A series of thermoplastic polyimide resins with a low coefficient of thermal expansion(CTE)were prepared by blending a rigid resin system 3,3’,4,4’-biphenyltetracarboxylic dianhydride(BPDA)/p-phenylenediamine(PDA)wi...A series of thermoplastic polyimide resins with a low coefficient of thermal expansion(CTE)were prepared by blending a rigid resin system 3,3’,4,4’-biphenyltetracarboxylic dianhydride(BPDA)/p-phenylenediamine(PDA)with a flexible resin system 4,4’-[isopropylidenebis(pphenyleneoxy)]diphthalic anhydride(BPADA)/PDA.The effects of the blending ratio on the macromolecular coil size,free volume,and CTE of the mixed system were studied.The mixing is carried out in the prepolymer poly(amide acid)(PAA)stage,which makes the two systems more compatible and is conducive to the formation of a semi-interpenetrating network structure between the rigid molecular chains and flexible molecular chains.The flexible structure of the BPADA/PDA system is used to ensure the melt processing performance.The rigid characteristics of the BPDA/PDA system can inhibit the movement of molecular chains and reduce the free volume fraction,thereby reducing the CTE value.When the rigid system content reaches 30%,the CTE can be reduced to 38 ppm/K.This method provides a new approach for studying low CTE thermoplastic polyimide resins.展开更多
Triphase polyimide nanocomposite films were fabricated using barium titanate （BaTiO3） with high dielectric constant and silver （Ag） with high conductivity as fillers. In situ method was utilized to obtain the homo...Triphase polyimide nanocomposite films were fabricated using barium titanate （BaTiO3） with high dielectric constant and silver （Ag） with high conductivity as fillers. In situ method was utilized to obtain the homogeneous dispersion of nanoparticles. The in situ polymerization of polyimide precursor-poly（amic acid） was performed in the presence of BaTiO3 particles. Silver compound 1,1,1-trifluoro-2,4-pentadionato silver（I） was added into the BaTiO3 containing poly（amic acid） solution to achieve silver nanoparticles via in situ self metallization technique. The thermally induced reduction converted silver （I） to metallic silver with concomitant imidization of poly（amic acid） to polyimide. Both BaTiO3 and silver nanoparticles were uniformly dispersed in the polyimide substrate. The dependence of dielectric behavior on the BaTiO3 and Ag contents was studied. The incorporation of small amount of silver nanoparticles greatly increased dielectric constant of composite films.展开更多
A series of polyimide(PI)films derived from pyromellitic dianhydride(PMDA)and 4,4'-oxydianiline(ODA)were prepared with the employment of chemical pre-imidization,and the pre-imidization degree(pre-ID)was found inf...A series of polyimide(PI)films derived from pyromellitic dianhydride(PMDA)and 4,4'-oxydianiline(ODA)were prepared with the employment of chemical pre-imidization,and the pre-imidization degree(pre-ID)was found influential on structures and properties of the films obtained.Specifically,a certain degree of chemical imidization could promote the in-plane orientation of molecular chains inside the film,which then enhanced the mechanical strength and reduced the coefficient of thermal expansion(CTE)of the films.Further,such pre-imidization process could expand the internal space gap inside the films,thereby lowering their dielectric constant and glass transition temperature.Our study provides a new approach for preparing high-performance PI films through chemical imidization.展开更多
Ladder-like polysilsesquioxanes （LPSQs） with different amino contents have been synthesized by controlling of the dosage of Pd/C catalyst. The concentration and activity of amino groups were investigated by Fourier ...Ladder-like polysilsesquioxanes （LPSQs） with different amino contents have been synthesized by controlling of the dosage of Pd/C catalyst. The concentration and activity of amino groups were investigated by Fourier transform infrared spectroscopy. Polyimide （PI）/LPSQ hybrid films have been prepared by incorporating of the obtained LPSQs with different amino contents into PI matrix, respectively. The interfacial interactions between PI matrix and LPSQ were studied with scanning electron microscopy and X-ray photoelectron spectroscopy, meanwhile the thermal and mechanical properties of the hybrid films were studied using dynamic mechanical analysis and tensile tests. The results indicate that the functionality of LPSQ has great effects on the interfacial interactions and the properties of hybrid films. With the increase of amino content, both the interracial interactions and the cross-linking density of hybrids enhanced, which results in the decline of surface silicon concentration, increase of Young＇s modulus and drop of elongation at break. Excessive amino content makes the hybrid films brittle and leads to incomplete imidization.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51773007)the Fundamental Research Funds for the Central Universities(No.XK1802-2)。
文摘A series of thermoplastic polyimide resins with a low coefficient of thermal expansion(CTE)were prepared by blending a rigid resin system 3,3’,4,4’-biphenyltetracarboxylic dianhydride(BPDA)/p-phenylenediamine(PDA)with a flexible resin system 4,4’-[isopropylidenebis(pphenyleneoxy)]diphthalic anhydride(BPADA)/PDA.The effects of the blending ratio on the macromolecular coil size,free volume,and CTE of the mixed system were studied.The mixing is carried out in the prepolymer poly(amide acid)(PAA)stage,which makes the two systems more compatible and is conducive to the formation of a semi-interpenetrating network structure between the rigid molecular chains and flexible molecular chains.The flexible structure of the BPADA/PDA system is used to ensure the melt processing performance.The rigid characteristics of the BPDA/PDA system can inhibit the movement of molecular chains and reduce the free volume fraction,thereby reducing the CTE value.When the rigid system content reaches 30%,the CTE can be reduced to 38 ppm/K.This method provides a new approach for studying low CTE thermoplastic polyimide resins.
基金financially supported by the National Natural Science Foundation of China(No.51073020)
文摘Triphase polyimide nanocomposite films were fabricated using barium titanate （BaTiO3） with high dielectric constant and silver （Ag） with high conductivity as fillers. In situ method was utilized to obtain the homogeneous dispersion of nanoparticles. The in situ polymerization of polyimide precursor-poly（amic acid） was performed in the presence of BaTiO3 particles. Silver compound 1,1,1-trifluoro-2,4-pentadionato silver（I） was added into the BaTiO3 containing poly（amic acid） solution to achieve silver nanoparticles via in situ self metallization technique. The thermally induced reduction converted silver （I） to metallic silver with concomitant imidization of poly（amic acid） to polyimide. Both BaTiO3 and silver nanoparticles were uniformly dispersed in the polyimide substrate. The dependence of dielectric behavior on the BaTiO3 and Ag contents was studied. The incorporation of small amount of silver nanoparticles greatly increased dielectric constant of composite films.
基金This work was financially supported by the National Key Research and Development Program of China(No.2017YFB0308103)the National Natural Science Foundation of China(No.51773007)the Fundamental Research Funds for the Central Universities(No.XK1802-2).
文摘A series of polyimide(PI)films derived from pyromellitic dianhydride(PMDA)and 4,4'-oxydianiline(ODA)were prepared with the employment of chemical pre-imidization,and the pre-imidization degree(pre-ID)was found influential on structures and properties of the films obtained.Specifically,a certain degree of chemical imidization could promote the in-plane orientation of molecular chains inside the film,which then enhanced the mechanical strength and reduced the coefficient of thermal expansion(CTE)of the films.Further,such pre-imidization process could expand the internal space gap inside the films,thereby lowering their dielectric constant and glass transition temperature.Our study provides a new approach for preparing high-performance PI films through chemical imidization.
基金financially supported by the National Natural Science Foundation of China (No.51073020)
文摘Ladder-like polysilsesquioxanes （LPSQs） with different amino contents have been synthesized by controlling of the dosage of Pd/C catalyst. The concentration and activity of amino groups were investigated by Fourier transform infrared spectroscopy. Polyimide （PI）/LPSQ hybrid films have been prepared by incorporating of the obtained LPSQs with different amino contents into PI matrix, respectively. The interfacial interactions between PI matrix and LPSQ were studied with scanning electron microscopy and X-ray photoelectron spectroscopy, meanwhile the thermal and mechanical properties of the hybrid films were studied using dynamic mechanical analysis and tensile tests. The results indicate that the functionality of LPSQ has great effects on the interfacial interactions and the properties of hybrid films. With the increase of amino content, both the interracial interactions and the cross-linking density of hybrids enhanced, which results in the decline of surface silicon concentration, increase of Young＇s modulus and drop of elongation at break. Excessive amino content makes the hybrid films brittle and leads to incomplete imidization.
