Yuhiko Yamashita

Synthesis and characterization of poly(oxy-2,6-naphthalenediylcarbonyl) whiskers from 2-acetoxy-6-naphthoic acid

Abstract The synthesis and characterization of poly(oxy-2,6-naphthalenediylcarbonyl) (PON) whiskers from 2-acetoxy-6-naphthoic acid are described. The important factors in controlling PON crystal morphologies during high-temperature solution polymerization are polarity of solvent, concentration of monomer and stirring. Less-polar solvents like liquid paraffin or Therm S 800, low concentration of monomer and no stirring are desirable for making PON whiskers. The size of the whisker prepared in liquid paraffin is 7–17 μm in length and 0.5-1.0 μm in width. From its electron diffraction patterns, it was found that this whisker exhibits a single-crystal nature and the polymer chains align along the long axis of the whisker. Owing to the close packing of polymer chains in this crystal, the whisker has the highest thermal stability compared with the other fibrillar and slab-like crystals. The formation mechanism of PON whiskers is also investigated in comparison to that of poly(oxy-1,4-benzenediylcarbonyl) whiskers.

Solvent effect on the morphology of poly(oxy-1,4-benzenediylcarbonyl) whiskers from p-acetoxybenzoic acid

Abstract Poly(oxy-1,4-benzenediylcarbonyl) (POB) whiskers from p -acetoxybenzoic acid were prepared in mixtures of liquid paraffin having many branched carbons (LP) and completely linear paraffin (SW). The crystal shapes of the POB whiskers obtained were largely changed by the mixing ratio of LP and SW. When the content of SW in the solvents increased: (i) both the length and the width of the whiskers decreased; (ii) the tip angle of the whiskers increased; and (iii) radial growth of the whiskers increased. The size of the POB whiskers was attributed to both the number and the size of those lamellar crystals with screw dislocations (primary nuclei for whisker growth) which had formed in the early stages of polymerization. In SW, larger numbers of smaller lamellar crystals were formed than in LP, owing to the lower solubility of POB oligomers at 330°C in SW; that is, the higher supersaturated state of the POB oligomers produced a larger number of smaller primary nuclei for whisker growth. Hence, whiskers having smaller lengths and widths were obtained as the content of SW increased. The other characteristic changes in whisker shapes, i.e. tip angles and radial growth, also seemed to be attributable to the degree of supersaturation of the POB oligomers, though further study is required. The thermal properties of the whiskers were evaluated by differential scanning calorimetry and thermogravimetric analysis.

Synthesis of novel fluorine‐containing poly(aryl ether ketone)s

The high-performance fluorinated polymers have been receiving considerable attention as interesting advanced materials. The incorporation of fluorine atoms into polymer chains leads to polymers with increased solubility, flame resistance, thermal stability and glass transition temperature while also leading to decreased color, crystallinity, dielectric constant and moisture absorption. 2,3,4,5,6-Pentafluorobenzoic acid (PFBA) is a valuable intermediate for pharmaceuticals, pesticides, perfumes, cosmetics and so on, and it is available as a commercial product. However, the polymers derived from PFBA have not been reported so far. In this paper, we report the synthesis and characterization of novel fluorinated poly(aryl ether ketone)s (PEKs) containing 2,3,5,6-tetrafluoro-1,4-phenylene moieties derived from PFBA. Novel fluorinated PEKs are prepared from PFBA by aromatic nucleophilic substitution reaction, of which Mn values range from 2.28 × 104 to 1.04 × 105. They have all para connected linear structures. The aromatic fluorine of the para position to the carbonyl groups of monomers is preferentially substituted by phenoxide and this para orientation is mainly attributed to the steric effect rather than π-electron density. The obtained PEKs except 8F-PEKEK (BP) show excellent solubilities in common solvents and can be cast into tough transparent films. They also exhibit high glass transition temperatures depending on the structures and outstanding thermal stabilities. Furthermore, these fluorine-containing PEKs exhibit low dielectric constants from 2.87 to 3.52 at 1 MHz. Copyright

Synthesis and characterization of poly(4-mercaptobenzoyl) whiskers from S-acetyl-4-mercaptobenzoic acid

Abstract Poly(4-mercaptobenzoyl) (PMB) whiskers were obtained from S-acetyl-4-mercaptobenzoic acid by high-temperature solution polymerization. The whisker prepared in liquid paraffin at a concentration of 1.0% at 300°C has an almost uniform width of 0.3–0.5 μm and a length of 5–8 μm. These whiskers show radial growth from the centre. The optimal conditions for preparing them are by using liquid paraffin as a solvent and polymerization temperatures of 260–300°C. Electron diffraction reveals that the PMB whiskers show single crystal nature and the polymer chains are aligned along the long axis of the whisker. D.s.c. analysis of the PMB whiskers shows the presence of the reversible solid-solid transition as already reported by Kricheldorf et al. The transition temperature and enthalpy of the PMB whiskers are higher and larger than those of PMB crystals with other morphologies. Another endotherm is found at ∼ 420°C, but only when measurement is carried out using a faster heating rate of 100°C min−1. This is deduced to be a solid-liquid crystal transition from the observation of the nematic domain structure in a quenched specimen using an optical microscope. Finally, the formation mechanism of the PMB whiskers is discussed from the polymerization time dependencies of the length, the degree of polymerization and the yield.

Novel optical oxygen sensing material: metalloporphyrin dispersed in fluorinated poly(aryl ether ketone) films

Abstract A series of new fluorine-containing poly(aryl ether ketone)s (8F-PEKEK(Ar); Ar: 2-2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane (6FBA), 2,2-bis(4-hydroxyphenyl)propane (BA), 2-(4-hydroxyphenyl)-2-(3-hydroxyphenyl)propane (3,4′-BA) or 9,9′-bis(4-hydroxyphenyl)fluorine (HF)) are synthesized and applied to the matrix of optical oxygen sensing using phosphorescence quenching of metalloporphyrins, platinum and palladium octaethylporphyrin, (PtOEP and PdOEP) by oxygen. The phosphorescence intensity of PtOEP and PdOEP in 8F-PEKEK(Ar) films decreased with increase of oxygen concentration. The ratio I0/I100 is used as a sensitivity of the sensing film, where I0 and I100 represent the detected phosphorescence intensities from a film exposed to 100% argon and 100% oxygen, respectively. For PtOEP in 8F-PEKEK(Ar) film, I0/I100 values are more than 20.0 and large Stern–Volmer constants more than 0.19%−1 are obtained compared with PtOEP in polystyrene film. For PdOEP in 8F-PEKEK(Ar) film, on the other hand, the large I0/I100 values more than 143 are obtained. However, the Stern–Volmer plots of PdOEP in 8F-PEKEK(Ar) films exhibit considerable linearity at lower oxygen concentration range between 0% and 20%. These results indicate that PtOEP and PdOEP films are useful optical oxygen sensor at the oxygen concentration range between 0% and 100% and between 0% and 20%, respectively. The response times of PtOEP and PdOEP dispersed in 8F-PEKEK(Ar) films are 5.6 and 3.0 s on going from argon to oxygen and 110.1 and 160.0 s from oxygen to argon, respectively.

Whisker of poly(p-oxybenzoyl-co-p-mercaptobenzoyl)—influence of sequence on polymer morphology

Aromatic polymers are expected to possess outstanding properties. However, in many cases they do not show good processability because of their chain regidity. We have been studying the morphology control of rigid polymers during polymerization to overcome this problem and succeeded in preparing the whiskers of poly (p-oxybenzoyl) and poly (p-mercaptobenzoyl) by the polymerization in liquid paraffin at around 300 °C. These whiskers are formed by the reaction induced crystallization of oligomers during solution polymerization. The preparation of copolymer whiskers is very interesting to design the new materials which are endowed with novel functions. The aim of this study is to prepare the whisker of poly (p-oxybenzoyl-co-p-mercaptobenzoyl) and to clarify the influence of the copolymerization on the morphology, especially focusing on the sequence regularity. The introduction of comonomer unit into polymer chain structure extinguishes the crystal habit due to the lower crystallizability and the whiskers can be obtained by the random copolymerization of 4-acetoxybenzoic acid (ABA) and S-acetyl-4-mercaptobenzoic acid (AMBA) only when κf (the molar ratio of ABA/AMBA in feed) is 1.0–0.7 and 0.05–0. However, the copolymer whiskers are obtained by the polymerization of OS, OOS and SSO monomers which produce the alternating and periodic copolymers. These copolymer whiskers consist of the alternating or periodic copolymer chains and their chains align along the long axis of the whisker. The sequence regularity enhances the crystallizability of cooligomers and this leads to the formation of the whiskers. The sequence regularity in copolymers is a very influential parameter to control the morphology and the copolymer whiskers can be prepared by giving the regular sequences. Copyright

Morphology of oriented calcium alginate gels obtained by the flow-gelation method

Abstract Cylinder-shaped oriented gels of calcium alginate were prepared by extruding a 2.6 wt% aqueous solution of sodium alginate (guluronate rich) into CaCl 2 solution through a glass tube. Effects of flow rates on chain orientation in solution and in the gel were examined by polarized optical microscopy. During flow, chains underwent planar orientation along the tube wall, which was reflected in the gel state. Increasing the flow rate increased the coil-stretch transition in solution but led to disorientation of chains in the gel due to increasing die swell and longitudinal shrinkage. This effect resulted in the occurrence of the highest anisotropy of the gel at low flow rate. Chain orientation in the gel was characterized by tilting towards the tangential direction with the appearance of a small negative birefringence, which was transformed to a large positive birefringence on drying due to chain realignment in the longitudinal direction. The morphology of the gel was deduced to be sheet-like structures stacked cylindrically with strong intrasheet binding. Scanning electron microscopy and wide-angle X-ray diffraction were both used in the investigation.

Structure change of polyacetylene-Ix− complex by iodine doping

Abstract Specially oriented polyacetylene fibrillar films were prepared by the epitaxial polymerization technique. The fibrils were doped with iodine to various levels, and the structural change was studied using electron microscopy. At low doping levels iodine preferentially takes the form of the I 3 − anion making a periodic lattice within the polyacetylene matrix. Increasing the iodine concentration generates I 5 − anions which disturbe the I 3 − periodicity. Based on these structural results, a transition in the conduction mechanism will be proposed.

Morphologies of oriented alginate gels crosslinked with various divalent metal ions

Abstract Optically anisotropic cylinder-shaped alginate gels crosslinked with various divalent metal ions such as Ca, Cu, Zn, and Pb were prepared by the flow-gelation method in which semidilute sodium alginate solution was extruded through a tube into metal nitrate salt solutions. Effects of metal ions on the morphological and structural features of the gels were examined mainly by polarized optical microscopy. The chain orientation was characterized by a planar orientation where the mean chain orientation is primarily parallel to the gel surface and normal to the total flow direction, due to diametric expansion and longitudinal shrinkage on gelation. The degree of chain extension and orientation was shown to increase in the order Pb > Cu > Ca > Zn. Scanning electron microscopy of the gels dried rapidly under vacuum showed that all the metal alginate gels had cylindrically developed sheet strucures. Molar ratios of metal ions bound to alginate chains were estimated, using plasma spectroscopy, to be in th...

Control of the Length of Aromatic Polyester Whiskers

The control method of poly(p-oxybenzoyl) (POB) whisker length is reported, with the main focus being on how to make the length of the whiskers longer. The POB whiskers were prepared by the polymerization of p-acetoxybenzoic acid in LPF at 330°C. The increase in whisker length is caused by the way oligomer lamellaepileupalongthelongaxisoftheneedle-likecrystalswithspiralgrowth. From the present detailed morphological observations during polymerization, the tip angle of the whiskers is constant at 80° up to a time 10 min, whereas it becomes significantly sharper to 12° at 30 min. This sharpening of the tip angles seems to be highly related to the degree of supersaturation of the oligomers dissolved in solution. In order to depress the sharpening of the tip angle and to extend the steady-state growth for increase of the whisker length, oligomers were added twice into the polymerization system, after 10 min just before the tip angle becomes sharper and then after 20 min. The addition of oligomers extended the steady-state growth period, and the length was increased from 40 μm to 47 μm with the first addition and then to 50 μm with the second addition. The addition of oligomers during steady-state growth gives the most favourable conditions for continuous growth with spiral growth.