PHYSICAL AGING PHENOMENA IN POLY(TERT-BUTYLACETYLENE) - INFLUENCE OF THE MICROSTRUCTURE

Ageing phenomena in cast films of poly(tert-butylacetylene) (PTBA) of different tacticity were studied by dilatometric and calorimetric tech niques and by morphological observations. Films of different density ( rho) obtained by varying solvent evaporation times, both from cis/tran s or 100% cis PTBA, show during the first dilatometric run the presenc e of a temperature T-p at which a packing effect occurs. Therefore, fi rst dilatometric curves show two linear tracts, the latter representin g the sum of thermal dilation and simultaneous packing induced by mole cular motions leading to a better packing. Following measurements show a linear increase of the specific volume. The packing process is also revealed by differential scanning calorimetry as a broad endotherm. D elta rho is the more pronounced the lower the initial density of the s ample for mixed cis/trans PTBA, but, quite surprisingly, in 100% cis P TBA the trend is opposite and, in this case, denser samples undergo a more relevant packing. A tentative explanation is inferred on the basi s of a conformational model recently proposed. An improvement of the c hain packing is responsible for the fast ageing process of this polyme r, as suggested by a preliminary X-ray diffraction analysis.