Synthesis And Properties Of Cyano-Containing Polyimides

Due to the unique chemical structure as well as outstanding properties, polyimides have attracted much attention and been applied to many fields such as engineering plastic, gas separation membrane, fuel cell, bionics, luminescent materials and flexible copper clad laminate(FCCL). From the perspective of structural controllability, relations between chemical structure and properties have been investigated by designing the chemical structure of molecular chain in many aspects. For this purpose, cyano-containing PI films possessing high thermostability as well as dimentional stability were designed and synthesized successfully and the relationship between cyano groups and properties of PI will be discussed. Besides, for the pupose of decresing CTE value as well as improving interfacial adhesion, the PI films will be applied to 2L-FCCL field for research. The details are described as follows.In the first part, 1,4-bis(4-amino-2-cyanophenoxy) biphenyl(CN-BP-DA) and 1,4-bis(4-aminophenoxy) biphenyl(BP-DA) were synthesized by nucleophilic substitution and hydrogen reduction. Based on CN-BP-DA and BP-DA, a series of PI films with cyano groups and another series of PI films without cyano groups were prepared through a traditional “two-step” polymerization successfully. After characterization, the series of PI films with cyano groups were found possessing more excellent thermostability(Tg above 250°C, Td5% above 550°C), mechanical property(maximum tensile strength 164MPa), dimensional stability(CTE value 37.98-61.23 ppm/K) and optical property. Besides, both series of PI films exhibited good dielectric properties, solvent resistance and low hygroscopicity. In order to further enhance dimensional stability or to decrease the coefficient of thermal expansion(CTE value), benzoxazole-copolymerized PI film and a series of biphenyl-copolymerized PI films were prepared successfully and the CTE values of two kinds of copolymerized PI films decreased significantly compared with homopolymerized PI films. The CTE values were closed to Cu(CTE value 17.7 ppm/K) or lower than it via adjusting copolymerization ratio. Moreover, thermostability and mechanical property can be futher enhanced.In the second part, 2,5-bis(4-amino-2-cyanophenoxy)-1-(4-cyanophenyl) benzene(CNDA) with multiple cyano groups was synthesized by the same method discussed in the first part. Based on CNDA monomer, a series of PI films with multiple cyano groups were prepared successfully, they had equally remarkable thermostability(Tg above 245°C, Td5% above 540°C), mechanical property(maximum tensile strength 164MPa) and dimensional stability. Otherwise, the processability and solubility can be improved to a certain extent due to the existence of 4-cyanophenyl pendant groups as well as ether linkages.In the third part, based on prepared PI films with cyano groups, PI films of the first part and second part or their prepolymers were utilized to conduct FCCL research, 2L-FCCL was prepared through two kinds of processes, coating and lamination. After peel strength characterization, 2L-FCCL adopting coating treatment method possessed higher peel strength than 2L-FCCL adopting laminated treatment method, 2L-FCCL using PI films with cyano groups possessed higher peel strength than 2L-FCCL using PI films without cyano groups, the test results proved that cyano groups contributed to interfacial adhesion between membrane and copper foil. For intractable copolymerized PI films, surface treatment method was adopted which is due to the increased surface energy and wettability of membrane, such as Na OH treatment. It was found that peel strength was improved obviously.