Polybutadiene solution process

A flow scheme of m-1,4-polybutadiene production involving polymerisation with cobalt-based Ziegler-Natta catalysts in a solution process with the removal of catalyst residues from the polymer is presented in Figure 5.13 [227]. 

Polybutadiene is usually produced by alkali metal, and transition metal coordination solution processes. Most production is based on the solution processes because of the ability to obtain preferred microstructures by these routes. 

Fig. 16.2. Flow diagram for a typical solution process for the manufacture of polybutadiene. (Courtesy of Firestone Polymers, Akron, Ohio.)...

Both the monomer and polymer are soluble in the solvent in these reactions. Fairly high polymer concentrations can be obtained by judicious choice of solvent. Solution processes are used in the production of c(5-polybutadiene with butyl lithium catalyst in hexane solvent (Section 9.2.7). The cationic polymerization of isobutene in methyl chloride (Section 9.4.4) is initiated as a homogeneous reaction, but the polymer precipitates as it is formed. Diluents are necessary in these reactions to control the ionic polymerizations. Their use is avoided where possible in free-radical chain growth or in step-growth polymerizations because of the added costs involved in handling and recovering the solvents. 

Solution polymerization. Solution polymerization involves polymerization of a monomer in a solvent in which both the monomer (reactant) and polymer (product) are soluble. Monomers are polymerized in a solution that can be homogeneous or heterogeneous. Many free radical polymerizations are conducted in solution. Ionic polymerizations are almost exclusively solution processes along with many Ziegler-Natta polymerizations. Important water-soluble polymers that can be prepared in aqueous solution include poly(acrylic acid), polyacrylamide, poly(vinyl alcohol), and poly(iV-vinylpyrrolidinone). Poly(methyl methacrylate), polystyrene, polybutadiene, poly(vinyl chloride), and poly(vinylidene fluoride) can be polymerized in organic solvents. 

The manufacture of polybutadiene rubber (BR), which is carried out mainly in solution processes using butyllithium or the Ziegler-Natta-type catalysts mentioned in Table 1, has some general features in common, despite the different catalyst systems [83]. The feed requirements for polymerization using Ziegler-Natta or... 

Polybutadiene is usually produced by alkali metal or transition metal coordination solution processes, which allow the production of a variety of the desired DPs and microstructures. Alkali metal-based polymerization (usually alkyllithium) produces a product with about 36% cw-1,4-, 54% ran -l,4-, and 10%i 1,2-PB. The polymerization process is conducted in an aliphatic... 

The solution of the inverse MWD problem using the Tikhonov regularisation method has revealed that the traditional polybutadiene polymerisation process with TiCl4-A1(2-C4H9)3 occurs in the presence of four types of AC. The location of the maximums on the kinetic inhomogeneity curves corresponds to the following intervals of MW values (each type synthesises different polymer fractions) lnM = 9.2-10.4 - Type I 11.2-11.4 - Type II 12.9-13.2 - Type III and 14.1-14.7 - Type IV. 

The polybutadiene produced by solution processes must be adequately des-olvated in order to maintain low residual monomer and solvent in the product. Steam stripping is often employed in commercial processes in order to recover the solvent for recycling, followed by mechanical dr5ung (extruder) and/or hot air drying of the wet polymer crumb. 

Developments in the anionic polymerization of butadiene were adopted for manufacture of solution SBR. While the emulsion process gave primarily 1,4-cis microstructure in the final product, the solution process gave a lower level of 1,4-cis level, typically around 45%. Furthermore the cis content as well as 1,2-vinyl content could be modified. In addition, better control of branching and molecular weight distribution attainable with anionic process made solution SBR suitable for tire applications, challenging the established use of cold SBR. Developments in the anionic process also led to new copolymer structures in which blocks of polybutadiene can be coupled to blocks of polystyrene, generating a imique class of polymers. Developments in SB block copolymers led to new materials which were thermoplastic in character, unlike SBR which is an elastomer. Solution-processes-based thermoplastic SB block copolymers form the basis of the transparent impact polystyrene (TIPS) as well as the other block copolymers used in plastics modification. The block copolymers of styrene and butadiene are the subject of the second part of this article. 

Koike, A. Nemot, N. Watanabe, Y. Osaki, K. (19%) Etynamic Viscoelasticity and FT-IR Measurements of End-Crosslinking a, co-Dihydroxyl Polybutadiene Solutions near the Gel Point in the Gelation Process, Polym.., Vol.28, 942-950. 

Polybutadiene is first solubilized in styrene, which plays the role of a solvent. Upon polymerizing, the polystyrene formed is still in a minor proportion— compared to the polybutadiene present—and is thus dispersed as nodules in the polybutadiene solution. As the yield of styrene increases, the polystyrene phase becomes predominant, provoking an inversion of phases and in turn the dispersion of the polybutadiene phase in the PS matrix. Figure 5.37 shows the various steps of such a process. 

M ass Process. In the mass (or bulk) (83) ABS process the polymerization is conducted in a monomer medium rather than in water. This process usually consists of a series of two or more continuous reactors. The mbber used in this process is most commonly a solution-polymerized linear polybutadiene (or copolymer containing sytrene), although some mass processes utilize emulsion-polymerized ABS with a high mbber content for the mbber component (84). If a linear mbber is used, a solution of the mbber in the monomers is prepared for feeding to the reactor system. If emulsion ABS is used as the source of mbber, a dispersion of the ABS in the monomers is usually prepared after the water has been removed from the ABS latex. 

In process variants for HIPS ( 7, 28), the feed solution to the first reactor, besides styrene and ethylbenzene, will also contain dissolved polybutadiene rubber along with antioxidants, chain transfer agents, and possibly mineral oil. 

The information on physical properties of radiation cross-linking of polybutadiene rubber and butadiene copolymers was obtained in a fashion similar to that for NR, namely, by stress-strain measurements. From Table 5.6, it is evident that the dose required for a full cure of these elastomers is lower than that for natural rubber. The addition of prorads allows further reduction of the cure dose with the actual value depending on the microstructure and macrostructure of the polymer and also on the type and concentration of the compounding ingredients, such as oils, processing aids, and antioxidants in the compound. For example, solution-polymerized polybutadiene rubber usually requires lower doses than emulsion-polymerized rubber because it contains smaller amount of impurities than the latter. Since the yield of scission G(S) is relatively small, particularly when oxygen is excluded, tensile... 

Firestone and Shell started commercial production of cis-polyisoprene by the anionic process in the 1950 s but these plants are no longer in operation now. About the same time, Phillips started the manufacture of polybutadienes by the anionic route and ever since, there has been a steady growth in their use, particularly in the tire-tread as well as tire-carcass formulations. These solution polybutadienes, generally, have low vinyl contents but recently, Phillips has found some interesting applications for medium vinyl polybutadienes as well.14 Polybutadienes with 50-55 percent vinyl contents behave like emulsion polymerized SBR in tire tread formulations and exhibit very similar tread... 

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