The Preparation And Characterization Of The Polyimide Containing Siloxane Moiety In The Main Chain

As one of the most important high temperature polymers, polyimides (PIs) exhibit many useful engineering properties such as outstanding thermal and chemical stability, excellent mechanical and electrical properties. Thus, they are widely used in many advanced and novel technologies such as aerospace, aeronautical, electrical and mechanical industries. However, in order to meet the new development of these fields, some drawbacks of the polyimide materials should be modified, such as poor processability induced by the insoluble and infusible natures of the polymer backbones; high water absorption ratio; weak adhesion on materials; poor functionality and high dielectric constant. Recently, the research in this area has been focused on the modification and functionalization of the polyimide structures.In this work, the soluble polyimides containing various organic silicone moieties in the main chain were synthesized by the conventional two-steps method. And the polymers'structures and properties were discussed. There are four parts to be included in this paper:1. Bis-(3-aminopropyl)-1,3-dimethyl-1,3dimethoxydisiloxane were synthesizedby the hydrolyzed condensation of 3-aminopropylmethyldimethoxysilane and water in the presence of methyol. The products were characterized by elemental analysis, IR, and 1H-NMR. And the factors influencing the product yield were discussed. The results indicated that, at room temperature, the quantitative water was dropped into the mixture of methanol and 3-aminopropylmethyldimethoxysilane, which was carried out by stirring method .Then the reaction continued refluxing on 70℃for 24h, the main product was obtained through distillation and its yield is 52%.2. Di(ethylamino)dimethylsilane was synthesized with dimethyldichlorosilane and diethylamine in the presence of THF. The bis(p-aminophenoxy)dimethylsilane was prepared by the condensation of by di(ethylamino)dimethylsilane and p-aminophenol, which was recrystallized from benzene-petroleum ether. The products were characterized by emental analysis, melting points, IR, and 1H-NMR measurements. The factors of reaction temperature, the solvents, and recrystallization on influencing the product yield were also discussed. The results show that dimethyldichlorosilane (1mol), was added dropwise to a stirred solution of excess diethylamine (8mol) in THF, which was maintained at 0℃.The di (ethylamino) dimethylsilane was distilled and represented 82%.Then di (ethylamino) dimethylsilane was added dropwise to refluxing of sublimed p-aminophenol, in benzene, which was heated at 80℃for 4h and recrystallized from benzene-petroleum ether (4:6 by volume) in 65% yield, as amber crystals mp. 61-62℃.3. Di (ethylamino)methylphenylsilane was synthesized with methylphenyldichloro- silane and diethylamine in the presence of THF. The bis(p-aminophenoxy)methylpheny- lsilane was prepared by the condensation of by di(ethylamino)methylphenylsilane and p-aminophenol , which was recrystallized from benzene-petroleum ether. The products were characterized by emental analysis, melting points, IR, and 1H-NMR measurements. The factors of reaction temperature, the solvents, and recrystallization on influencing the product yield were also discussed. The results show that methylphenyldichlorosilane (0.5mol), was added dropwise to a stirred solution of excess diethylamine (4mol) in THF, which was maintained at 0℃.The di(ethylamino)methylphenylsilane was distilled and represented 76%.Then di(ethylamino)methylphenylsilane was added dropwise to refluxing of sublimed p-aminophenol,in toluene, which was heated at 110℃for 2h and recrystallized from benzene-petroleum ether (4:6 by volume) in 55% yield,as amber crystals mp 107-109℃.4. polyimides containing silane were synthesized by the copolymerization of diaminosiloxane such as bis(3-aminopropyl)-1,3-dimethyl-1,3dimethoxydisiloxane, bis(4-aminophenyloxy)-dimethylsilane, bis(p-aminophenyloxy)methylphenylsilane ,4,4'-diaminodiphenylether(ODA) and 3,3',4,4'-benzophenone tetraacarboxylic dianhy- dride (BTDA). The polymers were characterized by FT-IR spectrum and 1H-NMR and their properties of polymers were also discussed. The results show that these polyimides have excellent solubility in conventional organic solvents such as NMP, DMF, and DMSO, that The Tg of these polyimides were ranged in 225~325℃. The polyimides containing silane have better adhesive properties, which are increased with the increasing amounts of organic silicone, compared with the PIs without organicsilicone moiety. However, the thermal stability of the resulting polyimides was obviously decreased owing to the organicsilicone moiety. Still, it was confirmed that the polyimindes containing phenyl moiety in organicsilicon are of more excellent thermal stability than no phenyl moiety in organicsilicon.