https://scholar.google.com/citations?view_op=view_citation&hl=en&user=2YWD-4gAAAAJ&sortby=pubdate&citation_for_view=2YWD-4gAAAAJ:eq2jaN3J8jMC#:~:text=Poly(styrene%2Dco%2Dmaleic%20anhydride)%20modified%20with%20nickel%20sulfate%20and%20its%20application%20in%20the%20synthesis%20of%202%2Damino%2D4H%2Dchromenes