New unsymmetrical diamine monomers, 2-trifluoromethyl-4,4′-diaminodiphenyl ether and 2-trifluoromethyl-4,4′-diaminodiphenyl sulfide, and symmetrical diamine monomer, 2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenyl sulfide, were synthesized, and polymerized with PMDA, BPDA, BTDA, and ODPA using solution imidization method and conventional thermal imidization method to obtain the corresponding polyimides. While the polyimides prepared by thermal imidization method were insoluble or had poor solubility, all the polyimides prepared by solution imidization method except the polyimide from 2-trifluoromethyl-4,4′-diaminodiphenyl ether and PMDA were soluble in polar aprotic solvents regardless of the number of trifluoromethyl groups. However, in the case of the polymerization of ODPA with 4,4′-diaminodiphenyl ether that does not have trifluoromethyl group, precipitation occurred during solution imidization. The enhanced solubility of the synthesized polyimides is attributed to the unsymmetrical introduction of trifluoromethyl pendent group. All synthesized polyimides have excellent thermal stability and high $T_g$ values above 234℃.
A series of para-linked aromatic polyamides having inherent viscosity of 0.53-0.91 dL/g were prepared from the above three diamine monomers and 2-cyano-4,4′-diaminodiphenyl ether. The polyamides containing trifluoromethyl or cyano pendent groups were soluble in polar aprotic solvents while the corresponding polyamides without pendent groups showed limited solubility requiring LiCl in NMP even though they have flexible ether or thioether linkages. The para-linked polyamides without flexible ether or thioether linkages prepared from 3,3′-bis(trifluoromethyl)-4,4′-diamino-1,1′-biphenyl also showed limited solubility while the meta-linked one showed good solubility in organic solvents. These solubility results indicate that the position of pendent groups is also an important factor to control the solubility of aromatic polyamides. All synthesized polyamides showed good thermal stability and high $T_g$ or $T_m$ values.
A series of aromatic polyamides and polyimides containing pendent pyrazole rings with amino and cyano groups were prepared from the diamine, 1-(2,4-diaminophenyl)-3-phenyl-4-cyano-5-aminopyrazole which was prepared from (chlorophenylmethylene)propanedinitrile and 2,4-dinitrophenyl hydrazine with 2 steps. The amino and cyano groups on the pyrazole ring were not affected during the polymerization. The synthesized polymers having inherent viscosities of 0.33-0.53 dL/g were soluble in various organic solvents. They showed no $T_g$ before degradation and high thermal stability in spite of polar functional groups.
New soluble polyimides with improved adhesion to copper were synthesized from 6,4′-diamino-2-phenylbenzimidazole (BIA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride via one-pot synthetic method. Precipitation or gelation did not occur during imidization, and the synthesized polyimides having inherent viscosities of 0.86-1.74 dL/g were dissolved well in polar aprotic solvents and phenolic solvents. Flexible and fingernail-creasable films were formed on casting. $T_g$ values of the polyimides were in the range of 320-351℃ and 5% weight loss in both nitrogen and air occurred above 520℃ in all cases. Water absorption and dielectric constant of the polyimides are in the range of 0.57-1.18% and 2.74-2.94, respectively. The polyimides containing equimolar amount of BIA and TFDB showed good adhesion to copper without adhesion promoter, and the polyimides containing higher content of benzimidazole ring exhibit higher adhesion to copper.
Four novel AB type monomers containing hydroxyl and nitro groups, 4′-hydroxy-4-nitro-3(2)-trifluoromethylbiphenyl and 3′-isomers, were synthesized, and polymerized to poly(biphenylene oxide)s. An AA type monomer, 2,2′-bis(trifluoromethyl)-4,4′-dinitro-1,1′-biphenyl was also synthesized, and converted to poly(arylene ether)s with several bisphenols. The polymerization was accomplished by nucleophilic displacement of the nitro leaving group which was activated by trifluoromethyl group. Surprisingly, the nitro leaving group activated by trifluoromethyl group not only at ortho position but also at meta position is quantitatively displaced resulting in high molecular weight polymers. The polymers having weight average molecular weight of 42,100-105,000 g/mol were obtained without side reactions. All the synthesized polymers were amorphous and dissolved in a wide range of organic solvents. Transparent and flexible films were obtained by solution casting. They showed good thermal stability. $T^g$′s of the polymers are in the range of 148-201℃ depending on their structure.
