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 monom er 2,5-bis[(4-butylbenzoyl)oxy] styrene, BBOS, was investigated. BBOS is a substituted styrenic monomer, which polymerizes an order of magnitude faste r than styrene under identical bulk polymerization conditions. A comparativ e study of the polymerization behavior in bulk and solution for BBOS and a model compound was undertaken to elucidate the effect of both electron-with drawing substituents and liquid crystallinity of the monomer on the polymer ization kinetics. Molecular simulation was used to identify a non-LC model monomer, 2,5-diacetoxystyrene (DAS). DAS was polymerized by stable free rad ical polymerization both in bulk and in solution. In all cases narrow molec ular weight distribution (<1.4) was obtained. In bulk, DAS polymerized sign ificantly slower than BBOS, whereas in a dilute solution, the rate of polym erization was quite similar. In-situ X-ray studies carried out during polym erization of BBOS in the neat monomer indicate the presence of a nematic ph ase which could lead to localized ordering of the monomers during polymeriz ation. In comparison, DAS was found to be more reactive than styrene, becau se of the electronic effect of the acetoxy groups. However, p-acetoxystyren e (PAS) was found to have almost the same observed rate of polymerization a s DAS, indicating that steric factors also play an important role in O-subs tituted compounds.