On the length scale dependence of microscopic strain by SANS

We present a SANS study on the length scale dependence of chain deformation patterns in dense cross-linked elastomers. Three different polyisoprene ne tworks of long primary block-copolymer chains of the HDH-type were analyzed . The total length of the primary chains is identical, while the length of the deuterated middle block was varied in order to cover several length sca le regimes of interest. The scattering data are analyzed in the frame of th e tube model of rubber elasticity in combination with the random phase appr oximation (RPA), which is used in order to account for the interchain corre lations. We show experimentally that for the longest labeled path the rubbe r elastic response is dominated by both cross-link and entanglement contrib utions, whereas it is of clear phantomlike chain behavior if the labeled mi ddle block of the chain is shorter than the distance between two successive entanglements, i.e., the tube diameter. We further propose schemes to quan tify nonaffine deformations on various length scales and chain scissioning processes during the radical cross-linking process.