PVT-STUDIES ON POLYMERIC AND OLIGOMERIC COMPOUNDS .1. LINEAR DIBLOCK PERFLUOROALKYL ALKANES

The pressure dependence of transitions in perfluorododecyloctane - F12H8 - and in perfluorododecylhexadecane - F12H16 - has been measured from 10 to 200 MPa, from room temperature up to 220-degrees-C. The two transitions within this range - the transition of the alkane block from crystalline to mesomorphic, T(ss), and the transition to melt, T(m) - exhibit different pressure coefficients, As a pecularity, for F12H16 T(ss) and T(m) superimpose at 10 MPa, in accordance to atmospheric pressure DSC data. Pressure dependences of transitions are given as well as their melting enthalpies. It has been shown, that PVT-measurements open up the possibility to gain new insight into the nature of certain phase transitions. A transition formerly to be thought of as a melting transition, turned out to be actually composed of two contributions, one due to disordering and the other due to melting.