bdtiment "Le Chablais," 73376 Le Bourget-du-Lac, France SYNOPSISThe crystallization and melting behaviors of poly (aryletheretherketone) (PEEK) films were investigated, using differential scanning calorimetry and metallurgy concepts. The shape of the time-temperature-transformation (TTT) diagram, established for PEEK, results from both nucleation and growth phenomena. The double melting behavior exhibited by isothermally crystallized PEEK samples are discussed through the TTT diagram and the influence of the thermal history in the molten state. The upper melting peak arises first and the lower melting peak is developed later. The location of such a second endotherm is shifted toward the higher temperature with increasing either the crystallization temperature or the annealing time while the location of the upper melting peak seems to be unchanged. The double melting behavior is related to a bimodal distribution in size and/ or perfection of lamellae developed in a two-step crystallization. With increasing temperature and/or annealing 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 thermal degradation leading to a cross-linking of the polymer.
RCsumC : Cette ttude a pour objectif une analyse conformationnelle d'unitts moltculaires telles que le diphtnyl tther (DPE) et la diphtnyl &tone (DPC) constitutives du squelette de polymbres tels que PEK, PEEK et le PEEKK, par des calculs semi empiriques en CND012. Deux types de modtlisations ont t t t rtalists : une premibre strie de calculs a t t t effectute sans prendre en compte les interactions tlectroniques et de zones d'imptnttrabilitt de van der Waals et une deuxibme en considtrant ces diverses interactions. La conformation d'tnergie minimale absolue pour le diphtnyl tther correspond j. la position dtfinie par les angles de torsion (01,02) = (30°,1500) avec et sans interaction, et j. la position (01,02) = (90°,900) pour la diphtnyl cttone sans prendre en compte les interactions. Dans les regions sous vitreuses et i contrainte sttrique tgale au sein d'une chaine de PEK, PEEK ou PEEKK, on peut stipuler que I'unitC moltculaire DPE sera sensiblement plus facilement mise en mouvement que I'unitt DPC.Mots cl6s : analyse conformationnelle, diphtnyl tther, diphtnyl cCtone, CNDOI2, barribres de rotation. Abstract: Diphenyl ether (DPE) and diphenyl ketone (DPK) are the molecular constituents of polymers such as PEK, poly(ether-ketone); PEEK, poly(ether-ether-ketone), and PEEKK, poly(ether-ether-ketone-ketone).A conforrnational analysis of DPE and DPK is examined by means of semiempirical calculations using CND012 (Complete Neglect of Differential Overlap). The modelization is first run disregarding electronic interactions and steric effects, then introducing them in the calculations. We found that the absolute minimum energy conformer has torsional angles (0,,€12) = (30°,1500) for the DPE (with and without interactions) and (0,,0,) = (90°,900) for the DPK (without interactions). Considering the polymer chains of PEK, PEEK, and PEEKK, the motion of DPE is expected to be easier than that of DPK in regions of local motions and for equivalent steric effects.
SYNOPSISMolecular mobility of both the polystyrene homopolymer and a series of styrene-co-methacrylic acid copolymers with various amounts of methacrylic acid is analyzed in the temperature range from 100 to 450 K, by high-resolution dynamic mechanical spectrometry, IR, and differential scanning calorimetry. Isochronal spectrometry exhibits for polystyrene homopolymer two relaxations, the @ and a relaxations, with increasing temperature. Styreneco-methacrylic acid copolymers exhibit three mechanical relaxations, the ?, @, and a relaxations, from 100 to 450 K. These relaxations could be related to the progressive occurring of motions of the side groups and of the backbone chains when increasing the temperature. This could be due to the progressive breakdown of hydrogen bonds, which could show a somewhat wide range of magnitude. Furthermore, the decreasing of the magnitude of the a relaxation with increasing methacrylic acid content could suggest the presence of a stable network of chemical cross-links induced by the presence of anhydride so that molecular mobility could be partially inhibited above TE. The remaining of a fluctuation network of hydrogen bonds (labile contacts) above TE could also emphasize the decrease in molecular mobility. 0 1993 John Wiley & Sons, Inc.
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