The effects of different kinds and amounts of fillers, e.g., carbon black N220 and silicasilane, on molecular structure and dynamics of styrene-butadiene rubber (SBR) and the effects of vulcanization on filled SBR systems are studied by Hahn echo and rotating-frame longitudinal relaxation T 1F NMR techniques as well as mechanical measurements, with the emphasis of quantitative comparison between microscopic and macroscopic results. The calculation based on a theoretic model for transverse relaxation in elastomeric networks reveals that filler aggregates or clusters behave like additional crosslinking points and thus lead to a decrease in the molecular mass between cross-linking points M c, an increase of intercross-link chains, or accordingly a decrease of dangling and free chains, ultimately to the increasing cross-link modulus G c, to the extent that depends on the type and, in particular, content of fillers. Compared with SBR filled with silica-silane, SBR filled with carbon black N220 shows more network chains due to its stronger binding ability or adsorbability but results in less cross-link density due to its higher inhomogeneity. The filler dependence of segmental and overall chain mobility is definitely different for both SBR systems, cross-linked and un-cross-linked, which is attributed to the restriction of filler on chemical cross-linking reaction occurred in a SBR matrix. A recent concept of hydrodynamic reinforcement by filler clusters and stress-induced cluster breakdown is combined with a tube model of rubber elasticity for modeling the typical stress softening effect of filled rubber for uniaxial stress-strain measurements. The evaluated material parameters deliver information about cross-link densities and filler specific polymer-filler couplings. The resulting densities ν mech of network junctions are fairly consistent with NMR-derived ones within experimental errors; the differences can be used to estimate the content of different types of cross-links and chain entanglements. Finally, the related observations have been schematically represented using different physical models.

A series of cross-linked styrene-butadiene rubbers (SBR) filled with different amounts of carbon black and silica are investigated by proton multiple-quantum nuclear magnetic resonance (NMR). The method yields reliable information on residual dipolar couplings and their distribution, which in turn are related to local chain order and the effective cross-link density in these systems. Fundamental differences between the response of a linear precursor, which undergoes reptational motion, and vulcanized SBR are discussed. For the latter, it is found that the average chain order parameter as well as its distribution does not change significantly with the amount and the type of filler. This is in surprising contrast to recent results from Hahn-echo relaxometry applied to the same samples, which indicated a significant filler effect on the cross-link density.