Emulsion Copolymerization Of Butadiene Research Articles

Modelling and Simulation of the Chemical Homogeneity of the Butadiene—Styrene Copolymer in High-Conversion Emulsion Copolymerization

The emulsion copolymerization of butadiene with styrene is an example of a commercial process whose selectivity and specificity may be highly improved by technological means feasible now through modelling and simulation, although the basic chemical reactions are neither selective nor specific. To obtain optimum properties of the final rubber, optimum chemical composition is necessary; but since the composition changes during the copolymerization with the conversion of monomers, the resulting copolymer has a heterogeneous chemical composition. This is one of the obstacles to effecting the high-conversion copolymerization. Simulation of the copolymerization under dosing of the more reactive monomer, i. e., butadiene has shown that an improvement in the chemical homogeneity of the copolymer by 17 times at the conversion of 98% is feasible. A mathematical model accounting for all important effects in the emulsion copolymerization was developed; the most plausible parameters of the model were evaluated by starting from published data; and the simulation was performed by means of programs developed in Fortran for the ICL 2903 computer.

Regulation of molecular weight of styrene–butadiene rubber. II. Influence of variation of polymerization recipe on the regulating efficiency of diisopropyl xanthogen disulfide

AbstractThe influence of kind and amount of an anionic emulsifier, pH of water phase, addition of free rosin, and content of conjugated structures in rosin on the regulation efficiency of diisopropyl xanthogen disulfide in emulsion copolymerization of butadiene with styrene at +5°C. was studied. The apparent chain transfer constant C decreased in the order: Li+ > Na+ > K+, for the cations with the hydrolysis of rosin soap. This soap is replaceable with other anionic emulsifiers, C being dependent on the absorption area of one soap molecule. With increasing amount of soap the value of C decreased. With the decreasing pH of the water phase, the value of C increases. This fact can be explained by the increase in hydrolysis of carboxylic groups of rosin and oleate soaps and an increase in the permeability of the monomer–polymer particle surface to molecules of regulator. This tendency does not exist in the case of sulfonate‐type soaps. After addition of free rosin to the monomer phase, a similar increase in C is noted. The value of C increased also with an increase in the content of conjugated structures characterized by a value δ, which is related to the retardation of polymerization. The standard polymerization recipe at pH 10.8 is suitable from the point of view of using diisopropyl xanthogen disulfide as a molecular weight regulator.

Emulsion copolymerization of butadiene and styrene in the presence of carbon black

AbstractCarbon blacks inhibit and retard free radical polymerization in bulk and solution. The mechanism of this is discussed in terms of the chemical groups present on the carbon surface. It is shown that the number of free radicals which react during the induction period (polymerization of styrene with AIBN) is much less than the number of quinone groups but of the same order of magnitude as the number of easily oxidizable groups. Inhibition by carbon black was also found in an emulsion polymerization system with cumene hydroperoxide as initiator (no reducing components). By use of highly active redox recipes, reasonable rates of polymerization were obtained at both 50°C. (sugar‐iron‐hydroperoxide recipe) and 5°C. (peroxide‐polyamine recipe), with as much as 40 parts of black per 100 parts of monomers. In these systems, the carbon black was charged as an aqueous dispersion stabilized with Daxad 11; the latices were stable and showed evidence of association between some of the carbon black and some of the latex particles. The coagulated rubber stocks, when compounded and cured, gave properties closely similar to those of dry mixed stocks.

Copolymerization of dienic hydrocarbons with alkyl vinyl ethers Communication 2. Low-temperature emulsion copolymerization of butadiene with alkyl vinyl ethers

1. In the emulsion copolymerization of butadiene with alkyl vinyl ethers in an alkaline medium the specific action of carbon tetrachloride is suppressed and the process proceeds almost entirely by the free-radical mechanism. 2. Introduction of ether units greatly reduces the molecular weight of polybutadiene (from 108,000 to 3,000). 3. The introduction of up to 20% of ether units in the polybutadiene chain has little effect on its stability to frost (TV = − 84°). When there is a predominance of ether units (70%), the stability to frost is greatly reduced (TV = − 30°), though the chemical stability is increased.

Redox recipes. VI. Redox systems containing potassium chromate as oxidizing constituent

AbstractThe emulsion copolymerization of butadiene (75)‐styrene (25) is initiated by redox systems containing potassium chromate as oxidizing constituent. In alkaline (soap) recipes, the system chromate‐arsenic trioxide is especially effective, giving a rate of conversion of about 20% per hour at 30°C. with 5 parts of potassium myristate (0.3 part of potassium chromate and 0.07 part of arsenic trioxide per 100 parts of monomers). Other fatty acid soaps or sodium alkyl sulfate may be used instead of myristate, although no other soap or emulsifier tested gives a rate as large as does myristate. Mercaptan has a slight accelerating effect but the presence of mercaptan is not necessary for initiation of polymerization. The use of arsenic trisulfide as reducing agent gives rise to rapid polymerization but the rates vary with different suspensions of arsenic trisulfide. Potassium antimonyl tartrate also may be used in combination with chromate to give rapid polymerization at 40°C. with fatty acid soap. Tin(II) is much less effective than either arsenic(III) or antimony(III). Inorganic reducing agents which in combination with chromate are inefficient in initiating the copolymerization include iron(II), thallium(I), dithionite, hydrazine, hydroxylamine, and sulfide.

Emulsion Copolymerization of Butadiene and Styrene at Low Temperatures1

Emulsion Copolymerization of Butadiene and Styrene at Low Temperatures¹

Use of cobalt complexes as activators in emulsion copolymerization of butadiene and styrene

AbstractCobalt complex compounds exhibited varying degrees of activation and retardation in butadiene‐styrene‐soap emulsion polymerization systems at 20–50°C. An accompanying effect was the wasting of modifier, particularly by large concentrations of activator. The most active complexes for use with dodecyl mercaptan were those in which the cobalt was coordinated with two or more negative groups other than thiocyanate, and in which the neutral coordinated groups were not ethylenediamine.

Mercaptans as promoters and modifiers in emulsion copolymerization of butadiene and styrene using potassium persulfate as catalyst. I. Mercaptans as promoters

AbstractThe rate of emulsion copolymerization of butadiene and styrene, with soap as emulsifier and potassium persulfate as catalyst, is extremely small at 50°C. The presence of very small amounts of high‐molecular mercaptans promotes the copolymerization reaction. The promoting effect is at a maximum for primary, secondary, and tertiary dodecyl mercaptans and decreases for mercaptans of either higher or lower molecular weight. The promoting effect is independent within wide limits of the amount of mercaptan added after the minimum quantity has been exceeded. Mercaptans which are poor promoters may be so because they fail to bring about chain initiation or because they aid in chain termination. The low‐molecular mercaptans which are poor promoters prevent the high‐molecular mercaptans from exerting their good promoting effect when a mixture of both types of mercaptans is used. The mechanism of the promoting effect of mercaptans upon the emulsion copolymerization of butadiene (75 parts) and styrene (25 parts) or upon the polymerization of butadiene alone is not yet clear.

Mercaptans as promoters and modifiers in emulsion copolymerization of butadiene and styrene using potassium persulfate as catalyst. II. Mercaptans as modifiers

AbstractA close correlation exists between the modifying effect of mercaptans in emulsion copolymerization of butadiene (75 parts) and styrene (25 parts) and mercaptan consumption during the polymerization. A procedure is described for the rapid amperometric titration of mercaptans in latices. Mercaptan disappearance curves (i.e., mercaptan used at various conversions) are given for a series of primary and tertiary mercaptans of widely varying molecular weight and of two secondary mercaptans. The consumption of (and modification by) primary mercaptans is affected to a much greater extent by the molecular weight of the mercaptan than that of tertiary mercaptans. The consumption of pure and of commercial n‐dodecyl mercaptan is greatly affected by the mode and rate of agitation during the polymerization, manner of preparation of the charge (preformed soap and soap “in situ,” separate emulsification of the modifier), dilution of the monomers with inert organic solvents, excess of free caustic in the charge, amount and kind of emulsifier, and the presence of substances which from complexes with the mercaptan. The consumption of tertiary dodecyl mercaptan is not affected by these variables. The difference in behavior between the two mercaptans is interpreted as a faster rate of solubilization into the locus of the reaction of tertiary mercaptans than of primary mercaptans of the same molecular weight. The disappearance curve of a mercaptan from a mixture of two mercaptans remains unaffected by the presence of the other mercaptan. At the same conversion the consumption of a mercaptan increases with decreasing temperature. Disappearance of mercaptan during the polymerization as a result of nonmodifying reactions is discussed.

Mercaptans as promoters and modifiers in emulsion copolymerization of butadiene and styrene using potassium persulfate as catalyst. III. Calculation of molecular weights and intrinsic viscosities of polymers from mercaptan consumption data

AbstractAn empirical equation is described which predicts the intrinsic viscosities of 75:25 butadiene‐styrene emulsion copolymers from data on mercaptan consumption. The form of the equation is as follows: where [η] is the intrinsic viscosity, P is the conversion, R is the fraction of mercaptan consumed, R0 is the mercaptan charged, and a, b, and c are constants equal to 0.22, 1.12, and 0.66, respectively. Evidence is given that the intrinsic viscosity of mutual‐recipe polymers can be described satisfactorily in terms of mercaptan consumption.

Mercaptans as promoters and modifiers in emulsion copolymerization of butadiene and styrene using potassium persulfate as catalyst. IV. Definition and calculation of modifier efficiency

AbstractThe calculation of the “theoretical” minimum modifier requirement, TMMR, for butadiene‐styrene (75:25) copolymers of given intrinsic viscosities at various conversions is described. The TMMR of 75% conversion polymer of intrinsic viscosity 2.0 is R0 = 0.28, which is only about 60% of the value of R0 for commercial primary dodecyl mercaptan (C.M.) in large‐size reactors. The efficiency, E, of a modifier for 75:25 butadiene‐styrene copolymerization using soap as emulsifier and persulfate as catalyst has been defined by and calculated from the equation: where Mv is the intrinsic viscosity molecular weight of the polymer at conversion, P, with an amount of mercaptan, R0, charged with the monomers. For all modifiers the efficiency is low at low conversions and gradually increases to a maximum with increasing conversion. For different modifiers this maximum may be as at low as 10% conversion or at higher than 80% conversion. After the maximum the efficiency decreases with further increase of conversion. The most efficient modifier for the production of polymers of intrinsic viscosity, [η], at conversion, P, will meet the following conditions, R = 1 at conversion, P, and dP/dR is constant. Inefficient modifiers may be made more efficient by changing the conditions or procedure of polymerization in such a way that the modifier more nearly complies with the above conditions.