Study On The Preparation And Performance Of Semi-crystalline PI/PA66 Block Copolymer

With the rapid development of automotive,medical technology,electronic and electrical technology,mechanical manufacturing,and national defense aerospace,the demand for the performance of polymer materials are becoming higher and higher.As an engineering plastics which possesses high performances,the semi-aromatic polyamide has many good properties,such as high T_g,high temperature resistance,low water absorption,high strength,easy processing and corrosion resistance,etc.,especially the PA6/6T and PA9T has attracted great attentions.As a kind of polyamide products,the nylon 66?PA66?is the earliest developed,and most widely used.It is also one of the most important products of polyamide materials.Its T_g is only approximately 70°C,which is easy to absorb water;and after the vitrification,its modulus drops greatly,which makes its operating temperature be not high and limits its application.The polyimide?PI?has excellent comprehensive performances,its high temperature resistance is up to 400^oC,the long-term operating temperature is-200?300^oC,it has a high insulation performance and no obvious melting point.Its biggest disadvantage is difficult to process.In order to obtain higher heat resistance for PA66 products,the PI segment is introduced into PA66 to synthesize a semi-crystalline PA-PI copolymer and its performance is characterized.Firstly,the pure nylon 66 is synthesized via salt formation and high temperature and high pressure solution method,and then the PI is introduced into the PA66 to obtain PA66-PI copolymers with different PI contents by the copolymerization.The chemical structure and crystal structure is confirmed by the FTIR,¹³C NMR,intrinsic viscosity and XRD.In the synthesis,the process conditions for PA66 are optimized,and the optimal reaction temperature is determined to be 270^oC,the optimal pH value for PA66 salt is 8.6,and the optimal amount of catalyst is 0.6wt%.The influence of different PI contents on the PA-PI copolymer system is discussed,and its thermal performance,stability,dynamic performance and processing performances are discussed in detail.The results of the DSC,TGA and DMA studies on the PA-PI copolymer show that the thermal properties of the PA-PI copolymer will improve with the increase of PI content,the melting point decreases from 261^oC?PA66?to 223^oC,and the crystallization temperature also decreases,which is much lower than that of PA6/6T and PA9T.The thermal stability of PA-PI copolymer is good,and the amount of residual carbon after the complete combustion will increase with the increasing PI content.The DMA shows that the glass transition temperature?T_g?rises from 70^oC?PA66?to 90^oC,and the initial storage modulus of PA-PI is higher than that of PA66.The modulus attenuation of PA-PI-3?PA:PI=7:3?after T_g is almost the same as that of PA6/6T.The rheological studies on the processing properties of copolymers show that the processing temperature range of PA-PI copolymers can reach70^oC and the copolymers with different PI contents show different processing viscosities.The PA-PI-1?PA:PI=9:1?and PA-PI-2?PA:PI=8:2?are suitable for the processing method of general thermoplastic resin,however,the melt viscosity of PA-PI-3 and PA-PI-4?PA:PI=6:4?is relatively large,even higher than that of PA6/6T and PA9T,however the melt viscosity is less dependent on the time and can be processed for a long time.In addition,the water absorption rate?about 1.8%?and the dielectric constant of PA-PI are similar to those of PA6/6T.The dynamic properties of PA66 and PA-PI-2 in the hygroscopic state show that the initial storage modulus of PA66 decreases significantly,and the T_g drops from 70^oC to 60^oC.When the temperature reaches 87 ^oC?T_g?,the storage modulus of PA-PI-2 can also be 1.1GPa,which indicates that it can adapt to higher strength applications.In order to investigate the crystallization performance of PA-PI copolymer,the non-isothermal crystallization process and the kinetics of PA-PI copolymer is studied via Jeziorny's method correcting Avrami equation and Mo Zhishen's method.With different PI component contents,the crystal growth modes of PA-PI copolymers are various and the F?T?and“a”values of the copolymers are calculated.The non-isothermal crystallization activation energies of the copolymers with 10%,20%,30%,and 40%PI contents are calculated by the Kissinger method which are-364.6kJ/mol,-264.2kJ/mol,-315.9kJ/mol,and-253.7kJ/mol respectively.