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.     

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     

气相法聚乙烯工艺冷凝态操作模式的稳定性和动态行为

气相法聚乙烯工艺冷凝态操作模式由于显著提高了循环气移热能力和反应器时空产率,已成为流化床乙烯聚合工艺的主流操作模式。建立了气相法聚乙烯工艺冷凝态操作模式的数学模型,包括流化床反应器模型,多级换热器模型和反应温度、压力以及循环气组成的控制模型。基于此,采用流程模拟方法,计算了系统在反应器温度采用闭环控制时的稳态解;根据系统对小扰动的动态响应特点,定性判断了反应器温度采用开环控制和闭环控制时聚合反应系统的稳定性;考察了系统对1-己烯分压和催化剂进料速率的阶跃响应特性。结果表明,反应器温度采用闭环控制时,聚合反应系统在所考察操作条件下均是稳定的,而采用开环控制时,解曲线被分叉点分割为稳定区域和不稳定区域。反应器温度对1-己烯分压阶跃变化的动态响应表明聚合反应系统存在长、短周期两类振荡,表明冷凝态操作模式下乙烯聚合反应过程是一个多控制回路耦合的复杂过程。     

Highly active peroxides in the radical polymerization of ethylene under high pressure — conversion and initiator usage

By using highly active peroxides, it is possible to reduce the polymerization temperature necessary for the synthesis of low density polyethylene. In order to examine a number of peroxides for their suitability as low temperature initiators, polymerization tests were carried out at 1900 bar, 70–140°C, with an average residence time of 30 s in a continuously operating laboratory facility equipped with a stirred autoclave. Apart from a number of perneodecanoates, two peroxy dicarbonates, a sulphonyl peroxide, and a difunctional peroxide were used. The initiator consumption was high at polymerization temperatures below 100°C. The results obtained with the different peroxides varied considerably. As the temperature increased, the initiator consumption decreased rapidly to reach almost the same level for all the individual peroxides at above 120°C. The difunctional compound that proved highly suitable for the low polymerization temperatures desired was 1,4-di-(2-neodecanoyl peroxy isopropyl)benzene, the consumption at 100°C of which amounted to 13 g initiator/kg PE. Using a quantity of 40 g initiator/kg PE, a reactor temperature of 82°C could be employed. The peroxy dicarbonates and tertiary butyl perneodecanoate gave less satisfactory results.     

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).     

Mathematical model for the bulk polymerization of styrene chemically initiated by sequential and total decomposition of the trifunctional initiator diethyl ketone triperoxide

This work experimentally and theoretically investigates the use of the symmetrical cyclic trifunctional initiator diethyl ketone triperoxide (DEKTP) in the bulk polymerization of styrene (St). The study focused on temperatures of 150 to 200°C, considering chemical initiation by both sequential and total decomposition reactions. The experimental work consisted of a series of isothermal batch polymerizations at higher temperatures, 150 and 200°C, with an initiator concentration of 0.01 mol/L. The mathematical model is based on a kinetic mechanism that includes thermal and chemical initiation (both sequential and total decomposition reactions), propagation, transfer to monomer, termination by combination and re‐initiation reactions. Experimental and theoretical results show that the decomposition mechanism of the initiator is modified by the reaction temperature and can be modeled as a set of two parallel reactions with different temperature dependences. The developed mathematical model simulates the bulk polymerization of St in the presence of DEKTP for a wide temperature range (120–200°C). It was found that due to these two decomposition mechanisms, the system may behave as a “dead‐end” polymerization system above a certain temperature, yielding low molecular weights and a limiting conversion value. Simulation results indicate the value of this temperature to be about 185°C. POLYM. ENG. SCI., 55:145–155, 2015. © 2014 Society of Plastics Engineers     

新型过氧化物引发剂引发氯乙烯悬浮聚合动力学

研究了新型过氧化物引发剂过氧化新癸酸 1,1 二甲基-3-羟基丁基酯(Lup 610)在51.3与56.8℃以及过氧化新庚酸叔丁酯(Lup 701)和过氧化新戊酸叔己酯(HPV)在61.8℃单一引发剂引发氯乙烯悬浮聚合动力学,并采用模型计算结果绘制转化率 时间曲线,取与实验数据符合最好的f值作为引发剂的引发效率,求得引发剂Lup 610在51.3与56.8℃的引发效率分别为0.80与0.75,引发剂Lup 701和HPV在61.8℃下的引发效率分别为0.55和0.50。研究了上述引发剂与过氧化二碳酸二(2-乙基己酯)、过氧化新癸酸叔丁酯在各温度下复合引发剂引发氯乙烯悬浮聚合的动力学,与模型值相比较,发现两者能很好吻合。     

Thermal polymerization of thiol–ene network‐forming systems

The thermal polymerization of a tetrafunctional thiol (PETMP) and divinyl ether (TEGDVE) was monitored by temperature‐ramping differential scanning calorimetry (DSC) and the effects of inhibitor type and concentration, oxygen inhibition and initiator type were studied. The incorporation of inhibitors was required to produce a stable system at room temperature. Butylated hydroxytoluene (BHT) inhibited polymerization at low temperatures, but was inefficient at high temperatures and polymerization rates, and hence BHT is an ideal stabilizer. In contrast, a nitroxide inhibitor (NO‐67) was a very effective inhibitor and no polymerization occurred until all of the nitroxide was depleted. The presence of oxygen retarded the onset of polymerization but did not change the final conversion significantly. Polymerization with initiators having higher half‐life temperatures shifted the DSC peak to higher temperature because the rate of initiator decomposition and thus initiation was slower. Rheological investigations of the cure at different temperatures revealed that the gel time decreased significantly with increasing cure temperature, and the calculated apparent activation energy for PETMP/TEGDVE was 54 kJ mol^?1. Dynamical mechanical thermal analysis of the cured material was undertaken and frequency‐superposed results revealed that the glass transition region of PETMP/TEGDVE/azobisisobutyronitrile was much narrower than that of free‐radically cured dimethacrylate, but was similar to that of an epoxy resin cured with an aromatic diamine. This behaviour could be attributed to PETMP/TEGDVE network homogeneity, or to the less constrained crosslinks in the PETMP/TEGDVE network. Copyright © 2007 Society of Chemical Industry     

Vinyl chloride suspension polymerization with constant rate. A numerical study of batch reactors

Based on the analysis of a simple mathematical model, different temperature profiles are generated in order to provide vinyl chloride (VCM) suspension polymerization with constant reaction rates in batch reactors. In order to reproduce these temperature profiles in industrial-scale reactors, some process variables, such as coolant temperature, initiator concentration, and rate of water and monomer condensation, have to be manipulated. It is shown that those temperature practices can almost never be applied to large-scale reactors if the jacket temperature is the only variable that can be manipulated. It is also shown that developing an initiator feed procedure or using a reflux condenser may be advantageous.     

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     

Minimum end time policies for batchwise radical chain polymerization,part V—multicomponent copolymerization with one charge of comonomers

For batchwise radical chain solution multicomponent copolymerization, the minimum end time problem for the predetermined monomer conversion and number average molecular weight has been studied by considering the initiator concentration (or feed rate) and temperature as the two control variables. Applying the maximum principle and “unit segment treatment” (by which the co-polymerization can be treated as homo-polymerization in the kinetic analysis), it is found that for initiator addition processes the optimal initiator addition policy is to make the rate of initiation constant for the optimal temperature variation case, and the initiator concentration constant for the isothermal case as in homo-polymerization. For single charge of initiator processes, the optimal initial initiator concentration is such that it should be maintained at the lowest possible value (by which the polymerization is strongly dead-end) for the optimal temperature variation case without chain transfer steps, and at some optimal value (by which the polymerization is near dead-end) for the best isothermal case.     

Dynamics of a continuous stirred tank reactor for styrene polymerization initiated by a binary initiator mixture. II: Effect of viscosity dependent heat transfer coefficient

The dynamic behavior of the solution polymerization of styrene in a continuous stirred tank reactor is analyzed with a mixture of tert-butyl perbenzoate and benzoyl peroxide as an initiator system. In the modeling of the reactor, a viscosity dependent reactor wall heat transfer coefficient is used to account for the changing heat transfer efficiency as monomer conversion and polymer molecular weight increase. The steady state and bifurcation behaviors have been investigated with the reactor residence time, initiator feed composition, initiator concentration, feed solvent volume fraction, and coolant temperature as bifurcation parameters. Unlike the reactors with constant heat transfer coefficient, the present system exhibits relatively simple steady state and dynamic bifurcation behaviors. Oscillatory behavior is observed only when the solvent volume fraction in the feed exceeds 0.2. The dynamic simulation of the reactor also indicates that a feedback temperature controller may fail to maintain the reactor temperature when the heat transfer coefficient changes as a result of process disturbances.     

高单体进料浓度下丙烯腈连续水相沉淀共聚的研究Ⅱ聚合物颗粒形态

以ＫＰＳ－ＮａＨＳＯ３－Ｆｅ２＋ 为引发体系,在５ 升ＣＳＴＲ 中进行了高单体进料浓度（＞ ２８％ ）的丙烯腈（ＡＮ）－丙烯酸甲酯（ＭＡ）－苯乙烯磺酸钠（ＳＳＳ）三元连续水相沉淀共聚,系统考察了搅拌条件、单体进料浓度、引发剂浓度及配比、ｐＨ 值、平均停留时间和聚合温度等工艺因素对聚合物颗粒形态的影响。结果表明,有利于提高聚合反应速率的因素,包括提高单体进料浓度、引发剂浓度、ｐＨ值和聚合温度等均有利于改善颗粒形态,其中搅拌强度和单体进料浓度影响最明显。适当延长平均停留时间也对颗粒形态稍有改善。     

Free‐radical bulk polymerization of styrene with a new trifunctional cyclic peroxide initiator

The bulk free‐radical polymerization of styrene in the presence of a new cyclic trifunctional initiator, 3,6,9‐triethyl‐3,6,9‐trimethyl‐1,4,7‐triperoxonane, was studied. Full‐conversion‐range experiments were carried out to assess the effects of the temperature and initiator concentration on the polymerization kinetics, molecular weight, and polydispersity. Gel permeation chromatography was used to measure the molecular weight and the molecular weight distribution of polystyrene. When this multifunctional initiator was used for styrene polymerization at higher temperatures, it was possible to produce polymers with higher molecular weights and narrower molecular weight polydispersity at a higher rate. This showed that the molecular weight and polydispersity were influenced by the initiator concentration and the polymerization temperature in an unusual manner. Moreover, polystyrene, obtained with trifunctional peroxide, had O? O bonds in the molecular chains and was investigated with differential scanning calorimetry and gel permeation chromatography. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1035–1042, 2004     

ASPAA/MMA/AN三元共聚物的合成与表征

在合成N-[4-(磺酰胺)苯基]丙烯酰胺(ASPAA)单体,并进行结构表征的基础上,以N,N-二甲基甲酰胺为溶剂,过氧化苯甲酰为引发剂,采用自由基溶液聚合合成了ASPAA／甲基丙烯酸甲酯／丙烯腈三元共聚物,用IR和^1H—NMR图谱确认了结构。共聚结果表明85℃和95℃,引发剂浓度1．0％～1．5％时,聚合初期速率较高;共聚物分子量随聚合温度和引发剂浓度增加而降低。随ASPAA含量的增加,共聚物的玻璃化温度和酸值均升高,并通过ASPAA含量来调节。     

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     

Exotherm control in the thermal polymerization of nona-ethylene glycol dimethacrylate (NEGDM) using a dual radical initiator system

The curing behaviour of a long-chain dimethacrylate with a series of peroxide initiators was examined by temperature-ramping DSC. The effect of oxygen inhibition on the onset and peak temperatures cure was confirmed and the peak exotherm temperature was correlated with the decomposition rate of the initiator. The gel point temperature, obtained from temperature-ramping rheology studies, was directly related to the onset of cure from temperature-ramping DSC measurements. A combination of two peroxides with significantly different initiation rates was found to reduce the maximum heat flow and spread the polymerization process over a broader range of temperatures, thus effectively counteracting the auto-acceleration effect without significantly affecting the degree of cure. This behaviour was also predicted by with a free radical polymerization kinetic model. In order to further improve the cure behaviour, Nofmer was used as a chain transfer agent to control the propagation reaction in the polymerization. The use of a dual initiator system in the presence of Nofmer yielded a smooth polymerization process occurring over a wide range of temperatures and with low heat flow. Isothermal rheological studies confirmed the delay in the gel point by Nofmer.     

Kinetic model for crosslinking free radical polymerization including diffusion limitations

A kinetic model for crosslinking free radical polymerization is derived to predict the effect of temperature, inhibitor concentration, and initiator concentration on the rate of cure. The model is based on evidence from the literature that termination and comonomer reactivity differences can be ignored in many crosslinking free radical systems. Because of the complexity of the crosslinking chemistry, empirical relationships are used for decreasing initiator efficiency and radical mobility during cure. A sequential parameter fitting procedure is devised for isothermal curing data, and predictions are affirmed with both divinyl benzene and vinyl ester resin at several temperatures and concentrations of initiator and inhibitor. The key advantages of this kinetic model over previous models are its accuracy at high conversions and its ability to predict the effect of inhibitor and initiator concentrations on the rate of cure. This model is readily applicable to process modeling in the polymer composites manufacturing industry, which largely uses unsaturated polyester and vinyl ester resin matrices.     

“饥饿”反应器中自由基聚合动力学(Ⅰ)──关于长链假定适用性的讨论

在建立自由基聚合动力学模型时，由于聚合度很大，通常假定聚合速率等于链增长速率，认为用于链引发所消耗的单体量极少，将其忽略不计，即所谓的长链假定．本文对这一假定进行了详尽的分析，通过计算表明：在高温或／和高引发剂浓度下，特别是在“饥饿”反应器中，长链假定不再适用，建立更为精确的聚合动力学模型时，须考虑长链假定适用性．     

Dynamics of a CSTR for styrene polymerization initiated by a binary initiator system

The steady state and dynamic behavior of a continuous stirred tank reactor has been analyzed for free radical solution polymerization of styrene initiated by a mixture of two initiators having different thermal stabilities. From the steady state analysis of the reactor model with a mean residence time as a bifurcation parameter, four unique regions of steady state solutions are identified in an operating parameter space for a given initiator feed composition. A variety of complex bifurcation behavior such as multiple steady states, Hopf bifurcation and limit cycles have been observed and their stability characteristics have been analyzed. The effects of feed initiator composition and the concentration of the initiator in the feed stream on the reactor dynamics are also presented.