Synthesis And Characterization Of Thermoplastic Polyimide Based On Diketone Anhydride

Polyimides(PIs) have excellent mechanical properties, high temperature resistance, corrosion resistance, radiation resistance and low dielectric constant, etc.Therefore they are widely applied in high-tech sectors such as aerospace,microelectronics industry. However, many PI applications are limited owing to process difficulties, as their insolubility in organic solvents, their extremely high melt temperatures, poor resistance to impact toughness and high manufacturing costs. The modification of PI structure is a major research interest.Some general approaches have an emphasis on reducing molecular regularity,rigidity. One approach to improve solubility and processability of PI is by the introduction of flexible linkage groups. Processing property and heat resistance is two contradictory properties, finding a reasonable balance to synthesis good properties PI is important. Research shows that in the molecular chain of ketone-anhydride PI,introduction of ketone group can regulate the structure and properties, improve PI material processing molding, and maintain its high thermal stability.4,4’-terephthaloydiphthalic anhydride(TDPA) is a para-substituted diketone-anhydride, its low manufacturing costs is helpful to decrease the cost of the preparation of PI. The diketone structure can preclude close packing of molecular chain, improve the flexibility of molecular chain, is beneficial to improve the PI processing properties. Aromatic ketone group possess big bone energy, can keep the PI excellent thermal stability at the same time.Based on the analysis of relationship between structure and properties of PI,TDPA and aromatic diamine contain double ether-group were used as monomers, the para-substituted diketone-anhydride PIs were prepared. The main research contents and results are as follows:(1) High molecular weight polyamide acids(PAAs) were prepared from TDPA and 1,3-double(4-amino phenoxy) benzene by polycondensation in DMAc.TDPA/BAPB polyimides, part of the crystalline polymer, were meltable and synthesized by thermal imidization and three kinds of chemical imidizations.Different process about chemical imidization can make the PI obtain different degree of order structure, the one-step method was more advantageous to form crystallization than the two-step method. The PI film had excellent tensile strength(118.3 MPa), the PI powder had good solubility.(2) High molecular weight polyamide acids(PAAs) were prepared from TDPA and 2,2’-bis[4-(4-aminophenoxy) phenyl]propane(BAPP) by polycondensation in DMAc. TDPA/BAPP polyimide films and powders were synthesized by thermal imidization and chemical imidizations. The tensile strength of the PI film could reach159.1 MPa, the PI powder was meltable and had good solubility. A small number of phthalic anhydride(PA) was used as sealing agent, could adjust the molecular weight of PAA, and improved the PI thermal properties to some extent.(3) Used BAPP and para-phenylene diamine(PPD) as diamine monomers,reacted with TDPA, copolyimides(CPIs) were obtained. Changing the ratio of two kinds of diamine, could adjust the ratio of soft and hard segments of the system, thus improved the CPI required properties. The ratio of BAPP to PPD was 0.5:0.5, the tensile strength of the CPI film could reach 112.8 MPa, and the CPI powder had good solubility.