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.