Research On The Relationship Between Structure And Properties Of The Crosslinkable High Molecular Weight Polyarylene Ether Nitrile

Polyarylene ether nitrile?PEN?exhibits excel ent mechanical properties,electrical properties,resistance to chemicals,wear resistance,dimensional stability,non-toxic due to its special molecular structure that contains rigid groups and heat-resistant oxyether.Besides,the presence of pendant nitrile group endows the PEN with good adhesion to many substances,thus high performance functionalized composites can be prepared.Therefore,PEN has attracted considerable attention in the commercial and academic fields.However,the conventional PEN is a kind of linear thermoplastic engineer ing plastic,which has poor heat resistance and rigidity.With the rapid development of high technology and military,the research about ultra-high temperature materials and self-flame retardant materials is imminent.At present,only the phthalonitrile polymer can meet the flame retardant standard of the US Navy.However,phthalonitrile resin,as a class of thermosetting engineering plastics,has some difficulties in the molding and processing.Therefore,based on the above research background,a novel phthalonitrile end-capped poly?arylene ether nitrile?was synthesized at the present work,which combined with the advantages of poly?arylene ether nitrile?and phthalonitrile resin.Various shapes of materials can be prepared through the thermoplastic processing technology before the high temperature heat treatment,and then it possesses excel ent higher temperature resistance performance through the hightemperature heat treatment.Moreover,the relationship between structure and properties of crosslinkable PEN is of great significance to the development and application of the PEN.In this paper,a novel polyarylene ether nitrile terminated with phthalonitrile?PEN-Ph?was synthesized by a simple solution polycondensation of biphenyl?BP?and hydroquinone?HQ?with 2,6-dichlorobenzonitrile?DCBN?,followed by termina t io n with 4-nitrophthalonitrile.The structure of the PEN-Ph was confirmed by infrared spectrum and nuclear magnetic resonance spectrum.A series of crosslinkable Polyaryle ne ethernitriles with different molecular weights were obtained by changing the proportion of the excess amount of biphenyl,and the effect of molecular weights on the thermal,mechanical and electrical properties of PEN-Ph was investigated.The results show that there are some dramatic difference in the thermal and mechanical properties between the high molecular weights and low molecular weights of the PEN-Ph before heat treatment.However,the thermal and mechanical properties of PEN-Ph with different molecular weights are close after heat treatment although the molecular weights of the PEN-Ph varied widely.Besides,a series of PEN-Ph with different structures were obtained by adjusting the molar ratio of BP to HQ.The relationship between structure and properties of the PEN-Ph was also investigated in detail.The results show that with the increase of the proportion of HQ,the PEN-Ph possessed worse crystallization ability.When the molar ratio of BP to HQ is 83:20,the PEN-Ph showed the best mechanical properties as well as good crystallization ability.In the PEN-Ph system,the crosslinking reaction and crystal ization exist simultaneously,which is confirmed by the rheological,DSC and XRD analysis.In this paper,the crystal ization kinetics of PEN-Ph was studied through Jeziorny method.The results show that the crystal of PEN-Ph was spherical and the crystal morphology is verified by polarizing microscope.The activation energy of the crosslinking reaction and crystal ization were calculated by Kissinger method,and the value were 174.8 KJ/mol and 152.7 KJ/mol,respectively.Moreover,the effect of heat treatment temperature on the crosslinking reaction of the PEN-Ph and its properties was studied.It was found that the crosslinking degree increased with the increase of heat treatment temperature.However,when the heat treatment temperature reached 300 oC at normal pressure,there is no PENPh crystals forming due to the more intense cross-linking reaction.Thus,the crystal ization behavior and crosslinking behavior exist simultaneously in the PEN-Ph system when only with the appropriate heat treatment temperature.Based on the above research,PEN-Ph single component composites were prepared by hot-pressing method.The effect of hot-pressing temperature and hot-pressing time on its properties were studied systematically.When the temperature is less than 280 oC,the crosslinking reaction is very slow,so that a large amount of crystals are formed in the PEN-Ph system.In the range of 240-280 oC,with the increasing of the hot-pressing temperature or hot-pressing time,the crystal inity of PEN-Ph single component composites changed little,while the degree of crosslinking increased greatly.Therefore,the crystals were solidated in the PEN-Ph resin through the crosslinking reaction in the amorphous region,and the comprehensive properties of the PEN-Ph single component composites were improved.In this PEN-Ph single component composite,the mechanica l and thermal properties of the materials are influenced by not only the crosslinking degree but also the crystal inity.Finally,PEN-Ph/SiO₂ composites were prepared by simply fil ing method.The PEN-Ph/SiO₂ composites with 12 wt% SiO₂ possessed best tensile strength,which was 14 % higher than that of the pure PEN-Ph film.The PEN-Ph/Fe₃O₄ magnetic hybrid microspheres with excel ent microwave absorbing properties were prepared by solvothermal method.There are some nitrile groups existing on the surface of Fe₃O₄ magnetic hybrid microspheres,which would react with the PEN-Ph resin.Thus,the PENPh/hybrid microsphere composite films with good magnetic performance were prepared by casting method combined with heat treatment.Moreover,the PEN-Ph/GO-CNT composites were prepared.The GO sheets were efficiently isolated and bridged by CNTs through copper ion coordination.In the presence of copper ions,crosslinking reaction occurs in the PEN-Ph system to form the copper phthalocyanine.Therefore,the PEN/GOCNT possessed high dielectric constant as well as high strength.In summary,high molecular weight crosslinkable PEN will have a potential application in the high-tech fields.