Synthesis,Isomerization And Aggregation Structure Of Novel Six-Membered Alicyclic Polyamide PA10-CHDA

High temperature resistant polyamide engineering plastics play an important role in high-tech fields such as electronics,automobiles,and aerospace.Six-membered alicyclic polyamides are expected to be the next generation of high-temperature polyamides compared to the higher water absorption of short-chain aliphatic resistant high-temperature polyamides and the weaker thermo-oxidative stability of semi-aromatic resistant high-temperature polyamides.Unlike the planar rigid aromatic ring,the six-membered alicyclic ring has a configurational isomerism(cis/trans).The current research focuses on the effect of the cis-trans configuration of the six-membered alicyclic unit on the heat resistance of the polyamide.However,the cis-trans isomerization behavior of the six-membered alicyclic structure,especially the isomerization behavior induced by temperature field,is rarely involved,which has caused problems in the process of bulk polymerization and melt processing of such polyamide materials.In this paper,a new type of polyamide cis/trans-PA10-CHDA containing six-membered alicyclic ring was synthesized by interfacial polymerization with decanediamine and cis/trans-1,4-cyclohexanedicarboxylic acid(cis/trans-1,4-CHDA).The effects of the cis and trans configurations of six-membered alicyclic structural units of PA10-C on their thermal properties,aggregation structure were investigated.The cis-trans isomerization behavior of six-membered alicyclic structural units induced by temperature field and the evolution of aggregated structure caused by it are emphatically studied.The main contents are as follows:1.Study on the controllable polymerization of PA10-C:The interfacial polymerization process of PA10-C was studied by single factor experiment.The effects of reaction temperature,type of acid binding agent,amount of acid binding agent,monomer concentration and monomer molar ratio on the molecular weight of the product were investigated.The optimum polymerization conditions are as follows:molar ratio of monomer to monomer is 1:1,monomer concentration is 0.1 mol/L,molar ratio of triethylamine to monomer is 1.4:1,and reaction temperature is 70 ℃.The Mn of trans-PA10-C(cis:trans=0:100)and cis-PA10-C(cis:trans=95:5)were 21000 and 18500,Mw was 45000 and 4200,PDI was 2.1 and 2.3,respectively.The configuration content of six-membered alicyclic structural units in polymers was consistent with that of monomers.2.Study on thermal performance:The thermal decomposition temperature and phase transition temperature of cis/trans-PA10-C were investigated by thermogravimetric analysis(TG),differential scanning calorimetry(DSC)and microscopy.The results show that trans-PA10-C and cis-PA10-C lose weight at 5%temperature,10%temperature,maximum decomposition rate temperature and final decomposition temperature in NZ atmosphere are 408 ℃,444 ℃,483 ℃,504 ℃ and 335 ℃,442 ℃,483 ℃,504 ℃ respectively.The melting point of trans-PA10-C is 353 ℃,the glass transition temperature is about 186 ℃,the viscous flow temperature of cis-PA10-C is 140～150 ℃,and the glass transition temperature is about 100 ℃.3.Study on isomerization behavior induced by temperature field:DSC was used to simulate the effect of temperature field and the ratio of cis-trans configuration was determined by NMR spectroscopy.The kinetics and thermodynamics of the isomerization of trans-PA10-C and cis-PA10-C were studied.The results of reaction kinetics showed that the critical temperature for trans-PA10-C isomerization reaction was 300 ℃,the apparent activation energy was 326.83 kJ/mol,the critical temperature for cis-PA10-C isomerization reaction was 204 ℃,and the apparent activation energy was 93.14 kJ/mol.The results of reaction thermodynamics showed that the equilibrium ratio of six-membered aliphatic ring unit configuration in PA10-C was 23:77(cis:trans).4.Studies on aggregation:The aggregated structure of cis/trans-PA10-C at room temperature was studied by X-ray diffraction(XRD),polarizing microscope(PLM)and fourier transform infrared(FT-IR).The results show that the cis six-membered alicyclic structure is not conducive to the formation of ordered hydrogen bonds between molecules and the formation of crystallization by ordered arrangement of molecular chains,while the trans six-membered alicyclic structure is conducive to the formation of ordered hydrogen bonds between molecules and the formation of crystallization by ordered arrangement of molecular chains.Trans-PA10-C is a crystalline polymer with y crystal structure and spherulite,while cis-PA10-C is an amorphous polymer.The evolution of hydrogen bonds in cis/trans-PA10-C under temperature field was tracked by variable temperature infrared spectroscopy(VT-FTIR).The results show that the intermolecular hydrogen bonds of trans-PA10-C are mainly ordered hydrogen bonds at room temperature.With the increase of temperature,the intermolecular hydrogen bonds gradually dissociate.The intermolecular hydrogen bonds in cis-PA10-C are mainly disordered hydrogen bonds.As the temperature increases,the hydrogen bonds gradually dissociate.When the temperature reaches above the critical reaction temperature of isomerization,the ordered hydrogen bonds will form in the aggregates.The change of aggregation state of cis/trans-PA10-C under temperature field was observed by PLM.The results show that trans-PA10-C does not change before melting,and melts when the temperature reaches the melting point,and after melting of cis-PA10-C,the melt can form crystalline domains above the critical temperature of isomerization.