New fabricate of styrene-butadiene rubber/montmorillonite nanocomposites by anionic polymerization

Styrene-butadiene rubber/montmorillonite (SBR/MMT) nanocomposites were successfully synthesized by in situ living anionic polymerization with n-BuLi as initiator. The results from kinetics study and ¹H NMR indicated that the addition of organophilic montmorillonite (OMMT) did not changed the living copolymerization and the components of the copolymer on the whole when OMMT content was lower than 3 wt %. However, gel permeation chromatography showed that the introduction of OMMT resulted in small amount of high-molecular weight fraction of SBR in the composites, leading to an increase in the weight-average molecular weight and polydispersity index, but the unchangeableness of the number-average molecular weight. The result from transmission electron microscopy and X-ray diffraction revealed that a completely exfoliated structure existed in the nanocomposite with 25 wt % styrene and OMMT content from 1 to 4 wt %, and styrene played an important role in the expanding of OMMT layers. Moreover, the nanocomposites possessed higher glass-transition temperature, thermal stability, tensile strength and elongation at break than SBR when the OMMT content ranged from 2.5 to 4 wt %. A schema was proposed to illustrate the formation of the nanocomposite and the exfoliation structure with physical cross-linking between SBR chains and OMMT.