Block copolymers of polystyrene

Block copolymers of polystyrene with rubbery polymers are made by polymerizing styrene in the presence of an unsaturated rubber such as 1,4 polybutadiene or polystyrene co-butadiene. Some of the growing polystyrene chains incorporate vinyl groups from the rubbers to create block copolymers of the type shown in Fig. 21.4. The combination of incompatible hard polystyrene blocks and soft rubber blocks creates a material in which the different molecular blocks segregate into discrete phases. The chemical composition and lengths of the block controls the phase morphology. When polystyrene dominates, the rubber particles form 

---

Fig. 7. Data of Parsonage et al. [77] on the adsorption of a series of block copolymers of polystyrene-poly-2-vinylpyridine. The ordinate is the measured surface density ( d 2) reduced by the density required for the nonadsorbing chains to overlap the abscissa is the solvent-enhanced size asymmetry of the block copolymer defined under Eq. 26. The form of this plot is that suggested by Eq. 28...

Mani S, Weiss RA, Williams CE, Hahn SF. Microstructure of ionomers based on sulfonated block copolymers of polystyrene and poly(ethylene-afe-propylene). Macromolecules 1999 32 3663-3670. 

For (b), a block copolymer, in which one side of the block has affinity to the solvent and the other block to the polymer particle, is the most reasonable stabilizer. Block copolymers of polystyrene/halogenated polybutadiene, polystyrene/ polyethyleneglycol, and polystyrene/PDMS are examples of this type of stabilizer (12). When using a block copolymer, it is possible to provide appropriate amphiphilic and other surface properties by changing the block ratio. For example, when using a block copolymer of polystyrene/PDMS for polymerization of methyl methacrylate in hexane, the ratio of polystyrene/polydimehtylsiloxane should be below 4.4 (13). If the ratio is above 4.4, the block copolymer forms a stable micelle and will not function properly as a stabilizer. 

Block copolymers of polystyrene (PSt, hydrophobe) and polyoxyethylene (PEO, hydrophile) form spherical micelles in water when the length of water soluble PEO is significantly larger than that of the insoluble PSt portion of the molecule [62]. In analogy with low molecular weight surfactants, one defines the onset of intermolecular association as the critical micelle concentration (CMC). Theories of polymer micellization predict that the concentration of free, unassociated block copolymers is close to that of the CMC. 

Stabilization in Nonaqueous Radical Dispersion Polymerization with AB Block Copolymers of Polystyrene and Poly(dimethyl siloxane)... 

Molded foam copolymers with 10-30% glycidyl acrylate may be crosslinked by heating in the presence of polyamines. Heat resistance may be increased to as high as 150°C. by this treatment (25). Use of certain allyl or diallyl esters to control the crosslinking of polystyrene to the desired very light extent has been disclosed as a means of obtaining foams of improved and regular cell structure (135). Block copolymers of polystyrene, polydiene (particularly polyisoprene), and polystyrene... 

Thermoplastic elastomers are most commonly formulated from elastomeric polyurethane or block copolymers of polystyrene-elastomer, polyamide-elastomer, or polyether-elastomer bases. Thermoplastic elastomers are provided as a raw material in pelletized form for subsequent compounding. The internal domain structure that is required for thermoplastic-elastomeric performance has been established by specific considerations of blending and structural-chemical interactions. In compounding operations, specific temperature ranges are required to assure that phase separation does not occur in the TPE base polymer. 

A series of well-defined A-B block copolymers of polystyrene-block-polyethylene oxide (PS-PEO) were synthesised [6] and used for the emulsion polymerisation of styrene. These molecules are ideal as the polystyrene (PS) block is compatible with the PS formed, and thus it forms the best anchor chain. The PEO chain (the stabilising chain) is strongly hydrated with water molecules and extends into the aqueous phase where it forms the steric layer necessary for stabilisation. 

The most promising approach for preparing block copolymers of polystyrene (A) and polydimethylsiloxane (B) involves polymerization of cyclosiloxane monomers with living a,polystyrene anions (6). The original approach, however, gives materials contaminated with the... 

A related method was developed by Pepper and Goethals (139). Taking advantage of the dormant character of polystyrene prepared at low temperature with perchloric acid (in the form of a macroester) they prepared well-characterized block copolymers of polystyrene with cyclic amines. 

Block copolymers of polystyrene and PFOA, PS-6-PFOA, in CO2 were also extensively studied by SAXS, SANS (46, 47), high-pressure, high-resolution (HPHR) NMR (48) and pulsed magnetic field gradient (PFG) NMR (49). Neutron scattering data (46) showed that the micellar size increases with the PFOA mass, when holding MW of the PS component constant. The effect of CO2 density (0.27 to 0.84 g.cm ) at constant temperature (60 °C), and of temperature (29.5 to 76.2 °C) at constant CO2 density (0.733 g. cm ) was studied on PFOA/CO2 systems by HPHR NMR (48). 

Lotz B, Kovacs A (1969) Phase transitions in block-copolymers of polystyrene and polyethylene oxide. ACS Polym Prepr 10 820-825... 

Wilczek-Vera, G., Danis, P. O., and Eisenberg, A., Individual Block Length Distributions of Block Copolymers of Polystyrene-block-Poly(a-methylstyrene) by MALDI/TOF Mass Spectrometry, Macromolecules, 29, 4036, 1996. 

New block copolymers of polystyrene and poly(e-caprolactone) have recently been prepared with a combination of coordination catalyst and anionic polymerization( An amorphous styrene block was prepared by conventional anionic polymerization at room temperature, and terminated with ethylene oxide. After hydrolysis the terminal - OH groups were substituted by oxo-Al-Zn alkoxide. A crystalline block was then added by coordination polymerization of e-caprolactam. 

There exist two approaches to the synthesis of rod-coil block copolymers first, the grafting from approach where one component is used as a macroinitiator for the preparation of the other, and, secondly, the grafting onto method where the second component is covalently attached to a suitably end-functionalised first component. The first approach was used to prepare block copolymers of polystyrene (PS) with PPP 207 (Scheme 95) by Francois and coworkers [304-308] and by Advincula and coworkers [309]. In this synthesis, cyclohexadiene was added to living polystyrene to give a precursor polymer 208, which was then aromatised to 207 using chloranil in refluxing xylene. 

Sankar et al [48] have studied A/B block copolymers of polystyrene (PS) and poly(methylmethacrylate) (PMMA) by observation of C-detected where neither, one or the other, and both blocks were perdeuterated. They found that the carbons in each block of the copolymers were experiencing primarily their own protons, indicating some degree of phase separation, but the for each block differed somewhat from the measured for the PS and PMMA homopolymers. Annealing quenched samples apparently increased the degree of phase separation, because their values more closely approached the homopolymer values. 

Figure 10. The effect of carbon black contents on Couette correction of styrene block copolymer. SBR706 is the block copolymer of polystyrene and polybutadiene [31].

---