Surface tension measurements on ethene-butene random copolymers and different polypropenes

The pendant drop apparatus is used in order to study the surface tension of ethene-1-butene random copolymer melts over the whole range of composition s, including poly(1-butene) (P-1-B) and at different temperatures. Furtherm ore, the surface tensions of isotactic polypropene (i-PP) and syndiotactic polypropene (s-PP) are measured. The surface tension of the melt of random copolymers decreases as a function of copolymer composition from pure polye thene (PE) to pure P-1-B in a nearly exponential manner, and the surface te nsions of copolymers with a P-1-B content in the range of approximately 40 wt % match the surface tension of i-PP and s-PP. This indicates the possibl e existence of a window of miscibility. This result is verified by the calc ulation of the solubility parameters from additional sessile drop measureme nts on solid copolymers at room temperature and from pressure-volume-temper ature data of the melts applying the Flory-Orwoll-Vrij equation-of-state th eory. Also, the theory of the conformational parameter beta (Bates and Fred rickson) leads to the same conclusion. All results are consistent with micr oscopic observations discussed in the literature.