Synthesis And Characterizaton Of Liquid Crystalline Copolymers And Compatibilities To The In-Situ Composites Containing PEEK Matrix

PEEK is semicrystalline aromatic engineering plastics with balanced properties as excellent thermal stability widely applied in aerospace, automobile and electrical industries. The systems of PEEK blended with TLCP are considered to reduce the melt viscosity of PEEK and reinforce with the rigid TLCP as suggested by the concept of "in-situ composites to form a new kind of composites material. But the compatibilities between PEEK and TLCP are poor even in the case of in-situ fibrils. The common approach of compatibilization of polymer blends is to decrease the interfacial tension between the blend partners. Compatibilization by block or random copolymers containing segments chemically similar to the blend partners is the route used in this study.By introducing bulky pendent group onto the polyester, the regularity of chain structure was destroyed. Tm was reduced to348℃, which satisfied the processing conditions of in-situ composites. The polymer with higher molecular weight was obtained by high temperature solution condensation. The liquid crystallinity, texure of polyester were investigated by using a variety of experimental techniques including DSC, PLM and WAXD. It was found that polyester showed the typical nematic texture under Ti which was observed only by PLM.Hydroxy-terminated trimer was synthesized using HQ and DF. Random copolymer was synthesized using trimer, FH and TPC. DSC, PLM and WAXD results showed copolyester was nematic thermotropic liquid crystalline. The random copolymer was used to be compatibilizer of the blends.Multi block copolymer containing different lengths of thermotropic liquid crystalline polyesters (TLCP) and poly(aryl ether ketone) (PAEK) units were prepared for the first time by high temperature solution polymerization of TLCP monomers and hydroxy terminated PAEK containing BPA and DF. The chemical structure, thermal properties and liquid crystallinity of the block copolymers were investigated by FTIR, DSC and PLM respectively. A single glass transition revealed the two blocks had good compatibility. The TLCP segment length of the copolymers had a significant influence on their melting points. The block copolymer PAEK (7797)-b-TLCP (7691) and PAEK (7797)-b-TLCP (5497) showed typical nematic threaded texture which differed from the texture of polyester. When the molecular weight of TLCP reducing to 2965, liquid crystallinity of copolymer disappeared. The influence of synthetic conditions on its properties were investigated. For in-situ composites, DSC and WAXD results showed the crystallinities and crystal structure of PEEK in blends were not changed with the increment of TLCP content. The melt viscosity considerablely decreased after the addition of TLCP. The toque-time plot in the extruding process also showed the same results. The small amout TLCP improved the processability of PEEK distinctively.The compatibilizing effects of random and multi block copolyesters were studied. Tesile properties were measued for blends compression sheet containg multi block copolymer as compatibilizer. The tensile modulus of two blend systems were not changed, tensile strength increased after addition of block copolymer. SEM results of fracture surface of extrudates showed the dimension of TLCP dispersion phase became smaller and the interface became indistinct. These results showed the interface adhesion between two phases. Tesile properties were measued for blends molding speciemen containg random copolymer as compatibilizer. The results showed tensile properties of molding speciemen was better than the compression ones with the same TLCP content because the TLCP tended to align along the molding flow direction under appropiate processing conditions. The increment in the tensile modulus with increasing TLCP content led to improvements in tensile strength. After addition of compatibilizer to the blends, the tesile modulus increased, tensile strength and enlongation at break were not changed. These results showed the random copolymer served as compatibilizer. The crys...