Disclosed are antifouling agents used in compositions and methods to reduce or prevent foulants in synthetic feedstocks derived from plastic. A method of reducing or preventing fouling in a plastic-derived synthetic feedstock composition may include adding an antifouling agent including a carboxylic acid anhydride or a copolymer of a dicarboxylic acid anhydride and alpha olefin to a synthetic feedstock composition derived from plastic pyrolysis containing a foulant to provide treated pyrolysate. The foulant may include, for example, nylon, polyvinyl chlorides, polyethylene terephthalate, polyamides, caprolactam, benzoic acid, phenol, p-cresol, dimethylphenol, isopropyl phenol, tert-butylphenol, dimethylethylphenol, napthalenol, varying lengths of alkenes and alkanes, propylene, tolune, pentene, butane, tetramethylindole, ethylbenzene, ethyldimethylpyrrole, dimethylfuran, tetrahydroquinoline, and any combination thereof.