| Abstract
| - We present a small-angle neutron scattering (SANS) investigation of the relaxation processof branched polymer melts under deformation. The selected model polymer is an H-shaped polyisoprenehaving deuterium-labeled blocks at the dangling tips of the arms. The melt is step strained in a strainrig especially built for that purpose, where the sample temperature and its deformation conditions areprecisely controlled. Uniaxial extensions to values of 2 and 3 are performed at a temperature above thepolymer glass transition temperature Tg. The sample is then allowed to relax during a given time beforebeing quenched to below its Tg in order to freeze the chains conformation to perform the SANS experiments.Very large anisotropies in S(q) develop on time scales corresponding to the relaxation of the danglingarms. The experimental structure function is then compared to theoretical ones obtained by the randomphase approximation applied to the tube model. While theory describes well the scattering for short times,it seems not to be able to describe the increase of intensity in the direction parallel to the strain at highertimes, even when highly nonaffine processes such as arm retraction and branch point withdrawal aretaken into account.
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