Crystallization of defect-free polyethylene within block copolymer mesophases

We report the morphology and orientation of the crystals which form within the microdomain structures of diblock copolymers of linear polyethylene and glassy poly(vinylcyclohexane), LPE/PVCH, across the spherical, cylindrical, and lamellar morphologies. Compared with short-branched polyethylene (such as hydrogenated polybutadiene), confinement of LPE within spheres, within cylinders, or between PVCH cylinders directly limits the crystal thickness and thereby the crystal melting point. Conversely, crystals formed within LPE lamellae are stacked orthogonally to the LPE/PVCH microdomain layering, so there is no direct limitation imposed on crystal thickness by confinement. As with LPE homopolymer, LPE crystals within lamellae thicken when annealed below the melting point, ultimately forming crystals whose thickness is significantly larger than their lateral extent, set by the bounding PVCH layers. The ribbon-like crystals which form within LPE cylinders or lamellae have a strong orientational coupling to the microdomains; prealignment of the cylindrical or lamellar mesophase by extensional flow yields macroscopic specimens with pronounced b-axial and a-axial orientations, respectively, after subsequent quiescent crystallization.