Liquid-crystalline phase chain propagation

The photoinitiated polymerization of a sterically hindered semi-fluorinated monomer, which is characterized by a hindered radical chain propagation site, was followed both in an isotropic and a highly ordered smectic liquid crystalline phase. The polymerization rate is slower in the smectic phase than in the isotropic phase, presumably a result of a decrease in both the propagation and termination rate constants. The decrease in the propagation rate results in a very slow persistent increase in polymer molecular weight after the initiating light source is removed. Polymerization firom the smectic phase of the monomer proceeds in a non-equilibrium matrix. 

The thermodynamics of TOX polymerization, studied extensively by Enikolopyan and reviewed recently in a book by Berlin et al. entitled Polyoxymethylenes (in Russian), is more complex. This is due to the fact that propagation proceeds simultaneously with phase transition phase transition of the monomer molecule from liquid phase to crystalline phase occurs simultaneously with its incorporation into a polymer chain. Thus, the overall Gibbs free energy (AG ) for the propagation step is the sum of the energy changes associated with chemical reaction and phase transition. Gonsequently, equilibrium is shifted more toward polymer and TOX... 

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