Study On Preparation And Properties Of Novel Polyimides And Their Composites

In this paper,artificial zeolite and natural melanin particles were used as modifiers for polyimide(PI).The influence rules for the mechanical properties,thermal properties,dielectric properties,and UV-shielding properties of the prepared polyimide-based composite materials were investigated by studying the factors such as the surface treatment and the addition amount of modifiers.These two composites exhibited excellent thermal,low dielectric and UV-shielding properties and had potential applications in the fields of microelectronics and aerospace.Meanwhile,soluble fluorinated copolyimides and fluorinated hyperbranched polyimides were prepared,which laid the foundation for the preparation of PI composites.The specific works are as follows:(1)A series of fluorinated random co-polyimide/amine-functionalized zeolite MEL50 composite films(co-FPI/MEL50-NH2)were successfully prepared with the addition of MEL50-NH2(e.g.0,1,3,5,7 wt%of the co-FPI).Thereinto,zeolite MEL50 was synthesized by hydrothermal method and co-FPI was obtained by random copolycondensation from BPADA,6FDA and ODA.The results showed that the thermal properties and low dielectric properties of the hybrid films were markedly enhanced to achieve the optimum with the addition of 3%MEL50-NH2.In our results,the glass transition temperature and 5%weight loss temperature in nitrogen increased up to 266℃ and 527℃,respectively from 243℃ and 517℃ of the pristine co-FPI film.The dielectric constant decreased down to 2.68 from 3.21 of the pristine co-FPI film.This convenient approach provides a possibility of making PI possess both enhanced thermal properties and low dielectric constant,which is more applicable to microelectronics.(2)To investigate the effects of pure silica zeolite nanoparticles(PSZN)and amine-functionalized pure silica zeolite nanoparticles(APSZN)on PI films with different chain structure,a series of PI films,PI/PSZN blend films and PI/APSZN composite films were successfully prepared by random copolycondensation.Thereinto,PSZN were synthesized by hydrothermal method.The polyimides were derived from 4,4’-diaminodiphenyl ether(ODA),and three adjustable molar ratios(3:1,1:1,1:3)of BPADA and 6FDA.The results showed that the thermal and mechanical properties of PI films were drastically impaired after adding PSZN.On the contrary,the strength,toughness and thermal stability were improved after adding APSZN.Moreover,the dielectric constants of the PI/APSZN composite flims were lowered but UV-shielding properties were enhanced.Interestingly,we found that the greatest effects were obtained through introducing APSZN in PI derived by the 1:1 ratio of BPADA:6FDA.The corresponding PI/APSZN composite flim exhibited the most reinforced and toughened properties,the largest decrement of dielectric constant and the best UV-shielding efficiency,which made the composite flim be used as ultraviolet shielding material in outer space filled with high temperature and intensive ultraviolet light.Meanwhile,this work also provided a facile way to synthesize composite materials with adjustable performance.(3)Novel fluorinated copolyimide/amine-modified sepia eumelanin(ASE)nanocomposites were successfully fabricated via covalent bonds.To achieve this,the polyimide(PI)was synthesized by random copolycondensation.The effects of ASE on the structure and properties of the PI were investigated.A multilinked network was formed with ASE acting junctions in the nanocomposites.The mechanical properties of the PI were significantly improved by the addition of ASE,and the optimal tensile strength and elongation at break were 79.7 MPa and 85.42%,respectively.UV-vis transmittance,methylene blue(MB)photodegradation and recyclability measurements confirmed that the PI/ASE nanocomposites were transparent to visible light at low ASE loadings and showed outstanding UV-shielding properties and lifetimes under intense UV irradiation owing to the synergistic absorption of UV light by the PI matrix and ASE.Furthermore,the PI/ASE nanocomposites had enhanced thermal properties with initial degradation temperatures above 500℃.These properties endowed the nanocomposites with great potential for UV-shielding in the conditions with high temperature and intense ultraviolet light.(4)A novel fluorinated aromatic triamine,named 1,3,5-tris(4-(2-trifluoromethyl-4-aminophenoxy)phenyl)benzene(TTFAPOPB),with several-CF3 groups,prolonged chain segments and ether bonds was first successfully synthesized via a three-step reaction.Then a series of fluorinated hyperbranched polyimides(FHBPIs)with terminal amino or anhydride groups were prepared by condensation polymerization,which were derived from three commercial dianhydrides and the obtained triamine.The prepared FHBPIs,showed excellent optical properties with the transmittance reaching 94.5%at 800 nm,favourable UV-shielding property with only 27%photodegradation of methylene blue solution after intense UV irradiation for 50 min,good thermal stability with glass transition temperature between 225.2℃ and 263.9℃,10%weight loss temperature of 520.3-555.0℃and 509.67-541.67℃ respectively in nitrogen and air atmosphere.They also exhibited relatively good mechanical properties with tensile strength,tensile modulus and elongation at break values of 64.2-84.2 MPa,1.2-1.5 GPa and 6.0-10.0%,severally.Moreover,the introduction of-CF3 and hyperbrached architecture reduced the dielectric constants of the FHBPIs to 2.69-2.92 and increased the solubilities,which laid the foundation for thepreparation of functionalized PIs.Thus,the FHBPIs are promising to be used as dielectric or ultraviolet shielding materials.