Research On Process,Mechanism And Crystal Structure Of Solid State Polymerization Of Nylon 66 Salt

Direct solid state polymerization(DSSP)is a polymerization method with no pollution,low reaction temperature,short reaction time and it can get products with high molecular weight.It is a new hot spot in the research field of nylon in recent years.In particular,the method can solve the technical problem of long reaction period(prepolymerization and solid state post polymerization),high energy consumption,and difficulty in obtaining high molecular weight products in the synthesis method of the long carbon chain semi-aromatic nylon(such as nylon 12T,nylon 10T)and other nylon with high melting point.In order to further optimize process and understand the effect of the process on its properties,it is necessary to research the process,mechanism and crystalline structure of DSSP of nylon salt.Considering that the semi-aromatic nylon salt and the products have the characteristics of small crystal size,high melting point and easy to oxidation,this paper has mainly researched the large size nylon 66 salt single crystal,which plays an important reference role in solid state synthesis of high melting point nylon resin.The results show below:1.This paper had prepared the large size nylon 66 salt single crystal,and it was characterized by several test methods,such as differential scanning calorimetry(DSC),thermogravimetric analysis(TG),X-ray single crystal diffraction and wide-angle X-ray diffraction(WAXD).The results show that for nylon 66 salt,the initial decomposition temperature(1%weight loss)is 186?,the melting point is 202.5?,the crystal system is monoclinic system,the space point group is P21/c,the unit cell parameters are a=5.5923 A,b=15.5673 A,c=8.5068 A,?=90°,?=102.821°,?=90°,and the grain size of the main crystal plane ranges from 26 to 68 nm.2.This paper researched the effect of polymerization conditions on the molecular weight of nylon 66.The results show that the molecular weight of the polymer increases with the increase of the reaction temperature in the high pressure period,and increases slowly when the reaction temperature exceeds 195?;it increases with the increase of the reaction time in the high pressure period,and it tends to be stable or even decreases when the reaction time exceeds a certain value which decreases with the increase of the reaction temperature and the amount of the auxiliary agent;it increases with the increase of the amount of auxiliary,and it decreases when the amount of auxiliary exceeds a certain value which decreases as the reaction temperature increases;it increases with the reaction temperature increases and the reaction time increases in the negative pressure period.3.This paper had researched the crystal structure of the solid state polymerized nylon 66 by comparison with the melted state polymerized product.The DSC results show that the solid state polymerized sample had a crystallinity of 60%,and the primary melting heat was about twice that of the secondary melting heat;While the melted state polymerized sample,the crystallinity is 32%,the primary and secondary melting heats are close.The WAXD results show that the solid state polymerized sample has a crystallinity of 50%and it's TB is 205 ?;While the melted state polymerized sample has a crystallinity of 32%and it's TB is 175 ?.The results of small angle X-ray scattering(SAXS)show that the long period of the solid state polymerized sample is 76.99 nm,which remains unchanged with the increase of temperature;While the long period of the melted state polymerized sample is 95.49 nm,which gradually increases to 129.81 nm as the temperature increases.The results of polarized light microscopy(PLM)and scanning electron microscopy(SEM)show that the crystal size of the solid state polymerized sample is significantly smaller than that of the melted state polymerized sample.The reason for these differences is that the surface spacing of hydrogen bonding surfaces is large,the crystal preferentially grows on the hydrogen bond surface,and there may be extended chain crystals.4.This paper had researched the influencing factors of the crystal structure of the solid state polymerized nylon 66.The XRD results show that the formation of the crystal structure of the solid state polymerized sample is related to the crystal structure of nylon salt and the polymerized conditions.Both the increase of the reaction temperature and the amount of the additive cause an increase in the destruction of the salt crystal,which converts the crystal structure of the product into the crystal structure of the molten crystal;the reaction time in the negative pressure period has no effect on the crystal structure of the solid state polymerized product.5.This paper had researched the process and mechanism of direct solid state polymerization of nylon 66 salt.The PLM results show that the nylon salt is partially melted during the solid state polymerization.The results of ultra-deep-field microscopy(UDM)and gel permeation chromatography(GPC)show that the polymer nucleation sites are random and the polymer grows around the polymer core after nucleation.The mechanism of direct solid state polymerization of nylon salt reveals:(1)when the reaction temperature is lower than the actual decomposition temperature of the nylon salt,the crystal defect of the salt single crystal is the nucleation site;(2)when the reaction temperature is higher than the actual decomposition temperature of the nylon salt,with the diffusion of the hexamethylene diamine in the surface layer,the salt crystal causes the salt crystal defects to promote nucleation,and the end group moves faster under the action of temperature,resulting in effective collision and accelerated polymerization.The reaction temperature can promote two nucleation effects at the same time;(3)the water is formed after the nucleation of the polymer,and the diffusion of water causes the surrounding salt crystals to melt,so that the end groups frozen in the salt crystal lattice are free to move,which can increase effective collisions and accelerated polymerization.