Motowo Takayanagi

Polymer composites of rigid and flexible molecules: System of wholly aromatic and aliphatic polyamides

Abstract As an extension of reinforcing principles of composite materials in which macroscopic fibers are dispersed in a ductile matrix, rigid microfibrils of wholly aromatic polyamides such as poly(p-phenylene terephthalamide) (PPTA), poly-p-benzamide (PBA), and their block copolymers with blocks of nylon 6 or nylon 66 were dispersed in a matrix of nylon 6 or nylon 66. On blending polyaramides with aliphatic polyamides, the spherulitic texture disappeared and a locally birefringent homogeneous texture was obtained. Electron microscopy revelaed that microfibrils of PPTA with diameter of 15-30 nm were dispersed in a fractured surface of the polymer composite. Strong interaction between the fibril surface and the matrix was suggested by the fact that the crystallization of matrix polyamides was induced by the rigid polyaramides. Wide-angle x-ray diffraction intensity curves, DSC curves of cooling process from the melt, and isothermal crystallization curves indicated a marked tendency for induced crystalliza...

Crystal and molecular structure of a collagen-like polypeptide (Pro-Pro-Gly)10☆

Abstract (Pro-Pro-Gly)10 forms single crystals, providing X-ray diffraction data to 0.22 nm resolution. In the crystals, the polypeptides form triplexes that aggregate end-to-end in quasi-infinite helices with axial translation per tripeptide h = 0.287 nm and the corresponding rotation t = −102.9 °. The structure, which may be an allomorph of collagen, has been refined by the linked-atom least-squares procedure. In addition, three water molecules per tripeptide have been detected by Fourier difference syntheses. One of them forms an intrachain hydrogen-bonded bridge O(Pro2) - - - W - - - O(Gly). There are also interchain hydrogen bonds (Gly)NH - - - O(Pro1) within the triplex.

Crystal orientation and some properties of solid-state extrudate of linear polyethylene

Transparent and highly oriented samples of high dimensional stability were obtained by extruding crystallised linear polyethylene through a tapered die at temperatures higher than 80° C and below the melting point. The crystal orientation of the extrudate was examined by X-ray techniques, and it was found that there was a preferential a-axes orientation parallel to the radial direction of the rod-shaped extrudate. Electron micrographs of the fractured surface of the extrudate revealed closely packed thin fibrils of diameters of about 300 Å. Small angle X-ray scattering showed a long period of 200 to 300 Å along the longitudinal direction of fibrils, depending on the extruding conditions. This fact suggests the existence of the lamellar structure in the fibrils.

Role of tie molecules in the yielding deformation of isotactic polypropylene

We examined the effects of the tie-molecule fraction on the yielding behavior of two isotactic polypropylenes, one having little ethylene content and the other as the homopolymer with no ethylene. The tie-molecule fraction of the samples used in this study was controlled by blending ethylene-α-olefin of an α-olefin content above 50 mol % in the blend of which the copolymers were incorporated into the amorphous regions of polypropylene (PP). An excellent linear relationship was observed between the measured yield stress and the tie-molecule fraction estimated from the Huang–Brown model, suggesting that the tie-molecule fraction and lamellar stiffness determine whether the lamellar fragmentation is easily activated or not, depending on the PP composition. Furthermore, an extended Huang–Brown model predicts a lamellar cluster connecting about five lamellae, which has a potential to account for morphological transformation of the spherulitic structure into a fibrillar one. Comparing the immiscible blends showing a phase-separated morphology with the partially miscible blends mentioned above, the yield stress was lowered by the presence of rubber phase, apparently in a similar manner; but the yielding processes were clearly discriminated between both cases when the yield stress was plotted against the tie-molecule fraction.

Microphase separated structure, surface composition and blood compatibility of segmented poly(urethaneureas) with various soft segment components

Properties, surface composition, and blood compatibility of segmented poly(urethaneureas) (SPUUs) with various soft segment components were investigated. The microphase separated structure between hard and soft segments improved with an increase in molecular weight (Mn) of polyether diol in soft segment. The amount of absorbed water depended on the nature of the polyether component. X-ray photoelectron spectra of the surface of SPUU revealed that the surface composition depended on Mn and surface free energy of polyether component. Blood compatibility of SPUU depended on the state of microphase separated structure and surface composition.

Study of fine structure of viscoelastic crystalline absorption in polyethylene single crystals

Abstract Viscoelastic measurements were made on polyethylene single crystals prepared from dilute solution under isothermal crystallization conditions and on annealed crystals of the same samples. As the long period of the isothermally crystallized samples increases, both the absorption temperature and the intensity of the crystalline absorption (αc) also increase. On the other hand, thickening of single crystals by annealing causes the intensity of the absorption to decrease, whereas the absorption temperature shifts to higher values. These findings are interpreted in terms of the introduction of defect regions into the crystalline phase by annealing. The socalled crystalline absorption is further classified into four separate mechanisms. A peak characteristic of the annealed samples (αc) is found at the lowest temperature of the crystalline dispersion region. A second peak (αf) is found in both the isothermally crystallized samples and the annealed ones. A third peak (αm) appears to consist of three sep...

Tensile yield of isotactic polypropylene in terms of a lamellar-cluster model

In this study, the structural factors controlling the yield in isotactic polypropylene materials were theoretically investigated. To describe the yielding behavior of spherulitic polypropylenes, we introduced a new structural unit, lamellar clusters, which are several stacked lamellae bound by tie molecules. It was shown that tie molecules between adjacent lamellar clusters produce a concentrated load acting on the cluster surface, leading to the bending deformation of the lamellar clusters. The yielding behavior can be explained if one assumes that the disintegration of the lamellar clusters occurs when the elastic-strain energy stored by the bending deformation reaches a critical value. By applying the fracture theory of composites to a system consisting of lamellar clusters and tie molecules, we found the yield stress σy to be proportional to , in which EY is the Youngs modulus and Uy is the yield energy. The proportional coefficient between σy and depends only on the cluster size and tie-molecule density, so this proportionality is expected to be true for other spherulitic semicrystalline polymers such as polyethylenes, being independent of temperature and tensile rate.

Microphase separated structure and blood compatibility of segmented poly(urethaneureas) with different diamines in the hard segment

Abstract The properties, structures and blood compatibility by platelet adhesion and deformation of segmented poly(urethaneureas) (SPUUs) with various aliphatic diamine chain extenders were investigated. The SPUUs containing diamines with an odd number of methylene units showed a remarkable degree of phase mixing between the hard and soft segments. I.r. spectra of SPUUs indicated that the state of hydrogen bonding depended on the number of methylene units in the diamine. XPS measurements revealed that the surface concentration of soft segment was independent of diamine structure but the state of microphase separation strongly depended on the number of methylene units in the diamine. The SPUUs with an even number of methylene units in the diamines showed less platelet adhesion and deformation than those with an odd number of methylene units in the diamines.

Analysis of the α-relaxation process of bulk crystallized polyethylene based on that of single crystal mat

Abstract A new concept of the nature of the α1-relaxation mechanism of high-density polyethylene is proposed. This concept is based on the mechanical properties observed in the α-temperature range for as-grown single crystal mats and for samples of bulk crystallized material. The decomposition of the α-multiple-relaxation process into separate α1 and α2-processes was carried out using several different assumptions. These were based on the magnitude of activation energy, on the absorption curve profile of the α2-mechanism, and on the morphological aspects of hollow pyramidal single crystal and lamellar platelets. Based on the paracrystalline analysis proposed by Hosemann, it is suggested that the lamellar platelets of bulk spherulites are composed of a mosaic block structure. These mosaic blocks have diameters of 130∼180 A, heights of 170∼400 A, and intermosaic block distances of several angstroms with specific values depending upon the annealing temperature. The magnitude of the energy dissipation produce...

Structural studies of the high temperature form of trans-1,4-polybutadiene crystal

Abstract It is known that trans-1,4-polybutadiene shows a crystal transformation at about 76°C. The crystal structure of the high-temperature form of trans-1,4-polybutadiene has been studied by X-ray diffraction. The chain conformation of the high-temperature form is similar to that of the low-temperature form. Above the crystal transformation temperature, the CH2─CH2 bond remains trans, but the internal rotation angles around two CH2─CH bonds are decreased to 80° and −80° from 109° and −109°, respectively. The molecular chains, however, are considered to be in a considerably distorted state due to torsional oscillation about the C─C bonds. It is shown that the X-ray diffraction pattern of the high-temperature form can be explained by taking into account the rotational motion of the chain segments around the molecular axes.