Spherical silica particles were treated with a mixture of silane coupling agents with mercapto functional groups and dialkoxy or trialkoxy groups. The surface coverage, which indicates the number of layers covering the silica surface, was in the range from 1.6 to 6.0. The molecular mobility of the treated layer was analyzed with 1H‐NMR spectroscopy. The silane chain became more flexible with increasing dialkoxy structures in the mixture and with increasing surface coverage. The stress–strain behavior was measured for a composite consisting of the treated silica and vulcanized polyisoprene rubber (PIR). There was no influence of the dialkoxy and trialkoxy mixing ratio for near monolayer coverage. In the case of the pure dialkoxy and low trialkoxy contents, a higher stress was observed at the same strain for surface coverages of 2.4–3.8. However, a longer length flexible silane chain, that is, with a surface coverage of 6.0, was disadvantageous for the reinforcement effect. The results of pulse NMR analysis of the unextracted PIR on the particle surface and swelling test indicate that the reinforcement effect was strongly affected both by entanglement and the crosslinking reaction between the silane chain and PIR at the interfacial region. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Polysulfide‐type silane coupling agents containing two or four sulfur atoms were incorporated into a styrene‐butadiene rubber/silica composite by two different loading methods and the tensile properties were measured. The pretreatment method and the integral blend method were compared. To improve the 200% modulus of the composite, the combination of silane with four sulfur atoms and the pretreatment method was effective. Whereas, the combination of silane with four sulfur atoms and the integral blend method was effective for improving the fracture elongation. The fracture elongation of the integral blend using the silane with four sulfur atoms was higher than that of the untreated silica‐filled composite. The sulfur atoms in the silane should contribute to the crosslinking of rubber in the vulcanization process. The silane with much sulfur atoms strengthens the interface effectively and raises the 200% modulus in the pretreatment method. It is considered that the unreacted silane molecules in the rubber acted as a plasticizer in the integral blend method and the effect was better with four sulfur atoms. The 1H pulse nuclear magnetic resonance spectroscopy was measured for the unvulcanized rubber/silica mixture. The measured relaxation time was found to be in good correlation with the 200% modulus. It was found that the molecular mobility of rubber is lowered by the entanglement with the silane chains on the silica surface at the interfacial region, and it was more effective in the pretreatment method than in the integral blend method. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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The influences of alkoxy group number and loading method of silane coupling agents on the mechanical properties of a styrene-butadiene rubber/silica composite were investigated. Mercapto functional silane coupling agents with dialkoxy and trialkoxy structures were used. The pre-treatment method and the integral blend method were compared. Both the fracture stress and modulus at 200% strain were higher in the pre-treatment than in the integral blend for dialkoxy type composites. However, they were higher in the integral blend than in the pre-treatment for trialkoxy-type composites. The interaction between the silane chains on the silica surface and the rubber molecular chains at the interfacial region was estimated by 1 H pulse nuclear magnetic resonance spectroscopy using an unvulcanized silica/ rubber mixture. It was found that the binding of rubber molecular chains by the silane chains was higher in the pre-treatment system for dialkoxy-type composites, whereas it was higher in the integral blend for trialkoxy-type composites. The reason is proposed as follows: in the pre-treatment for dialkoxy type, a linear silane chain formed in the case of multi-layer coverage. The silane chain entangled with the rubber chain in the interfacial region and improved the reinforcement effect. For the trialkoxy type, a network structure formed using the pre-treatment method, lowering the amount of entanglement. However, in the integral blend for trialkoxy type, the formation of the silane network and the entanglement progressed simultaneously during the preparation process. A well-entangled interfacial region was formed.

The surface treatment of spherical silica particles using a silane coupling agent with a glycidoxy group was conducted and the effect of the alkoxy group number on the molecular mobility of the silane chain was investigated by 1 H pulse nuclear magnetic resonance (NMR). Silanes with di-alkoxy and tri-alkoxy structures were used, and the silica particles were treated with 2-propanol solution and heated at 120°C for 24 h after solvent evaporation. The surface coverage of the silica surface was in the range from two to three layers. For multilayer coverage, linear chain and network structures were expected to form on the surface by polycondensation reaction using the di-and tri-alkoxy structures, respectively. However, the relaxation times for silane chains with both di-and tri-alkoxy structures measured by pulse NMR were short, which indicates that both silane chains formed rigid network structures. Fourier transform infrared spectroscopic analysis revealed that ring opening of the epoxy group occurred, followed by reaction to form the network structure, even with the di-alkoxy structure. Ring opening of the epoxy group could be reduced by setting the heating temperature at 80°C. There was a significant difference in flexibility between the silane-layers with di-and tri-alkoxy structures after heating at 80°C, as reflected by the relaxation time.