Influence of Structural and Topological Constraints on the Crystallization and Melting Behavior of Polymers. 2. Poly(arylene ether ether ketone)

Abstract

The secondary crystallization and its influence on the glass transition are studied as a function of crystallization temperature and time by differential scanning calorimetry for PEEK. The multiple melting behavior resulting from isothermal annealing from the glass or crystallization from the melt is discussed in the context of models considering either a melting-recrystallization-remelting process or a bimodal population of primary and secondary crystals. The heating rate dependence of the multiple melting behavior indicates that reorganization of primary crystals occurs during heating for samples annealed from the glassy state but is insignificant for those crystallized from the melt. For either mode of crystallization, the high-and low-temperature endothermic regions are associated with the melting of primary and secondary crystals, respectively. Investigations of the low endotherm transition temperature and heat of fusion as a function of crystallization time and temperature lead to the following conclusions: the melting temperature of secondary crystals increases linearly with the logarithm of secondary crystallization time at a rate, B(T), increasing linearly with decreasing temperature; the Avrami exponent, which characterizes the initial stage of secondary crystallization, is constant below ca. 310 °C (n ) 1 /2) but increases gradually with temperature above 310 °C; the late stage of secondary crystallization is characterized by a linear increase in crystallinity with logarithm of time. Studies of the evolution of the glass transition after secondary crystallization indicate that the calorimetric Tg increases linearly with the logarithm of time at a rate, b(T), increasing with decreasing temperature. Finally, a qualitative model of polymer crystallization of semiflexible polymer chains is proposed. This model considers the effect of structural constraints (chain stiffness) on the nature of the amorphous phase after primary crystallization and the effect of topological constraints (pinning of amorphous chains) on the secondary crystallization behavior.

Equilibrium melting temperature and crystallization kinetics of α- and β′-PBN crystal forms

“…More than one DSC endothermic peak can result from the melting of different crystal types within the sample if each is present before thermal treatment. [6][7][8] Multiple endothermic peaks can also be caused by the partial melting of some or all of the original material and its reorganization into material of higher order during the thermal analysis, before the final melting. 9,10 The observed dependence of the multiple endotherms on the crystallization temperature permits to hypothesize the origin of each peak.…”

Analysis of Thermal Ageing Effect (Hold Time - Crystallinity Rate - Mechanical Property) on High Density Polyethylene (HDPE)

“…Previous studies of structure-property relations focused mainly on structure, whereas mechanical properties remained of secondary importance. In recent work, many authors [8][9][10][11] note that after ageing and annealing of many semicrystalline polymers it is observed a change of the microstructure and the morphology of this material expressed by a secondary crystallization and a creation of small-organized volumes in the amorphous phase.…”

Poly(Ether‐ b ‐Amide) Thermoplastic Elastomers: Structure, Properties, and Applications

“…A new non-negligible endotherm near 50°C is observed after storage. According to studies by Marand et al [11] on other semicrystalline polymers, this "physical aging" observed at a temperature above the polyamide and polyether glass transitions, could be attributed to a secondary crystallization phenomenon inside the polyamide-rich phase during the storage period. This new melting endotherm is related to an increase in the product elastic modulus during the storage period.…”