| Nylon 6(PA6)is a widely used general-purpose semicrystalline polymer exhibiting good mechanical and processing properties.However,its use is limited in automotive and electronic components and other fields that require high heat-resistant materials.Therefore,to improve the heat resistance of composite materials based on the principle of Mark triangle,a series of binary copolymer heat-resistant agents were synthesized via molecular design.Moreover,the synthesis kinetics was discussed to provide a theoretical basis for fabricating new macromolecular heat-resistant agents.To equationte the macro molecular heat-resistant agent strategy,the motion of the PA6 molecular chain segment was restricted by introducing a rigid structure.The crystal structure of the new heat-resistant agent and PA6 composite was constructed by introducing a hydrogen-bond-induced crystallization strategy.A new heat-resistant agent and PA6 solid-state interface crosslinking structure wereconstructedusingthe reactivity function to form the network structure strategy.A model structure of the PA6 composite material modified using the heat-resistant agent was proposed,and the mechanism of the heat resistance modification was expounded.The main conclusions are listed:1.The synthesis of the heat-resistant agent containing a rigid structure named poly(N-phenyl maleic imide-alt-styrene)(PNS)and their mechanism in PA6 research:(i)Optimizing the one-step synthesis process of adding inhibitor hydroquinone shortened the reaction time and the entire process,saving 50%of the amount of reaction solvent.The synthesis of N-phenyl maleic imide(NPMI)yield reached 95%,under mild reaction conditions.The chemical structure and molecular weight of NPMI were characterized using Fourier-transform infrared spectroscopy(FTIR),nuclear magnetic resonance hydrogen spectroscopy(1H NMR),nuclear magnetic resonance carbon spectroscopy(13C NMR),and high-resolution mass spectrometry(HRMS).(ii)PNS was prepared by the copolymerization of NPMI and styrene(St)using a free radical solution.The numerical average molecular weight(Mn)was 12.2k,and the glass transition temperature(Tg)was 213.2?.The conversion rate of monomer St was obtained at different reaction temperatures using in situ 1H NMR.Theapparent activation energy(Ea)of PNS synthesis under the action of initiator benzoyl peroxide(BPO)was calculated as 22.1kJ/mol,and the optimal reaction temperature was 100?±5?.(iii)PNS with different mass fractions(5%,10%,15%,and 20%)were added to PA6 to prepare PA6/PNS composites,and their heat resistance and mechanism were studied.Thermogravimetric(TG)analysis showed that the addition of PNS had insignificant influence on the thermal stability of PA6.When 15%PNS was added to PA6,the heat deformation temperature(HDT)of the PA6/PNS composite material reached its highest value(138.5?),which was 42.7%higher than that of pure PA6.Dynamic thermo-mechanical(DMA)and rheological results showed that PNS,as a rigid particle,limited the freedom of PA6 molecules and improved the rigidity and viscosity(?)of the PA6/PNS composite.DSC,XRD,and POM findings indicated that the addition of PNS could improve the crystallinity of PA6 and induce its transformation to crystal.Scanning electron microscopy(SEM)showed that the PNS rigid particles dispersed in PA6 could not only induce PA6 crystallization but also limit the degree of freedom of molecular chains,hinder the molecular motion of PA6,and improve its heat resistance.2.The synthesis of carboxyl-containing PNS,(poly(N-(4-carboxyphenyl)maleimide-alt-styrene),PCS),and its heat resistance mechanism in PA6:(?)One-step synthesis of carboxyl-containing NPMI(N-(4-carboxyphenyl)maleimide)(CPMI)induced a yield of 93%.The chemical structure and molecular weight of CPMI were characterized using FTIR,1H NMR,13C NMR,and HRMS.(?)Under the action of initiator BPO,PCS was synthesized by the copolymerization of CPMI and St.The values of Mn,Tg,Ea,and optimal reaction temperature were 9.2k,226.2?,59.5 kJ/mol,and 110?±5?,respectively.(?)PCS with different mass fractions(5%,10%,15%,and 20%)was compounded with PA6 to study the heat resistance and mechanism of PA6/PCS composites.TG analysis showed that the initial degradation temperature of the PA6/PCS composite slightly decreased with the addition of PCS but all were higher than the processing temperature of PA6 at 240?.The heat resistance of the PA6/PCS-10%composite material was optimal with the HDT of 164.8?,which was 35.1%higher than the HDT of the PA6/PNS-10%composite material.The DMA and rheology results showed that with the addition of a carboxyl group,the PA6/PCS composite exhibited stronger rigidity and better ? than the PA6/PNS composite.DSC and POM findings indicated that the crystallinity of PA6 could be improved by the addition of PNS with a carboxyl group.SEM observations showed that with the introduction of a carboxyl group,the interface between PCS and PA6 became fuzzy and the interaction between PCS and PA6 was enhanced.The heat resistance of the PA6/PCS composite was better than that of the PA6/PNS composite.3.The synthesis of fluorine-containing PNS(poly(N-(4-fluorine-phenyl)maleimide-alt-styrene),PFS)heat-resistant agent,and its heat resistance mechanism in PA6:(i)The one-step synthesis of fluorine-containing NPMI(N-(4-fluorine-phenyl)maleimide(FPMI))induced a yield of 93%under optimal technological conditions.The chemical structure and molecular weight of FPMI was characterized using FTIR,1H NMR,13C NMR,and HRMS.(ii)Under the action of initiator BPO,PFS was synthesized by the copolymerization of FPMI and St.The values of Mn,Tg,Ea,and optimal reaction temperature were 10.2k,212.9?,54.1KJ/mol,and 110?±5?,respectively.(iii)ThePA6/PFS composite was prepared by adding 2.5%,5%,7.5%,and 10%of PFS,and its heat resistance and mechanisms were studied.The heat resistance of the PA6/PFS-10%composite was optimal with the HDT of 182.3?,which was 10.6%higher than the HDT of the PA6/PCS-10%composite.DMA and rheological results showed that the introduction of the fluorine base improved the rigidity of the composite material.DSC,XRD,FTIR,SEM,and transmission electron microscope(TEM)showed that the introduction of the fluorine base allowed PFS to form a hydrogen-bonding complexation with PA6,transformation ability enhancement of PA6 from ? crystal type to ? crystal type.The heat-resistant properties of PA6/PCS composite material were better than those of the PA6/PCS composite materials.4.The synthesis of poly(N-(4-carboxyphenyl)maleimide-alt-triallylisocyanate)(PCT)containing a crosslinked structure,and its heat resistance mechanism in PA6:(i)The reactive binary copolymer macromolecule PCT was designed and synthesized with Mn of 6k and Tg of 168.4?.(ii)Irradiated PA6/PCT composite material at 100kGy dose induced a solid-state interface reaction between PCT and PA6.The introduction of a crosslinking structure was studied to improve the heat resistance and mechanism of the PA6/PCT composite material.TG analysis revealed that the thermal stability of the PA6/PCT composite material did not show considerable changes before and after irradiation.When the addition of 10%PCT,the HDT of the i-PA6/PCT composite containing a crosslinked structure was 194.3? after irradiation,which was 6.5%higher than that of the PA6/PFS-10%composite.The gel content,FTIR,X-ray photoelectron spectroscopy(XPS),and SEM findings showed that reactive PCT was uniformly dispersed in PA6 and produced a solid-state interface reaction with PA6 under irradiation conditions.The DMA and rheology results indicated that the i-PA6/PCT-10%composite,which caused the solid-state interface reaction between PCT and PA6 after irradiation,exhibited an improved ratio to the PA6/PFS-10%composite and enhanced the rigidity and ?.Therefore,the occurrence of solid-state interface crosslinking reaction between PCT and PA6 was confirmed,which formed a network structure and resulted in optimal heat resistance performance of the i-PA6/PCT-10%composite.The ability to improve the heat resistance of PA6 when adding 10%:i-PA6/PCT>PA6/PFS>PA6/PCS>PA6/PNS. |
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