Styrene-diene diblock copolymer

Although styrene-diene diblock copolymers are used in some applications, particularly in the area of viscosity index improvement (VII) additives for motor oil, styrenic block copolymers are most often used as thermoplastic elastomers. In these applications the styrene blocks phase separate, crosslinking the rubber blocks in a thermally reversible fashion. The simplest structure capable of exhibiting this behavior is a linear styrene-diene-styrene triblock. The most obvious way to produce such a molecule is by sequential polymeriza-... 

In lamellar styrene-diene diblock copolymers, SANS studies showed that the segment Rg contracts to 70% of the unperturbed value parallel to the interface and expands to 160% of the unperturbed value perpendicular to the interface (Hasegawa et al 1985, 1987). These values were found for both the styrene and diene blocks. A smdy of stretching SIS block copolymers having spherical styrene phases showed that the deformation in the direction of stretch was greater than affine, while the deformation perpendicular to the stretch was much less (Richards and Welsh, 1995). 

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. 

Fully methacrylic triblocks, containing a central rubbery poly(alkyl acrylate) block and two peripheral hard poly(alkyl methacrylate) blocks, are potential substitutes for the traditional styrene-diene-based thermoplastic elastomers (TPEs), which have relatively low service temperatures. Fully methacrylic triblock copolymers are able to cover service temperatures due to the varying Tg from — 50 C (poly(isooctyl acrylate)) to 190 C (poly (isobornyl methacrylate) [210]. Poly(methyl methacrylate)-Z)-poly(n-butyl acrylate)-Z)-poly(methyl methacrylate) triblock copolymers, which are precursors for poly(methyl methacrylate)- -poly(alkyl acrylate)-Z)-poly(methyl methacrylate) via selective transalcoholysis, have been synthesized by a three-step sequential polymerization of MMA, ferf-butyl acrylate (t-BuA), and MMA in the presence of LiCl as stabilizing ligand [211,212]. Various diblock copolymers, such as poly(methyl methacrylate)-Z)-poly( -butyl acrylate) and poly(methyl methacrylate)-Z)-poly( -nonyl acrylate), have been synthesized... 

On of the most unique aspects of living anionic polymerizations is the ability to synthesize block copolymers by sequential monomer addition. Thus, the product of the alkyllithium-initiated polymerization of styrene (Scheme I) can be reacted with a diene such as butadiene or isoprene to produce a living diblock copolymer as shown in eq, 2 for butadiene. It is important to note that the alkyllithium-initiated poly-... 

Excellent reviews on micelles formed in organic solvents have been published by Hamley [2], Chu et al. [86], and Riess [14]. From these overviews it appears that a wide range of styrene-, (meth)acrylates-, and dienes-based block copolymers were investigated and that the formation of micelles in organic solvents can generally be considered as an entropy-driven process. AB diblock and ABA triblock architectures were systematically compared. All these previous investigations have been summarized by Hamley [2], We will therefore not perform an extensive review of all these systems, since this information has already been provided by others, but we will briefly outline some selected examples. 

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