Molecular Modeling Assisted Study On Thermal Performance,Configuration Isomerization And Brill Transition Of PA 10C

Poly(1,4-cyclohexanediformyl decanediamine)(PA 10C)is a class of polyamide with cycloaliphatic rings,which is a special engineering plastics with excellent mechanical,optical,aging and electrical properties.This study focus on the relationship and mechanism between PA 10 C chain segment conformations,main chain structures,crystal structures and performances by first principle calculations,molecular dynamics simulations,experiments analysis,etc.,and explains the excellent heat resistance,reverse isomerization reaction mechanism and Brill transition mechanism of t-PA 10 C.This study is benefit to better understand synthetic processing conditions,conditions of use,properties design of PA 10 C.The main findings and results are as follows:1.Study of thermal performance:High temperature polyamide PA10 T and t-PA10 C were successfully synthesized by interface polymerization.DSC tests have shown that the six-way fat cycloamide t-PA 10 C Tm and Tg are higher than the semi-aromatic polyamide PA10 T and have better thermal properties.Based on the ideal crystal model,the XRD is simulated,which is consistent with the experimental XRD.Through the cell parameters and configuration of the ideal crystal model,the effects of methyl fragments,alamide groups,aromatic rings and hexavalent fat rings on the chain structure are analyzed;The competition between benzene ring ?-? accumulation and hydrogen bond geometry is the reason why PA 10 T hydrogen bond strength is smaller.Through energy decomposition,it is shown that hydrogen bonds play an important role in the short range of the two polyamides.2.Study of the reverse isomer reaction mechanism: through DFT calculations,it is determined that the hexagonal ring in the cis-trans isomer configuration is a chair structure,and the trans structure energy is the lowest.The transition state of transverse isomerization is determined,and the reaction mechanism of transverse isomerization under different conditions is calculated.The energy gap of the reaction path indicates that the aggregate state,inter-molecular force,moisture,etc.all have an effect on the reaction temperature.The balance ratio at different temperatures is illustrated by the energy calculation of isomers.3.Study of Brill transition:The results of t-PA 10C's crystal spacing and grain size changing with temperature by VT-WAXD and VT-FTIR.The temperature at the time of the Brill transition at t-PA 10 C is 160 °C.The results of the ideal cell calculation are compared with the experiment by simulating XRD,and the cell parameters of the stable phase at room temperature are obtained.Based on the ideal cell model of high and low temperature phase,the NPT molecular dynamics simulation of Brill transition is carried out,and the simulation results show that the low temperature stable phase is the lowest energy phase,which is the ideal thermodynamic structure,while the experimental high temperature phase is presumed to be a mixture of crystals with thermodynamically unstable dynamics.Through the configuration analysis of the NPT simulation results of chain segment motion,it can be seen that the structure of the ring is stable,and the amine-side methyl and methyl chain segments,as the most active parts of the chain movement,are the two most obvious chain segments when the Brill transiton occurs,of which the methyl side chain segment movement is the key factor.The emergence and rebalancing of gauche conformations are the result of the movement of methyl when heated,which may be the direct cause of the change of high TB.With the reversible appearance and disappearance of the Brill transition characteristic peak corresponding to the heating and cooling,it is the dynamic result that the molecular chain movement,crystal surface spacing and crystalline structure are adapted with the change of the thermal motion of the methyl chain segment.