The syllabus for this sub-topic covers the use of plasticizers to make PVC flexible but it does not actually cover what they are. Probably the most commonly used plasticizers are the phthalates which are mentioned in sub-topic A.7 Environmental impact - plastics. Technically phthalate plasticizers are dialkyl or alky-aryl esters of phthalic acid, 1,2-benzenedicarboxylic acid.General formula for phthalate esters