Synthesis And Properties Studies On The Polyimides Containing Pyridine Group And Fluorine

The development of new energy field including Electronic photovoltaic(PV),and other emerging fields have brought great convenience to people's life, and meanwhile they provide powerful motivation for the generation of high-performance polyimide materials. Although traditional aromatic polyimides(PIs) have excellent heat resistance and good mechanical properties, and widely used in our daily life.However PIs are still unable to meet the higher requirements of the chip industry and the flat display industry due to the high dielectric properties and coloration or low optical transparency. The study on the structure modification of PIs offers the potential of tailoring some specific performance to adapt to the different areas of application. This thesis mainly deals with structural design, monomer and polymer synthesis and structure-properties relationship study with an aim to forge a novel series of polyimides with improved specific applied properties which was built on the basis of the maintained wholly-balanced properties strategy.Three kinds of novel diamines have been synthesized by using readily accessible inexpensive reagents and uncomplicated method in laboratory. We introduced the functional group of pyridine ring and fluorine-containing group into the structure of polyimides, thereby synthesizing a variety of novel functional PI materials. Aromatic pyridine heterocycle possesses many good characters, which can effectively improve the heat resistance of the polymer, and improve the original mechanical properties.The C=C bond possesses the molar refraction index of 1.73 lower than that of C-N=C bond in pyridine which is 4.10. Consequently, The Introduction of pyridine heterocyclic ring can effectively enhance the refractive index and light transmittance.At the same time, the bulkier pyridine ring can reduce the degree of intermolecular aggregation, block the intermolecular interaction, increase the interchain distance of the PI's and thus promote their solubility.Fluorine can reduce the rate of the overall polarization of polymers, weaken the intermolecular interaction, increase molecular free volume and spacing, and reducethe difficulty of solvent molecules penetrating into the molecular, thereby improving the solubility of the polymers. Fluorine atom with large electronegativity can cut off the conjugation between the PI molecules, and so lead to polymeric film with higher optical transparency. Since the molar polarizability of the C-F bond is very small, the dielectric constant of the polymer can be reduced, generally the fluorine-containing PI material can have the dielectric constant decreased to 2.5 or even lower.Bulky trifluoromethyl and triphenylmethane structure may endow the polyimide with greater intermolecular spacing value, weaken the interchain interaction, thus the solubility of the polymer can be greatly improved, simultaneously with the reduced dielectric constant and increased solubility.Our work mainly includes the following aspects.Firstly, the nucleophilic addition reaction of benzaldehyde with phenol was used to synthesize the diphenol 4, 4-dihydroxy-triphenyl methane(DHTM), which react with 2-chloro-5-nitropyridine to offer the dinitro compound 1,1-bis[4-(5-nitro-2-pyridinoxy)phenyl]-1-phenyl methan(BNPPM).The reduction of BNPPM was carried out to obtain the final diamine 1,1-bis[4-(5-amino-2-pyridinoxy)phenyl]-1-phenyl methane(BAPPM).Secondly, p-fluorobenzaldehyde or 2,2,2-Trifluoroacetophenone was reacted with phenol to generate the diphenol FDTM or DTTE, which was further reacted with2-chloro-5-nitropyridine to give the dinitro compound. The obtained dinitro compound was reduced to offer the diamines 1,1-bis[4-(5-amino-2-pyridinoxy)phenyl]-4-Fluoro-1-phenyl-methane or 1,1-bis[4-(5-amino-2-pyridinoxy)phenyl]-1-phenyl-2,2,2-Trifluoroethane.Thirdly, ODPA or 6FDA was used to prepare polyimide with the above synthesized diamines, respectively. We conducted a comprehensive properties test and analysis of the six synthetic polyimide material. The solubility of polymer is greatly improved by fluorine-containing diamine and dianhydride. The structure of the trifluoro-containing diamine leads to the best solubility when polymerized with the same kind of dianhydride. The tensile strength of PIx(1-3) range in 57.6-115.3MPa, elongation at break 2.6-6.8%, modulus of elasticity 2.4-3.2GPa, and the maximum tension 35.97-55.36 N. The data show that the introduction of afluorine-containing groups on the diamine, whether trifluoromethyl or fluorine atom structure, has a marked effect in improving the mechanical properties. Mechanical properties of fluorine-containing structure is better than non- fluorine structure.Introducing the trifluoromethyl group structure shows more significant effect in improving the mechanical properties including the elastic modulus and tensile strength of the film materials. While DSC data show that the introduction of fluoride structure increases the glass transition temperature of the material to improve the thermal performance of the material.Fluorine-containing polyimide material is more hydrophobic than non-fluorinated analogue, the hydrophobic properties of the material has greatly improved with hexafluoro dianhydride in the main chain, while the trifluoromethyl diamine structure has more excellent hydrophobicity relative to the single fluoro structure polymer. Trifluoromethyl is a bulky group, consisting of three C-F bonds that are hydrophobic groups, and the bond energy is very large. By comparing the dielectric constant and dielectric loss of PI-2, BPI-1, BPI-2, it was found that the introduction of a fluorine-containing unit can reduce the dielectric constant of the material, also did for a low dielectric loss. 6F dianhydride structure also improved the dielectric properties of of the film.-CF3 State is an asymmetrical structure with a large presence of polarization dipole moment, its bulky structure will hinder the intermolecular charge transfer, reducing the intermolecular interactions,coupled with a fluorine atom itself is very low rate helps reduce the dielectric constant, thus resulting in the low dielectric constant. BPI-3 had a significantly higher optical transmittance at 500 nm than BPI-1 and BPI-2, and has a minimum cutoff wavelength 386 nm. We can see that trifluoroacetic diamine have better permeability than single fluorine atom or a nonfluorine-containing structure. At the same time the structure of a single fluorine atom has better optical transmission than nonfluorine structure. In short, we synthesized the PI materials containing trifluoroacetic structure possess good mechanical, optical, dielectric properties, and overcome the shortcomings of poor organosolubility.