ORIENTATION AND 2ND HARMONIC-GENERATION IN DOPED POLYSTYRENE AND POLY(METHYL METHACRYLATE) FILMS

Glassy polymers such as polystyrene (PS) and poly(methyl methacrylate) (PMMA) doped with optically characterized second harmonic generating dyes were examined for their nonlinear optical properties' as determined by sample treatment and physical aging. The authors results can be related to the mobility in the polymer films and free volume theory for physical aging in polymer glasses. When secondary relaxations, associated with limited molecular mobility, are considered for PMMA and PS, it is seen that at room temperature the mobility of PMMA should be much greater due to the greater mobility of the acrylate side chain on the PMMA. Even though both polymers have glass transition temperatures at about 100 degree C or slightly above, the broad secondary transition for PMMA occurs between about minus 50 and minus 30 degree C and for PS at about 35-50 degree C.