Effects of physical aging on the structure

mechanical and other properties of atactic polystyrene (a PS) films and fibers are studied by modulated differential scanning calorimetry(MDSC)

density

solvent diffusing rate

stress strain behavior and sonic velocity measurements

and the corresponding observations are tentatively explained from the viewpoint of cohesional entanglements.It is shown that the glass transition temperature (Tg)

relaxation enthalpy ( ΔH ) and its peak value (Tmax ) in the MDSC curves

as well as the initial modulus(E)

yield strength(σy)and strength at break(σb) all rise with the increase of physical aging time.On the other hand

the solvent diffusing rate slows down after being annealed below is Tg

while the sonic wvlocity and density nearly keep unchanged.The weak interaction(i.e.cohesional entanglements) introduced by the physical aging is similar to van der Waals'force from its physical characteristic.All experimental results are interpreted by the assumption that the number of cohesional entanglements increase during physical aging.