Branching structure and thermal stability of poly(vinyl chloride)

Low molecular‐weight model compounds structurally related to polyvinyl chloride undergo thermal changes in considerably different manners depending on their molecular structures. For example, 3‐chloro‐4‐ethyl‐n‐hexane is far more stable than 3‐chloro‐3‐ethyl‐n‐pentane when heated under nitrogen. This suggests that the type of atom attached to the tertiary carbon at the sites of branching in polyvinyl chloride would play an important role in the thermal degradation of the polymer. Results of the present study using polyvinyl chloride and varieties of model compounds indicate that most, if not all, of the tertiary carbons in the polyvinyl chloride molecules carry hydrogen atoms rather than chlorine atoms. It is furthermore shown that the number of branchings does not affect the thermal stability to any significant extent. It thus seems conceivable that the branching structures of polyvinyl chloride do not contribute to the initiation of the thermal decomposition, at least under the ordinary processing conditions.