THERMOGRAVIMETRIC STUDIES OF POLY(OXYMETHYLENE-CO-DIMETHYLSILOXANE) COPOLYMERS

The thermal stability and kinetic parameters of a series of poly(oxyme thylene-co-dimethylsiloxane) copolymers have been studied by thermogra vimetry from 303 to 846K under nitrogen flow. The new copolymers, obta ined by ring-opening copolymerization of 1,3,5-trioxane and hexamethyl cyclotrisiloxane, contain different concentrations of oxymethylene and dimethylsiloxane comonomer units. The results of the thermal studies were compared with data corresponding to pure poly(oxymethylene) and p oly(dimethyl-siloxane). The copolymers with low concentration of dimet hylsiloxane comonomer units show only one degradation process, but cop olymers richer in this co-unit degrade in two stages. Copolymers with an even higher concentration of dimethylsiloxane co-unit have three de composition processes. The TGA results indicate that the molecular str ucture of the copolymers correspond to block copolymers and random cop olymers bonded to segments formed by both pure poly(oxymethylene) and poly(dimethylsiloxane). The structures depend on the composition of th e copolymers. The pre-exponential factors, the reaction orders and the activation energies have been determined from non-isothermal thermogr avimetric data.