Thermogravimetry and differential scanning calorimetry of some poly-p-xylylenes containing halogen atoms

Abstract

Poly-p-xylylene and three halogen-containing poly-p-xylylenes prepared by the Gorham method from purified dimers were characterized by thermogravimetry and differential scanning calorimetry to determine their relative thermal stabilities in nitrogen and air. As judged by these techniques, thermal stability in nitrogen is not greatly changed by halogenation of the cyclic dimer from which polymer is made. However, thermal oxidative stability depends on the type and degree of halogenation. Aliphatic fluorine atoms greatly improved upon the thermal oxidative stability of poly-p-xylylene. To a lesser but significant degree, two aromatic chlorine atoms, poly(dichloro-p-xylylene), also improved upon the thermal oxidative stability of poly-p-xylylene or poly-(chloro-p-xylylene). Oxidative degradation caused a rapid exothermic weight loss near 300°C for poly(dichloro-p-xylylene) and near 250°C for poly-p-xylylene and poly(chloro-p-xylylene) when films were heated at 10°C/min. Poly(dichloro-p-xylylene) maintained a constant weight during an induction period before it started to lose weight when it was heated isothermally at temperatures below 300°C. However, poly-p-xylylene and poly(chloro-p-xylylene) gained weight during oxidation before they lost weight when heated isothermally below 250°C.