Macromol. Rapid Commun. 15,949-953 (1994) zyxwv 949 zy Selective staining of the interfacial region in block copolymers Hartmut Fischer H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Royal Fort Bristol, BSS-ITL, U. K. (Received: July 18, 1994; revised manuscript of August 15, 1994) Introduction Block copolymers composed of incompatible block segments form in general a micro-domain morphology in the solid state. This morphology of the separated micro- phases depends on the thermodynamic interaction parameter zyx x, on the temperature and on the molecular weights of the constituent block chains. Due to the chemical link between the components, the dimensions of the microphases formed by the phase separation are limited. The region between the microphases, i. e., the interface, is a major factor in determining bulk properties of block copolymers as well as of polymer blends. This region must comprise, in the case of block copolymers, chain parts of both block components and will be of limited thickness. However, the chain parts are linked together, and therefore improved mechanical properties can be expected in comparison to polymer blends. Studies have been carried out to obtain information about the width of the interface of block copolymers. The thickness of interfacial layers has been measured by means of small angle X-ray scattering zyxwv 1-4) and neutron reflectivity5)in a rather extensive and sophisticated way. It was found that the thickness of the interface between the phase- separated blocks of polystyrene-b-polyisoprene block copolymers (about 2 nm) is independent of the molecular weight of the block components 3, and of the volume fraction of both block components’). Anastasiadis et al. 5, described the system polystyrene-b-poly(methy1 methacrylate), and they also found that the interfacial thickness (5 nm) was not dependent on the molecular weight of the block copolymers. Other attempts have been made to evaluate the interfacial thickness by transmission electron microscopy (TEM)6), however, as yet no direct method to measure the interfacial thickness has been described. Recently, we reported experiments concerning block copolymers with one or two amorphous block(s), polystyrene (PS), and one liquid crystalline block, poly[2-(3-chol- z esteryloxycarbony1oxy)ethyl methacrylates] (PChEMA), PS-b-PChEMA as diblock copolymer 7, (Scheme 1) and PChEMA-b-PS-b-PChEMA as triblock copolymer zy *). There, the morphology displayed was investigated using small angle diffraction techniques and TEM 7-9). Sufficient contrast for the TEM investigation was achieved by staining of the polymers with RuO, vapour. The typical morphologies for block copolymers, spherical and rodlike structures embedded in the matrix of the other block component and lamellar structures, were found. Now new features have been observed. z 0 1994, Huthig & Wepf Verlag, Zug CCC 1022-1336/95/$02.50