关键词: 电子自旋共振, 含萘环聚芳醚酮类聚合物, 分子设计, 交联反应机理, 自由基

Abstract: In recent years aromatic polyether ketones have achieved remarkable positions among other thermoplastic polymers because of their unique combination of toughness, stiffness, thermooxidative stability, electrical performance, flame retardancy and retention of physical properties at high temperatures. So they have been successfully applied to many fields such as aviation, spaceflight, nuclear energy, communication, telecom, petroleum, machine manufacturing and traffic. But following the booming development of new science and technology revolution in world, the high performance materials have been required extensive and urgent. In order to improve the characterization of poly(aryl ether keonte)s further, and fulfill the requirement of some extreme environment like the high temperature and irradiation environment, it is made them to take place crosslinking reaction. It is thermoplastic material before process that can be molded or casted, and then becomes thermoset through crosslinking reaction after process, so it has advantage of both kinds of materials. It′s required to introduce crosslinking group. It can not be used the generally aliphatic crosslinking group over the polymer material because it can decease thermal stability of poly(aryl ether keonte)s, but only to look for the material which has aromatic crosslinking group. The aim of the dissertation is from the design of molecular structure to synthesize new monomers and then to synthesize new poly(aryl ether ketone)s containing naphthalene with different chemical environment and linking position through the nucleophilic displacement condensation reaction. Electric Spin Resonance (ESR) as the major method was used to investigate the thermal crossliniking behavior, discussed the affection of naphthalene with different chemical environment and linking position, and made up the mechanism of crosslinking reaction.

We used 1, 5-dihydroxynaphthalene(1, 5-DHN), hydroquinone(HQ) and 4, 4′-Difluorobenzophenone (DFB) to synthesize the new high molecular weight glass poly(ether ether ketone)s random copolymers containing 1, 5-naphthalene moieties. The glass transition temperature (T_g) increases and the melt temperature(T_m), crystallinity decreases with increasing the content of naphthalene moieties. The mechanical property of copolymers decreases a little but basically retains the advantage of poly(aryl ether ketone). These results can be attributed to the disturbance of the segmental movement and the destruction of the symmetry and regularity of the molecular chains due to the introduction of the naphthalene moiety. The thermal crosslinking reaction was monitored by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), when the poly(ether ether ketone)s random copolymers containing 1, 5-naphthalene moieties were treated above 320 ℃ under oxidative conditions. Both of speeds about the increment of T_g and decrement crystallinity increase following increasing the content of naphthalene and treated temperature. When the treated samples were measured with ESR quantificationally, typical spectra of single peaks were observed and its intension increased with increasing of treated time. When the microwave power was increased, a weak shoulder beside the single peak discovered was slowly appearing. The microwave power saturation method was used to confirm and differentiate the two kinds of free radical R₁ and R₂. Supposing from the character of spectra, whose samples treated under different air condition, R₁ is RO· free radical and links with naphthalene on molecular chains by counting method. The simulation method was used to confirm R₂ is naphthalene free radicals. As the concentration of R₁ free radicals is higher than that of R₂ free radicals, R₁ free radicals take a predominant role in crosslinking reactions. The variations of radical concentration with time for two kinds of free radical are same: the concentration increased fast at first, and then maintained, finally increased fast again. The method of isothermal degradation was used to find the degradation reaction happened when 1, 5-BFPN was treated at 340 ℃. The mechanism of crosslinking reaction about the copolymers containing 1, 5-naphthalene was made out through the above results.

We synthesized a new monomer 1, 4-bis (4-fluorobenzoyl) naphthalene(1, 4-BFN) using the acyl chloride reaction and Friedel-Crafts acylation reaction of 1, 4-Naphthalenedicarboxylic acid with fluorobenzene. Poly (aryl ether ketone) copolymers possessing various compositions of 1, 4-naphthylene and 1, 4-phenylene moieties were prepared by the reaction of hydroquinone(HQ) with 1, 4-bis(4, 4′-fluorobenzoyl) naphthalene (1, 4-BFN) and 4, 4′-difluorobenzophenone (DFB). The glass transition temperature and solubility increase, while the melting temperature decreases with increasing of 1, 4-naphthalene moieties, and the mechanical of 1, 4-PEEKNK is as well as that of PEEK. The samples of 1, 4-PEEKNK treated above 260 ℃ were detected by DSC, and the T_g increases following increasing the treated time and temperature. Based on the results of FT-IR and NMR, the crosslinking reaction takes place on the naphthalene. ESR was used to research the category of crosslinking reaction too. The variations of radical concentration with time also can be divided into three steps, which can be concluded the crosslinking reaction is free radical reaction. Meanwhile, when the samples were treated at different temperature for 8hrs, the radical concentration increased little at 260 ℃ and 300 ℃, but much at 340 ℃, which means other free radicals were generated at 340 ℃. Though the crosslinking reaction takes place at 340 ℃, it′s not beneficial to application for there are much free radicals left. The method of isothermal degradation was used to find the degradation reaction did not happen when 1, 4-PEEKNK was treated at 260 ℃. We made out the mechanism of crosslinking reaction about PEEKNK.

Concluding from above, we have synthesized two kind of new poly(aryl ether ketone)s containing naphthalene with different chemical environment and linking position through the nucleophilic displacement condensation reaction, and researched their basic characterization. We find both of them can take place crosslinking reaction via several research methods, but the mechanisms of crosslinking reaction are different. Colligated all of the property and requirement, PEEKNK containing diketo 1, 4-naphthalene has excellent applied foreground as aromatic crosslinking poly(aryl ether ketone).

Key words: electric spin resonance(ESR), poly(aryl ether ketone)s containing molecular design, naphthalene, mechanism of crosslinking reaction, free radical