Certain five-membered dioxaheterocyclic compounds (hetero atoms may be P, Si, S, etc.) contain a strained carbon–carbon bond
which may undergo homolytic thermolysis at modest temperatures to generate a diradical capable of initiating vinyl polymerization.
If substituents contain flame-retarding moieties this represents a convenient method for imparting flame retrdancy to a polymeric
material. Of particular interest has been 2,4,4,5,5-pentaphenyl-1,3,2-dioxaphospholane. The thermal degradation of this compound
has been studied using 13C NMR spectroscopy. This may conveniently be done by monitoring the intensity of the signal for the benzylic carbon atom as
a function of time and temperature. A simple transformation is the conversion of the cyclic compound to the linear polymer.