Styrene/butadiene star block copolymer

Tuzar and coworkers [294] investigated the micellization behavior of styrene-butadiene star-block copolymers with four arms and polybutadiene inner blocks in the mixed solvent tetrahydrofuran/ethanol, selective for polystyrene blocks. 

The viscoelastic properties of concentrated solutions of styrene-butadiene star-block copolymers were studied by Masuda et al. [296] in good solvents for both blocks and in selective ones. A significant dependence of the loss and storage moduli on the strain amplitude was observed in the case of dibutylphthalate, a selectively good solvent for the PS blocks at temperatures below 60 °C, which indicates the presence of a microdomain structure due to self assembling of the insoluble blocks. At a certain value of the applied strain the microdomain structure in solution was disrupted. 

Adh Adhikari, R., Buschnakowki, M., Henning, S., Huy, T. A., Godehardt, R., Michler, G. H., Each, R., Geiger, K., Knoll, K. Double yielding in a styrene/butadiene star block copolymer. Macromol. Rapid Commun. 25 (2004) 653-658. 

I Epoxy resin with 30 wt.% epoxidized SBS (styrene butadiene) star-block copolymer [1] ... 

Table 3. 2D results for the styrene/butadiene star block copolymer. 

Figure 17.8 TEM images of thin sections of (a) styrene/butadiene star block copolymer and (b) the blend of the star block copolymer with 80% by weight of general-purpose polystyrene [69].

Figure 17.8a is the TEM image of a styrene/butadiene star block copolymer containing 74% (by volume) styrene. The nanostmctured morphology arises from the fact that the constituents - that is, polystyrene (PS) and polybutadiene (PB) chains -are connected chemically by covalent bonds which do not permit a macroscopic segregation of the polymer chains. Due to the presence of a unique molecular architecture of the copolymer, the star block copolymer was found to show a cocontinuous arrangement of the nanostmctures [69-72]. The star block copolymer specimen was treated -with osmium tetroxide vapor prior to TEM imaging such treatment... 

Using the same method Storey et al. prepared ionic star—block copolymers.55-58 Styrene was oligomerized followed by the polymerization of butadiene. The living diblock copolymer was subsequently linked with methyltrichlorosilane to provide a three-arm star—block copolymer of styrene and butadiene. Hydrogenation of the diene blocks and sulfonation of the styrene blocks produced the desired ionic star-block structure having ionic outer blocks and hydro-phobic inner blocks, as depicted in Scheme 13. 

Despite the drawbacks of this method, it has been used to prepare a tremendous number of polypeptide hybrid block copolymers (Table 1), and when carefully executed provides reasonably well-defined samples. Synthetic polymer domains have been prepared by addition polymerization of conventional vinyl monomers, such as styrene and butadiene, as well as by ringopening polymerization in the cases of ethylene oxide and e-caprolactone. The generality of this approach allows NCA polymerization off of virtually any primary amine functionality, which was exploited in the preparation of star block copolymers by polymerization of sarcosine NCA from an amine-terminated trimethyleneimine dendritic core [37]. In most examples, the polypeptide domain was based on derivatives of either lysine or glutamate, since these form a-helical polypeptides with good solubility characteristics. These residues are also desirable since, when deprotected, they give polypep-... 

Workers have reported the use of silicon tetrachloride to prepare 3 or 4 arm star-block copolymers of butadiene-styrene(17,18) Silicon tetrachloride terminates several living macroanions at a single junction by halogen exchange. A 4-arm star block copolymer is represented below. 

The contour plot clearly revealed the broad chemical heterogeneity (y-axis, chanical composition) and the wide MMD (x-axis) of the mixture. The relative concentrations of the components were represented by colors. Sixteen major peaks were resolved with high selectivity. These correspond directly to the components. For example, peak 1 corresponds to the component with the highest butadiene content (80%) and the lowest molar mass (molar mass IM) whereas peak 13 relates also to a molecule with 80% butadiene content but a molar mass of 4M. Accordingly, peak 16 is due to the component with the lowest butadiene content and a molar mass of 4M, representing a four-arm star block copolymer with a styrene-butadiene content of 80 20. 

Serrano, E., Zubeldia, A. et al. Effect of different thermal treatments on the self-assembled nanostructures of a styrene-butadiene-styrene star block copolymer. Polymer Degradation and Stability, 83 (2004), p. 495-507... 

Michler GH, Adhikari R, Lebek W, Goerlitz S, Weidisch R, Knoll K. Morphology and micromechanieal deformation behavior of styrene/butadiene-bloek eopolymers. 1. Toughening mechanisms in asymmetric star block copolymers. J Appl Polym Sci 2002 85(4) 683-700. 

Closely related to these but thermoplastic rather than rubber-like in character are the K-resins developed hy Phillips. These resins comprise star-shaped butadiene-styrene block copolymers containing about 75% styrene and, like SBS thermoplastic elastomers, are produced by sequential anionic polymerisation (see Chapter 2). 

Block copolymer chemistry and architecture is well described in polymer textbooks and monographs [40]. The block copolymers of PSA interest consist of anionically polymerized styrene-isoprene or styrene-butadiene diblocks usually terminating with a second styrene block to form an SIS or SBS triblock, or terminating at a central nucleus to form a radial or star polymer (SI) . Representative structures are shown in Fig. 5. For most PSA formulations the softer SIS is preferred over SBS. In many respects, SIS may be treated as a thermoplastic, thermoprocessible natural rubber with a somewhat higher modulus due to filler effect of the polystyrene fraction. Two longer reviews [41,42] of styrenic block copolymer PSAs have been published. 

Styrene-butadiene block and star copolymers ABA block copolymers (A = styrene, B = butadiene or isoprene) Polycarbonates... 

Figure 9-19. A universal gel-permeation chromatography calibration curve obtained from measurements on linear poly(styrene) (O), comb-branched poly(styrene) (O ), star-branched poly(styrene) ( ), poly(methyl methacrylate) ( ), poly(vinyl chloride) (a) c -l,4-poly-(butadiene) (A), poly(styrene)-poly(methyl methacrylate) block copolymer (Qj ), random copolymer from styrene and methyl methacrylate O), and ladder polymers of poly(phenyl siloxanes) ( ) (according to Z. Grubisic, P. Rempp, and H. Benoit).

In addition, block copolymers can be produced by adding a second monomer once the first one has completely reacted. Tri- and multi-block copolymers can be prepared by subsequent additions of different monomers. Thus, styrene-butadiene-styrene tri-block copolymers produced by anionic polymerization are used as thermoplastic elastomers. Also, star and hyperbranched polymers can be obtained through this technique by simply using suitable initiation systems [17]. 

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