Melt Properties of Poly(styrene‐<i>co</i>‐acrylonitrile) and Poly(butylene terephthalate) and their Interfacial Tension

Pressure‐volume‐temperature and surface tension behaviour were studied for random copolymers of styrene and acrylonitrile (SAN) and for poly(butylene terephthalate) (PBT). Results served to determine reduction parameters for the equation‐of‐states by Flory‐Orwoll‐Vrij and by Simha‐Somcynsky as well. Surface tension as a function of copolymer composition displays negative deviation from additivity. It indicates surface excess of styrene units. Similar behaviour with respect to copolymer composition was found for variation of interfacial tension between SAN and PBT. Thickness of surface region is around 1 nm and does not change with copolymer composition whereas extension of interfacial region between PBT and SAN copolymers varies strongly with copolymer composition between around 2 and 60 nm. magnified image