CRYSTALLIZATION AND MELTING BEHAVIORS OF POLY(ARYLETHERETHERKETONE)(PEEK) ON ORIGIN OF DOUBLE MELTING PEAKS

The crystallization and melting behaviors of poly(aryletheretherketone ) (PEEK) films were investigated, using differential scanning calorime try and metallurgy concepts. The shape of the time-temperature-transfo rmation (TTT) diagram, established for PEEK, results from both nucleat ion and growth phenomena. The double melting behavior exhibited by iso thermally crystallized PEEK samples are discussed through the TTT diag ram and the influence of the thermal history in the molten state. The upper melting peak arises first and the lower melting peak is develope d later. The location of such a second endotherm is shifted toward the higher temperature with increasing either the crystallization tempera ture or the annealing time while the location of the upper melting pea k seems to be unchanged. The double melting behavior is related to a b imodal distribution in size and/or perfection of lamellae developed in a two-step crystallization. With increasing temperature and/or anneal ing time in the molten state, the pattern of the endothermic curves is modified. The observed changes are discussed through two origins: the progressive disappearance of remnants of the former crystals and a th ermal degradation leading to a cross-linking of the polymer. (C) 1994 John Wiley and Sons, Inc.