SOLID-STATE NMR INVESTIGATION OF ANTIPLASTICIZATION OF POLYSTYRENE BYMINERAL-OIL

The effects of mineral oil plasticization of polystyrene were investig ated as a function of polystyrene molecualr weight and mineral oil con centration. Solid state NMR, thermo/mechanical methods and positron an nihilation spectroscopy (PAS) were used to study the molecular dynamic s and free volume effects of this blend. Antiplasticization was observ ed in the low (40,000) molecular weight polystyrene samples as an embr ittlement of the system. In contrast, the flexural modulus was not aff ected by the presence of mineral oil in the higher (270,000) molecular weight polymers but a decrease in the flexural strength was observed with increasing mineral oil concentration. The NMR and PAS data indica ted that the mineral oil was not dissolved in the polymer at ambient t emperature, rather it phase separated even at very low concentrations. This caused antiplasticization in low molecular weight polymers becau se the small free volume holes were filled causing a densification of the system. With high molecular weight polystyrene, this phase separat ion was manifested as a decrease in the flexural strength.