非等温DSC法研究环氧树脂固化反应动力学过程

采用非等温DSC(差示扫描量热)法研究了环氧树脂(EP)体系的固化过程,并采用Kissinger方程、Crane方程和T-β(温度-升温速率)外推法计算出该EP体系固化反应的动力学参数和固化温度。研究结果表明:当m(EP)∶m(填料)∶m(固化剂)∶m(促进剂)=100∶30∶90∶0.4时,EP体系固化反应的表观活化能为78.90 kJ/mol、指前因子为2.58×109min-1和反应级数为0.914,其最佳固化条件为"从室温升温至92℃(开始凝胶)→继续升温至140℃(恒温固化)→最后升温至169℃(进行后固化处理)"。     

A kinetic study of ‘living’ coordination polymerization of propene with the soluble V(acac)3-Al(i-C4H9)2Cl system

The soluble V(acac)₃-Al(i-C₄H₉)₂Cl system initiated living polymerization of propene at ?78°C affording monodisperse polymers ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{= 1.15 ± 0.10}$). A kinetic study (of the living polymerization) was carried out to evaluate the rate coefficients for propagation. The equilibrium constant K_M for a propene monomer coordinated to an active vanadium and the rate constant k_p for a subsequent insertion of coordinated monomer into a living polymer chain were determined and compared with the values for the polymerization of propene with other soluble vanadium-based catalyst systems. The relation between K_M and k_p revealed that a strong interaction between vanadium and propene is unfavourable for the insertion of the coordinated propene into a living polymer chain. The mechanism of an initiation reaction involving alkylation and complexing of V(acac)₃ with Al(i-C₄H₉)₂Cl has been proposed.     

The kinetic evidence for the formation of multiple active species in a bis(phenoxy-imine) zirconium dichloride/MAO catalyst during ethylene polymerization

The effects of polymerization time and temperature on the molecular weight and molecular weight distribution of polyethylene, produced over homogeneous catalyst bis[N-(3-tert-butyl salicylidene)anilinato]zirconium(IV) dichloride ^tBu-L₂ZrCl₂/MAO have been studied. The data on the number of active centers (C_P) and propagation rate constants (k_P) at different polymerization time have been obtained as well. It was found that at a short polymerization time two types of active centers, producing low molecular weight PE (M_w = (4-10) × 10³ g mol⁻¹) are formed. The number of these centers was estimated to be 11% of total zirconium complex and their reactivity is very high (the k_P value was found to be 54 × 10³ L mol⁻¹ s⁻¹ at 35 °C). High initial activity of the catalyst fell with the increase in polymerization time, whereas the polydispersity values of the resulting PE increase due to formation of new centers, producing high molecular weight PE (M_w = (30-1300) × 10³ g mol⁻¹). It was found that the decrease in activity is caused by reducing the initial active centers number and lower reactivity of the new-formed centers (k_P = 17 × 10³ L mol⁻¹ s⁻¹).     

过氧化二异丙苯(DCP)交联聚乙烯的非等温结晶动力学研究

采用扩散的方法,在低于PE熔点的温度下,使过氧化二异丙苯(DCP)均匀扩散进入PE切片内部,并在180°C交联0.5 h得到交联PE。通过DSC测试对其结晶行为及其非等温结晶动力学进行了研究,研究表明,DCP交联对PE的结晶行为影响较大,与纯PE相比,在DCP用量较低时,交联PE的结晶峰向低温方向移动,结晶温度随着DCP用量的增加而降低,但继续增加DCP的用量,结晶温度反而会增加;纯PE及交联PE的结晶温度Avrami指数n介于3.2~4.2之间,DCP用量较低时,随着DCP含量的增加而增加,n呈增长趋势,继续增加DCP含量,n反而降低,交联PE的结晶速率常数Zc与n呈相同变化趋势。     

Kinetics of the anionic ring‐opening polymerization of octamethylcyclotetrasiloxane initiated by potassium isopropoxide

Kinetics of the anionic ring‐opening polymerization of octamethylcyclotetrasiloxane (D₄) in bulk initiated by potassium isopropoxide was studied. Several promoters including N‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethylformamide (DMF), and diglyme were used. It is indicated that the reactions are first‐order in D₄ during the initial stage of polymerization. The polymerization rate of D₄ is influenced by a number of factors, such as the nature of promoters, the molar ratio of promoter to initiator (C_p/C_i ratio), and the reaction temperatures. With the use of NMP as promoter, the polymerization rate constant at 30°C is 10.482 h^?1 with the C_p/C_i ratio equal to 3.0. As the C_p/C_i ratio increases, the polymerization rate constant increases sharply and the cyclic oligomers content in polymer decreases evidently. The back‐biting reaction that leads to the formation of decamethylcyclopentasiloxane (D₅) occurred in the polymerization of D₄. The rate of the D₅ formation relatively to the rate of D₄ conversion increases with the conversion of D₄. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3510–3516, 2006     

Poly(ethylene naphthalate) formation 2. polymerization of bis(hydroxyethyl)naphthalate

Bis(hydroxyethyl)naphthalate (BHEN) was polymerized to polyethylenenaphthalate (PEN) in the presence of various metallic catalysts. The influence of the nature and concentration of these catalysts on the rate of polymerization has been investigated. The order of decreasing catalytic influence of various metal ions on the polymerization of BHEN was found to be: Ti > Sb > Zn > Co > Pb > Ni (Mg). The effect of the reaction temperature has also been studied. The optimal concentration of these catalysts and reaction temperature were found to be 30 × 10^–5 (mol/mol B HEN) and 285°-293°C. Because of its insolubility in ordinary solvent, the molecular weight of PEN was measured using the light scattering method.     

用热重法研究代森锰锌的非等温热分解动力学

用非等温热重法研究了代森锰锌的热分解反应动力学。研究是在氮气气氛中、升温速率范围为1．0～20．0K／min内进行的。用统计方法处理测得的实验数据,计算得到代森锰锌的热分解活化能,为研究代森锰锌的热分解动力学提供了基础数据,以及用于鉴定代森锰锌的待征温度外推始点Te和峰温Tp及对升温速率的拟合曲线。测定了所研究代森锰锌样品的X衍射光谱、红外光谱,同时对样品进行了“斑点”试验,不但说明了样品是“真正”的代森锰锌,而且将上述谱图和文献已发表的进行了对比和讨论。     

基于非等温法的废弃环氧树脂电路板热解动力学分析

热解技术在处理废弃电路板，回收电路板中的金属，实现树脂、玻璃纤维等非金属成分的资源化方面发挥愈来愈重要的作用，但目前对于不含任何电子元件、含少量铜箔的废弃环氧树脂电路板的热解机理研究尚不明确。为阐述其热解催化作用，采用同步热分析仪和气相色谱-质谱联用(GC-MS)仪对不同升温速率(5, 10, 15, 20℃/min)下电路板的热解特性及热解机理进行分析。结果表明，废弃电路板热解过程主要分为四个阶段：表面残余水蒸发或其他小分子散逸、环氧树脂侧链基团氧化、四溴双酚A的分解和热解残留物分解；运用Kissinger法、Flynn-Wall-Ozawa法及Friedman法等明确单一反应的热解区间并求解热分解反应动力学参数，最终得到指前因子1.14×1022 min-1和活化能218.533 kJ/mol；采用?atava-?esták法和主曲线法进行机理函数对比分析，最终表明废弃环氧树脂电路板适用随机成核与增长模型：Avrami-Erofeev方程模化。研究结果可为促进热解技术的应用提供理论支撑。     

The exothermal effects of superimposed processes of activated anionic polymerization of ε-caprolactam and crystallization of the polymer formed

We have carried out a calorimetric investigation of the anionic polymerization of ε-caprolactam and of the crystallization of the polymer produced. Measurements were made at 160°–190°C under isothermal conditions with the use of activators of various chemical types and functionality. We have obtained the kinetic constants of the polymerization reaction which agree with the values found earlier in a non-isothermal experiment. The autocatalytic nature of this reaction has also been confirmed. The kinetics of the crystallization of poly-ε-caproamide have been studied and the values of the kinetic constants found. It has been shown that an increase in the functionality of the activator slows down the crystallization and increases the degree of crystallinity of the end product. A method is proposed for the calculation of the overall exothermal effect for the temperature range within which the polymerization and crystallization proceed simultaneously. This method is based on the assumption that only the polymerized portion of the reaction mass can be crystallized. The method has been verified by the experimental data obtained.     

Uptake of hazardous heavy metal ions by aqueous solution of poly(acrylamide) prepared through atom transfer radical polymerization process

Poly(acrylamide) (PACM) used in this study was prepared through an effective atom transfer radical polymerization process and characterized by NMR, FTIR, and thermo gravimetric analysis. Resulting polymer was used for the uptake of heavy metal ions from aqueous solution. Partition coefficient, retention capacity, and metal ion uptake behavior in aqueous solution of PACM at different monomer percent conversions and effect of parameters for optimization of polymerization reaction gives thermally stable PACM. Efficiency of metal ion uptake of different molecular weights of PACM were tested in batches for Ni²⁺, Pb²⁺, Cu²⁺, Zn²⁺, and Hg²⁺ ions in single metal solution. Metal ion sorption capacities increase with increase in polymer concentration. Metal ion sorption capacities in single metal system were 6.3 mg g^?1 Ni²⁺, 6.0 mg g^?1 Pb²⁺, 6.9 mg g^?1 Cu²⁺, 6.2 mg g^?1 Zn²⁺, 22.4 mg g^?1 Hg²⁺ for PACM of 88% conversion (Mn = 19,850). Uptake by the PACM indicates that they are effective in removing metal ions from single metal ion solutions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Probing the reaction kinetics of vinyl acetate free radical polymerization via living free radical polymerization (MADIX)

Living free radical polymerization technology (macromolecular design via the interchange of xanthates (MADIX)) was applied to give accesses to chain length and conversion dependent termination rate coefficients of vinyl acetate (VAc) at 80 °C using the MADIX agent 2-ethoxythiocarbonylsulfanyl-propionic acid methyl ester (EPAME). The kinetic data were verified and probed by simulations using the PREDICI^® modelling package. The reversible addition-fragmentation transfer (RAFT) chain length dependent termination (CLD-T) methodology can be applied using a monomer reaction order of unity, since VAc displays significantly lower monomer reaction orders than those observed in acrylate systems (ω(VAc, 80 °C)=1.17±0.05). The observed monomer reaction order for VAc is assigned to chain length dependent termination and a low presence of transfer reactions. The α value for the chain length regime of log(i)=1.25−3.25 (in the often employed expression ) reads 0.09±0.05 at low monomer to polymer conversion (10%) and increases significantly towards larger conversions (α=0.55±0.05 at 80%). Concomitantly with a lesser amount of midchain radicals, the chain length dependence of k_t is significantly less pronounced in the VAc system than in the corresponding acrylate systems under identical reaction conditions. The RAFT(MADIX)-CLD-T technique also allows for mapping of k_t as a function of conversion at constant chain lengths. Similar to observations made earlier with methyl acrylate, the decrease of k_t with conversion is more pronounced at increased chain lengths, with a strong decrease in k_t exceeding two logarithmic units from 10 to 80% conversion at chain lengths exceeding 1800.     

Reversible addition fragmentation transfer (RAFT) polymerization of styrene in a miniemulsion: A mechanistic investigation

The RAFT polymerization of styrene in miniemulsion using 1-phenylethyl phenyl-dithioacetate (PEPDTA) as a RAFT agent was investigated, in attempt to reveal the mechanism for the often observed inferior performance such as low polymerization rate, broad molecular weight distribution and particle size distribution in the RAFT miniemulsion polymerization with regular levels of surfactant and co-stabilizer (1 wt% sodium dodecyl sulfate and 2 wt% hexadecane). It is strongly evident that a few of large oligomer particles consisting of oligomer, RAFT agent (RAFT agent refers to the original RAFT agent), and monomer would be formed in the early stage of the polymerization due to the superswelling of the first nucleated droplets. With the regular levels of surfactant and co-stabilizer, the observed low polymerization rate, broadened molecular weight distribution, slow conversion of the RAFT agent, lower N_p, and broadened particle size distribution could be well explained by the formation of these large oligomer particles and their prolonged existence. When the formation of the oligomer particles was suppressed by increasing surfactant and co-stabilizer levels and wise selection of types of RAFT agent, the molecular weight distribution could be narrowed to around 1.3 and particle size distribution could be close to that of the conventional non-living miniemulsion polymerization.     

Polymerization of lactams, 28. Effect of reaction conditions on the anionic polymerization of 2-pyrrolidone (part 5)

The effect of temperature, activator concentration, and polymerization time on the anionic polymerization of 2-pyrrolidone was studied using the method of statistical planning of the experiments. Sodium tert-butoxide or sodium dihydrido-bis(2-methoxyethoxy)aluminate was used as initiator; N-acetylpyrrolidone served as activator in both cases. Results obtained with both initiation systems were presented in the form of explicit mathematical equations.     

Kinetics of the in situ polymerization and in situ compatibilization of poly(propylene) and polyamide 6 blends

In previous articles, we reported on a novel reactive extrusion process to obtain a compatibilized blend of polymer A and polymer B. It consisted in polymerizing the monomer of polymer A in the presence of polymer B. A fraction of the latter contained initiating sites from which the polymerization of monomer A took place. As such, both polymer A and a graft copolymer of polymer A and polymer B were formed in the process. That process was called in situ polymerization and in situ compatibilization of polymer blends. Its feasibility was illustrated for in situ polymerized and in situ compatibilized poly(propylene) and polyamide 6 (PP/PA6) blends. The latter were prepared by activated anionic polymerization of ?‐caprolactam (CL) in the presence of PP in a batch mixer and a twin‐screw extruder, respectively. A fraction of the PP contained isocyanate groups from which PA6 grafts were formed. Sodium caprolactam (NaCL) was used as the catalyst and a diisocyanate compound was used as the activator. In this study, we report on the effects of various parameters on the kinetics of the anionic polymerization of CL in the presence of PP. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1498–1504, 2004     

Ability of nitrones of various structures to control the radical polymerization of styrene mediated by in situ formed nitroxides

The ability of several nitrones to control the radical polymerization of styrene at 110 °C has been investigated by high-throughput experimentation. The nitrone/free radical initiator pair dictates the structure of the nitroxide and the alkoxyamine formed in situ, which determines the position of the equilibrium between the active and the dormant species operating in the nitroxide-mediated polymerization. For the styrene polymerization to be controlled, the nitrone must be reacted with 2,2′-azo-bis-isobutyronitrile (AIBN) at 85 °C, prior to addition of styrene and polymerization at 110 °C. The effect of the nitrone structure on the kinetics of the styrene polymerization has been emphasized. Amongst all the nitrones tested, those of the C-phenyl-N-tert-butylnitrone (PBN) type are the most efficient in terms of polymerization rate, control of molecular weight and polydispersity. Electrophilic substitution of the phenyl group of PBN by either an electrodonor or an electroacceptor group has only a minor effect on the polymerization kinetics. Importantly, the polymerization rate is not governed by the thermal polymerization of styrene but by the alkoxyamine formed in situ during the pre-reaction step. The initiation efficiency is, however, very low, consistent with a limited conversion of the nitrone into nitroxide and alkoxyamine.     

非等温热重法研究聚苯硫醚热分解动力学

采用非等温热重法对聚苯硫醚的热分解动力学进行研究,通过比较计算结果选定拟合结果更好的迭代法计算反应活化能,采用积分法结合36种动力学函数来判断聚苯硫醚热分解的机理函数。得到了聚苯硫醚热分解动力学参数平均活化能E、指前因子A和对应的热分解动力学方程。     

Studies on a dicyanate containing four phenylene rings and polycyanurate blends. 2. Application of mathematical models to the catalysed polymerization process

Selected blends of bis-4-(4-cyanatophenoxy)phenyl sulphone with a commercial dicyanate, 2,2-bis(4-cyanatophenyl)propane are analysed using differential scanning calorimetry (DCS) to examine the processes of the aluminium-catalysed thermal polymerisation. Kinetic treatment of these data show that the kinetics of the formation of the bis-4-(4-cyanatophenoxy)phenyl sulphone homopolymer were fitted with just two processes, but three processes were required for the 2,2-bis(4-cyanatophenyl)propane homopolymer, for which a more complex thermogram was obtained. When considering the polymerisation kinetics of binary blends of the monomers it was necessary to select the minimum number of kinetic parameters to obtain the best fits to the data. The binary blends generally show trends in the data that reflect the monomer composition. The parameters derived from two kinetic methods are broadly in agreement; the kinetic treatment of the thermal data for 2,2-bis(4-cyanatophenyl)propane monomer suggests the presence of at least one impurity and this is supported by spectroscopic and chromatographic analyses. The latter was not observed for bis-4-(4-cyanatophenoxy)phenyl sulphone, a monomer found to be of a higher purity by chromatography. From the kinetic analysis of the thermal data (from dynamic DSC), the mathematical model predicts that, following an isothermal cure regime at 450 K, bis-4-(4-cyanatophenoxy)phenyl sulphone should reach a conversion of 90% after ca. 33 min. The empirical data for this isothermal experiment show that bis-4-(4-cyanatophenoxy)phenyl sulphone reaches a conversion of 73% after 33 min and 87% after 2 h at 450 K.     

Polymerization of lactams, 95 Preparation of polyesteramides by the anionic polymerization of ε-caprolactam in the presence of poly(ε-caprolactone)

Preparation of polyesteramides-poly[(ε-caprolactam)-co-(ε-caprolactone)]s by anionic polymerization of ε-caprolactam in the presence of poly(ε-caprolactone) at 150 °C was studied in this paper. ε-Caprolactam magnesium bromide was used as an initiator of polymerization and polymeric materials containing 5-25 wt% ε-caprolactone units were obtained. Thermal methods (DSC and DMA) were employed for characterization of poly[(ε-caprolactam)-co-(ε-caprolactone)]s and their mechanical properties were also evaluated. By introducing the activator with N-acyllactam structure, the polymerization rate increased and it was possible to carry out the polymerization at 110 °C. Mechanical properties of polyesteramides were influenced by both the content of ε-caprolactone units incorporated into copolymer and polymerization temperature. The mechanism of incorporation of poly(ε-caprolactone) is discussed. The results show that it is not possible to restrict exchange transacylation reactions, progressing in the course of polymerization, by kinetic tools.     

Winsor I-like (micro)emulsion polymerization of styrene initiated by oil-soluble initiator

Batch emulsion polymerization of styrene initiated by an oil-soluble initiator and stabilized by non-ionic emulsifier (Tween 20) has been investigated. The rate of polymerization vs. conversion curve shows the two non-stationary rate intervals typical for the non-stationary-state polymerization. This behavior is a result of the continuous particle nucleation and the decrease of monomer concentration at the reaction loci with increasing conversion. The initial increase of the polymerization rate is attributed to the increase of particle number and the polymerization proceeding under the monomer-saturated condition—the Winsor I-like (micro)emulsion polymerization. The decrease of the polymerization rate is the result of the depressed transfer of monomer from the monomer reservoir to the reaction loci. Above 50 °C the monomer emulsion separates into two phases: the upper transparent monomer phase and the lower blue colored (microemulsion) phase. The polymerization mixture consists of the microdroplets (act as the reaction loci) and large degradable monomer droplets (act as the reservoir monomer and emulsifier). The continuous release of emulsifier from the monomer phase and the microdroplets induce the continuous particle nucleation up to high conversion. The initial formation of large particles results from the agglomeration of unstable growing particles and monomer droplets. The size of large (highly monomer-swollen) particles decreases with conversion and they merge with the growing particles at ca. 40-50% conversion. The coarse initial emulsion transformed during polymerization to the fine (semitransparent) polymer emulsion as a result of the continuous particle nucleation, the shrinking of highly monomer-swollen polymer particles and the depletion of monomer droplets. The low overall activation energy of polymerization is mainly ascribed to the decreased barrier for entering radicals into the latex particles with increasing temperature.     

Mechanistic and kinetic investigation of Cu(II)-catalyzed controlled radical polymerization enabled by ultrasound irradiation

Controlled radical polymerization (CRP) under external field has been an attractive research area in these years. In this work, a new electron transfer mechanism, that is, sonochemically induced electron transfer (SET) was introduced to mediate polymerization for the first time. The activator Cu^IX/L complex was (re)generated from Cu^IIX₂/L in dimethylsulfoxide (DMSO) by the SET process in the presence of free ligand tris(2-dimethylaminoethyl)amine (Me₆TREN). The investigation of polymerization including the mechanistic insights and effect of experimental conditions on the rate of reaction has been undertaken. Kinetics of Cu(II)-catalyzed CRPs via SET under different conditions (i.e., Me₆TREN concentration, catalyst loading, targeted degree of polymerization, and sonication power) were conducted in an unprecedentedly controlled manner, yielding polymers with predetermined molar masses and low dispersities (Đ < 1.12). Attractively, the polymerization can be performed without the piezoelectric nanoparticles and exogenous reducing agent. Contamination by nonliving chains formed from sonochemically generated radicals is avoided as well. All of these results supported that Cu(II)-based catalyst activation enabled by ultrasonication has a promising potential in scale-up of CRP.