Synthesis And Degradability Study Of Chiral Polyamide-imides Based On Various Amino Acids

In today's society,polymer materials play an important role in our daily lives.While polymer materials give us convenience,they also bring countless plastic wastes to our homes,serious damage to the ecological environment.Therefore,the development and application of non-polluting biodegradable polymers to replace non-degradable materials is the future development trend.Polyamide-imides(PAIs)are promising high temperature resistant amorphous thermoplastic engineering plastic,which combine the excellent mechanical properties of amide groups and the high thermal stability of imide groups.The introduction of natural amino acids into the main chain of PAIs,on the one hand,PAIs have optical activity,and have potential application prospects in the fields of biomedicine,liquid crystal and enantiomeric separation.On the other hand,it enhances the solubility and biocompatibility of PAIs,which have good processing property and biodegradability.In this paper,six L-type natural amino acids and two D-type unnatural amino acids were condensed with pyromellitic anhydride to prepare eight diacid monomers containing imide groups.Then,a variety of diacid monomers and 4,4'-diaminodiphenyl ether were polycondensed to form four kinds of PAIs with the same ratio of L(D)-alanine and L(D)-leucine structures,five kinds of PAIs with different ratios(5:1,3:1,1:1,1:3,1:5)of Lalanine and L-phenylalanine structures,and four kinds of PAIs with three amino acids structures or more.The optical activity of various monomers and PAIs were measured,indicating that the synthesized monomers and PAIs have optical activity,and their optical rotation direction and specific optical rotation change with the change of amino acids.The thermal properties of the polymers were obtained through thermogravimetric analysis and differential scanning calorimetry analysis.The temperature of mass loss of 5 % and10 % are greater than 320 °C and 370 °C,respectively.The residual carbon rate at 800 °C is more than 49 %,and the limiting oxygen index is greater than 37,indicating that PAIs are self-extinguishing materials and have flame retardancy.The alternating amide groups and imide groups in the main chain of PAIs ensure high thermal stability,but the structure and configuration of the introduced amino acids will affect the thermal properties of PAIs.The thermal performance of L-D and D-L configuration PAIs are better than that of L-L and D-D configuration,and the thermal performance of L-L configuration PAIs are better than that of D-D configuration.When the side chain structure of PAIs is different,the more complex side group structure content,the thermal performance of PAIs will decrease due to the volume effect.The synthesized PAIs were subjected to indoor soil degradation experiments and phosphate buffer degradation experiments.The results showed that during the degradation of the PAIs films,microorganisms preferentially attack the amide and imide groups at both ends of the amino acid,resulting in the exposure of the hydrophilic groups and the continuous reduction of the water contact angle.At the same time,the main chain of PAIs is broken,and the molecular weight continues to decrease.The scanning electron microscope images directly show the erosion process of the PAIs films by microorganisms.Different PAIs have different degradability.Among them,the degradability of PAIs containing natural L-amino acids is better than that of non-natural D-amino acids.The higher the content of simple amino acid structure in PAIs,the easier it is to be degraded by microorganisms.As the number of copolymers increases,the regularity of the polymer chain was destroyed,and the PAIs with four amino acid structures have the best degradability.The prepared PAIs with controllable degradation rate and high degradability have wider application prospects.