STRUCTURAL CHARACTERIZATION OF THE KNITTING PATTERN IN HYLENE-CO-BUTYLENE)-BLOCK-POLY(METHYLMETHACRYLATE) TRIBLOCK COPOLYMERS

In a yrene-block-polybutadiene-block-poly(methacrylate) triblock copol ymer (SBM) a morphological transition from a lamellar (II) morphology (with sequence ABCB) to the knitting pattern (kp) morphology occurs up on 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 fo rming the hp morphology displays a more complex SAXS pattern. From the TEM images of the knitting pattern the two-dimensional space group ha s been determined to be c2mm. This morphology represents a first examp le of a planar morphology for which the two sides of the unit cell are unequal (a not equal b). The determination of the space group from TE M allows the satisfactory assignment of the SAXS pattern. Furthermore this new kp morphology is the first example in block copolymers provid ing a highly nonconstant mean curvature (NCMC) intermaterial dividing surface. Varying the casting solvent for this material (from CHCl3 to toluene) results in a lamellar morphology as demonstrated by TEM and S AXS. This morphological change is explained as the consequence of the borderline situation of the hp morphology as an intermediate between t he 12 and Ic morphology where B cylinders of the center block are loca ted at the lamellar A/C interface.