Ordered structure in blends of block copolymers. 1. Miscibility criterion for lamellar block copolymers

Abstract

Morphology of binary mixtures of polystyrene-Mocfe-isoprene) (SI) having different compositions /ps of the polystyrene block in SI and total molecular weights was investigated on the solution-cast film with toluene as a neutrally good solvent. In the range of the composition /ps = 0.35-0.69 covered, the two SI copolymers were found to be totally miscible on the molecular level at all compositions, forming a single microdomain morphology, if their molecular weight ratio is smaller than about 5. They were found to be only partially miscible, if their molecular weight ratio is greater than about 10, forming macroscopically phase-separated coexisting lamellar microdomains with different domain spacings. In the partially miscible pairs, the copolymer with the larger molecular weight was found to solubilize the copolymer with the smaller molecular weight up to about 30 wt %, but the copolymer with the smaller molecular weight was found to hardly solubilize the copolymer with a larger molecular weight. A new but unidentified bicontinuous ordered microdomain structure was found for a miscible pair.

Crystallization Process in Binary Blends of Poly(ε-caprolactone)-block-Polybutadiene Copolymers

“…That is, if the two copolymers are miscible they make a single microdomain structure and the average spacing changes continuously with composition. 21 If they are macroscopically segregated, on the other hand, we can observe two microdomain structures, the spacing of which exactly corresponds to those of the constituent copolymers if the shorter block does not dissolve partially in the domain consisting of longer one. 32 The SAXS intensity curves are logarithmically plotted in Figure 1 moves continuously with composition.…”

“…21,[32][33][34][35] Hashimoto et al, 21,32 for example, demonstrated that when the constituent copolymers were satisfied with the condition of M α /M β < 5 (where M α and M β are the molecular weight of copolymer α and β, respectively), they made a single microdomain structure even if there was a difference in composition between the copolymers. Furthermore they showed that the binary blend of block copolymers with unequal chain length might change the interface curvature of microdomains to result in a morphological transition from the lamella into the bicontinuous structure even if both the constituent copolymers took the lamellar morphology.…”

“…In addition, at the limit of φ M11 → 0 an unrealistic elongation of the shorter PB block and therefore an extremely large elastic energy are suggested if we keep the situation shown in Figure 8a. Therefore we will have to consider the change in the interface curvature between lamellar crystals and amorphous layers as suggested by Hashimoto et al for the binary blend of symmetrical amorphous-amorphous diblock copolymers, 21 or the localization of the shorter PB block in the lamellar morphology (Figure 8b), as suggested by Sakurai et al for the microdomain structure consisting of shorter and longer amorphous-amorphous diblock copolymers. 35 We can easily suppose for the former case that the lamellar crystal is hard to change the interface curvature to accommodate both the longer and shorter PB blocks in the amorphous layer.…”

“…That is, it is possible to change widely the crystallization rate by changing the molecular weight and/or block ratio with keeping the miscibility between constituent copolymers, where miscibility means that the components do not segregate macroscopically but make a single microdomain structure in the melt. 21 The crystallization of these binary blends is reminiscent of molecular fractionation, as demonstrated for polyethylene samples with a wide molecular weight distribution. [22][23][24] That is, the crystallization of PCL blocks in binary copolymer blends has a possibility to bring about the macroscopic segregation into individual domains.…”

Morphologies of Binary AB/AC Diblock Copolymer Blends

“…The phase boundary between SI87 and SVP macrodomains and SVP-rich macrodomains are shown, respectively. copolymer ((AB) a /(AB) b [13][14][15][16] or AB/AC [17,18] ) give another route to control the morphology. Here C denotes the chemically different component from the blocks A and B.…”