C9 hydrocarbon petroleum resin is a kind of thermal plasticizing resin produced by C9 fraction,by-products of petroleum cracking,through pretreatment,polymerization and distillation.It isn't a high polymer but a low polymer with the molecular weight between 300-3000.Featared by acid value,easy mutual solubilities, resistant to water,resistant to ethanol and chemicals.It has the chemical stabilizing property to acid and alkaline,viscosity adjusting and thermal stabilizing.Generally,the petroleum resins are not used independently,but have to be used together with other kinds of resins as promoters,adjusting agents and modifiers.