymerization into this protein cage. THS possesses pores that are wide enough to release polymers into solution. The nanoreactor favorably influenced the polymerization of N‐isopropyl acrylamide and poly(ethylene glycol)methylether acrylate. Narrowly dispersed polymers with polydispersity indices (PDIs) down to 1.06 were obtained in the protein nanoreactor, while control reactions with a globular protein–catalyst conjugate only yielded polymers with PDIs above 1.84.     

Simulation of Styrene Polymerization by Monomolecular and Bimolecular Nitroxide‐Mediated Radical Processes over a Range of Reaction Conditions

Simulations of polymerization rate, molecular weight development and evolution of the concentrations of species participating in the reaction mechanism over a range of operating conditions, and a parameter sensitivity analysis showing the effects of temperature, activation/deactivation equilibrium constant and initial concentrations of controller and initiator (if present) on these variables are presented for the nitroxide‐mediated radical polymerization of styrene. The simulations were performed with a computer program based on a detailed reaction mechanism. The simulated profiles of conversion, number average molecular weight ( ), and polydispersity agree well with experimental data. Previously unknown activation energies for reactions involved in the mechanism are estimated. The temperature dependence of the kinetic rate constants obtained in this study will be useful for future modeling and optimization studies.