Highly Reactive 2,5-Disubstituted Styrene-Based Monomer Polymerized via Stable Free Radical Polymerization: Effect of Substitution and Liquid Crystallinity on Polymerization

The stable free radical polymerization (SFRP) of a liquid crystalline monomer 2,5-bis[(4-butylbenzoyl)oxy]styrene, BBOS, was investigated. BBOS is a substituted styrenic monomer, which polymerizes an order of magnitude faster than styrene under identical bulk polymerization conditions. A comparative study of the polymerization behavior in bulk and solution for BBOS and a model compound was undertaken to elucidate the effect of both electron-withdrawing substituents and liquid crystallinity of the monomer on the polymerization kinetics. Molecular simulation was used to identify a non-LC model monomer, 2,5-diacetoxystyrene (DAS). DAS was polymerized by stable free radical polymerization both in bulk and in solution. In all cases narrow molecular weight distribution (<1.4) was obtained. In bulk, DAS polymerized significantly slower than BBOS, whereas in a dilute solution, the rate of polymerization was quite similar. In-situ X-ray studies carried out during polymerization of BBOS in the neat monomer indicate the presence of a nematic phase which could lead to localized ordering of the monomers during polymerization. In comparison, DAS was found to be more reactive than styrene, because of the electronic effect of the acetoxy groups. However, p -acetoxystyrene (PAS) was found to have almost the same observed rate of polymerization as DAS, indicating that steric factors also play an important role in O-substituted compounds.