| There is a considerable interest in the aromatic polymer poly(aryl ether ketone)s (PAEK)s because of its excellent mechanical properties, good environmental resistance and high thermal and thermo-oxidative stability as well as its potential for a variety of applications. All these merits make it very attractive as a high performance engineering thermoplastics. The commercial poly(ether ether ketone) (PEEK) is a typical variety. But unfortunately, it has a relatively low Tg which results in a decrease of the modulus at elevated temperature. This limits its widespread application. With development of high technology and need for material with comprehensively excellent properties, many papers have appeared in the literature. For example, dealing with blends based on PEEK with other high performance thermoplastics, such as polysulfone (PSF), poly(ether sulfone) (PES), poly(amide imide) (PAI), poly(ether imide) (PEI), poly(phenylene sulfide) (PPS), poly(ether ketone) (PEK), etc. However, most of these blends possess a phase-separated structure, which makes them essentially unusable. In addition, there is considerable interest being directed toward the synthesis of structurally related the polymers which have higher Tgs and Tms. It has been shown that increased benzoyl contents or carbonyl to ether ratios in poly(aryl ether ketone)s lead to stiffer backbones, giving higher Tgs and melting points. Some of the authors have synthesized copolymers which involve more rigid monomer units of 4,4'-di(p-fluorobenzoyl) biphenyl and 4,4'-biphenol. It has been found that the Tm is 468℃. But with increasing of Tgs and melting points, these polymers are very difficult to process due to their high softening temperature and high melt viscosity. Therefore, the development of readily processible precursors of high-performance polymers would be more and more valued. The other one way to improve application temperature of PAEKs is to introduce cross-linking point into PAEK backbone. Some research works has not been succeeded. In this paper, we present a successful facile synthesis of a novel monomer containing thioether moieties. And then the controllable cross-linking poly(ether ether ketone)s have been synthesized by introducing of thioether moiety into PEEK backbone in the molecular design, in which sulfur acts as a cross-linking point. The structures and properties of the monomer and polymers were investigated conveniently by DSC, TGA, DMA, TMA, GPC, NMR, POM, rheometer and mechanical machine. The optimal cross-linking reactions were determined by DSC and DMA method. The polymers can be thermal cross-linked when heated to 380℃. Importantly, the happening of cross-linking reaction didn't accompany with happening of degradation reaction and releasing of by-products of volatile. The novel polymer exhibited excellent thermal stability, thermal oxidative stability, and mechanical properties after cross-linking. Many properties after cross-linking were improved obviously than before cross-linking.The properties of poly(ether ether ketone)s containing thioether moieties can be controlled through adjusting the content and distribution of thioether moieties in PEEK backbone. The novel polymers can be processed as conveniently as thermoplastic PEEK before cross-linking and has a high application temperature as thermosetting plastics after cross-linking. This novel material was combined successfully with advantages both of thermoplastic plastics and thermosetting plastics and can be applied as high performance resin and resin matrix of advanced complex material.It is obvious that the variation of tan δ is more pronounced shifted to higher temperature in comparison with increasing of annealed time by DMA. This fact can be explained by existance of the cross-linking bond in process of annealing. The difference in the degree of cross-linking has a distinct effect on the dynamic mechanical behavior. The formation of cross-linking networks retarded the extent of chains migration of the polymer and enhanced chain entangl... |
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