Studies On The Solid-state Cross-linking Polymerization Of Semi-crystalline Poly(Arylene Ether Nitrile)

Semi-crystalline poly（arylene ether nitrile）（PEN）is a type of polyethylene with aryl cyanogroup on the main chain and regular structure.The cyanogroup contained in its structure is a kind of functional group with high chemical reactivity.The cyclization reaction can form stable aromatic heterocycles structure.Therefore,semi-crystalline PEN has crystallinity and cross-linkability,and has great potential in preparing high temperature resistant,high strength and high modulus polymer products.Because of the competitive relationship during the processing of the crystallization and crosslinking of polymers,it is important to control the reaction conditions so that they can coexist and enhance synergistic effect.In this dissertation,through the molecular structural design,controlling the crystallization behavior and cross-linking reaction conditions,the crystalline behavior of semi-crystalline PEN,molecular weight,molecular weight distribution,and solid-phase cross-linking of PEN by nucleation and crosslinking agents are systematically discussed.In order to reveal the structure and crystallinity of PEN on the solid-phase cross-linking reaction on the effect of the cross-linking reaction process and behavior,which can propose ways and methods to optimize the solid-phase cross-linking of crystalline polymer materials,to provide the theoretical basis for the design and preparation of the comprehensive performance of crystalline functional polymer materials.Firstly,by condensation polymerization reaction of nucleophilic substitution to synthesize semi-crystalline PENs with terminal cyano groups and terminal hydroxyl groups.In order to study the influence of pendant nitrile groups on the cross-linking reaction,synthesized poly（aryl ether sulfone）（PAES）with terminal cyano groups.Use FT-IR and ¹H-NMR test methods to characterize the structures of the synthesized three polymers.By gel content,glass transition temperature（T_g）and cross-linking density of the crosslinked films to study the degree and activity of solid-phase cross-linking reaction of different structures PEN.At the same time,TGA and mechanical properties testing were used to characterize the performance of different poly（arylene ether）s after solid-phase cross-linking reaction.The results show that the temperature required for the solid-phase cross-linking reaction of the hydroxy-terminated PEN is the lowest and the reaction activity is the highest.A obvious solid-phase cross-linking reaction can occur at 280°C.However,the PEN terminated with nitrile group needs about 320°C to take a solid-phase cross-linking reaction with a faster rate.It shows that the terminal hydroxyl group has obvious catalytic effect on the side chain cyano cyclization cross-linking reaction.After 8 hours of solid-phase cross-linking treatment at 320°C,the gel content and cross-linking density of the hydroxyl-terminated PEN film reached 99.3%and 1021 mol/m³,respectively.At the same time,the obvious solid-phase crosslinking reaction of cyano-terminated PAES film can occurred at 340°C.It indicates that the presence of pendant cyano groups is conducive to the solid-phase cross-linking reaction of poly（aryl ether）terminated with cyano group.Secondly,study the effect of the crystallization behavior of the nitrile group terminated PEN on the system of solid-phase cross-linking reaction.Solution crystallization and cold crystallization were used to study the crystallization behavior of semi-crystalline PEN and PEN films with different crystallinities were produced.Then,control the solid-phase cross-linking reaction conditions to study kinetic parameters of the cross-linking of PEN with different crystallinity.Meanwhile,use micro-region fluorescence and UV-vis spectroscopy to real-time monitor the crystallization process of semi-crystalline PEN.By the datum of gel content,T_g and thermal stability,evaluated the influence of crystallinity of semi-crystalline PEN on the solid cross-linking reactivity and the application performance of the polymer.The results show that the crosslinking reaction of semi-crystalline PEN occurs preferentially in the amorphous part.After the solid-phase cross-linking reaction occuring,a partially three-dimensional cross-linked network structure is formed between the semi-crystalline PEN molecular chains.The formation of this structure can significantly improve the thermal stability of the semi-crystalline PEN.Combined with the contribution of the crystal structure to thermal stability,the synergistic effect of the two can further improve the high-temperature use characteristics of PEN films.Semi-crystalline PEN systems with different molecular weights and molecular weight distribution were produced by polymer synthesis and compounding technology design.The cross-linking characteristics of gel content,glass transition temperature were used to study the effect of molecular weight and molecular weight distribution of semi-crystalline PEN on solid-phase crosslinking reaction.It was found that under the premise of controlling the crystallinity,the lower the molecular weight,the stronger the molecular chain’s ability to move,and the faster the solid-phase crosslinking reaction rate.The higher the content of the low molecular weight components in the compound system,the higher the activity of the solid-crosslinking reaction of the system.The performance of the crystallization-crosslinking coexistence system obtained by solid phase cross-linking at around 310°C is the best,and the solid-phase reaction rate is faster at this temperature.When the molecular weight distribution is wide,the mechanical and thermal properties of the semi-crystalline PEN of the crystalline-crosslinked coexistence system are more prominent.This research found that micro-domain fluorescence and UV-vis spectroscopy analysis can realize real-time monitoring of the solid-phase cross-linking process of PEN.Through the above studies,it was found that by controlling temperature and time,crystalline and cross-linking coexisted semi-crystalline PEN can be produced and its comprehensive application performance is prominent.However,without nucleator and promoter,crystallization and cross-linking process requires a higher heat treating temperature and a longer time,which is not conducive to popularization and expansion.Therefore,in this part of the work,a Fe₃O₄/FePc organic-inorganic hybrid sub-micron spheres are prepared by solvothermal method,in order to promote the crystallization-crosslinking process of semi-crystalline PEN with hybrid particles.As above,the crystallization-crosslinking process of the semi-crystalline PEN composite film was systematically studied by means of gel content,T_g and crystallization kinetics analysis.The results show that the hydroxyl-terminated PEN grafted Fe₃O₄/FePc hybrid material can be used as nucleating agent and cross-linking agent for semi-crystalline PEN.Among them,the Fe₃O₄/FePc hybrid submicron spheres grafted by Steglich esterification to seal the end of the PEN by hydroxyl had the best comprehensive promotion effect,which had a significant improvement effect on mechanical and thermal properties of the PEN solid intersecting composites.At the same time,the improving effect of hybrid particles on the dielectric property and magnetic functionalization of the composite system expanded the application field of the composite system.Finally,a brief introduction to the study of the crystallization-crosslinking method of semi-crystalline PEN,and the application of composite materials in the field of functional materials.Use the crystallization-crosslinking behavior and morphology of semi-crystalline PEN to surface roughening of high-performance fibers,and use simple heat treating to achieve the modification of the fiber surface by the polymer coating.Combining the similarity and intermiscibility and roughening theory to realize the optimization of the interfacial properties and reinforcement of its overall performance of high-performance thermoplastic composites.Using the three-dimensional network microstructure of semi-crystalline PEN solid-phase crosslinking film and outstanding high-temperature using characteristics,combined with the functional characteristics of nano-silver particles,special dielectric functional materials suitable for high-temperature and harsh conditions are prepared.Using the solid-phase cross-linking polymerization characteristics of semi-crystalline PEN,to prepare fiber-reinforced high-performance thermoplastic composite materials.The fiber reinforced polymer matrix composite not only has the characteristics of thermoplastic rapid processing and forming,but also can achieve the similar preformance as thermosetting resin.