This application relates to an additive having a structure of general formula I, where R1 and R2 are each independently hydrogen or a C1-C12 alkyl group; R3 and R4 are each independently hydrogen, halogen, or a C1-C12 alkyl group; R5 is hydrogen or a C1-C12 alkyl group; R6 is a 4-20-membered nitrogen-containing heterocyclic group unsubstituted or substituted with a substituent group or a 5-20-membered nitrogen-containing heteroaryl group unsubstituted or substituted with a substituent group, where the substituent group is halogen, a hydroxyl group, a primary amino group, a secondary amino group, a C1-C12 alkyl group, or a C1-C12 alkoxy group; m is an integer ranging from 1000 to 10000; and n is an integer ranging from 10 to 1000. In the additive in this application, the group R6 is a nitrogen-containing heterocyclic group or a nitrogen-containing heteroaryl group.