Miniemulsion copolymerization of styrene–methyl methacrylate

Miniemulsion copolymerization of 50 : 50 weight fraction of styrene–methyl methacrylate monomer, using hexadecane as the cosurfactant, was carried out in both unseeded and seeded polymerizations. Effects of the hexadecane concentration and the ultrasonification time on the conversion–time curves and particle size of the final latex were investigated for unseeded polymerization. The kinetic and particle size distribution results showed that an increase in hexadecane concentration and ultrasonification time cause faster polymerization rate and smaller particle size. The mechanism of mass transport from miniemulsion droplets to polymer particles was also investigated for seeded polymerization. For this purpose a monomer miniemulsion was mixed with a fraction of a previously prepared miniemulsion latex particles prior to initiation of polymerization, using residual oil-soluble initiator in the seed latex. The concentration of hexadecane and a water-insoluble inhibitor (2,5 di-tert-butyl hydroquinone) in the miniemulsions were the main variables. Seeded polymerizations were also carried out in the presence of miniemulsion droplets containing a water-insoluble inhibitor and water-soluble initiator. The inhibitor concentration and the agitation speed during the course of polymerization were the experimental variables. The kinetic and particle size results from these seeded experiments suggested that collision between miniemulsion droplets and polymer particles may play a major role in the transport of highly water-insoluble compounds.     

On the miniemulsion polymerization of very hydrophobic monomers initiated by a completely water‐insoluble initiator: thermodynamics,kinetics, and mechanism

Successful miniemulsion polymerizations of very hydrophobic monomers, such as lauryl methacrylate and 4‐tert‐butyl styrene, initiated by very hydrophobic (i.e., completely water‐insoluble) lauroyl peroxide, are reported. Conversion‐time histories, as well as final latex properties, for example, the particle size distribution, are different from similar miniemulsion polymerizations in the presence of water‐soluble initiators. The observed differences can be attributed to the average number of radicals inside a miniemulsion particle; the system obeys Smith‐Ewart case I rather than Case II kinetics. Albeit the pairwise generation of radicals in the monomer droplets, substantial polymerization rates are observed. Water, present in the droplet interfacial layer, is supposed to act as chain transfer agent. The product of a chain transfer event is a hydroxyl radical, exit of this hydroxyl radical allows for the presence of single radicals in particles. The proposed mechanisms allow for agreement between initial droplet and final particle size distributions in miniemulsion polymerization initiated by lauroyl peroxide. © 2016 The Authors Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2731–2745     

Kinetic and thermodynamic aspects of miniemulsion copolymerization

Miniemulsion polymerization involves initiation of polymerization in preformed stable monomer emulsion droplets with average droplet diameter of 50–500 nm. At the end of the polymerization, only a fraction of the initial number of monomer droplets become polymer particles. The emulsifier system used for the preparation of such emulsions comprises a mixture of ionic surfactant and a fatty alcohol or long chain alkane (termed cosurfactant). The cosurfactant is essential for the formation of stable emulsion droplets and in addition it plays an important role in the interparticle monomer transport. Kinetic results are presented on conventional emulsion and miniemulsion copolymerization of different pairs of monomers, showing the main differences for both processes. These differences were related to the particle formation mechanism and the influence of the cosurfactant in the miniemulsion process. A theoretical model was developed, based on mass balances and equilibrium thermodynamics, which was found to describe accurately the experimentally generated data on comonomer distribution during the course of the copolymerization process and the interdroplet mass transport process.     

Miniemulsion copolymerization of vinyl acetate and butyl acrylate. II. Mathematical model for the monomer transport

A mathematical model is presented to describe the monomer transport between monomer droplets, aqueous phase, and polymer particles during the course of an emulsion polymerization. The model was used to investigate the role of the cosurfactant (hexadecane) in the miniemulsion copolymerization of 50:50 molar ratio vinyl acetate-butyl acrylate monomer mixture, as well as the effect of the different components and process variables on the rate of copolymerization, monomer distribution between phases, and composition of the copolymer.     

Comparative study of monomer droplet nucleation in the seeded batch and semibatch miniemulsion polymerisation of styrene

Monomer droplet nucleation in the seeded miniemulsion polymerisation of styrene under monomer-flooded and monomer-starved conditions was studied. The miniemulsion feeds were added to the reactor either batchwise or semibatchwise. The droplets preserved longer under flooded conditions. As a result, the batch operation led to a larger number of particles (N_p) than the semibatch operation. For the miniemulsion droplets containing predissolved polymer, the final N_p was independent of the way that the feed was added to the reactor and was equivalent to the number of monomer droplets in the original miniemulsion feed. The size distribution of the final latexes, however, was influenced by the operation type. For the batch operation, the rate of polymerisation (R_p) with the miniemulsion feeds was higher than that with the conventional monomer emulsion feed because of the monomer droplet nucleation. But for the semibatch operation, the opposite was true because of R_p controlled by the rate of monomer diffusion from rather stable miniemulsion droplets to the growing polymer particles.     

聚合过程中原位生成助稳定剂的细乳液聚合

以甲基丙烯酸十二氟庚酯(DFMA)、甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)为共聚单体,不加任何传统的助稳定剂进行细乳液聚合.在共聚体系中,由于DFMA在初期反应生成的聚合物中占有较高比例,初期形成的少量低聚物可以起到助稳定剂作用,因此DFMA作为反应单体的同时,又可以原位生成助稳定剂,维持单体液滴或乳胶粒子的稳定,以细乳液聚合的方式进行聚合.分别采用油溶性引发剂(AIBN)和水溶性引发剂(KPS)引发聚合,考察细乳液聚合过程中乳胶粒子粒径的变化规律,粒径由初始时刻的400nm左右减少到80nm左右,最终与使用传统的助稳定剂得到的粒径相当.提出了原位生成助稳定剂的细乳液聚合机理,并使用交联剂验证了提出的原位生成助稳定剂的细乳液聚合机理.     

Effect of the presence of polymer in miniemulsion droplets on the kinetics of polymerization

Solution of polystyrene in styrene were dispersed in an aqueous gel phase comprising sodium lauryl sulfate, cetyl alcohol, and water using an emulsification process known to produce monomer droplet sizes inthe submicron size range (referred to as miniemulsion droplets). The shelf-life stabilities of these miniemulsions were studied to determine their relative droplet sizes, and the emulsions were concommitantly polymerized in an isothermal batch reaction calorimeter. The polymerization kinetics and final particle sizes produced were compared with miniemulsion and conventional emulsion polymerizations prepared using equivalent recipes without the addition of polystyrene. The results indicate that polymerization of miniemulsions prepared from polymer solutions produce significantly different kinetics than both miniemulsion and conventional emulsion polymerizations. In general, a small amount of polymer greatly increases the rate of polymerization and the final number of particles produced in the polymerization to the extent where even conventional polymerizations carried out above the critical micelle concentration of the surfactant polymerize more slowly. The results are explained by considering the system to be comprised of small, stable pre-formed monomer-swollen polymer particles which are able to efficiently capture aqueous phase radicals. This enables the system to produce a large final number of particles, similar to the initial number of pre-formed polymer particles, as opposed to miniemulsions and micelles in which only a relatively small fraction of the initial number of species (droplets or micelles) become polymer particles. © 1994 John Wiley & Sons, Inc.     

Copolymerization kinetics of methyl methacrylate-styrene obtained by PLP-MALDI-ToF-MS

The combination of MALDI-ToF-MS and pulsed laser polymerization has been used to study the propagation rate coefficients for the copolymer system styrene-methyl methacrylate. For the first time, complete information regarding mode of termination, reactivity of photoinitiator-derived radicals, copolymer molecular mass, chemical composition, and copolymerization rates is obtained interrelated. The polymerizations were carried out in bulk with varying styrene concentrations at a temperature of 15.2 degrees C by an excimer pulsed laser with varying frequencies. Both chemical composition distributions and molecular weight distributions were determined by MALDI-ToF-MS. The data were fitted to the implicit penultimate unit model and have resulted in new point estimates of the monomer and radical reactivity ratios for the copolymer system styrene-methyl methacrylate: r(St) = 0.517, r(MMA) = 0.420, s(St) = 0.296, s(MMA) = 0.262. Comparison between Monte Carlo simulations and the obtained results further confirmed the very successful combination of pulsed laser copolymerization experiments with MALDI-ToF-MS. The obtained results are believed to be the most accurate and complete set of copolymerization parameters to date.     

On the Reaction Characteristics of Miniemulsion Polymerization with Aqueous Phase Initiation – Experiments and Modeling

Miniemulsions, consisting of submicron droplets of very hydrophobic lauryl methacrylate or 4‐tert‐butyl styrene, are successfully polymerized using water‐soluble sodium persulfate. Monitoring the calorimetric profile as well as the droplet and particle size distribution with conversion manifests a process of monomer redistribution, droplet disappearance, and narrowing of the particle size distribution. The observed reaction characteristics could be modeled adequately, using thermodynamic principles. The results of the work presented do not only have predicting value, but also enfeeble the idea of a one‐to‐one translation of monomer droplets into polymer particles in miniemulsion polymerization.     

On the main locus of radical formation in emulsion polymerization initiated by oil-soluble initiators

The effect of the monomer/water ratio on the rate of polymerization per polymer particle in both seeded emulsion polymerizations and miniemulsion polymerizations was used in an attempt to elucidate the main locus of radical formation in emulsion polymerization initiated by an oil-soluble initiator (AIBN). It was found that, for the rest of conditions constant, the polymerization rate per polymer particle increased when the monomer/water ratio increased, namely when the amount of initiator dissolved in the aqueous phase per polymer particle decreased. This is an evidence against a dominant aqueous phase formation of radicals. On the other hand, these results are consistent with a mechanism in which the radicals are mainly produced in the oil-phase with significant aqueous phase termination.     

Copolymerization of polar and non-polar monomers in direct and inverse emulsion systems

Some problems connected with the use of monomers with different solubilities in water and oil phases for copolymerization in direct and inverse (micro)emulsions are discussed. We have shown that by choosing appropriate model systems which can simulate specific effects connected with the transfer of reactants between various phases and swelling ability of polymer particles, one can contribute to the answering the questions of the propagation locus (loci) of copolymerization and of its (their) history during emulsion copolymerization as well as to recognize the effect of the nature of the interlayer in the inverse (micro)emulsion system in relation to the kinetics and mechanism of the copolymerization process and structure of the copolymer formed. The method was demonstrated on the examples of seeded methyl methacrylate emulsion polymerization, of the emulsion copolymerization of styrene and divinylbenzene and of the inverse (micro)emulsion copolymerization of acrylamide and methyl methacrylate and/or acrylamide and styrene.     

Miniemulsion polymerization: An approach to control copolymer composition

The copolymerization of vinyl acetate (VAc) and vinyl 2-ethylhexanoate (V2EH) via miniemulsion polymerization is being investigated with the goal of better copolymer composition control. The reaction kinetics and final particle sizes were compared for homopolymerizations and copolymerizations of the two monomers. Enhanced polymerization rates were seen for the miniemulsion polymerizations over their conventional counterparts despite a decreased number of particles. This was attributed to the influence of the reactive surfactant sodium dodecyl allyl sulfosuccinate and low water solubility of the V2EH monomer. Increased nucleation of miniemulsion droplets was sought by incorporation of small amounts of polymer into the droplets. This was first shown to be effective for styrene miniemulsion polymerizations and was subsequently successfully extended to the VAc/V2EH system     

Emulsion copolymerization of styrene and methyl methacrylate

Chain transfer constants to monomer have been measured by an emulsion copolymerization technique at 44°C. The monomer transfer constant (ratio of transfer to propagation rate constants) is 1.9 × 10^?5 for styrene polymerization and 0.4 × 10^?5 for the methyl methacrylate reaction. Cross-transfer reactions are important in this system; the sum of the cross-transfer constants is 5.8 × 10^?5. Reactivity ratios measured in emulsion were r₁ (styrene) = 0.44, r₂ = 0.46. Those in bulk polymerizations were r₁ = 0.45, r₂ = 0.48. These sets of values are not significantly different. Monomer feed compcsition in the polymerizing particles is the same as in the monomer droplets in emulsion copolymerization, despite the higher water solubility of methyl methacrylate. The equilibrium monomer concentration in the particles in interval-2 emulsion polymerization was constant and independent of monomer feed composition for feeds containing 0.25–1.0 mole fraction styrene. Radical concentration is estimated to go through a minimum with increasing methyl methacrylate content in the feed. Rates of copolymerization can be calculated a priori when the concentrations of monomers in the polymer particles are known.     

Styrene miniemulsion polymerization initiated by 2,2′-azobisisobutyronitrile

The effects of various parameters on the dodecyl methacrylate (DMA) or stearyl methacrylate (SMA) containing styrene miniemulsion polymerizations were investigated. These parameters include the type of initiators [2,2′-azobisisobutyronitrile (AIBN) vs. sodium persulfate (SPS)], the size of the homogenized monomer droplets, the AIBN concentration, and the SDS concentration. A small quantity of a water-insoluble dye was also incorporated into the polymerization system to study the related particle nucleation mechanisms. The oil-soluble AIBN promotes nucleation in the monomer droplets, whereas homogeneous nucleation predominates in the reaction system with the water-soluble SPS. Homogeneous nucleation, however, cannot be ruled out in the DMA or SMA containing polymerizations with AIBN as the sole initiator. Increasing the level of AIBN or SDS enhances formation of particle nuclei via homogeneous nucleation. The reaction kinetics is primarily controlled by the competitive events of monomer droplet nucleation and homogeneous nucleation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2537–2550, 1999     

Controlled synthesis of styrene and methyl methacrylate copolymers in the presence of reversible addition-fragmentation chain-transfer agents

Molecular-mass characteristics of styrene-methyl methacrylate copolymers formed via the reversible addition-fragmentation chain transfer copolymerization mediated by dithiobenzoates have been studied. Low-molecular-mass reversible-addition fragmentation chain-transfer agents active in the homopolymerization of both monomers and in the homopolymerization of only one of the monomers (styrene) can be used for the controlled synthesis of narrow dispersed copolymers. Conditions for the synthesis of narrow dispersed block copolymers with the desired structure and molecular mass of the blocks have been found. The polymer reversible addition fragmentation chain-transfer agent determines the composition and molecular mass of the first block. The structure of the second block is defined by the composition of the monomer mixture, and the molecular-mass characteristics are set by the concentration of the agent and the conversion of monomers.     

Effect of monomer hydrophilicity on ARGET–ATRP kinetics in aqueous mini-emulsion polymerization

Activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP)-based aqueous miniemulsion polymerization where the polymerization takes place in the stabilized monomer droplets is described. In this work, we compared styrene, n-butyl methacrylate (nBMA) and tert-butyl methacrylate (tBMA) and investigated the influence of their hydrophobicity on dispersity, molecular weight and particle stability based their partition coefficients (logP) (2.67, 2.23, and 1.86, respectively). Tetrabutylammonium bromide (TBAB) was used as a phase transfer agent for the controlled delivery of Cu²⁺-Br/tris(2-pyridylmethyl)amine (TPMA), a hydrophilic catalyst, into monomer droplets of varying hydrophobicity. The resulting dispersity and particle stability of each polymer is a function of its logP value, with the most hydrophobic monomer (styrene) displaying the narrowest dispersity and most control (Đ < 1.3), and the most hydrophilic polymer poly(tert-butyl methacrylate) (PtBMA) having reduced emulsion stability, determined by the observation of aggregate formation. Selected polymerization parameters, including effects of total ascorbic acid feed concentration and the monomer concentration and their effects on dispersity are reported. The controlled polymerizations of hydrophilic monomers using ARGET-ATRP in miniemulsion conditions and understanding the effect of monomer hydrophilicity on the emulsion stability will broaden the use of ARGET-ATRP in emulsion polymerization for the synthesis of polymer-grafted nanoparticles with hydrophilic corona.     

Emulsion co- and terpolymerization of styrene,methyl methacrylate,and methyl acrylate. I. Experimental determination and model prediction of composition drift and microstructure in batch reactions

In Part I of this series the reactivity ratios of the comonomer pair methyl acrylate-methyl methacrylate were determined with low-conversion bulk polymerizations. It was shown that the binary reactivity ratios of the systems styrene-methyl acrylate, styrene-methyl methacrylate, and methyl acrylate-methyl methacrylate describe composition drift in low-coversion bulk terpolymerizations with these monomers reasonably well. A computer model was developed to simulate the composition drift in emulsion co- and terpolymerizations. The composition drift in two batch emulsion copolymerization systems (styrene-methyl acrylate and methyl acrylate-methyl methacrylate) and one emulsion terpolymerization system (styrene-methyl acrylate-methyl methacrylate) was investigated both experimentally and with the model. Experimental results were compared with model calculations. The copolymer chemical composition distributions (CCD) were determined with gradient polymer elution chromatography (GPEC®). This technique was also used for the first time to obtain information about the extent of composition drift in emulsion terpolymerizations. Cumulative terpolymer compositions were determined with ³H-NMR as a function of conversion and with this information the three-dimensional CCD was obtained. The composition drift was analyzed with respect to free radical copolymerization kinetics (reactivity ratios) and monomer partitioning. It was shown that in most emulsion copolymerizations the composition drift is mainly determined by the reactivity of the monomers and to a lesser extent by monomer partitioning, except in systems where there is a large difference in water solubility. The model predictions for cumulative terpolymer composition as a function of conversion and the three-dimensional terpolymer CCD showed excellent agreement with the experiments. The GPEC® elution chromatogram of the terpolymer was found to be in accordance with the predicted CCD and the experimentally determined CCD. © 1996 John Wiley & Sons, Inc.     

甲基丙烯酸3-三甲氧基硅丙酯/苯乙烯细乳液共聚合过程中的水解及缩合反应

研究了甲基丙烯酸3-三甲氧基硅丙酯(MPS)和苯乙烯(St)细乳液聚合过程中的水解及缩合反应.用气相色谱仪测定聚合过程中水解产物——甲醇的含量来研究MPS的水解度.MPS分子主要在细乳液液滴与水的界面以及乳胶粒与水的界面上发生水解反应.MPS和St比例、介质pH值、乳化剂用量、引发剂类型和用量都会影响MPS的水解程度.缩合产物用29Si固态核磁共振表征,中性条件下,缩合反应受到抑制,在高MPS/St比例的体系中也只生成少量缩合产物.酸性和碱性条件下,缩合产物量均增加,但碱性条件下,体系中仍有一定数量未缩合的硅氧烷存在,这与细乳液聚合独特的液滴成核机理及聚合过程中较少液滴间物质交换有关.     

PVC miniemulsion polymerization II. Particle and droplet growth as a function of conversion

Growth of two droplet families and a polymer seed family as a function of percent monomer conversion in PVC miniemulsion synthesis demonstrates that polymerization in droplets predominates to ～ 30–40% conversion, whereupon polymerization of seed becomes favored. This difference appears to be due to a liquid-to-solid phase change in the forming particles during the course of polymerization.     

Kinetics and mechanisms of emulsion polymerization initiated by oil-soluble initiators. IV. Kinetic modeling of unseeded emulsion polymerization of styrene initiated by 2,2′-azobisisobutyronitrile

To explain the kinetic features of particle formation and growth in unseeded emulsion polymerization initiated by oil-soluble initiators, a mathematical kinetic model is proposed, based on the assumption that when initiator radicals or monomer radicals in the water phase enter monomer-solubilized emulsifier micelles, initiate polymerization, and propagate to a chain length which is long enough not to desorb from the micelles, the micelles are regarded to be transformed into polymer particles. It is demonstrated by comparing the experimental results obtained in the emulsion polymerization of styrene initiated by the oil-soluble initiator, 2,2'-azobisisobutyronitrile, with sodium lauryl sulfate as emulsifier that the proposed kinetic model satisfactorily explains the kinetic features such as the effects of initial emulsifier, initiator, and monomer concentrations on both the number of polymer particles produced and the monomer conversion versus time histories. © 1993 John Wiley & Sons, Inc.