Thermal decomposition of cycloadducts of vinylnaphthalenes with electron-deficient dienophiles

Abstract

The thermal polymerization of styrene is a long-known and well-practiced phenomena. While the mechanism of the thermal initiation event has been the subject of several investigations, it is not yet well understood. In an attempt to gain further insight as to the details of possible initiation from styrene dimer, analogous stable cycloadducts (maleic anhydride, tetracyanoethylene) of 1- and 2-vinylnaphthalene have been synthesized, fully characterized spectroscopically, and subjected to thermal decomposition. In the main, the major thermal event observed for these styrene dimer mimics is retro cycloaddition. This process is characterized by an activation enthalpy of approximately 30 kcal mol^–1. Aminor process which accompanies the major reaction is the homolysis of a carbon–hydrogen bond to generate a carbon radical which may be trapped as a stable adduct of the 2,2,6,6-tetramethylpiperinyloxy (TEMPO) radical.