Physical ageing 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 techniques and by morphological observations. Films of different density ( p ) obtained by varying solvent evaporation times, both from cis / trans or 100% cis PTBA, show during the first dilatometric run the presence of a temperature T p at which a packing effect occurs. Therefore, first dilatometric curves show two linear tracts, the latter representing the sum of thermal dilation and simultaneous packing induced by molecular 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. Δρ is the more pronounced the lower the initial density of the sample for mixed cis / trans PTBA, but, quite surprisingly, in 100% cis PTBA the trend is opposite and, in this case, denser samples undergo a more relevant packing. A tentative explanation is inferred on the basis of a conformational model recently proposed. An improvement of the chain packing is responsible of the fast ageing process of this polymer, as suggested by a preliminary X‐ray diffraction analysis.