Block copolymers basic properties

As previously described, all microspheres discussed in this chapter were synthesized from AB type diblock copolymers. Precursor block copolymers, poly(styrene-b-4-vinyl pyridine) (P[S-b-4VP]) diblock copolymers, were synthesized using the additional anionic polymerization technique [13]. The basic properties of the block copolymers were determined elsewhere [24,25] and are listed... 

The actual knowledge of the basic molecular structure property relationships relies mainly on the availability of well defined linear architectures the di, tri- and multiblock copolymers. New and well controlled molecular structures could undoubtedly provide a deep understanding of the behavior of block copolymers and a more efficient mastering of their applications. ... 

The synthesis and characterization of these ABA block copolymers of styrene and dienes have been described elsewhere (JO, 11). Since the polystyrene end blocks aggregate into glassy domains which act as network junctions, the elastic center blocks must virtually represent the network chains/ The polystyrene domains should also act as a finely divided filler. Hence it might be expected that the mechanical properties of these materials could depend on the two basic parameters polystyrene content and length of center block ( molecular weight between crosslinks ). 

In dilute aqueous solutions, polyelectrolyte block copolymers self-assemble into micelles consisting of a hydrophobic core and a polyelectrolyte shell. The study of their structural properties is expected to provide a basic understanding of the properties of dense polyelectrolyte layers, electro-steric stabilization mechanisms, and actuator functions based on variations in the electrostatic interactions. 

The intramacromolecular complexation of the block copolymer of poly(sty-renesulfonic acid) (PSS)-poly(2-vinylpyridine) (P2VP) has recently been reported. Varoqui et al.435) have synthesized this block copolymer and investigated its solution properties. They observed a great increase in the basicity of the pyridyl groups in the block copolymer. This phenomenon was explained by invoking a stoichiometric interaction between oppositely charged blocks. 

Systematic relationships are required between synthesis, architecture and basic properties. The array of basic characterisation tools now at our disposal should also be used to pin down the architectures in more detail. For example, fractionating a block copolymer across the molecular weight distribution... 

One of the basic problems confronting molecular composites is the difficulty of finding miscible combinations of rigid rod polymers with flexible chain polymers. Poly(p-phenylene benzobisthiazole)/poly(-2,5(6)-benzimidazole block copolymers have been reported by Tsai et al. [1985] and are noted to exhibit better processability and mechanical properties than the simple blends of the block copolymer constituents. Chang and Lee [1993] prepared poly(p-benzamide)/Pl block copolymers and reported on the liquid crystalline behavior. Such approaches would appear to have future implications. As an example PA e.g., PA-66) block copolymers with rigid rod polyamides could be prepared and used in blends with PA-66 to yield the desired molecular composite. 

SMPUs are basically block copolymers of soft segments, which are polyols, and hard segments built from diisocyantes and chain extenders (see Figure 4.31). Depending on the types and compositions of soft and hard segments, and preparation procedures, the structure-property relationships of SMPUs are extremely diverse and easily controlled, and hence shape recovery temperature can be set at any... 

Produced by a solution polymerization process, this material exhibited an ordered molecular structure with the styrene monomer located at the ends of the butadiene monomer chain. In addition, other monomers such as isoprene, ethylene, butylene, and others, could be added to the polymer chain, which further modified basic properties. These materials possess a continuous rubber phase for resilience and toughness, and a discontinuous plastic phase for solubility and thermoplasticity. A variety of different grades are also available for this type of SBR, with differences in molecular weight, differences in the types of monomers used, differences in structural configuration, and differences in the ratio of endblock to midblock. Both emulsion and solution polymerized grades of SBR are available as solvent-based and water-based adhesives and sealants. Block copolymers are extensively used for hot melt formulations and both water-based and solvent-based pressure sensitive adhesive applications. Today, SBR elastomers are the most popular elastomers used for the manufacture of adhesives and sealants. 

In the next section the basic properties of block copolymers and liquid crystalline polymers will be summarized. Furthermore, we discuss the block microphase separation and its interaction with the LC ordering in one of the blocks in a systematic way. In the remaining sections a couple of examples (see Table 1) will be discussed of competing hierarchical ordering at surfaces, with emphasis on the possibilities for controlled nanopatterning. 

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