CHAIN-SEGMENT ORDER AND DYNAMICS IN A GRAFTED POLYMER MELT - A DEUTERIUM NMR-STUDY

The dynamics of polymer chains grafted on solid substrates is investig ated, using deuterium NMR. The experiments are performed on perdeutera ted polydimethylsiloxane melts end grafted on porous or planar silica. The method consists in observing how nuclear interactions are time av eraged by the molecular motions. One of the main results of this NMR s tudy is that the chain segments exhibit uniaxial reorientations around the direction normal to the solid-polymer interface. Studies versus l ayer thickness demonstrate that this motional uniaxiality is due to th e squeezing of the chains and characterized by a negative order parame ter. The orientational fluctuations of segments are preferentially par allel to the grafting plane throughout the whole layer. This implies t hat orientational correlations take place between chain segments.