Published online by Cambridge University Press: 25 February 2011
A totally unexpected phenomenon has been observed for the first time a few years ago when studying, by small angle neutron scattering, rubbery networks containing a small proportion of uncrosslinked labelled (deuterated) chains [1].When such a system is elongated, the scattered intensity strongly increases with the extension ratio λ for q vectors parallel to the stretching direction (and for low q values). Conversely, in the direction perpendicular to the elongation axis, the scattered intensity slightly decreases at low q for small extension ratios and then remains approximately constant when λ is further increased. The changes which are observed occur therefore in a direction opposite to the “conventional” one, i.e. that corresponding to chains effectively linked by at least two chemical junctions to the network and thus oriented on an average along the direction of stretching.