The three polymorphs of isotactic polybutene‐1 : Dilatometric and thermodynamic fusion properties

Abstract Melting temperature, enthalpy and entropy of a sample of highly isotactic polybutene‐1 in each of the three polymorphic modifications as yet recognized, are determined by the method of the depression of the melting point in the presence of diluents. Two diluents are chosen: α‐chloronaphthalene and decalin, as respectively poor and good solvents of poly‐butene. In the presence of α‐chloronaphthalene melting points of the modifications 1 and 2 are measured as the highest melting temperatures of biphasic polymorphic precipitates, which were obtained by crystallizing mixtures with the diluent under different cooling conditions. On the contrary, precipitates consisting only of modification 3 were obtained both in decalin or by quenching mixtures with α‐chloronaphthalene. The fusion enthalpies of the three polymorphs have mean values around 1500 cal./unit and any difference between them is comprised within experimental errors (150–300 cal./unit). Similarly, entropies of fusion have mean values around 3.8 cal./unit · °K. Polymorphic equilibrium transitions were not observed in the temperature range explored. Their existence is discussed, but monotropy seems to be the most probable situation.