Study On Synthesis And Properties Of Novel Polyimides Containing Thiazole Moiety In Main Chain

Aromatic polyimides generally possess excellent thermal and mechanical, electrical, and chemical properties. Therefore, they are being used in many applications such as electrics, coatings, composite material, and membranes. However, the commercial use of these materials is often limited because of their poor solubility, and high softening or melting temperatures. To overcome these problems, more and more attempts have been focused on the preparation of novel polyimides with improved properties.This paper discussed the structural characteristics of polyimides with excellent properties, and analyzed the contributions of several structural modification methods to each aspect of polyimide properties. Four novel thiazole-containing aromatic diamines, i.e. 2-amino-5-(4-aminophenyl)-thiazole (AAPT), 2-amino-5-[4-(4'-aminophenoxy) phenyl]-thiazole (APPT), 2-amino-5-[4-(2'-aminophenoxy)phenyl]-thiazole (AAPPT) and 2-amino -5-[4-(2'-trifluoromethyl-4'-aminophenoxy)phenyl]-thiazole (AFAT) were designed and synthesized based on the viewpoint of molecular design and combined the characteristics of heteroaromatic thiazole ring, which structures were confirmed by elementary analysis, FT-IR, NMR and MS. Derived from the resulted diamines and dianhydrides such as 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4'-Oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and Pyromellitic dianhydride (PMDA), several series of novel polyimides were successfully synthesized. The polymer constructions were confirmed by elementary analysis, FT-IR and ~1H-NMR. Their solubility, thermal property, mechanical property, aggregate structures, and dielectric property were investigated and discussed.The series of polyimides based on AAPT have a good solubility in aprotic amide solvents and cresols. Meanwhile, strong and flexible polyimide films were obtained, which have good thermal and thermooxidative stability with the glass transition temperatures (Tg) of 276.7-301.5℃, the temperature at 5% weight loss of 451 -492℃in nitrogen and 422-440℃in air, as well as have outstanding mechanical properties with the tensile strengths of 94-122 MPa, elongations at breakage of 5-18%. These films also had dielectric constants of 3.12-3.38 at 10MHz.Taken p-hydroxyacetophenone and p or o-chloronitrobenzene as starting materials, two novel thiazole-containing aromatic diamine monomers, i.e. 2-amino-5-[4-(4'-aminophen-oxy) phenyl]-thiazole (APPT), 2-amino-5-[4-(2'-aminophenoxy) phenyl]-thiazole (AAPP-T), were successfully synthesized and employed in the preparation of thiazole-containing polyimides by polycondensation with several aromatic dianhydrides via the one-step method. The glass transition temperatures and the temperature at 5% weight loss in nitrogen of APPT series and AAPPT series were 268.2-28.8℃and 216.0-288.6℃, and 452-507℃and 422-474℃, respectively. The tensile strengths and modulus of APPT series are 105.4-125.3 MPa and 2.19-2.48 GPa, respectively. The obtained APPT films were also found fairly low dielectric constant of 3.01-3.44 at 10 MHz. Compare to the APPT series, the AAPPT series have better thermooxidative stability derived from the supply electron effect of o-ether group.A series of novel polyimides containing thiazole moieties and trifluoromethyl in main chain was prepared by the polycondensation of the thiazole-containing diamine monomers-AFAT via one-step method. These polymers were subjected to solubility and thermal, optical, and dielectric property measurements. The resulte indicated that polyimides have excellent properties, such as fairly high molecule weight, good solubility, outstanding thermal stability and low dielectric constant etc. The glass transition temperatures and the temperature at 5% weight loss in air atmosphere of the resulted polyimides were 204.9-282.5℃and 393-440℃, respectively. The dielectric constants ranged from 2.53 to 3.10 at 100 KHz. The polyimides derived from trifluoromethyl-containing diamine exhibited better solubility and dielectric property than the non-fluorinated analogies.