The dynamic light scattering (DLS) technique was applied to polystyren
e fractions of different molecular weights dissolved in the near-Theta
solvent trans-decahydronaphthalene and confined in a porous glass bea
d. Diffusion coefficients were measured for the polymer in the interio
r of the porous medium and in the surrounding free solution. Diffusion
, when normalized to take into account solvent viscosity and temperatu
re, was slower in the Theta solvent than in the good solvent 2-fluorot
oluene, a result being ascribed to a stronger hydrodynamic interaction
for a compact Gaussian chain in the pore channels than for a chain wi
th excluded volume. At higher temperatures, the decrease in the reduce
d diffusivity was larger than expected for the increased radius of gyr
ation of the polystyrene chain in the better solvent. At the same time
, the DLS autocorrelation function exhibited a pronounced deviation fr
om a single-exponential decay. Enhanced interaction between swelling p
olymer chains in the narrow pore channels is considered to have increa
sed the concentration coefficient of the friction coefficient for tran
slational motion and thus to have resulted in the decrease of the diff
usion coefficient at a low, but nonzero, polymer concentration.