Of styrene-butadiene block

Anionic polymerization, if carried out properly, can be truly a living polymerization (160). Addition of a second monomer to polystyryl anion results in the formation of a block polymer with no detectable free PS. This technique is of considerable importance in the commercial preparation of styrene—butadiene block copolymers, which are used either alone or blended with PS as thermoplastics. 

Table 16.6 Some typical properties of styrene-butadiene block copolymer thermoplastics (Phillips K-Resins)...

The work was planned on the basis of a model of a dispersed solid particle onto which one type of sequences of a BG copolymer is adsorbed selectively while the other type sequence is dissolved in the dispersion medium. A sketch of this model is shown in Figure 1. The model is the result of applying the same arguments which had been advanced (12) in discussing the mechanism of stabilization of polymeric oil-in-oil emulsions by BG copolymers to the problem of stabilization of dispersions of solid particles in organic media. Previously, essentially the same arguments had led to the demonstration of micelle formation of styrene-butadiene block copolymers in organic media under certain conditions (15). 

Morphology and Dynamic Viscoelastic Behavior of Blends of Styrene-Butadiene Block Copolymers... 

The Impact Strength of Styrene-Butadiene Block Copolymer and Its Dependence on the Continuous Phase... 

Other rubber systems have been commercially successful. Styrene block copolymers yield a HIPS product with a small particle size and provide high gloss. A mixed rubber system consisting of styrene-butadiene block rubber and/or ethylene-propylene diene modified (EPDM) rubber can be blended with the polybutadiene to form bimodal rubber particle size distribution for a... 

In the case of mass ABS, the variety of rubber particle morphology is less diverse. Typical examples of morphology are shown in Figure 14.6. If polybutadiene rubber is used (linear or star), cellular particles are obtained with SAN occlusions. In the case of styrene-butadiene block rubber (typically 30% styrene) also cellular particles are obtained but besides the SAN occlusions, polystyrene domains are clearly visible in the particles. To be able to make the other morphologies that are possible in HIPS, the interfacial tension has to be manipulated. Controlling the grafting reaction is a way to achieve this but the possibilities are limited with the tools (mainly initiator) that are currently available. 

Granger, A. T., Wang, B., Krause, S., and Fetters, L. J., Glass transitions of both blocks of styrene-butadiene block copolymers, Adv. Chem. Sen, 211,127-138 (1986). 

Recent theories (4,5) indicate that a sharp boundary does not exist in polystyrene-polydiene block copolymers, but rather, partial mixing exists in the interfacial region between the two thermodynamically incompatible phases. The thickness of the interface is temperature dependent. With increasing temperature, intermixing of the two phases increases at the expense of the pure phases, but the copolymers remain phase segregated. Indeed, structural changes continue to exist well into the melt, but the two phase structure of styrene-butadiene block copolymers... 

The methods of both papers assume that the hydrodynamic volumes of the block copolymer sequences are additive, implying a negligible interaction between unlike segments. Chang s method [5] gave lower molecular masses than Runyon s method [4], but in the case of styrene-butadiene block copolymers in tetrahydrofuran (THF), the difference was negligible [5]. 

Styrene-butadiene block copolymers (SBC) with a high (70-85 %) styrene content are commercially produced and marketed as transparent, stiff, and tough thermoplastic resins under the trade names of Styrolux (Styrolution), K-Resin (Chevron-Phillips), Finaclear (Total petrochemical), and Clearene (Denka-Kaguku). Unlike other more elastomeric types of styrene-butadiene block copolymers, the rigid SBC resins contain only <25 % polybutadiene rubber content. Structurally, these SBC polymers are composed of polystyrene (S) and polybutadiene (B) blocks, linked together in an unsymmetrical star-block [(S-B)x] structure. 

Fig. 5. Log-log plot of mean sphere size as a function of the molecular weight of the butadiene block of styrene-butadiene block copolymers. Upper dashed line from Helfand NIA theory lower dashed line is a fit to Hashimoto s results. Ref.

Fig. 3.11. Illustration of phase structure of a thermoplastic rubber composed of styrene-butadiene block copolymers. The polystyrene molecules aggregate in glassy styrene domains which are linked together by the rubbery matrix in which the polybutadiene blocks have congregated (after Bull).

Adhikari Rameshwar, and Michler Goerg. Influence of molecular architecture on morphology and micromechanical behavior of styrene/butadiene block copolymer systems. Prog. Polym. Sci. 29 no. 9 (2004) 949—986. 

Spevacek, J. (1982) Proton NMR study of styrene-butadiene block copolymer micelles in selective solvents. Makromol Chem. Rapid Commun., 3,697-703. 

Sakurai K, Shirakawa Y, Kashiwagi T and Takahashi T, Crystal transformation of styrene-butadiene block copolymer . Polymer, 1992, 35(19), 4288 9. 

Adhikari R, Michler G H, Cagiao M E and Balta Calleja F J (2003) Micromechaiiical studies of styrene/butadiene block copolymer blends, J Polym Eng 23 177-190. Michler G H, Balta Calleja F J, Puente I, Cagiao M E, Knoll K, Henning S and Adhikari R (2003) Microhardness of styrene/butadiene block copolymer systems Influence of molecular architecture, J Appl Polym Sci 90 1670-1677. 

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