Amorphous block copolymers

Of the amorphous block copolymers, styrenic block copolymers are the vast majority. These are synthesized anionically in solution, with butyl lithium commonly employed as the initiator [4]. There are three processes for this polymerization ... 

New family of TPV having heat and oil resistance based on ACM and polyamide Development of crystalline-amorphous block copolymers (Engage), mettalocene catalyzed TPEs, Polyolefin elastomer (POEs), application research on TPEs Protein-based block-copolymer... 

Abstract This chapter gives an overview of the research on the self-assembly of amorphous block copolymers at different levels of hierarchy. Besides the influence of composition and topology on the morphologies of block copolymers with linear, cyclic and branched topologies blends of block copolymers with low molecular weight components, other polymers or block copolymers and nanoparticles will also be presented. 

The melting of a crystalline-amorphous block copolymer of poly(tetrahydro-furan)-poly(isoprene) (PTHF-PI) was investigated using DSC by Ishikawa et al. (1991). They found a double melting peak, which was proposed to result from the semicrystalline structure of the crystalline PTHF layer, with less-ordered crystallites melting before those with well-ordered domains of chain-folded PTHF. Alternative explanations include fractionation of the polydisperse block copolymer or melting of crystals with different fold lengths. 

Block copolymers containing crystallizable blocks have been studied not only as alternative TPEs with improved properties but also as novel nanos-tructured materials with much more intricate architectures compared to those produced by the simple amorphous blocks. Since the interplay of crystallization and microphase segregation of crystalline/amorphous block copolymers greatly influences the final equilibrium ordered states, and results in a diverse morphological complexity, there has been a continued high level of interest in the synthesis and characterization of these materials. 

After a brief recall of the methods of synthesis of block copolymers, we shall describe the principal types of organized structures, which have been observed in block copolymers both in mesomorphic and dry states. Then we shall examine the structure and properties of the most important block copolymers dividing them in three categories copolymers with amorphous blocks, copolymers with amorphous and crystallizable blocks, copolymers with blocks presenting biological interest. However, in this review, only such properties will be taken into account that are related to the microdomain structure of block copolymers. 

Until now we have considered the basic origin of birefringence and some of the general techniques used for determining this optical parameter. It is necessary, however, to discuss certain limitations when interpreting this parameter. Until now no mention has been made of two or multiphase systems such as semicrystalline polymers, amorphous block copolymers or even plasticized or filled polymers. In such systems the measured birefringence can be expressed as... 

When one component of an amorphous block copolymer is replaced by a crystalline polymer, the domains or crystalline texture formed by the solvent cast should depend at least on two factors (a) crystallization of the crystalline block segment and (b) microphase separation resulting from the incompatibility of the A and B blocks. The crystalline texture observed in solid film is considered strongly dependent on the relative contributions of the two phase... 

Abstract We review thin-film morphologies of hybrid liquid-crystalline/amorphous block copolymers. The microphase separation of the blocks and the smectic hquid crystalline ordering within one of the blocks are treated systematically in terms of the interaction parameters. The competition of the tandem interactions in terms of length scales and of surface anchoring can be used advantageously to control the orientation of block interfaces for nanopatterning. 

The melt rheology of amorphous block copolymers, e.g., styrene-butadiene block copolymers (Arnold and Meier, 1968 Holden et al, 1969a Meier, 1969), has been described and interpreted already (Section 4.11). It is interesting to compare the amorphous block copolymers with block copolymers that have the additional feature of crystallizable sequences. A basic study of block copolymer rheology was carried out by Erhardt et al (1970), who determined the complex modulus and tan 6, and studied melt behavior at temperatures between about 60 and 200°C. A report on dielectric behavior by Pochan (1971) is also significant. 

A. Douy, R. Mayer, J. Rossi and B. Gallot, Structure of liquid crystalline phases from amorphous block copolymers. Mol. Cryst. Liq. Cryst. 7 103 (1969). 

Experimental phase diagrams for amorphous block copolymers were explored by Khandpur and co-workers (29). First, low-frequency isochronal shear modulus-temperature curves were developed on a series of polyiso-prene-h/ocA -polystyrene polymers to guide the selection of temperatures for the transmission electron microscopy and SAXS experiments to follow see Figure 13.14 (29). Both order-order (OOT) and ODT transitions were iden-tihed. The OOT are marked by open arrows, while the ODT are shown by hlled arrows. Since the ODT occurs as the temperature is raised, an upper critical solution temperature is indicated, much more frequent with block copolymers than with polymer blends. The regions marked A, B, C, and D denote lamellar, bi-continuous, cylindrical, and perforated layered microstructures, respectively. The changes in morphology are driven by the temperature dependence of Xn,... 

II. Introduction to the Microphase Diagrams of Amorphous Block Copolymers... 

So far we discussed systems with amorphous block copolymers only. A second level of self-assembly is the formation of liquid crystals or crystals within microdomains of block copolymers. 

A schematic illustration of the major domain structures that are found in pure amorphous block copolymers is illustrated in Fig. 5.25.(183) Here the diblock copolymer poly(styrene)-poly(butadiene) is taken as an example. In (a) poly-(styrene) spheres are clearly seen in a poly(butadiene) matrix the spheres change to cylinders with an increase in the poly(styrene) content, as in example (b). With a further increase in the poly(styrene) concentration, alternating lamellae of the two species are observed (c). At the higher poly(styrene) contents, (d) and (e), the situation is reversed. Poly(butadiene) cylinders, and then spheres, now form in a poly(styrene) matrix. More quantitative descriptions of the domain structures have been given.(184,186,187) Crystallization and melting often occur to or from heterogenous melts with specific microphase structures. 

The effect of changing the S B ratio appears to be consistent with general observations on block copolymers. It appears that three types of microphase segregation can occur in which one or other of the components are concentrated in spheres, rods or lamellae. The general effect of altering the volume fractions of the components in a two-component amorphous block copolymer is shown schematically in Fig. 17.3. 

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