## 3 Results and Discussion
As can be seen in Figure 1, PAI3a has the fastest degradation rate, higher than PAI3f, indicating that the microorganism preferentially degrades the PAIs of the L-configuration. This enantioselectivity \begin{table}
\begin{tabular}{c c c c c} \hline
**Polymer** & **Tg (\({}^{\circ}\)C)** & **T5 (\({}^{\circ}\)C) a** & **T10 (\({}^{\circ}\)C) b** & **Char Yield (\%) c** \\ \hline PAI3a & 241 & 313 & 354 & 58.67 \\ PAI3b & 196 & 323 & 390 & 48.90 \\ PAI3c & 147 & 278 & 323 & 46.15 \\ PAI3d & 189 & 297 & 340 & 47.25 \\ PAI3e & 206 & 296 & 329 & 47.86 \\ PAI3f & 238 & 310 & 357 & 56.15 \\ \hline \end{tabular}  
* Temperature at which 5% weight loss fully was recorded by TGA in a N2 atm. b Temperature at which 10% weight loss fully was recorded by TGA in a N2 atm. c Weight percent of the material left undecomposed after TGA at 800 \({}^{\circ}\)C in a N2 atm.  
\end{table} 
Table 1: Thermal properties of PAI3a–3f. stems from spin polarized interaction. This mechanism for the intermolecular interaction of chiral molecules results in a higher degradation rate of the PAI in the L-configuration [20; 21]. When the structure of the amino acid introduced into PAIs is different, the effect of the structure on the degradation effect is more obvious. The degradation of natural chiral PAIs is better than that of non-natural chiral PAIs. Figure 2 shows the infrared changes of PAI3a before and after degradation. It can be seen from Figure 2 that after 30 days of degradation, the symmetrical and asymmetric stretching vibration absorption bands of the carbonyl group at 1654 cm\({}^{-1}\) and 1658 cm\({}^{-1}\) are significantly weakened, and the bending vibration absorption band of CN at 1383 cm\({}^{-1}\) is also significantly weakened. In addition, the bending vibration absorption band of C=O at the 721 cm\({}^{-1}\) of the imide five-membered ring almost disappeared, indicating that the carbonyl and imide bonds from the amino acid are easily destroyed during the degradation process. It can be found that the fragmentation of polymer chains occurs mainly on the two ends of amino acid molecules. It is to say that the amide and imide bonds sourced from carboxyl and amino groups in amino acids are easily broken. Figure 3 is a nuclear magnetic diagram of the degradation product of PAI3a. As can be seen from Figure 3, the main \({}^{1}\)H NMR peak of the degradation product is very similar to that of the polymer, containing benzene ring, methyl group, carboxyl group, amino group and other functional groups. This further indicates that the degradation of the PAI films begins with the broken of amide bonds, and later extends to the damages of imide rings. The break of polymer chain and the formation of small molecules leads to the change of molecular weight. Figure 1: Weight average molecular remaining of PAI3a–PAI3f at each stage of degradation. X-ray diffractograms of PAI3b are shown in Figure 4. The other PAIs have similar X-ray diffractograms. PAI3b exhibited two broad halos in the range 20 = 20-25\({}^{\circ}\) and 15-20\({}^{\circ}\). The broad halos in XRD patterns indicates their amorphous nature [22]. Thus, the PAIs is completely amorphous. Figure 3: \({}^{1}\)H NMR spectra of PAI3a film before and after degradation. Figure 2: FTIR spectra of PAI3a film before and after degradation. Figure 5 shows the SEM images of different periods of PAI3a and PAI3b degradation, and that the other PAIs have the similar change rules. It can clearly be seen from Figure 5 that after 15 days of degradation, there is a significant change in the surface of the membrane. The formation of pores has occurred. After 30 days of degradation, the damage of the membrane surface is more obvious, and there are more holes. This may be because the enzyme damages the PAIs membrane from the outside to the inside, first destroying the surface layer of the membrane, then gradually deepening, and finally forming holes.