丙烯酰胺水溶液聚合反应的研究

探讨了聚乙二醇作为分散剂时丙烯酰胺水溶液聚合体系中单体含量、还原剂用量对聚合物分子量的影响，并探讨了聚合时间与转化率、单体含量与聚合体系粘度之间的关系。结果表明，在保持聚合体系能够流动的前提下，单体含量可提高到２０％，聚合物的分子量可达３００万以上。     

带路径约束的聚烯烃牌号切换操作优化方法

产品多样化需求使得聚烯烃生产过程中经常需要进行牌号切换操作。以往关于牌号切换优化的研究大多只关心切换过程结束后聚合物质量指标是否达到目标牌号值,对过渡过程中质量指标及状态变量的波动情况缺少关注,而过程的波动会影响到最终产物的质量性质和操作平稳性。为此,本文以聚乙烯气相流化床反应器为对象,通过在牌号切换优化命题中加入关于熔融指数等的路径约束,防止过渡过程中的状态变量剧烈波动影响聚合物树脂质量。为求解此类带路径约束的动态优化问题,对常规的控制变量参数化方法进行了改进,通过求解微分代数方程(DAE方程)将路径约束转化为控制变量约束。仿真结果表明,加入路径约束可以有效避免牌号切换中变量的剧烈波动,增强过程平稳性。     

Optimal operation of ethylene polymerization reactors for tailored molecular weight distribution

This work presents a comprehensive steady‐state model of the high‐pressure ethylene polymerization in a tubular reactor able to calculate the complete molecular weight distribution (MWD). For this purpose, the probability generating function technique is employed. The model is included in an optimization framework, which is used to determine optimal reactor designs and operating conditions for producing a polymer with tailored MWD. Two application examples are presented. The first one involves maximization of conversion to obtain a given MWD, typical of industrial operation. Excellent agreement between the resulting MWD and the target one is achieved with a conversion about 5% higher than the ones commonly reported for this type of reactor. The second example consists in finding the design and operating conditions necessary to produce a polymer with a bimodal MWD. The optimal design for this case involves a split of the initiator, monomer, and modifier feeds between the main stream and two lateral injections. To the best of our knowledge, this is the first work dealing with the optimization of this process in which a tailored shape for the MWD is included. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Diffusion-controlled semibatch emulsion polymerization of styrene

Semibatch emulsion polymerization of styrene under the monomer-starved condition is strongly affected by the gel effect. A mechanistic model based on diffusion-controlled reaction mechanisms is developed to predict the kinetics of semibatch emulsion polymerization. Experimental data available in the literature are employed to assess the proposed model. Reasonable agreement between the model predictions and experimental data is observed. The simulation results suggest that the reaction system approaches Smith–Ewart case II kinetics (n? = 0.5) when the concentration of monomer in the particles is close to the saturation value, whereas the reaction system under the monomer-starved condition is characterized by diffusion-limited reaction mechanisms (n?≥0.5). © 1995 John Wiley & Sons, Inc.     

Dispersion polymerization of acrylamide with quaternary ammonium cationic comonomer in aqueous solution

Copolymer particles consisting of acrylamide (AM) and acryloyloxyethyl dimethylbenzyl ammonium chloride (AODBAC) were prepared by dispersion polymerization in an aqueous solution of ammonium sulfate and in the presence of poly(acryloyloxyethyl trimethyl ammonium chloride) (PAOTAC) as the stabilizer. The average particle size ranged from 4 to 7 μm, and M_w and M_n were 2–6 ×10⁶ g/mol and 1–3 × 10⁶ g/mol, respectively. The effects of the AM/AODBAC ratio, monomer, initiator, salt, and stabilizer concentration on the particle size and molecular weight were studied. Increase of the AODBAC/AM ratio resulted in a decrease in the molecular weight and an increase in particle size. With the increase of the AODABA/AM ratio, the dispersion became less stable during long storage. Due to the presence of the salt, ionization of the quaternary ammonium groups in the dispersed particles is considered significantly suppressed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1101–1108, 2003     

Rheokinetics of free-radical polymerization of acrylamide in an aqueous solution

A method of rheokinetic analysis is applied to free-radical polymerization of acrylamide in a water solution initiated by an oxidizing reducing system. The special feature of this system is the second-order kinetics of the initiation stage. Theoretical analysis predicts the main effects, such as the time dependence of viscosity and the degree of polymerization, concentration influence of a monomer and an initiator, and the temperature dependence of the viscosity profile at different experimental conditions. Experimental data confirmed the idea about the second-order reaction of initiation. Observed dependencies were close to theoretical predictions. Rate constants of different individual stages of a reaction and “apparent” values of activation energy were found and compared with published values. The possibility of solving an inverse rheokinetic problem from viscometric data was confirmed.     

Modeling of semibatch styrene suspension polymerization processes

We developed a mathematical model to describe the behavior of semibatch styrene suspension polymerization processes, where the constituents of a typical emulsion polymerization process are added into the reaction vessel during the course of a typical suspension reaction. This technique was recently described for the production of core–shell polymer particles. The model assumes that the nucleated emulsion particles can agglomerate with the sticky and much bigger suspension particles and that the agglomeration rate constant is a function of the internal states of the suspended droplets. The proposed model presented good agreement with experimental conversion, average molecular weight, and molecular weight distribution data. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1950–1967, 2005     

Modeling and simulation of semibatch emulsion polymerization

By taking advantage of recent theoretical developments in emulsion polymerization and radical polymerization kinetics at high conversion, a model is developed for simulating seeded semibatch emulsion polymerization. The model is used to calculate the time evolution of the polymerization rate, the monomer conversion, the instantaneous degree of polymerization, the monomer concentration in particles, the average radical number per particle, and the propagation rate coefficient and termination rate coefficient over the whole course of the polymerization. Experimental observations by previous workers, including the existence of steady-state phenomenon and the broad distributions of molecular weight, are reproduced in the results of the simulation. The gel effect on emulsion polymerization and the open-loop stability of the semibatch process are discussed. © 1993 John Wiley & Sons, Inc.     

Magnetic field effects on the free radical solution polymerization of acrylamide

Systematic polymerization experiments quantified magnetic field (MF) influences on the free radical solution polymerization of acrylamide for various polymerization conditions. The type of initiation, the initiator concentration, the monomer concentration, and the viscosity of the aqueous medium were the subject of variation. The initiator efficiency (Φ) increased up to 60% and the initiator exponent of the overall rate expression raised from 0.1 to 0.28 when a weak MF of 0.1 T was applied to photochemical initiation. However, no appropriate effect was observed for thermal initiation. Kinetic analysis proved a reduction of the termination rate coefficient (k_t) up to 40%. Photochemically initiated polymerizations in media of enhanced viscosity revealed the highest increment of the initiator efficiency ratio Φ^MF/Φ and the most pronounced reduction of k_t^MF/k_t. On the contrary, the propagation rate coefficient (k_p) and the monomer exponent were not influenced by MF. Despite considerable increase of the polymerization rate in MF, no reduction of the molar mass was found. Compensation of increased Φ^MF and decreased k_t^MF are suggested as explanation. The singlet-triplet intersystem crossing mechanism for radical pairs served to explain the MF effects.     

RAFT polymerization of acrylamide manipulated with trithiocarbonates in poly(ethylene glycol) solution

The reversible addition fragmentation chain transfer (RAFT) polymerization of acrylamide (AM) in aqueous two‐phase system was successfully carried out in polyethylene glycol (PEG) aqueous solution. Because of phase transition involved in the polymerization process, the ln([M]₀/[M])‐time plots were indicated in two‐stages significantly. Both the initial homogeneous polymerization and the subsequent heterogeneous polymerization were under good control. The effects of various synthesis parameters such as polymerization temperature, concentration of CTA, and initiator on RAFT polymerization behaviors have been investigated. Furthermore, the evolution process of the droplet morphologies after separation was examined by transmission electron microscope. The results showed that the nuclei were formed throughout the whole heterogeneous polymerization and stable sphere particles with an average size of about 1 μm were produced finally. More importantly, it was also found that the viscosity played a significant role in the stabilization of the dispersion of polymer particles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43000.     

Population balance modeling of particle size distribution in monomer‐starved semibatch emulsion polymerization

The evolution of particle size distribution (PSD) in the monomer‐starved semibatch emulsion polymerization of styrene with a neat monomer feed is investigated using a population balance model. The system under study ranges from conventional batch emulsion to semicontinuous (micro)emulsion polymerization depending on the rate of monomer addition. It is shown that, contrary to what is often believed, the broadness of PSD is not necessarily associated with the length of nucleation period. The PSDs at the end of nucleation are found to be independent of surfactant concentration. Simulation results indicate that at the completion of nucleation the particle size is reduced and the PSD narrows with decreasing rate of monomer addition despite nucleation time increasing. The broad distribution of particles frequently encountered in semibatch emulsion polymerizations is therefore attributed to stochastic broadening during the growth stage. The zero‐one‐two‐three model developed in this article allows perceiving that the dominant kinetic mechanism may be different for particles with different sizes. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Molecular weight distribution control in a semibatch living-anionic polymerization. II. Experimental study

This work constitutes an indirect verification of a theoretical method that allows the production of polymers with prespecified molecular weight distributions (MWDs), through semibatch living-anionic homopolymerizations. The chemical system consisted of styrene with sec-butyllithium, in a solvent mixture of cyclohexane and tetrahydrofurane (THF). The necessary flow profiles were applied by a pair of computer-controlled pumps, and the produced MWDs were measured by size exclusion chromatography, with correction for nonuniform instrumental spreading. The main difficulty was the estimation of the initial moles of initiator and of the concentration of impurities in the monomer solution. For such estimation, a precalibration experiment was implemented.     

Kinetic and molecular weight control for methyl methacrylate semibatch polymerization. II. Open control

The gel effect will bring a violent increase of conversion for methyl methacrylate (MMA) polymerization in a short time. It will be very dangerous for the reactor, as it causes an increase of molecular weight and broadens the molecular weight distribution. To unify the kinetics, molecular weight, and its distribution, on the basis of the mathematical models for semibatch polymerization of MMA, three controlled objectives that are the heat load distribution index, the change in molecular weight, and molecular weight distribution index are presented. Three materials (monomer, solvent, and chain transfer agent) and their flow rate and feeding mode are analyzed for the open control of kinetics, molecular weight, and its distribution. The optimum flow rate and mode are obtained. The heat load distribution index and molecular weight distribution index are even less than 2.0 and 2.2, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4399–4405, 2006     

Studies of precipitated polymerization of acrylamide with quaternary ammonium cationic comonomer in potassium citrate solution

Copolymer particles consisting of acrylamide (AM) and cationic comonomer 2‐methyl acryloyloxyethyl trimethyl ammonium chloride (DMC) were prepared by precipitation polymerization in an solution of potassium citrate using ammonium persulfate ((NH₄)₂S₂O₈) and sodium sulfite (Na₂SO₃) as an initiator. The product poly(acrylamide‐2‐methyl acryloyloxyethyl trimethyl ammonium chloride) [Poly(DMC‐AM)] is a water‐soluble cationic polyelectrolyte. The solubility of DMC, AM and Poly(DMC‐AM) in potassium citrate solution were measured, combined with the theory of solubility parameter, and the experiment results indicate that the solubility of DMC and AM is much higher than that of Poly(DMC‐AM), and also the mechanism of copolymer precipitated in salt solution was discussed. The factors influencing the conversion of comonomers were examined, such as salt mass fraction, polymerization temperature, monomers mass fraction, initiator mass fraction, and so on. The results of experiments indicate that the best conditions are salt mass fraction = 57%, monomers mass fraction = 3%, m(DMC) : m(AM) = 3 : 1, initiator mass fraction = 0.08%, polymerization temperature = 50°C, reaction time = 2 h, and the conversion is 86.4%. And the qualitative analysis experimental method for copolymer by infrared absorption spectrum show that [Poly(DMC‐AM)] was successfully synthesized by precipitation polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Estimation of transfer constants in the aqueous solution polymerization of acrylamide with potassium persulfate initiator

An experimental investigation on the aqueous polymerization of acrylamide with potassium persulfate initiator is reported. Molecular weight averages were measured by viscometry. Non-Newtonian effects were accounted for by extrapolation to high shear rates where the polymer solutions approximated Newtonian behavior. Values for the transfer constants to the acrylamide monomer and to the persulfate initiator were estimated at 25 and 40°C and compared to literature values.     

Analysis of multiphase polycarbonate polymerization in a semibatch reactor

A physical and chemical model that describes the interfacial condensation of bisphenol-A to polycarbonate in a multiphase gas-liquid-liquid semi-batch reactor is presented. The particular polymerization kinetics model consists of initiation, propagation and termination reactions between dissolved bisphenol-A monomer, phosgene gas, a phenolic polymer chain growth stopper and various resulting polymer species. Using these kinetics, a physical model for a semi-batch stirred tank reactor is developed. The model accounts for finite liquid-liquid and gas-liquid mass transfer resistances and includes either plug-flow or complete backmixing of the gas bubbles as options for the gas flow pattern. The model equations are solved using the z-transform method from which the polymer MWD and the moments of the polymer MWD are obtained. The utility of the model as a quantitative means of assessing the effect of various kinetic and transport parameters on the polymer MWD is examined for a particular case.     

Precipitation polymerization of acrylamide with quaternary ammonium cationic monomer in potassium carbonate solution initiated by plasma

Precipitation polymerization of 2‐(methacryloyloxyethyl) trimethyl ammonium chloride (DMC)‐co‐acrylamide (AM) [poly(AM‐DMC)] has been successfully performed in potassium carbonate (K₂CO₃)‐water media by plasma initiation. K₂CO₃ solution was selected because not only the higher solubility of AM and DMC comparing with that of poly(AM‐DMC), but the higher intrinsic viscosity of poly(AM‐DMC) could be obtained. A set of experiments was performed using different K₂CO₃ concentration (from 50 down to 10% (w/w)), thus the precipitation architecture was not obtained below 20% (w/w). And particles size, particles size distribution (7–120 μm), and intrinsic viscosity of poly(AM‐DMC) (ranging up to 455 cm³/g) were also summarized in this article. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4060–4067, 2007     

Self-condensing vinyl polymerization of acrylamide

Summary A novel approach to branched polyacrylamide was described. The branched structure resulted from the amidyl radicals which were formed by the reaction of amide groups with Cu(III) of potassium diperiodatocuprate, K₅[Cu(HIO₆)₂], in alkaline medium and capable of initiating the vinyl polymerization of acrylamide monomer. The obtained polymer was characterized by ¹H NMR, FT-IR and intrinsic viscosity measurements. Received: 8 January 1999/Revised version: 26 May 1999/Accepted: 25 June 1999