CLASSIFICATION OF HOMOGENEOUS ETHYLENE-OCTENE COPOLYMERS BASED ON COMONOMER CONTENT

Ethylene-octene copolymers prepared by Dow's INSITE(TM) constrained ge ometry catalyst technology present a broad range of solid-state struct ures from highly crystalline, lamellar morphologies to the granular mo rphology of low crystallinity copolymers. As the comonomer content inc reases, the accompanying tensile behavior changes from necking and col d drawing typical of a semicrystalline thermoplastic to uniform drawin g and high recovery characteristic of an elastomer. Although changes i n morphological features and tensile properties occur gradually with i ncreasing comonomer content, the combined body of observations from me lting behavior, morphology, dynamic mechanical response, yielding, and large-scale deformation suggest a classification scheme with four dis tinct categories. Materials with densities higher than 0.93 g/cc, type IV, exhibit a lamellar morphology with well-developed spherulitic sup erstructure. Type III polymers with densities between 0.93 and 0.91 g/ cc have thinner lamellae and smaller spherulites. Type II materials wi th densities between 0.91 and 0.89 g/cc have a mixed morphology of sma ll lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities less than 0.89 g/cc have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting tempera ture, and the granular, nonlamellar morphology. (C) 1996 John Wiley & Sons, Inc.