Abstract:
In this research, surface segregation behaviors of polyimide blends between polysiloxane-block-polyimide (BSF30) and three polyimides of different chain flexibility [3,3’,4,4’-oxydiphthalic anhydride (ODPA)/ 4,4’- diaminodiphenyl ether (4,4’-ODA); 3,3’,4,4’-biphyltetracarboxylic dianhydride (s-BPDA)/ 4,4’- diaminodiphenyl ether (ODA), and 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA)/ 4,4’- diaminodiphenyl ether (ODA)] have been investigated. The polyimides were synthesized by a conventional two-step method via poly(amic acid) (PAA) precursor in N-methyl-2-pyrrolidinone (NMP) solvent. These polyimide blends, having various compositions of the silicon-containing block copolyimide, were processed by the solution casting method then undergone thermal imidization to yield the solid films. All film samples with 50 m thickness were characterized by contact angle measurement, surface profilometer, Attenuated total reflection Fourier transform infrared (ATR-FTIR), and ATR microscope. These techniques revealed that the surface segregation typed phase separation occurred between the two polymers for all three types of polyimide blends. In this study, the films at various BSF30 contents were processed on a glass substrate. At low concentration of BSF30 (less than 10 phr), three types of the polyimides tended to migrate to the glass-side surface, while BSF30 component tended to migrate to the air-exposed surface. For high concentration of BSF30 (i.e. 30 phr), the glass-side surface was covered with the polyimides whereas the air-side surface showed two different areas on the air-exposed surface of the films, i.e. hill area and valley area. With ATR microscope, the differences of % Si-C content on the valley area of three polyimide blends revealed the %Si-C content PMDA/ODA blending system exhibited the highest segregation level. That is believed to be related with the lowest chain flexibility of PMDA/ODA.
