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Some harmful volatile organic compounds (VOCs), such as formaldehyde, are regulated atmospheric pollutants. Therefore, development of a material to remove these VOCs is required. We focused on hydroxyapatite, which had been biomimetically coated on a polyamide film, as an adsorbent and found that formaldehyde was successfully removed by this adsorbent. The amount of formaldehyde adsorbed increased with the area of the polyamide film occupied by hydroxyapatite. The amount of adsorbed formaldehyde and its rate of adsorption were larger for hydroxyapatite deposited on polyamide film than for the commercially available calcined hydroxyapatite powder. This high adsorption ability is achieved by the use of nanosized particles of hydroxyapatite with low crystallinity and containing a large number of active surface sites. Therefore, hydroxyapatite biomimetically coated on organic substrates can become a candidate material for removing harmful VOCs such as formaldehyde.

Modification of organic polymer with silanol groups in combination with calcium salts enables the polymer to show bioactivity, that is, the polymer forms apatite on its surface after exposure to body environment. However, how modification with silanol groups influences ability of apatite formation on the polymer substrate and adhesive strength between polymer and apatite is not yet known. In the present study, polyamide containing carboxyl groups was modified with different amounts of silanol groups, and its apatite-forming ability in 1.5SBF, which contained ion concentrations 1.5 times those of simulated body fluid (SBF), was examined. The rate of apatite formation increased with increasing content of silanol groups in the polyamide films. This may be attributed to enhancement of dipole interactions. A tendency for the adhesive strength of the apatite layer on the polyamide film to be decreased with increasing content of silanol groups was observed. This may be attributed to swelling in 1.5SBF and having a high degree of shrinkage after drying. These findings clearly show that modification of organic polymers with the functional groups induces apatite deposition, and also determines the adhesive strength of the apatite layer to the organic substrates.

Preparation of poly(p-oxycinnamoyl) (POC) microspheres was examined by the reactioninduced phase separation of oligomers during the polycondensation of (E)-4-acetoxycinnamic acid in various solvents. Polymerization in liquid paraffin yielded the microspheres having a smooth surface at 270-330 °C, of which the average diameter was 4.6 µm. In contrast to this, the morphology of the products was drastically changed in Therm S 800 (TS8) and Therm S 900 (TS9) by polymerization temperature. When the polymerization was carried out at 310 °C in TS8 and 300 °C in TS9, the microspheres were obtained, of which the average diameter was 3.9 and 3.3 µm, respectively. The platelike crystals were formed under these temperatures, of which thickness was approximately 0.1 µm. The formation of the microspheres was highly related to the miscibility between the oligomers and the solvents. The average diameter of the microspheres increased with the decrease of the miscibility, and this tendency could be accounted for by the interfacial tension between two immiscible liquid phases. The microspheres were formed through the formation of the microdroplets by the liquid-liquid phase separation of the oligomers and the subsequent solidification of the microdroplets due to the further polymerization in them.

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Polymerization of 4-acetoxybenzoic acid (ABA) with 3,5-diacetoxybenzoic acid (DABA) was examined to create a novel morphology of poly(p-oxybenzoyl) (POB) by means of the phase separation of oligomers during polymerization. Polymerizations were carried out at a concentration of 1.0% in liquid paraffin at 320°C. Polymerization of ABA yielded the POB whiskers. On the other hand, the polymerization of ABA with DABA of which the concentration in the feed ( f) was 0.05-0.20 yielded the microspheres having needlelike crystals on the surface. The average diameter of the microspheres was in the range of 3.4-1.6 µm and the average length of the needlelike crystals was 3.2-0.3 µm. The diameter and length decreased with f. DABA acted as a liquid-liquid phase separation inducer and the liquidliquid phase separation of co-oligomers comprising 4-oxybenzoyl units and 3,5-dioxybenzoyl units was induced in the beginning of polymerization to form the core microspheres. Then the phase separation mode was changed to the crystallization of the homooligomers of the 4-oxybenzoyl unit and the homooligomers were crystallized as needlelike crystals on the surface of microspheres already precipitated. Solid-state polymerization occurred in the precipitates. The microspheres having needlelike crystals were prepared by the combination of liquid-liquid phase separation and the crystallization of oligomers during solution polymerization. The obtained microspheres having needlelike crystals possessed very high crystallinity and exhibited good thermal stability.