Methyl Tin Mercaptide

About This Product

Methyl tin mercaptide is an organotin heat stabiliser: a methyltin centre carrying sulphur-bearing mercaptoester ligands, supplied as a clear, low-colour liquid. It is not a single compound but a formulated mono- and di-methyltin mercaptide system, so identity is defined by the grade specification rather than by one CAS number. PVC degrades by losing hydrogen chloride from the polymer backbone. Once that starts it is autocatalytic: the liberated HCl accelerates further elimination, and the conjugated polyene sequences left behind absorb visible light, which is why unstabilised PVC yellows and then blackens as it is processed. A tin mercaptide intervenes on two fronts. The tin centre exchanges its mercaptide ligand for the labile chlorine on the chain, replacing the weak point with a stable substituent before elimination can propagate, and the released mercaptan scavenges HCl already in the melt. The practical consequence is efficiency: methyl tin mercaptides deliver very high clarity and early colour hold at addition levels well below those needed for mixed-metal systems, which is why they dominate rigid transparent applications. DX-181 is formulated for rigid granule, extruded sheet, profile, thermal shrink film and PVC medical rigid sheet, and is specified where transparency is the deciding property. DX-980 is aimed at calendered and extruded rigid sheet, magnetic card stock, shrink film and flexible products across high, middle and low grades.