Tadashi Kōmoto

Morphological study of the wear of crystalline polymers I: High density polyethylene

Abstract The morphology of the worn surface and wear debris of high density polyethylene (HDPE) slid against steel in air and water was studied. Electron micrographs and electron diffraction patterns of carbon replicas of the worn surfaces revealed that the molecular chains (crystallographic c axis) of HDPE were markedly oriented in the sliding direction. Annealing of the wear specimen caused lamellar crystals to form perpendicular to the sliding direction, suggesting folded-chain crystals linked by tie molecules and tie fibrils. Morphological consideration is also given to the wear mechanisms of HDPE in air and water.

Morphological study of the wear of crystalline polymers II: Isotactic poly(propylene)

Abstract The morphology of the worn surface and wear debris of isotactic poly(propylene) (PP) slid against steel in air and water was studied. From electron micrographs, electron diffraction patterns and X-ray diffraction patterns it was found that both the worn surface and the wear debris had a smectic structure. Plastic deformation of the surface of PP took place during frictional contact both in air and in water, giving rise to the formation of thick meandered fibrous aggregates with their longitudinal axes nearly perpendicular to the sliding direction and thin fibrils aligned parallel to the sliding direction.

Crystallization during polymerization with special reference to synthetic polypeptides

Abstract In order to pursue the possibilities of the extended chain crystals formed in the course of polymerization, kinetics of the heterogeneous polymerization of L- and DL-alanine N-carboxy anhydrides (NCA) in acetonitrile and the morphologies of the resultant polymers were studied. It was revealed that the growing chain molecules, when they attained a certain degree of polymerization (DP = 3 to 4), crystallized into the form of ribbon-like fibers in which molecules, with the β-conformation, were aligned perpendicularly to the fiber axis. As the growing chains attained a critical length by further polymerization, they began to take the α-helical conformation. The crystals grew successively thereafter, taking the α-helical conformation through addition of the monomer molecules onto the reactive chain ends. The grown polypeptide chains were extended α-helices in the crystals throughout the remainder of the polymerization. Possible mechanisms are proposed for the nucleation and the subsequent growth of the crystals in the course of polymerization. The polymerization of NCAs of glycine and β alanine has also been studied.