反应性乳化剂存在下半连续苯丙乳液共聚合表观动力学

研究了在反应性乳化剂SE-10N存在下,采用半连续滴加工艺进行苯丙乳液共聚合的表观动力学.首先利用间歇法研究了引发剂、乳化剂用量、单体总量和温度对聚合反应速率的影响,得到了相应的聚合反应速率方程为Rp =k[M]0.30[I]0.18[E]0.97,并计算得到聚合反应的表观活化能为90.8 kJ·mol-1.然后采用半连续滴加法,讨论了不同滴加速率对聚合表观速率Rp的影响,结果表明,随滴加速率Ra 的增加,反应速率Rp也增加,但增加的幅度逐渐减少,且聚合过程的状态不断远离饥饿态.要使该聚合过程的状态保持在稳定的饥饿态,单体滴加时间应控制在140 min 以上.     

Stabilization and kinetics in the emulsion copolymerization of butyl acrylate and methyl methacrylate

We carried out emulsion homopolymerizations and copolymerizations of butyl acrylate (BuA) and methyl methacrylate (MMA) with different types and concentrations of surfactants to determine the influence of these parameters on the particle size and particle size distribution and to elucidate the mechanism of particle formation. As expected, the mechanisms of nucleation above and below the critical micelle concentration were very different; however, it was also found that the presence of partially soluble monomers such as MMA in the water phase had a significant influence on the critical micelle concentration of Triton X‐405 (>50%). In addition, the nucleation mechanism during copolymerization seemed to be dominated by BuA, with the number of particles per liter being very similar to the number nucleated during its homopolymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2832–2846, 2001     

Modelling copolymerization kinetics

The composition and rate behavior of free radical copolymerizations is usually described by the Mayo-Lewis (ML) model and the associated reactivity ratios, r₁ and r₂. Particularly with respect to rate, a number of systems have been found to be poorly described by the simple ML model and the penultimate unit effect (PUE) model has been suggested as an explanation. A small but significant amount of work has been done with small model analogues of polymer chains and with ESR which has established the chemical feasibility of a PUE. This paper reviews recent work with pulsed laser polymerization kinetic measurements which are successfully described in terms of a modified PUE. It is concluded that the strength of the PUE correlates inversely with the monomer reactivity ratio product, r₁r₂. The effect is important for rate, but not for composition.     

Calorimetric monitoring of emulsion copolymerization reactions

An approach for monitoring both the overall conversion and the cumulative copolymer composition in emulsion copolymerization systems via calorimetric measurements was developed. The approach was checked by carrying out batch emulsion copolymerizations of methyl methacrylate/n-butyl acrylate, n-butyl acrylate/vinyl acetate, and methyl methacrylate/vinyl acetate and comparing calorimetric based estimations with off-line determinations of both the overall conversion and the cumulative copolymer composition. A good agreement was achieved for most of the cases studied. © 1993 John Wiley & Sons, Inc.     

Theory of colloid stability and particle nucleation kinetics in emulsion polymerization

The DLVO theory of colloid stability is applied to the uncatalyzed and catalyzed agglomeration of small primary particles formed in the earliest stages of emulsion polymerization in the manufacture of a carboxylic styrene/butadiene latex. The inverse 6th-power relationship between the stability ratio and the cation concentration revealed experimentally in an earlier work can be confirmed theoretically using variable Stern potentials. The Stern potential changes as parabolic function of log cation concentration. From the viewpoint of DLVO and Stern theory it is suggested that a spacer effect is crucial for the activity of the catalyst used.Presented at the 5th European and Interface Society Conference together with the 35th meeting of the Deutsche Kolloidgesellschaft on Trends in Colloid and Interface Science September 25–28, 1991, Maiz, FRG     

Estimation of reactivity ratios using emulsion copolymerization data

An approach for the estimation of reactivity ratios using cumulative copolymer composition–overall conversion data obtained in batch emulsion copolymerization is presented. The approach is based on an algorithm for parameter estimation in ordinary differential equations and takes into account the partition of the comonomers between the different phases present in the system. Both copolymer composition and conversion were considered to be affected by experimental errors. The method was first checked by using simulated data that included random errors. The effect of the initial guess and level of errors on the values of the estimated reactivity ratios was investigated. Once the approach was checked, it was used to estimate the reactivity ratios of the styrene–acrylonitrile system based on data obtained in unseeded batch emulsion copolymerizations of these monomers.     

Prediction of polymer composition in batch emulsion copolymerization

Monomer partitioning in emulsion copolymerization plays a key role in determining composition drift and polymerization rates. The combination of recently developed thermodynamically based monomer partitioning relationships with mass balance equations, makes predictions of monomer partitioning in emulsion copolymerizations possible in terms of monomer mole fractions and monomer concentrations in the particle and aqueous phases. Using this approach, the effects of monomer to water ratios and polymer volumes on the monomer mole fraction within the polymer particle phase in a nonpolymerizing system at thermodynamic equilibrium can be determined. Comparison of these monomer partitioning predictions with experiments for the monomer system methyl acrylate—vinyl acetate shows good agreement. Furthermore, composition drift occurring in a polymerizing system as a function of conversion can be predicted if the assumption is made that equilibrium is maintained during reaction. Comparison of predictions with experimental results for emulsion copolymerizations of the monomer systems methyl acrylate—vinyl acetate and methyl acrylate—indene shows good agreement. © 1994 John Wiley & Sons, Inc.     

Molecular weight distribution in composition controlled emulsion copolymerization

The effect of different strategies for copolymer composition control on the molecular weight distribution (MWD) and gel fraction in the emulsion copolymerization of methyl methacrylate and butyl acrylate was investigated. Starved and semistarved processes for copolymer composition control were both considered. For gel‐forming systems it was found that the starved process gave more gel and lower molecular weights than the semistarved process. The feasibility of simultaneous control of the copolymer composition and the MWD was assessed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1100–1109, 2000     

Automated batch emulsion copolymerization of styrene and butyl acrylate

This article describes a method for carrying out emulsion copolymerization using an automated synthesizer. For this purpose, batch emulsion copolymerizations of styrene and butyl acrylate were investigated. The optimization of the polymerization system required tuning the liquid transfer method, sufficient oxygen removal from the reaction medium and setting a proper sampling procedure. The monomer conversion‐time plots obtained with gas chromatography revealed a good reproducibility of the automated reaction kinetics. Furthermore, the particle size distributions and the properties of the final products were found to be highly reproducible. The performance of the automated reactions was subsequently compared with the conventional ones: similar reproducibility of either synthetic method was observed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

The emulsion copolymerization of styrene and sodium styrene sulfonate

The emulsion copolymerization of styrene and sodium styrene sulfonate has been shown to be a feasible preparative route to ionomeric sulfonated polystyrene. The properties of these copolymers are reported elsewhere. The copolymerization rate was found to be dramatically enhanced when compared to that for the emulsion copolymerization of styrene under identical conditions. This copolymerization was studied in detail and two mechanisms were proposed to account for these rate differences. An increase in the number of polymerizing particles in the copolymerization with consequent rate enhancement was substantiated by electron microscopy. However, the data indicate that the rate differences cannot be fully accounted for by this effect. In addition, a gel effect is proposed as a second contributor to the enhanced rate. This gel effect is believed to result from the intermolecular association of the incorporated metal sulfonate units in the growing polymer particles. When a third monomer that plasticizes the ionic interactions is used the polymerization rate decreases. This supports the gel effect hypothesis.     

Emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate

The kinetics of the emulsifier-free emulsion copolymerization of styrene and sodium styrene sulfonate have been examined over a range of comonomer compositions. The rate of polymerization was found to increase dramatically in the presence of small amounts of sodium styrene sulfonate. This increase is attributed to the increased number of particles formed when sodium styrene sulfonate was present and to a gel effect enhanced by ion association. At low concentrations of functional comonomer, where a monodisperse product was obtained, a homogeneous nucleation mechanism of particle generation is proposed. At higher concentrations, broader and then bimodal size distributions were obtained, and this is ascribed to significant aqueous phase polymerization of sodium styrene sulfonate. The water-soluble homopolymer is supposed to act as a locus of polymerization. The occurrence of this aqueous phase side reaction and the generation of secondary particles makes impossible the preparation of highly sulfonated polystyrene latexes by batch or seeded batch emulsion copolymerization.     

Semicontinuous emulsion copolymerization of methyl methacrylate and ethyl acrylate

The monomer addition policies required to produce homogeneous methyl methacrylateethyl acrylate copolymers of different compositions were determined by means of a semiempirical approach. This approach is useful for systems about which only a limited information is available. Applying this method only three reactions were needed to obtain homogeneous copolymers in a minimum process time. Comparisons were made between the results obtained using this monomer addition strategy and those from copolymerizations carried out under the classical starved conditions.     

Radiation-initiated emulsion copolymerization of styrene and carboxylic acid monomers

The emulsion Copolymerization of styrene and carboxylic acid monomers such as acrylic, methacrylic, and itaconic acids (AAc, MAAc, IAc) was studied by using ⁶⁰Co γ-rays as initiator and sodium do-decylsulfate as emulsifier. The polymerization behavior of these acid monomers was followed by simultaneous conductometric and potentiometric titrations for a latex sample taken in polymerization. The polymerization rate of these acid monomers increases in the following order of hydrophobicity: IAc < AAc < MAAc; this suggests that their polymerization sites are mainly the surface and/or subsurface regions of latex particles. The copolymerization rate of styrene and acid monomer increases with an increase in the acid monomer content for AAc and MAAc, whereas for IAc the rate decreases. The particle sizes determined by the stopped-flow method reveal that this variation of copolymerization rate cannot be explained by the number of growing particles and should be attributed to another factor; for instance, the transfer rate of styrene molecules from oil droplets to growing particles.     

Modeling composite emulsion polymerization kinetics

The conversion profiles of a number of factorial designed experiments used to study composite emulsion polymerization were modeled using a deterministic mathematical construct as well as an empirical neural network approach. In the deterministic modeling approach, existing mechanistic models for emulsion polymerization were employed for which estimates of rate constants were obtained from established literature sources as well as experiments. Fitting of the kinetic data was done using nonlinear fitting algorithms to adjust the estimated rate constants to provide the best fit of the conversion profiles. In the case of the empirical modeling using neural networks, the neural net inputs were in the form of the factor levels of the various experimental designs. Several nonrelated experimental designs could be combined in this way to serve as the input, whereas the conversion profiles were targeted as outputs. Following the successful implementation of both modeling strategies, a hybrid modeling approach was tested by combining the neural network predictive power to estimate values for rate constants while retaining the aforementioned mechanistic models to fit the data. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 101–117, 2013     

The kinetics of styrene emulsion polymerization

A study has been carried out on the kinetics of persulfate-initiated emulsion polymerization of styrene in the presence of an anionic (oleate) or mixed anionic-nonionic emulsifier. In both cases it appears that Smith-Ewart kinetics are obeyed, i.e., there is a constant-rate period up to 40–50% conversion, during which there is a concomitant constant molecular weight development. The sharp increases in molecular weight with conversion reported by Grancio and Williams appear to be an artifact resulting from the use of an impure emulsifier (Triton X-100), which acts as a chain transfer agent to reduce the molecular weight by approximately an order of magnitude. Hence there does not appear to be any kinetic justification for assuming an inhomogeneous swollen latex particle (“core-shell” morphology), and normal thermodynamic considerations should still apply to this swelling phenomemon.     

Modeling of unseeded emulsion copolymerization of styrene and methyl methacrylate

A mathematical model for the unseeded emulsion copolymerization of styrene and methyl methacrylate has been developed. This model, which includes a new rate coefficient for radical desorption, was used to analyze the effect of the styrene/methyl methacrylate molar ratio in the initial charge on the number of particles, overall conversion and copolymer composition. It was found that the number of particles increased with the methyl methacrylate content and that a drift of the copolymer composition resulted during the polymerization of styrene/methyl methacrylate molar ratios other than 50/50. Good agreement between experimental results and model predictions was achieved.