The morphology of ABC triblock copolymers based on poly styrene-5/oc/s-polybutadiene-6/oc&polyfmethyl methacrylate) [PS-i-PB-6-PMMA] (SBM series) and their hydrogenated analogues polystyrene-6Zoc&-poly(ethylene-co-butylene)-6Zoc£-poly(methyl methacrylate) [PS-6-PEB-6-PMMA] (SEBM series) block copolymers is governed by the relatively weak incompatibility of the end blocks PS and PMMA in comparison to the strong incompatibility of the polybutadiene or poly(ethylene-co-butylene) midblock. The paper describes the morphologies of high molecular weight (Mn ~200 000) block copolymers, which are symmetrical with respect to the PS and the PMMA blocks with a varying elastomeric center block (0.06 < wei < 0.38). Besides an ABC lamellar morphology (11) (38 wt % PB or PEB), two other lamellar morphologies are observed for shorter elastomer chains: At 17 wt % of the elastomeric center block a "cylinder at the wall" morphology is observed where PB or PEB cylinders are located at the lamellar PS/PMMA interface (lc). At 6 wt % of elastomer, the polybutadiene forms spheres at the PS/PMMA interface ("ball at the wall") (Is). In this case hydrogenation of the butadiene block, which is associated with a further increase in the immiscibility to the end blocks, induces a change of the overall lamellar structure into a cylindrical morphology in which PS cylinders surrounded by PEB rings are dispersed in a PMMA matrix (cr). The transition from the lamellar (11) morphology to the (lc) and (Is) morphologies is described by a simple extension of the Meier/Alexander/de Gennes/Semenov theories of AB block copolymers in the strong segration limit to ABC block copolymers. The theoretical description predicts that morphological transitions can be achieved in ABC triblock copolymers at constant composition even in the limit of strong segregation.

In asymmetric ABC triblock copolymers with C being the matrix-forming majority component, the formation of cylindrical morphologies is governed by the sum of the volume fractions of the components A and B (@A + t & )as well as by their ratio (@B/@A). The paper describes the morphologies of various polystyrene-block-polybutadiene-blockpoly(methy1 methacrylate) (SBM) and polystyrene-block-poly(ethy1ene-co-buty1ene)-block-poly(methy1 methacrylate) block copolymers (SEBM) in dependence on these parameters. In addition to previously reported cylinder in cylinder (tic, core shell) and helical (hel) morphologies, new microphase separated structures as cylinders at cylinder (c,c), undulatedperforated cylinder in cylinder (ucic) and spheres on cylinder (s,c) are discussed. Based on a simple theoretical approach the transitions between these various morphologies are predicted, especially focusing on the transition between the cic and c,c morphologies.

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In a polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymer (SBM) a morphological transition from a lamellar (ll) morphology (with sequence ABCB) to the knitting pattern (kp) morphology occurs upon hydrogenation of the center PB block. Structural information of the nonhydrogenated and the hydrogenated material is provided from small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). For the nonhydrogenated SBM sample the SAXS profile correlates well with a simple periodic lamellar structure. The hydrogenated sample forming the kp morphology displays a more complex SAXS pattern. From the TEM images of the knitting pattern the two-dimensional space group has been determined to be c2mm. This morphology represents a first example of a planar morphology for which the two sides of the unit cell are unequal (a * b). The determination of the space group from TEM allows the satisfactory assignment of the SAXS pattern. Furthermore this new kp morphology is the first example in block copolymers providing a highly nonconstant mean curvature (NCMC) intermaterial dividing surface. Varying the casting solvent for this material (from CHCl 3 to toluene) results in a lamellar morphology as demonstrated by TEM and SAXS. This morphological change is explained as the consequence of the borderline situation of the kp morphology as an intermediate between the ll and lc morphology where B cylinders of the center block are located at the lamellar A/C interface.

A new morphology of ternary ABC triblock copolymers is presented which results from the asymmetric interaction between a centre block (poly(ethy1ene-co-butene)) to different end blocks (polystyrene and poly(methy1 methacrylate)). This morphology with the appearance of a "knitting pattern" can be described as an intermediate of a morphology of A, B and C lamellae and a morphology of A and C lamellae with B cylinders at the A/C interface.Macroscopic phase separation of two immiscible polymer chains (A, B) is suppressed, if they are connected to each other in a block copolymer (AB). As a result of mutual immiscibility microphase separation into ordered microdomain structures occurs. While microphase-separated morphologies which form in linear AB or ABA block copolymers in the limit of strong segregation are basically defined by composition. the mesoscopic organization of block copolymers composed of three chemically different components A, B. C depends on the composition expressed by volume fractions @A, &, @, -, the block sequence (ABC + + BAC + + ACB), and the balance of the incompatibilities expressed by the surface tensions yAB, yHC, yAC. For compositionally symmetric polystyrene-hloLk-polybutadiene-hlock-poly(methy1 methacrylate) (SBM) triblock copolymers and their hydrogenated analogues, namely polystyrene-b~ock-poly(ethylene-co-butei~e)-hlock-poly(methyl methacry1ate)s Fig. I . Schematic description of (a) the 11-and (b) the Ic-morphologies: (a) SBMBS lamellar microstructure, (b) PB cylinders located at the S/M interface. (PS = polystyrene; PB = polybutadiene: PMMA = poly(methy1 methacrylate) 0