Dynamic compressibility of poly(vinyl acetate) and its relation to free volume

The complex bulk compliance (dyn a mlC compress ibili ty) of a commercial sample of poly(vinyl acetate), AYAT, was measured at fr equencies from 50 to 1,000 cycles p er second, temperatures from 0 to 100 C, and static hydrostatic stresses from 0 to 981 bars (gage pressure) using an alternating hyd rostatic s tress ge ner ated and detected by piezoelectric transducers mounted in an esse ntially noncompliant cavity with dimensions small in co mpa rison to a wa velength. The above temperature range was more than suffi cient to cover the dispers ion r eg ion in whi ch an inflection in the storage compliance and a maximum in t he loss compliance were observed. The data were reduced to fun ctions of reduced variabl es us ing t he WLF Equations extended to include static pressure wi th the "universal" vVLF Constants and dT/dP = 0.020 C/bar. The differe nce in limiting compliances at zero and infinite fr equencies wa la rger t ha n that predicted from the dT/d? shift us ing t he fr ee volume concept. A discussion is presen ted on poss ible processes that might contr ibute to an excessive value between limit in g co mplia nces.