Kazuo Itoya

Synthesis of aromatic polybenzoxazoles by silylation method and their thermal and mechanical properties

Various aromatic polybenzoxazole (PBO) films were prepared through the two-step silylation method by low-temperature solution polycondensation of trimethylsilyl-substituted bis(α-aminophenol)s with aromatic dicarboxylic acid chlorides yielding precursor poly(α-trimethylsiloxy-amide)s, followed by thermal cyclocondensation. Four aromatic PBOs had glass transition temperatures (T g ) in the range of 275-375°C, and the T g values were slightly lower than those of the structurally related polyimides. The temperatures of 10% weight loss of these PBOs ranged from 545-616°C in nitrogen, and the values were somewhat higher than those of the structurally similar polyimides. The films of the PBOs had tensile strengths of 105-135 MPa, elongations at break of 11-25%, and tensile moduli of 2.1-2.8 GPa.

A facile solid-state synthesis of crystalline oxydianiline-based polypyromellitimides via salt monomers

Abstract Two isomeric oxydianiline-based polypyromellitimides, P-44PM and P-34PM, were readily synthesized by the thermal solid-state polycondensation of the corresponding salt monomers, 44PME and 34PME, composed of 4,4′-oxydianiline and 3,4′-oxydianiline, respectively, and 2,5-di(ethoxycarbonyl)terephthalic acid derived from pyromellitic dianhydride. The thermal polycondensations of the salt monomers were conducted under reduced pressure or under high pressure, yielding highly crystalline polyimide oligomers. The P-44PM and P-34PM oligomers were subjected to solid-state post-polymerization at a high temperature up to 400°C, leading to the formation of higher molecular weight polyimides. The P-44PM polymer post-polymerized at 400°C had a high inherent viscosity of 1.11 d1 g −1 . During the thermal post-polymerization, the crystal structure of P-44PM markedly changed.

A new high pressure polymerization and simultaneous processing technique for the preparation of aromatic polycyanurates from aromatic dicyanate monomers

Abstract The high pressure polymerization of aromatic dicyanates was carried out by using a piston cylinder type hot-pressing apparatus, which led to the formation of crosslinked polycyanurate resins. In a model compound study, aromatic cyanates were found to cyclotrimerize under high pressure to give aromatic cyanurates, with the application of high pressure accelerating the cyclotrimerization process. Aromatic dicyanates polymerized at 150–280°C under pressures of 200–450 MPa, affording polycyanurates through a cyclotrimerization reaction. Polymerization under higher pressure required both higher temperatures and longer reaction times. After further curing of these crosslinked polymers, very hard resins were produced, with Vickers hardness values of 330–530 MPa and with a high modulus (> 2 GPa), when compared with the same polymers synthesized under normal atmospheric pressure.

Preparation and Properties of Aliphatic Polybenzoxazoles from 4,4′-Diamino-3,3′-Dihydroxybiphenyl and Aliphatic Dicarboxylic Acid Chlorides by the Silylation Method

Abstract A series of aliphatic polybenzoxazoles of high molecular weights was prepared in three steps by the low-temperature solution polycondensation of tetrakis(trimethylsilyl)-substituted 4,4′-diamino-3,3′-dihydroxy-biphenyl with aliphatic diacid chlorides with 7 to 12 methylene units yielding trimethylsilyl-substituted poly(o-hydroxysamide) precursor polymers, which were subjected to desilylation with methanol giving the poly(o-hydroxyamide)s, followed by thermal cyclodehydration. The aliphatic polybenzoxazoles had melting points in the 172 to 246 °C range with glass transition temperatures of 55-97°C. They were stable in the melt state up to 400 °C in nitrogen. These polybenzoxazoles and the corresponding bisbenzoxazole model compounds exhibited no liquid crystallinity.