Block copolymers structure function

Figure C2.1.11. Morphologies of a microphase-separated di-block copolymer as function of the volume fraction of one component. The values here refer to a polystyrene-polyisoprene di-block copolymer and ( )pg is the volume fraction of the polystyrene blocks. OBDD denotes the ordered bicontinuous double diamond structure. (Figure from [78], reprinted by permission of Annual Reviews.)...

The properties of the linear material 7.27 and the network copolymer 7.28 have been studied by dynamic mechanical analysis, DSC, and transmission electron microscopy. Evidence was obtained for the formation of highly ordered micro-phase-separated superstructures in the solid state from the materials 7.27. The Cu(bipy)2 moieties appear to form ordered stacks, and this leads to thermoplastic elastomer properties. In contrast, the network structure of 7.28 prevents significant microphase separation [51-53]. By means of related approaches, dinuclear Cu helical complexes have also been used to create block copolymers by functioning as cores [54], and polymer networks have also been formed by using diiron(II) triple helicates as cores for the formation of copolymers with methyl methacrylate [55]. 

This section deals with the influence of amphiphilicity on the formation of block copolymer structures. These block copolymers are either confined in the spherical shape of a nanodroplet or on a surface. Whereas in the first case, the fundamental aspects of mesoscospic structure formation are the focus of attention, we concentrate in the second case on a specific function, i.e., switchable wettability due to the... 

Evaluation of the above for a block copolymer with uniform random SI copolymer end-blocks with 60% styrene, leads to an estimate of Tr of about 90 C, well below the typical vulcanization temperatures of 145-160 C. The indication is that the proposed scheme of developing a temporary network which dissociates during the final vulcanization is feasable. This situation would be the epitome of a truely functional use of block polymers since, in this case, the block copolymer structure itself as well as its identity cease to exist after the function has been accomplished. 

In a sacrificial synthesis, cyclic monomers containing a cleavable group are incorporated into a block copolymer structure, as shown in Figure 3.7 [47]. A propagating ruthenium carbene complex is used as a macro initiator for the polymerization of the cleavable cyclic monomer to form a diblock copolymer. The polymer block composed of the cleavable monomer can be broken down into low molecular weight fragments (sacrificed), leaving just one functionality at the chain end of the first polymer block. 

Polymer II (a sample with [n] 0.35 dl/g) was used as a phenol for copolymerization with 2,6-dimethylphenol. The physical properties of the product (intrinsic viscosities as high as 0.68 dl/g no fractionation of VIII during methylene chloride complex-ation l no long range nmr effects) suggested a block copolymer structure for the product. Since it is likely that polymer II did not redistribute under the mild conditions of polymerization (Table I shows little equilibration with monomer even at 80 ), polymer II was functioning as a monofunctional consonant which did not readily co-equilibrate with the oth r oligomers. Polymer II can be viewed as a chain stopper for reaction (4) and the product can be represented by structure XIII. Colorless, hazy... 

The multifunctional initiators may be di- and tri-, azo- or peroxy-compounds of defined structure (c.g. 20256) or they may be polymeric azo- or peroxy-compounds where the radical generating functions may be present as side chains 57 or as part of the polymer backbone."58"261 Thus, amphiphilic block copolymers were synthesized using the polymeric initiator 21 formed from the reaction between an a,to-diol and AIBN (Scheme 7.22).26 Some further examples of multifunctional initiators were mentioned in Section 3.3.3.2. It is also possible to produce less well-defined multifunctional initiators containing peroxide functionality from a polymer substrate by autoxidalion or by ozonolysis.-0... 

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

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