  We present an investigation of the effect of the interaction between a thin
polystyrene film and its supporting substrate on its glass transition
temperature (Tg). We modulate this interaction by depositing the film on
end-tethered polystyrene grafted layers of controlled molecular parameters. By
comparing Tg measurements versus film thickness for films deposited on
different grafted layers and films deposited directly on a silicon substrate,
we can conclude that there is no important effect of the film-subtrate
interaction. Our interpretation of these results is that local orientation and
dynamic effects substantial enough to influence Tg cannot readily be obtained
by grafting prepolymerized chains to a surface, due to intrinsic limitation of
the surface grafting density.
