Effect of thermal treatment on solution grown crystals of isotactic propylene/butene-1 copolymers

The annealing behaviour of solution grown crystals of isotactic propylene butene-1 copolymers is studied in detail. Modifications in both position and number of the d.s.c. peaks in the thermograms of single crystal aggregates as a function of the annealing temperature, are observed and correlated with the presence of different crystalline phases. For all samples a maximum is observed when the overall apparent enthalpy of fusion is reported against the annealing temperature. The annealing temperature corresponding to the maximum is a function of the copolymer composition. The diagram is characterized by a minimum corresponding to a percentage of about 43% by wt in butene-1. The long spacing of crystal aggregates is a function of the annealing temperature. For some samples the long spacing has been correlated with the melting temperature of the crystalline phases and the equilibrium melting point calculated. For copolymer samples at high propylene content the examination of the wide-angle X-ray diffraction patterns leads to the conclusion that a certain number of butene-1 units, incorporated during the crystallization, as defects in the crystalline lattice of polypropylene, following the annealing process, are ejected in the amorphous phase. © 1977.