Block copolymer orientation

An intense interest, currently without abatement, in the characterization of rubber-toughened thermosets in general, and rubber-toughened epoxy resins in particular, has surfaced over the last several years. Riew (18) summarized work leading to the optimization of toughness in an epoxy/CTBN/piperidine model. Concurrently, Kaelble (19) reported on such systems from a block copolymer orientation and examined properties related to adhesive... 

Figure 3.6 Lamellar SBS block copolymer oriented by extrusion the lamellae lie normal to the plane of the paper and are aligned along the extrusion direction (ED) the butadiene phase Is stained by OSO4 ultrathin section, TEM micrograph...

It is easy to visualize how a block copolymer orients at the interface and binds two immiscible polymer phases together to give a strong interface and good practical compatibility. This is why most compatibilization research has concentrated on block copolymers as physical additives. Unfortunately, most block copolymers are difficult and expensive to synthesize, which is a serious liability in industry. 

When r was less than 0.46 (Fig. 9a), the P4VP layer surrounded some microspheres in groups (r = 0.33). The K r = 0.33 was 2.48. This indicates that the amount of B1 block copolymer was insufficient to surround each microsphere separately. When r was larger than 0.46 (Fig. 9c), the wide dark regions of P4VP were also observed. These regions were horizontally oriented lamellar microdomains of Bl, resulting in a minimization... 

The most desirable annealing temperatures for amorphous plastics, certain blends, and block copolymers is just above their glass transition temperature (Tg) where the relaxation of stress and orientation is the most rapid. However, the required temperatures may cause excessive distortion and warping. 

Fig. 6 Idealized heptablock copolymer molecular conformations for parallel and perpendicular orientations. The latter contains predominantly bridged chains, whereas the block copolymer is much more likely to loop along interfaces in parallel arrangement. From [44]. Copyright 2004 American Chemical Society...

The viscoelastic effects on the morphology and dynamics of microphase separation of diblock copolymers was simulated by Huo et al. [ 126] based on Tanaka s viscoelastic model [127] in the presence and absence of additional thermal noise. Their results indicate that for

bulk modulus of both blocks, the area fraction of the A-rich phase remains constant during the microphase separation process. For each block randomly oriented lamellae are preferred. 

However, a PS-fo-PI/PI blend shows direct L G transitions without appearance of the PL phase. The L microdomain is more favourable than the PL phase since the volume fraction of the PI block component and the symmetry of microdomains is increased by the addition of PI homopolymer. Hence, the PL phase may not be formed as an intermediate structure if relatively high molecular weight PI homopolymer is added. The latter is not able to effectively fill the corners of the Wigner-Seitz cells in consequence packing frustration cannot be released and the PL phase is not favoured [152]. In contrast, the addition of low molecular weight PI homopolymer to the minor component of the PL phase reduces the packing frustration imposed on the block copolymers and stabilizes it [153]. Hence, transition from the PL to the G phase indicates an epitaxial relationship between the two structures, while the direct transition between L and G yields a polydomain structure indicative of epitaxial mismatches in domain orientations [152]. 

Nylon blends, dyeing, 9 204 Nylon block copolymer, 19 762 Nylon carpet fibers, stain-resistant, 19 764 Nylon-clay nanocomposites, 11 313-314 Nylon extrusion, temperatures for, 19 789t Nylon feed yarns, spin-oriented, 19 752 Nylon fiber(s), 24 61 production of, 19 740 world production of, 19 7654 Nylon fiber surfaces, grafting of polymers on, 19 763-764... 

Since excellent reviews on block copolymer crystallization have been published recently [43,44], we have concentrated in this paper on aspects that have not been previously considered in these references. In particular, previous reviews have focused mostly on AB diblock copolymers with one crystal-lizable block, and particular emphasis has been placed in the phase behavior, crystal structure, morphology and chain orientation within MD structures. In this review, we will concentrate on aspects such as thermal properties and their relationship to the block copolymer morphology. Furthermore, the nucleation, crystallization and morphology of more complex materials like double-crystalline AB diblock copolymers and ABC triblock copolymers with one or two crystallizable blocks will be considered in detail. 

Ordered body-centered cubic structures were observed by shearing aqueous gels made from anionic PtBS-PMANa block copolymer micelles [163]. The emergence of the ordered gel state could be accounted for similar building up of a polyelectrolyte-based fibrillar network that can be oriented under shear. 

A seminal contribution by Mansky et al. on the preparation of oriented thin films of PS-PBD block copolymers that were then subjected to ozonolysis degradation conditions to give porous thin films for use as nanolithography... 

---