Block copolymers amorphous, crystalline

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... 

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. 

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. 

It has been clarified that the crystallization temperature of crystalline/amorph-ous diblock copolymers strongly affects orientation of the crystallite. Such preferential orientation of the crystallite is also observed when crystalline/ amorphous diblock copolymers are crystallized in a thin film [142,143]. These studies suggest that the morphology of crystalline/amorphous block copolymers can be controlled at the nanometer scale by combining spatial confinement and the appropriate crystallization temperature. 

Hong S., MacKnight W. J., Russell T. P., and Gido S. P. (2001a) Orientationally registered crystals in thin film crystalline/amorphous block copolymers. Macromolecules 34 2398-2399. 

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... 

EPDM and EPR copolymers are crystalline if block copolymer and depending on the ethylene/propylene ratio in blends with PE or PP they can extract to some extent (depending on the ethylene/propylene-ratio) amorphous low molecular weight molecules from the PP or PE phase that slightly influence the crystaUization and melting behavior... 

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). 

Liquid-crystalline side block copolymer with an amorphous A block and liquid crystalline B block has been synthesized from polybutadiene or butadiene-styrene copolymer on hydroboration with 9-BBN, followed by oxidation and esterification with cholesteryl chloroformate [4]. 

It is widely recognized that amorphous-amorphous diblock copolymers form a variety of microdomain structures when the segregation strength between different blocks is moderately large. When one block is crystalline and the other is amorphous (i.e., crystalline-amorphous diblock copolymers), it is easily supposed that the morphology formation at low temperatures is driven by a close interplay between... 

Figure 10.7 Schematic illustration showing the possible morphology formation in crystalline-amorphous diblock copolymers by the crystallization of constituent blocks. The upper route represents break-out crystallization, that is, the microdomain structure is completely replaced with the lamellar morphology, whereas the lower route shows confined crystallization, where the microdomain structure is preserved after crystallization, a-d indicate driving factors for the morphology formation.

Figure 10.9 Illustration showing possible conformations of crystalline and amorphous blocks in the lamellar morphology of crystalline-amorphous diblock copolymers, (a) n. = 1, (b) n. = 2, and (c) n = i, where represents the chain-folding number of crystalline blocks.

When of crystalline-amorphous diblock copolymers is sufficiently large, the soft microdomain structure is stable against the subsequent crystallization. Therefore, this structure is preserved through the crystalUzation process, that is, constituent blocks crystallize within the soft microdomain stmcture, to yield a crystalline microdomain structure (lower route in Fig. 10.7). Amorphous domains in the crystalline microdomain structure are not hard in this case, so that crystalline domains can deform moderately during crystalUzation in order to get a larger crystalUnity and/or favorable crystal orientation, which is criticaUy different from the crystallization of block copolymers with high-T amorphous blocks, as described in Section 10.3.2. 

The crystalline morphology formed in crystalline-crystalline diblock copolymers is more complicated as compared with that in crystalline-amorphous diblock copolymers, because two kinds of crystallization start from some microdomain structure existing in the melt. It is useful to classify this crystallization into two cases in terms of the crystallizable temperature of both blocks (Fig. 10.8) two-step crystallization when of one block is significantly higher than that of the other, and simultaneous crystallization when both values are sufficiently close. 

The basic research on the crystallization in more complicated systems started recently to find ouf unique morphologies formed in polymer systems. The crystallization of block copolymers is a striking example of such crystallization, which is intimately dependent on the molecular characteristics of crystalline block copolymers. For example, the crystallization of crystalline-amorphous diblock copolymers yields the lamellar morphology or crystalline microdomain structure depending on xN of block copolymers, Tg of amorphous blocks, crystallization conditions, and so on. These kinds of crystallization have the possibility of developing new crystalline polymer materials. Therefore, we strongly anticipate future advances in this research field. 

Similarly, the random introduction by copolymerization of stericaHy incompatible repeating unit B into chains of crystalline A reduces the crystalline melting point and degree of crystallinity. If is reduced to T, crystals cannot form. Isotactic polypropylene and linear polyethylene homopolymers are each highly crystalline plastics. However, a random 65% ethylene—35% propylene copolymer of the two, poly(ethylene- (9-prop5lene) is a completely amorphous ethylene—propylene mbber (EPR). On the other hand, block copolymers of the two, poly(ethylene- -prop5iene) of the same overall composition, are highly crystalline. X-ray studies of these materials reveal both the polyethylene lattice and the isotactic polypropylene lattice, as the different blocks crystallize in thek own lattices. 

Block copolymers can contain crystalline or amorphous hard blocks. Examples of crystalline block copolymers are polyurethanes (e.g. B.F. Goodrich s Estane line), polyether esters (e.g. Dupont s Hytrel polymers), polyether amides (e.g. Atofina s Pebax grades). Polyurethanes have enjoyed limited utility due to their relatively low thermal stability use temperatures must be kept below 275°F, due to the reversibility of the urethane linkage. Recently, polyurethanes with stability at 350°F for nearly 100 h have been claimed [2]. Polyether esters and polyether amides have been explored for PSA applications where their heat and plasticizer resistance is a benefit [3]. However, the high price of these materials and their multiblock architecture have limited their use. All of these crystalline block copolymers consist of multiblocks with relatively short, amorphous, polyether or polyester mid-blocks. Consequently they can not be diluted as extensively with tackifiers and diluents as styrenic triblock copolymers. Thereby it is more difficult to obtain strong, yet soft adhesives — the primary goals of adding rubber to hot melts. 

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