Shear Induced Morphology of Semicrystalline Block Copolymers
- PDF / 946,719 Bytes
- 7 Pages / 414.72 x 648 pts Page_size
- 7 Downloads / 200 Views
PETER KOFINASt AND ROBERT E. COHEN * t Department of Materials Science and Engineering * Department of Chemical Engineering Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
ABSTRACT A series of semicrystalline diblock copolymers of poly(ethylene) / poly(ethylenepropylene) (E/EP) were subjected to high levels of plane strain compression using a channel die. Deformations were imposed both below and above the melting point of the E block. The crystallographic and morphological textures were examined using wide-angle x-ray diffraction pole figure analysis and two dimensional small-angle x-ray scattering. The lattice unit cell orientation of the crystallized E chains with respect to the lamellar superstructure was determined, as well as the lamellar orientation relative to the specimen boundaries. When the diblocks are textured above the E block melting point at various compression ratios, the lamellae orient perpendicular to the plane of shear, while texturing below T.. causes the lamellae to orient parallel to the plane of shear. The orientation of the crystallized E chains was perpendicular to the lamellar normal, irrespective of the texturing temperature. The various shearinduced lamellar morphologies have potential applications in gas transport control to develop membranes for use in gas separations or as barrier materials. INTRODUCTION In previous investigations in this laboratory [1, 2], the lattice unit cell orientation with respect to the lamellar microstructure was determined for semicrystalline diblock copolymers containing an ethylene crystallizable block. The orientation of the crystallized ethylene chains was found to be perpendicular to the lamellar normals. This unusual chain alignment was attributed to the influence of interface dominated nucleation and topological constraints on growth when the ethylene block chains crystallize within the amorphous lamellar microdomains present in the heterogeneous melt phase of the block copolymers. Bates and co-workers [3, 4, 5] have studied the lamellar orientation of nearly symmetric amorphous poly(ethylethylene) / poly(ethylene-propylene) (EE/EP) diblock copolymer samples, which were textured using large strain dynamic shear. Near the order-disorder transition (ODT) temperature, and at low shear frequencies, the lamellae arrange parallel to the plane of shear, while higher frequency processing leads to lamellae perpendicular to the plane of shear. At temperatures further below the ODT the parallel lamellar orientation is obtained at all shearing frequencies. These interesting and unexpected results 523 Mat. Res. Soc. Symp. Proc. Vol. 321. ©1994 Materials Research Society
prompted us to enquire into the possibility that semicrystalline block copolymer systems might also exhibit the perpendicular lamellar morphology under shear. We have determined the lamellar orientation and chain organization upon crystallization for various processing histories in a series of diblock copolymers having crystalline quasi-poly(ethylen
Data Loading...
