Designed organo-layered silicates as nanoreactors for 1,3-butadiene stereospecific polymerization toward rubber nanocomposites synthesis

摘要

Organo-modified layered silicates were synthesized and used as inorganic carriers for CoCl_2(P~tBu_2Me)_2-MAO catalyst in the polymerization of 1,3-butadiene, yielding cis-1,4-enriched polybutadiene. The organoclays were prepared by: (i) intercalation of (ar-vinyl-benzyl)trimethyl ammonium chloride salt through an ion exchange reaction, and (ii) the edge-surface grafting by trimethylchlorosilane. The ammonium modifier acts as spacer increasing the layer d-spacing and as filler favoring the silylation of the edge-surface clay hydroxyls. The grafted silane prevents the MAO cocatalyst from reacting with the edge-OHs, by forcing it to react within the interlayer clay region. MAO lead to methylation of the cobalt complex and carbanion abstraction to give a cobalt-methyl cation that is stabilized by the MAO anion. The nanoconfined cationic alkylated species insert the butadiene on the Co-Me bond affording the growth of the polymer chains within the clay layers. The growing of the macromolecular chains fills the interlayer silicate region giving an intercalated polybutadiene rubber nanocomposite. The role of the silicate organo modification on the heterogeneous catalyst structural features, the polymerization behavior and the nanocomposite structures are discussed.