E/EP/E Triblock Copolymers near the Order-Disorder Transition

A series of semicrystalline triblock copolymers E/EP/E, of poly(ethy1ene) (E) and poly(ethylenepropylene) (EP) were subjected to high levels of plane strain compression using a channel die. The processing was carried out at 150 "C, a temperature which lies well above both the E block melting points (99-103 "C) and the quiescent order-disorder transitions (ca. 106 "C) for these samples. The lamellar orientation relative to the specimen boundaries was determined using two dimensional smallangle X-ray scattering. By using a 2.4 MPa applied stress on the channel die, the lamellae orient parallel to the plane of shear, while processing at an applied stress of 8.0 MPa causes the lamellae to orient perpendicular to the plane of shear. Gas permeability coefficients P for He and COz were measured at 25 "C for EIEPE 25150125 specimens and compared to modeling predictions. The upper bound (lamellae aligned in parallel with respect to the permeation direction) and lower bound (series lamellar alignment) models were compared to experimental permeation data on the corresponding oriented triblock specimens.