Emulsion Polymerization Of Butadiene Research Articles

Toward a better understanding of the emulsion polymerization of butadiene. I. Continuous conductivity measurements

ABSTRACTContinuous conductivity measurements were performed during the batch emulsion polymerization of butadiene along with kinetic and particle size measurements. The critical monomer conversion was obtained around 55% and the rate of polymerization was correlated to the surfactant concentration with an exponent of 0.35 which was not in agreement with the exponent offered by Smith and Ewart. In addition, the evolution of some particle‐related quantities such as particle size and number of particles during the three intervals of the emulsion polymerization and their agreements with Smith‐Ewart mechanism were investigated. The behavior of conductivity in the emulsion polymerization of butadiene normally containing a buffering agent was found to be completely different from the unbuffered one. Comparison of the conductivity profiles with the kinetic and particle‐related quantities represented that the conductivity of the reaction mixture is very sensitive to the changes in the particle size so that any small change in the forms of nucleation, growth, and coagulation is clearly observed in the conductivity profiles. Furthermore, the conductimetric data are capable of determining some important points during the polymerization such as the beginning of the reaction that can be important from the industrial process control point of view. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2017,134, 45262.

Effect of Surfactant Concentration on the Dispersion Coefficient for the Comparison of Model and Experimental Results in Emulsion Polymerization of Butadiene

In this work, a mechanistic model was developed on the basis of population balance equations for butadiene emulsion polymerization and validated with experimental data in a batch reactor. A combination of finite difference and weighted essentially nonconciliatory (WENO) schemes was used as a precise technique for the discretization of the population balance equations. The obtained values during the evolution of conversion and the average particle diameter values were in good agreement with the measured results for different surfactant concentrations. However, the simulated particle-size distributions (PSDs) were much narrower than the experimental PSDs. Therefore, to match the experimental PSDs, a stochastic term was included in the zero–one model. The effect of surfactant concentration, which is an important factor with a direct impact on the dispersion coefficient, was also investigated and confirmed with experimental results.

Ab initio RAFT emulsion polymerization of butadiene using the amphiphilic poly(acrylic acid-b -styrene) trithiocarbonate as both surfactant and mediator

Ab initio reversible addition fragmentation chain transfer (RAFT) emulsion polymerization of butadiene was investigated by using the amphiphilic poly(acrylic acidn-b-styrene5) trithiocarbonate as both surfactant and mediator. The neutralization on acrylic acid (AA) units played significant influence on the gelation. When half of the AA units were neutralized, the gelation occurred in the early stage of the polymerization so that the highest accessible molecular weight of polybutadiene was as low as 5 kg mol−1. In the non-neutralized conditions, the gelation was much retarded so that the highest accessible molecular weight was increased up to 23 kg mol−1. In the non-neutralized conditions, potassium persulfate could not initiate the polymerization. When azobisisobutyronitrile was used as initiator, the polymerization mediated by poly(acrylic acid27-b-styrene5) trithiocarbonate could proceed much faster than the solution polymerization did. The latex was stable. Before the gel point, molecular weight agreed well with the theoretical prediction while PDI was relatively high due to the branching reaction. The poly(butadiene-b-styrene) core/shell particles could obtained by extending polybutadiene. When the n value in poly (acrylic acidn-b-styrene5) trithiocarbonate was lower than 20, the coalescence would occur, leading to the formation of some coagulum. On the other hand, when n value was as high as 60, the molecular weight was out of control. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis of structured nanoparticles of styrene/butadiene block copolymers via RAFT seeded emulsion polymerization

The structured nanoparticles of styrene (St) and butadiene (Bd) block copolymers were prepared by RAFT seeded emulsion polymerization of butadiene. It was confirmed that the block copolymers of PSt-b-P(St-co-Bd) was formed with controlled molecular weight and rather low PDI at low composition of the P(St-co-Bd) segment. With more incorporation of butadiene, the branching reaction of polybutadiene became obvious, leading to higher PDI and positive deviation of Mn from the theoretical predication. At the gel point, the composition of the P(St-co-Bd) segment was estimated to be 0.72. After this, the gel fraction increased quickly. The morphology of structured nanoparticles could be largely tuned simply by the copolymer composition. With the composition of the P(St-co-Bd) segment increased from 0.37 to 0.92, the morphology within the structured particles changed from the polybutadiene domains-in-polystyrene matrix, perforated concentric-spherical layer, concentric-spherical multi-layers, bi-continuous, to broken layers of polystyrene in polybutadiene matrix. It was found that the morphology of the block copolymer within nanoparticles was dependent on d/L values, which was in excellent agreement with the theoretical prediction.

Monte Carlo simulation of tri-functional branching and tetra-functional crosslinking in emulsion polymerization of butadiene

A direct Monte Carlo method is used to simulate the effect of tri-functional long chain branching and tetra-functional crosslinking on molecular weight distribution in emulsion polymerization of butadiene. Butadiene polymerization, due to high extent of reaction with internal or pendant double bonds of polymer chains, can be used as a model to study the effect of tetra-functional crosslinking on polymer microstructure. In this simulation, elementary reactions included propagation, chain transfer to monomer, termination by disproportionation, transfer to C–H bond (BN3) and reaction with internal or pendant CC bond (CL4) of growing and dead polymer chains. The initial polymerization volume of the simulation was 105nm3. The ratio of monomer to initiator concentration and initiator to polymer particles were 500 and 2.5, respectively, and the number of simulated polymer particles were 400. For simulated conversions in the range of 20–75% a bimodal molecular weight distribution was observed. The maximum of the second peak of the bimodal distribution moved to higher molecular weights as the conversion was increased. As the conversion was increased from 20 to 75%, the increase in the number average molecular weight of the polymer was linear but a slight increase in the slope of the weight average molecular weight was observed. More importantly, as the conversion was increased, a relatively sharp change in the slope of the weight fraction of the second peak of the molecular weight distribution curve was observed at approximately 20% conversion. According to the results, in polymerization systems with high extent of tetra-functional crosslinking, the development of the molecular weight distribution in emulsion polymerization is different from bulk systems.

Stereoregular emulsion polymerization of butadiene

The stereoregular emulsion polymerization of butadiene was performed with a cobalt catalyst (J. N. Henderson et al., U.S. Patent 4,429,085, 1984; H. Ono et al., Jpn. Open Patent 85-147410, 1985; H. Ono et al., Jpn. Open Patent 85-161408, 1985; H. Ono et al., Jpn. Open Patent 85-14711, 1985; H. Ono et al., Jpn. Open Patent 86-69818, 1986; H. Ono et al., Jpn. Open Patent 86-23610, 1986). This is the first report of a successful highly stereoregular emulsion polymerization with water as the solvent (H. Ono et al., Jpn. Open Patent 85-14711, 1985; H. Ono et al., Jpn. Open Patent 86-69818, 1986; H. Ono et al., Jpn. Open Patent 86-23610, 1986); water is usually recognized as a strong inhibitor of transition-metal polymerization. By analyzing the addition order effect of the ingredients, we show that the reduction of cobalt in the presence of butadiene is necessary for the polymerization. Radical-polymerization inhibitors such as phenols did not terminate the polymerization reaction, but sulfur did. Moreover, the valence of the reduced cobalt butadiene complex catalyst is considered zero. The zero-valent cobalt is classified as a soft acceptor, butadiene is a soft donor, and water is a hard acceptor. In this article, we discuss the reason butadiene could be polymerized stereoregularly by an emulsion system.

Synthesis of poly(dimethylsiloxane) and poly(butadiene) composite particles and the properties of their grafted polymer particles

Micro separated composite polymer particles comprising of poly(dimethylsiloxane) (PDMS) and poly(butadiene) (PB) were prepared by an emulsifier-free seeded emulsion polymerization of butadiene with a radical initiator in the presence of a PDMS latex. The following three factors controlled the morphology of the particles: (i) cross-linking degree of PDMS; (ii) cross-linking degree of PB; and (iii) source of polymerization initiator. By decreasing the cross-linking degree of PDMS or PB, we obtain segregated PB from PDMS. An initiation system consisting of tert-butyl peroxylaurate and ferrous sulfate gave the hemispherical morphology in contrast to the core shell for potassium persulfate. Styrene and acrylonitrile were able to graft onto the PB phase of the particles with high efficiency. The corrections between the morphology of the composite polymer particles and the practical properties of poly(styrene-co-acrylonitrile)-modified graft polymers were also discussed.

Synthesis of poly(tetrafluoroethylene)/poly(butadiene) core-shell particles and their graft copolymerization

This article describes how to convert the unreactive surface of poly(tetrafluoroethylene) (PTFE) into poly(styrene-co-acrylonitrile) (SAN). Composite particles with a crosslinked poly(butadiene) (PB) shell covered over a PTFE core were prepared by an emulsifier-free seeded emulsion polymerization of butadiene in the presence of PTFE latex. It was found that the increase in the PB crosslink density resulted in depressing the formation of PB secondary particles. Then, styrene and acrylonitrile were able to graft onto PB shell in high efficiency of 70%. SAN-modified PTFE/PB core-shell particles could eventually be dispersed homogeneously in a SAN matrix. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:185–190, 1998

Particle growth in butadiene emulsion polymerization, 4. The promoting effect of mercaptans

AbstractThe observation that butadiene emulsion polymerizations in the presence of fatty acid emulsifiers need minimal amounts of tertiary or n‐dodecanethiols to polymerize at a reasonable rate is often referred to as the promoting effect of mercaptans and is evaluated in this paper. Experimental evidence is presented which shows that fatty acid emulsifiers can actively reduce the average number of radicals per particle. In this paper it will be shown that three components are necessary for retardation of the rate of polymerization in the absence of dodecanethiol to occur: (1) Only diene monomer polymerizations show retardation. (2) Only peroxodisulfate‐initiated polymerizations show retardation. (3) Retardation of the rate of polymerization only occurs in the presence of fatty acid emulsifiers. These three components are combined for the first time in a reaction scheme which is an extension of a reaction scheme proposed by Kolthoff in 1951. Experimental evidence justifies the suggestion that reaction between a fatty acid radical and butadiene play an important role in the promoting effect.

Particle growth in butadiene emulsion polymerization, 1. The use of Fremy salt as aqueous radical scavenger

AbstractThe kinetics of the seeded emulsion polymerization of butadiene in combination with variable Fremy salt (potassium nitrosodisulfonate) concentrations was investigated in order to monitor non‐steady state kinetics necessary for obtaining information on entry and exit of radicals from latex particles. Fremy salt is used because it is an entirely water‐soluble stable radical that in principle can scavenge water‐soluble radicals produced by a water‐soluble initiator like peroxodisulfate, but allegedly will not interfere with radicals within latex particles. Adequate buffering of the pH is a prerequisite for stable Fremy salt concentrations in time. Emulsion polymerizations in the presence of Fremy salt showed that not all radicals in the aqueous phase of a swollen polybutadiene latex are scavenged. The use of Fremy salt to monitor non‐steady state kinetics in the seeded emulsion polymerization of butadiene in the presence of tertiary dodecyl mercaptan yields no satisfying results. The use of Fremy salt seems to be restricted to systems where the rate of polymerization is strongly influenced by variation in initiator concentration, i.e. the styrene system or the butadiene system in the absence of tertiary dodecyl mercaptan.

Particle growth in butadiene emulsion polymerization, 2. Gamma radiolysis

AbstractThe kinetics of the emulsion polymerization of butadiene at 60°C in Smith‐Ewart interval III were investigated using gamma radiation to produce initiating species. The aim of this work was to determine radical desorption rate coefficients through monitoring non‐steady state kinetics. The acquired data of the average number of radicals per particle (n) were in good agreement with data obtained from chemically initiated experiments. It was shown that the approach to steady state is kinetically determined and that thermal background initiation is negligible in the butadiene emulsion polymerization. While radical desorption rate coefficient data was determined with high uncertainty, the results are consistent with the transfer diffusion mechanism of radical exit.

Particle growth in butadiene emulsion polymerization, 3. Radical adsorption and desorption rate coefficients

AbstractThe kinetis of the emulsion polymerization of butadiene at 60°C in Smith‐Ewart interval III were investigated using peroxodisulfate as initiator. The aim of this work was to obtain insight in the radical adsorption and desorption rate coefficients through monitoring non‐steady state kinetics. The acquired data shows an initiator concentration dependence of the desorption rate coefficients. This dependence explains the independences of the rate of butadiene emulsion polymerization of the peroxodisulfate concentration in the presence of tertiary dodecylthiols.

Seeded emulsion polymerization of butadiene. 2. Effects of persulfate and tert-dodecyl mercaptan

The kinetics of the emulsion polymerization of butadiene at 60 C in Smith-Ewart interval I11 were investigated using sodium peroxodisulfate (persulfate) as initiator. The aim of this work was to elucidate and model the persulfate initiator efficiency. Monomer conversion was based on gravimetrically calibrated on-line densitometry. Plots of the product of the propagation rate coefficient, k,, and the average number of radicals per particle, a, versus initiator concentration showed minimal dependence on the initiator concentration if tert-dodecyl mercaptan (TDM) was present during polymerization. These results could not be modeled using normal emulsion polymerization theory. The model used in the absence of TDM fits two separate sets of data, a versus particle diameter and a versus initiator concentration. In the absence of TDM, a depends strongly on the initiator concentration. The significant effect of TDM is ascribed to a decrease in the radical desorption. A possible effect on the radical absorption is refuted on the basis of theory and experiment.

Seeded emulsion polymerization of butadiene. 1. The propagation rate coefficient

The kinetics of the emulsifier free seeded polymerization of butadiene at 60-degrees-C in Smith-Ewart interval Ill was investigated using sodium peroxodisulfate as initiator. The aim of this work was to measure the propagation rate coefficient (k(p)) of butadiene at 60-degrees-C in emulsion polymerization. Model-independent techniques to measure propagation rate coefficients like spatially intermitted polymerizations1-3 (''rotating sector'' and ''laser flash'' photolysis) have not been used for butadiene so far since network formation prevents acquiring the necessary data from GPC. All experiments were conducted in the presence of tert-dodecylmercaptan, as is usual in industrial practice. The fractional conversion was based on gravimetrically calibrated on-line densitometry and was found to be highly accurate. By analogy with the well-known Ugelstad plots, the product of the propagation rate coefficient (k(p)) and the average number of radicals per particle (nBAR) versus seed latex particle diameter clearly shows Smith-Ewart caseI and case II regimes. From a constancy in values of k(p)nBAR (case II regime) in this plot, a value for k(p) could be calculated that was 3 times larger than the current literature value. It was found that negligible ''thermal background initiation'' is present in the butadiene system. Two linear regions in polymerization rate are observed in interval III. Model calculations are presented in excellent agreement with the experimental data. From these calculations a value of the rate coefficient for transfer to monomer, k(tr) could be estimated.

Emulsion polymerization of butadiene, 4. Effect of thiols

AbstractThe role of thiols of low water solubility, commonly used in the emulsion polymerization of butadiene, has been considered. The following effects have become apparent: (1) dodecanethiols act as efficient chain transfer agents in limiting the formation of heavily cross‐linked polymer networks; (2) the monomer concentration within the particles is not influenced by such thiols; (3) C12‐thiol radicals do not desorb because of their extremely low water solubility. The ‘promoting effect’ of thiols in emulsion polymerizations of diene‐hydrocarbons is still poorly understood, but it appears to be related to impurities present in the emulsifier, as it was found completely absent in emulsifier‐free polymerizations.

Emulsion polymerization of butadiene, 3. Kinetic effects of stirring conditions and monomer/water ratio

The stirring speed n influences the emulsion polymerization of butadiene, (1) by reducing the effective emulsifier concentration [E]eff available for particle nucleation and stabilization at high n, and (2) by limiting diffusion of monomer to the latex particles at low n. The large density difference between butadiene and water promotes the breaking up of droplets at high n, while the same condition constitutes a large driving force for (partial) phase separation at low n. Increasing the monomer/water ratio at constant [E] decreases [E]eff, and thus the final particle number. At monomer volume fractions >0,6 mixed emulsions are likely to be formed initially, reducing [E]eff even further. In the presence of mixed emulsions, polymerization in the monomer phase may no longer be neglected, giving rise to a complex kinetic behaviour.

Kinetic aspects of the emulsion polymerization of butadiene

Kinetic information on particle growth is obtained for the ab initio emulsion polymerization of butadiene. It is shown that the decrease in particle number by coagulation (induced by the high ionic strength) hardly affects polymerization rate, since the average number of radicals per particle (n) increases with particle size. From a rate analysis of intervals II and III it follows that the system is (n ≤ 0.5), i.e., termination is not rate-determining. Zero-one kinetics, in combination with a low initiator efficiency, explains the small effect of initiator concentration on polymerization rate. The radical loss mechanism responsible for the zero-one kinetics could not be established unambiguously, but chain transfer/desorption processes involving polybutadiene, thiol, surfactant, and the Diels-Alder dimer 4-vinyl-1-cyclohexene were all refuted on experimental grounds. Desorption of monomeric species seems a reasonable explanation, given the rather low estimate for the propagation rate coefficient.

Swelling of polybutadiene as latex particles and cast films by styrene and acrylonitrile monomers

During emulsion polymerization, the diene structure of butadiene leads to the formation of a network by crosslinking on the residual double bonds. Investigation of the swelling of polybutadiene particles and films cast from latexes, by styrene and acrylonitrile, was carried out in order to get more information on polymer structure and behaviour in the presence of monomers. A thermodynamic approach has permitted us to determine several parameters, such as the average number of butadiene units between two crosslinking points, which represents the crosslink density and was compared with data from simulation of butadiene emulsion polymerization. Swelling by monomer mixtures of various compositions has shown a preferential solvation of styrene as a function of comonomer composition. Comonomer composition in the particles is important in the final structure of an acrylonitrile-butadiene-styrene particle prepared by emulsion polymerization of styrene-acrylonitrile on a polybutadiene seed. Diffusion coefficients of monomers were determined after a kinetic study.

Emulsion polymerization of butadiene, 2. Polymerizations with sodium dodecyl sulfate

AbstractThe emulsion polymerization of butadiene was investigated with sodium dodecyl sulfate as emulsifier, and the results were compared with those obtained with the industrial‐grade emulsifier Dresinate 214. Limited coagulation was observed in both cases, caused by the high ionic strength of the aqueous phase. Sodium dodecyl sulfate was found to be a better stabilizer than Dresinate 214. The average rate per particle in interval II (corresponding to the linear portion of the conversion vs. time curve) depends strongly on particle size, but not on recipe parameters used to vary the final particle diameter, such as the type and amount of emulsifier and ionic strength. The dependence of particle number per volume of water N on initiator ([I]) and emulsifier concentration ([E]) is usually expressed as the exponent in the empirical relationship N ∼ [I]x · [E]y. Promoting coagulation by increasing the ionic strength decreases x towards zero, while y increases sharply. Increasing [I] at constant [E] and constant ionic strength induces limited coagulation, presumably because the rate of emulsifier adsorption becomes insufficient.

Emulsion polymerization of butadiene, 1. The effects of initiator and emulsifier concentration

AbstractThe kinetics of the emulsion polymerization of butadiene was investigated using Dresinate 214 as emulsifier and three dissociative initiators, viz. potassium peroxodisulfate, 4,4′‐azobis‐(4‐cyanopentanoic acid) and 2,2′‐azoisobutyronitrile. All experiments were conducted in the presence of a thiol as chain transfer agent, as usual in diene‐polymerizations. The polymerization rate in interval II, Rpol, was found to be highly insensitive to changes in the initiator concentration (Rpol ∝ [I]0,08). Primary radicals are generated in large abundance in interval I as compared with the final particle number, indicating that the initiator efficiency with regard to particle nucleation is very low. The development of particle number as a function of conversion at several emulsifier concentrations shows that limited coagulation is occurring in the present system. Rpol depends on the emulsifier concentration with an exponent of 0,61, while the final particle number after cessation of coagulation depends on the emulsifier concentration to the 1,6th power. As a consequence the average number of radicals per particle must be a function of particle size, because the monomer concentration in the latex particles is approximately constant in interval II. A certain analogy in behaviour between the emulsion polymerization of various polar monomers, kinetically dominated by radical desorption, and the emulsion polymerization of butadiene, suggests that similar events determine the kinetic course in the present system.