ABSTRACT:Molecular composite films of block copolyimides consisting of semi-flexible poly-N,N' -(oxydi-p-phenylene)pyromellitimide (PIOD) and rigid-rod poly-N,N' -(p-phenylene)-pyromellitimide were prepared by the usual two step ring-opening polyaddition and subsequent thermal imidization method, starting from pyromellitic dianhydride and either the aromatic diamines or their N-trimethylsilyl-substituted derivatives. The block copolyimide films were transparent and yellow in color over the whole composition ranges, and changed from brittle to ductile films with increasing PIOD content. As the PIOD content increased, the tensile modulus decreased monotonically, while the elongation at break and fracture energy increased in a similar fashion.

Aliphatic polyimides having inherent viscosities of 0.4-2.8 dL g1 were readily synthesized by the melt or solid-state polycondensation under high pressure of the salt monomers composed of aliphatic diamines having 6-12 methylene chains and 4,4'-oxydiphthalic acid at 140-330 O C under 250-650 MPa. It is notable that the high-pressure polycondensation proceeded rapidly with the elimination of water in the closed reaction vessel and was almost complete within 3 h. The polyimides having six and eight methylene units were highly crystalline yellowish white solids, whereas those with odd number carbons were amorphous pale yellow resinous products. The thermal behavior of the polyimides are also discussed.

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ABSTRACT:The simultaneous polymerization and processing under high pressure was carried out by using a piston-cylinder type hot pressing apparatus. Before the polymer synthesis, the Michael addition of aniline to N-phenylmaleimide was performed under high pressure as a model reaction, giving N,N'-diphenylaspartimide. The Michael-type polyaddition of 4,4'-methylenedianiline to 4,4'-bismaleimidodiphenylmethane under 150-820MPa at 180-300°C for 20-40h afforded the linear polyaminoimide having inherent viscosities in the range of 0.2-0.8dlg-1 . When the polymerization was carried out at higher temperature, the closslinked polymer was produced. The polymerization under higher pressure required higher temperature. The closslinked polymer synthesized under high pressure was very hard resin with Vickers hardness of 330-360 MPa and high modulus ( > 1.5 GPa), compared with the polymer obtained under ordinary pressure.KEY WORDS High Pressure Polymerization / Polyaminoimide / MichaelType Polyaddition / Bismaleimide / Polyaminoimide resins derived from aromatic bismaleimides and aromatic diamines are known as a class of high temperature thermosetting addition-type polyimides, and used widely as matrices for composite in electronics and aerospace industries. 1 -3 The advantage is that they contain reactive maleimide groups, which are thermally polymerizable without the elimination of volatile by-products that cause voids in highly closslinked polymeric materials.In the field of synthetic polymer chemistry, the reactive hot pressing technique has been developed for many years. 4 • 5 The concept of this technique is to simultaneously synthesize and mold intractable polymeric materials directly from solid monomers, and the technique was applied to the polymerizationprocessing of high temperature aromatic polymers. The application of high pressure to Michael addition reactions has been demonstrated to be extremely effective means due to both kinetic and thermodynamic backgrounds. 6 • 7 We already reported the application of high pressure to the cycloaddition polymerization of p-cyanobenzonitrile N-oxide and found that the solid state polymerization at room temperature giving poly-1,2,4-oxaziazole was accelerated under high pressure. 8 The present investigation was undertaken to explore high pressure polymerization and simultaneous processing for the polyaminoimide by the Michael-type polyaddition of 4,4' -bismaleimidodiphenylmethane (BMI) to 4,4'-methylenedianiline (MDI) without use of both solvent and catalyst [eq l].

New aromatic poly(diazetidinediones) having a strained four-membered heterocyclic ring structure, which we were unable to obtain by the polymerization under atmospheric pressure, were synthesized for the first time by the cyclodimerization polymerization of aromatic diisocyanates under high pressure without use of solvent or catalyst. As shown by a model compound study, aromatic monoisocyanates cyclodimerized almost quantitatively, yielding 1,3-disubstituted l,3-diazetidine-2,4-diones at 180-200 °C under 400-800 MPa for 20-40 h. Aromatic diisocyanates were converted cleanly to poly-(diazetidinediones) through the cyclodimerization polymerization at 200 °C under 700 MPa for 20 h.The polymers formed were pale yellow, opaque, hard solids with high crystallinity and insoluble in any solvent. They depolymerize drastically at around 270 °C in nitrogen into the parent diisocyanates.

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New phenolic hydroxyl-pendant aromatic polyimides were synthesized with the N-silylated diamine method in two steps: the ring-opening polyaddition of tetrakis(trimethylsilyl)-substituted 4,4Ј-diamino-3,3Ј-dihydroxybiphenyl to various aromatic tetracarboxylic dianhydrides, giving trimethylsiloxy-pendant poly(amic acid) trimethylsilyl esters, and thermal imidization. The hydroxyl-bearing polyimides were amorphous but insoluble in organic solvents. They had glass-transition temperatures greater than 370°C and temperatures of 10% weight loss greater than 415°C in nitrogen. The hydroxyl-pendant polypyromellitimide film had a high tensile strength and a high modulus of 310 MPa and 10 GPa, respectively.