Free radical solution oligomerization of styrene in a continuous-stirred tank reactor train

For free radical oligomerization of styrene, a scheme for calculating the molecular weight distribution and conversion in a continuous-stirred tank reactor (CSTR) train is developed, which also allows the calculation of molecular weight distribution (MWD) for batch reaction. Calculations show that under conventional or near dead-end condition: (1) increasing initial initiator concentration, reaction time and reaction temperature, and decreasing initial monomer concentration cause P?_n and P?_w to decrease and MWD to narrow; (2) increasing initial initiator concentration, reaction time and reaction temperature, and increasing monomer concentration cause monomer conversion to increase; (3) a single CSTR gives a lower rate of oligomer production, but a narrower MWD than does a batch reactor.     

沉淀聚合法合成聚丙烯酸的研究

聚丙烯酸用作锌锰电池凝胶剂可改善CMC胶凝剂易水解的弊病,使电池性能得到根本性提高。丙烯酸的聚合活性大,是一个强放热反应,特别是纯聚丙烯酸,难以用普通方法得到。以偶氮二异丁腈为引发剂、正己烷为溶剂,用沉淀聚合法制备聚丙烯酸。研究了引发剂用量、相对分子质量调节剂用量、单体浓度等因素对聚合物黏均相对分子质量的影响,合成出黏均相对分子质量在9000~270000之间的聚丙烯酸,且单体转化率在96%以上。扫描电镜显示产物为细腻蓬松的粉末。沉淀聚合法可直接得到粉末状产品,后处理简单,溶剂可回收利用,是一种高效、低成本的聚合方法。     

Experimental validation of the optimal trajectory of initiator concentration in a batch MMA polymerization reactor

This article presents a method to determine the trajectory of initiator concentration that will produce polymer with desired number‐ and weight‐average molecular weights at a prespecified level of monomer conversion. The optimal control theory is applied to the mathematical model for a batch methymethacrylate (MMA) solution polymerization reactor system. By imposing the constraint that initiator concentration should decrease within the range of self‐consumption by the initiation reaction, one can obtain the initiator concentration trajectory that can be tracked by feeding the initiator alone. A control scheme is constructed with a cascade proportional‐integral‐derivative (PID) control algorithm for temperature control and a micropump is installed to manipulate the initiator feed rate. The experimental results show satisfactory tracking control performance despite the nonlinear features of the polymerization reactor system. Also, the monomer conversion and the average molecular weights measured are found to be in fairly good agreement with those of model prediction, respectively. In conclusion, the polymer having desired molecular weight distribution can be produced by operating the batch reactor with the initiator supplement policy calculated from the model. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1256–1266, 2000     

聚合反应周期进料对分子量分布可控性分析

对聚合产品的分子量分布实现在线控制是保证高分子产品质量的重要任务。以实验室规模的乙烯基丁基醚管式阳离子聚合反应为研究对象,验证了单体、引发剂周期进料对分子量分布有加宽效应,并从混合平均分布的角度研究了周期进料对分子量分布的影响,从而分析了实现分子量分布控制的可行性。     

Polymerisation von α-methylstyrol unter hohem druck

The polymerization-depolymerization equilibrium of α-methyl styrene can be shifted by high pressures towards the polymerization step. The equilibrium concentrations of the α-methyl styrene monomer were calculated at different pressures and temperatures from already known data for ΔH and ΔS°. The equilibrium concentrations are reported for temperatures from 40 to 100°C and for pressures from 1–5000 kg/cm². The data show for example, that at 70°C and atmospheric pressure the polymerization of α-methyl styrene is not possible because the required equilibrium concentration (9,6 mole/liter) is greater than the highest possible monomer concentration (7,3 mole/liter). However, at the same temperature and a pressure of 3000 kg/cm², the polymerization should take place up to the monomer concentration of 1,1 mole/liter. Experiments demonstrate, that under these conditions polymeric α-methyl styrene of high molecular weight is obtained by free radical polymerization. Analogous experiments were carried out with anionic initiation of the polymerization by naphthalene-sodium.     

THE EFFECT OF IMPERFECT MIXING ON POLYMER QUALITY IN LOW DENSITY POLYETHYLENE VESSEL REACTORS

A mathematical model is developed for the calculation of polymer quality in low density polyethylene vessel reactors, taking into account mixing limitations at the initiator feed point. Model predictions show that imperfect mixing in the reactor can produce considerable variations in polymer molecular weight distribution. The effect of the most important process conditions, input feed temperature, solvent concentration, monomer flow rate and initiator type, on the final polymer quality is analyzed. The advantages of the design solution which divides the reactor in more compartments in series are also discussed.     

THE EFFECT OF IMPERFECT MIXING ON POLYMER QUALITY IN LOW DENSITY POLYETHYLENE VESSEL REACTORS

A mathematical model is developed for the calculation of polymer quality in low density polyethylene vessel reactors, taking into account mixing limitations at the initiator feed point. Model predictions show that imperfect mixing in the reactor can produce considerable variations in polymer molecular weight distribution. The effect of the most important process conditions, input feed temperature, solvent concentration, monomer flow rate and initiator type, on the final polymer quality is analyzed. The advantages of the design solution which divides the reactor in more compartments in series are also discussed.     

Molecular Weight Distribution of Polystyrene Produced in a Starved Feed Reactor

A starved feed reactor (SFR) is a semi-batch polymerization reactor where initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures, The added initiator decomposes instantaneously and the added monomer polymerizes immediately. The molecular weight (MW) and molecular weight distribution (MWD) of the product polymer can be effectively controlled by the feed ratio of monomer to initiator. This paper preaeats a study on the MWD of styrene polymerization in a SFR. The MWD model parameters are regressed with experimeatvJ data. Although the solids fraction in the SFR is high (higher than 50%), vlscceity is not too high and the “gel effect“ is weak due to the low molecular weight of the products. It is found that the termination rate constant is a power function of molecular weight, radicals terminate via 100% combination,the thermal iuitiation can be neglrcted even at high reaction temperature studied. And calculated results indicate that in the SFR, the validity of the long chain assumptinn becomes doubted. It appears that other alterative assumption should be found for an improved model.     

AUTOMATIC CONTROL OF A REACTOR FOR BULK POLYMERIZATION OF STYRENE

Automatic temperature and initiator feed control of a reactor for styrene bulk polymerization, initiated by A.I.B.N., was achieved.

We show that suitable temperature and/or initiator feed policies allow production with high conversions (>50%) of a polymer with narrower molecular weight distribution.

The good fit of experimental data on mathematical model (taking in account viscosity effect) allow us to find experimental conditions required to obtain a polymer with a predetermined molecular weight distribution (especially polydispersity).     

“饥饿”反应器中苯乙烯聚合动力学

本文对“饥饿”反应器中ＡＩＢＮ引发苯乙烯聚合行为进行了详细的研究，建立了相应的聚合动力学模型，在模型中，考虑了由于初级自由基与单体反应生成单体自由基时所消耗的单体量，并将链终止速率常数与聚合物的累积数均链长进行校正。利用实验数据对模型参数进行了回归。     

双硫酯作为链转移剂的苯乙烯本体聚合研究

研究了二硫代苯甲酸苄基酯（BDB）、二硫代苯甲酸苯乙基酯（PEDB）及二硫代苯甲酸异丙苯基酯（CDB）三种RAFT试剂作为链转移剂的苯乙烯本体聚合。动力学研究表明,当BDB及PEDB浓度和偶氮二异丁腈（AIBN）浓度同时增大时,AIBN浓度提高所导致的聚合反应速率提高起主导作用：当CDB和AIBN浓度同时提高时,CDB浓度提高所导致的聚合速率降低作用影响更显著。对CDB体系,随转化率提高分子量分布变宽。对BDB体系,当其浓度较高时,随转化率提高分子量分布变窄;当其浓度较低时,不利于实现可控,活性聚合,反应后期分子量分布变宽。动力学和GPC分析均表明以BDB为链转移剂时苯乙烯本体聚合的可控性最好。在同时考虑链转移剂和引发剂作用的基础上,提出了修正的聚合物分子量预测模型,该模型可有效预测以双硫酯为链转移剂的苯乙烯RAFT聚合体系的分子量。     

“饥饿”反应器中自由基聚合动力学(Ⅱ)──甲基丙烯酸甲酯聚合动力学

对“饥饿”反应器中甲基丙烯酸甲酯（MMA）聚合行为进行详尽研究,建立了聚合动力学模型,模型中考虑了由于初级自由基与单体反应生成单体自由基时所消耗的单体量;考虑了PMMA的高温解聚作用;考虑了体系中的凝胶效应,并将链终止速率常数与凝胶效应联系起来,反映在模型中．通过实验,优化回归求取了模型参数．     

KINETICS OF RADICAL POLYMERIZATION IN A STARVED FEED REACTOR (Ⅱ)──KINETICS OF METHYLMETHACRYLATE POLYMERIZATION

对“饥饿”反应器中甲基丙烯酸甲酯（MMA）聚合行为进行详尽研究,建立了聚合动力学模型,模型中考虑了由于初级自由基与单体反应生成单体自由基时所消耗的单体量;考虑了PMMA的高温解聚作用;考虑了体系中的凝胶效应,并将链终止速率常数与凝胶效应联系起来,反映在模型中．通过实验,优化回归求取了模型参数．     

Dynamics and stability of ethylene polymerization in multizone circulating reactors

Multizone circulating bed reactors (MZCR) have the exclusive characteristics of producing polymers of different molecular weights in a single particle. Traditional fluidized bed reactors, on the other hand, can produce only one kind of molecular weight with relatively narrow distribution. A dynamic model for the MZCR is used to illustrate the basic dynamic behavior of the new reactor design used for polyethylene production. The model is used to study the copolymerization of ethylene with butene. Several parameter sensitivity analyses are performed to show the computer-simulated time responses for reactor temperature, number-average molecular weight, weight-average molecular weight, catalyst feed rate and the monomer/comonomer concentration along the reactor length. At certain operating conditions dynamic instability is observed and the results for the effect of cooling water temperature, catalyst feed rate, monomer and comonomer initial feed concentration on the reactor temperature and polymer molecular weight reveal that the system is very sensitive to disturbances in the heat exchanger coolant temperature. Also, at some operating conditions, the reactor temperature oscillates above the polymer melting temperature. Temperature runaway above polymer softening point is a serious problem which may cause polymer melting and hence reactor shutdown. The oscillatory behavior of the reactor temperature necessitates a suitable temperature control scheme to be installed.     

Low Temperature Initiation by 3-Mercaptopropionic Acid-Ce(IV) or -KMnO4 Redox System for Polymerization of Acrylamide Monomer

Polymerization of acrylamide monomer was performed at low temperatures using 3-mercaptopropionic acid-cerium(IV) sulfate and 3-mercaptopropionic acid-KMnO₄ redox systems in acid aqueous medium. Water soluble polyacrylamides containing 3-mercaptopropionic acid end groups were synthesized. The effects of mole ratio of acrylamide to initiator(n_MSA= n_Ce(IV)), polymerization time, temperature, and concentration of sulfuric acid on the yield and molecular weight of polymer were investigated. The decrease in the mole ratio of acrylamide/Ce(IV) at constant monomer concentration resulted in an increase in the yield but a decrease in molecular weight of polymer. The increase of reaction temperature from 20° to 70°C resulted in a decrease in the yield but indicated generally a constant value for the molecular weight of polymer. With increasing of polymerization time, the yield and molecular weight of polymer did not change mainly. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions, respectively in the polymerization reaction. The existence of Ce(III) ion bonded to polymer was investigated by UV-visible spectrometry and fluorescence measurements. The amount of Mn(II) that is incorporated to the polymer was determined using graphite furnace atomic absorption spectrometry. The mechanism of this phenomenon is discussed.     

Kinetics of NMBA polymerization in a starved feed reactor

A starved feed reactor (SFR) is a semibatch polymerization reactor in which initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures. The added initiator decomposes instantaneously, and the added monomer polymerizes immediately. The monomer concentration in the SFR is very low, ideally approaching zero. The reactor is in a starved status for reactants. The molecular weight of the product polymer can be effectively controlled by the feed ratio of monomer to initiator. This article presents a study on the kinetics of NBMA polymerization in an SFR. The model parameters were regressed with the experimental data. Although the mass fraction of polymer in the SFR was high (higher than 50%), viscosity was not high and the “gel effect” was weak because of the low molecular weight of the products. It was found that the termination rate constant is a power function of polymer concentration, and the lumped rate constant, k_p/(k)^1/2, can be modeled by the Arrhenius equation. The initiator efficiency, f, remained constant at a temperature less than 120°C, and increased with the temperature increasing at temperatures greater 120°C. The other parameters remained constant in the experiment range. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2068–2075, 2001     

Multicomponent vapor deposition polymerization of poly(methyl methacrylate) in an axisymmetric vacuum reactor

An axisymmetric, multicomponent initiated chemical vapor deposition (i-CVD) apparatus was designed to study the vapor-phase growth of glassy poly(methyl methacrylate) (PMMA) films. Preheated monomer (methyl methacrylate) and initiator (t-butyl peroxide) vapors were metered into a pressure-controlled reaction chamber. Inside the chamber, gases pass through a high-temperature hot-zone where primary free radicals are formed. The gas mixture then condenses and polymerizes on a back-cooled target substrate. Key reactor operating parameters were systematically varied to understand film growth kinetics. These include the hot-zone temperature, reactor base-pressure, substrate temperature, and the monomer/initiator molar feed ratio. Polymer deposition requires good thermal contact between feed gases and the hot-zone. Packed with glass beads, the hot-zone reactor resulted in more efficient initiation and film growth. Experiments also show that polymer deposition rate is limited by thermal initiation of primary free radicals, transport of primary free radicals to the target substrate, and by monomer adsorption. Size exclusion chromatography of deposited polymers is used to relate molecular weight to the monomer-to-initiator feed ratio. The addition of a third vapor component, 1-butanol, was also found to affect polymer molecular weight.     

Kinetics of butylacrylate polymerization in a starved feed reactor

A starved feed reactor (SFR) is a semibatch polymerization reactor where initiator and monomer are fed slowly into a fixed amount of solvent. The polymerization is carried out isothermally at elevated temperatures. The added initiator decomposes instantaneously and the added monomer polymerizes immediately. The molecular weight of the product polymer can be effectively controlled by the feed ratio of monomer to initiator. This article presents a study on the kinetics of butylacrylate polymerization in an SFR. The model parameters are regressed with experimental data. Although the solids fraction in the SFR is high (>50%), viscosity is not high and the “gel effect” is weak because of the low molecular weight of the products. It is found that the termination rate constant is a power function of molecular weight, and the lumped rate constant k_p/(k)^1/2 can be modeled through an Arrhenius equation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1519–1525, 2004     

Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on the polymerization rate and polymer molecular weight

The emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles. Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 × 10⁻³ and 32.48 × 10⁻³ mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 777–793, 1999     

NaHSO_3-(NH_4)_2S_2O_8引发体系制备低相对分子质量聚丙烯酸钠

以丙烯酸和氢氧化钠为原料,NaHSO3-(NH4)2S2O8为氧化还原引发剂体系,NaHSO3为链转移剂合成低相对分子质量聚丙烯酸钠。研究了单体、引发剂及链转移剂的用量、反应温度和反应时间等对产物相对分子质量的影响。结果表明,反应温度为60℃、w(单体)=25%、w(引发剂)=0.6%、w(链转移剂)=2.0%、反应时间2h,可制得聚丙烯酸钠的粘均相对分子质量在2 000~3 000,单体转化率在98%以上。