Small-angle X-ray and neutron scattering analyses of highly crosslinked rubber with unsaturated carboxylic acid

We studied the structure of polybutadiene rubber (BR) crosslinked with zinc diacrylate (ZDA) by using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) to elucidate the regions of high crosslink density in the matrix rubber. The SAXS profiles of the swollen rubber materials with toluene were described well by a model that considers the hierarchical structure of the ZDA aggregates. By contrast, the SANS profiles of the swollen rubber materials with deuterated toluene were not well described by the same model, suggesting an influence of the high crosslink density region in the matrix rubber. We then considered the contributions of the high crosslink density segments of the BR (HC-BR) and the hierarchical structure of the ZDA aggregates, and succeeded in describing the SANS curves fairly well. This paper is the first report on high crosslink density segments in BR crosslinked with ZDA. We also performed tensile measurements on the sample and compared the results with those from the SAXS/SANS measurements, revealing that the size and the number density of the HC-BR and ZDA aggregates are related to the mechanical properties of the rubber material. Polymer Journal (2013) 45, 57-63; doi: 10.1038/pj.2012.200; published online 21 November 2012