Because of twisting correlation of crystallites along the radial direction, polyethylene spherulites are known to develop concentric band pattern. The mechanism of branching and reorientation of lamellar crystallites in the banded spherulites has been examined experimentally by optical and atomic force microscopies associated with quenching and chemical etching. The microscopic observation suggests a branching instability of lamellar crystals at the growth front of the spherulite. We propose a mechanism of consecutive branching and twisting reorientation of branches regulated by the inherent torsional stress expected for the banded spherulites and the branching instability. We have experimentally examined the relationships among the growth rate, the maximum lateral width of crystals at the growth front, and the period of bands for three different molecular weight fractions of polyethylene. The predicted relationship among them holds for the fractions.

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The three-dimensional morphology of polyethylene single crystals grown from dilute solution has been examined by atomic force microscopy. Single crystals were deposited on a soft ground of aqueous solution of poly(vinyl alcohol) (PVA) to avoid the collapse of thin lamellar crystals with thickness of 10 nm. The observation of single crystals on dried PVA clarifies the morphology of a chair type crystal as well as well-known hollow pyramidal type. It has been confirmed that the screw dislocations in the chair type follow a selection rule of the handedness in a manner to relieve the distortion in the chair type.

This paper describes a method of determinating the flowability and demolding property of molded polyurethane rigid foams by the dynamic viscoelasticity spectrometer. In response to periodic stimulations, the dynamic viscoelasticity gives us much physical information of polymers, including flowability and demolding properties. The flowability and demolding property can be determined from viscoelasticities and blowing pressures during the foaming process, which are measured with the newly developed apparatus. With this newly developed apparatus we show measurement examples on many kinds of systems, such as variation of base polyols (different functionalities) and blowing agent (CFC-11, HCFC-141b and cyclopentane), etc..