The Irreversible Tetragonal to Trigonal Transformation in Random Butene-1/Ethylene Copolymers

The study details the influence of temperature and time on the solid-solid transformation from tetragonal Form II mesophase to trigonal Form I crystals in isotactic poly(butene-1) and its random copolymers with ethylene. Incorporation of ethylene co-units into isotactic poly(butene-1) not only leads to a faster transformation rate, as already discussed in the literature, but it also affects the temperature of maximum transformation rate. At the initial stage of the process, a maximum rate is observed upon annealing at around -20 degrees C. Conversely, the transformation becomes much faster at around +20 degrees C when it approaches completion. The dual transition kinetics is discussed on the basis of a nucleation and growth mechanism. Ethylene co-units affect the transformation rate as well as its bimodal kinetics.