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.
Polymerization of 4‐acetoxybenzoic acid (ABA) with 3,5‐diacetoxybenzoic acid (DABA) was examined to control the morphology of poly(p‐oxybenzoyl) (POB). Polymerizations were carried out at a concentration of 1.0% in an aromatic solvent Therm S‐1000® (mixture of dibenzyltoluene) at 320 °C. Polymerization of ABA yielded the POB fibrillar crystals, but the polymerization with DABA at a concentration in the feed (χf) of 0.10–0.15 afforded novel network structures comprised of spheres connected by fibrillar crystals. The diameter of the spheres prepared at χf of 0.15, which were 0.7 and 5.0 μm, showed bimodality. The network distance, fibril length, and fibril width were 6.1, 2.6, and 0.1 μm, respectively. They possessed high crystallinity. The network structure was formed as follows. Co‐oligomers were first precipitated in the beginning of the polymerization by liquid–liquid phase separation to form the microdroplets. The fibrillar crystals were formed in the coalesced spheres by the crystallization of oligomers induced by the increase of molecular weight. The fibrillar crystals connecting the spheres gradually appeared owing to the shrinkage of the spheres. The fibrillar crystals grew from the surface of the spheres with the crystallization of homo‐oligomers of 4‐oxybenzoyl units, and finally the network structure was completed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1624–1634, 2005
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