Synchrotron X-ray Scattering Studies of Crystallization of Poly(ether-ether-ketone) from the Glass and Structural Changes during Subsequent Heating-Cooling Processes

Abstract

The evolution of structural parameters characterizing the semicrystalline morphology of poly(ary1-ether-ether-ketone) (PEEK), and its blends with poly(ary1-ether-imide) (PEI), has been determined as a function of temperature by means of small-angle (SAXS) and wide-angle (WAXS) X-ray scattering studies, using synchrotron radiation. By comparing the behavior of initially amorphous samples continuously heated in the beam and samples heated and cooled below and above their annealing temperature, a complete picture is drawn of the morphological changes occurring during the cold crystallization and subsequent heating-cooling of PEEK. Upon crystallization of an amorphous sample, new lamellae are progressively inserted in the free space left between existing ones. No decrease of the lamellar thickness is evident during this insertion mechanism. When the polymer is cooled below its last annealing temperature T,, only reversible morphological changes occur, which can be explained quantitatively by the effects of thermal expansion, provided one takes into account the existence of strains in the crystalline lamellae created by their coupling to the noncrystalline interlamellar regions. When the polymer is heated above T,, "irreversible" changes occur in the average thickness of the lamellar crystals and of the interlamellar noncrystalline regions, in the perfection of the crystals, and in the crystalline density. Cold-crystallized samples are shown to comprise a single lamellar population which undergoes a rapid melting-recrystallization process above T,. The double melting behavior of coldcrystallized PEEK results from this melting-recrystallization mechanism. IntroductionThe morphology and properties of a semicrystalline polymer depend on its thermal history. Therefore, when studying the morphology, changes in the structure as a function of the crystallization conditions and subsequent thermal treatments must be considered. Moreover, any

Crystalline structure of poly(methyl-n-propylsilane)

“…37 TEM micrographs were performed on a Philips EM301 microscope working at 80 kV. A PMPrS sample (PSi-1) that was allowed to crystallize several months at room temperature was cut in mers as PEEK, 38 PET, 39 PBT, 40 and has also been patterns.…”

Crystallization and melting behavior in syndiotactic polypropylene: Origin of multiple melting phenomenon

“…In the studies of isothermal crystallization under quiescent conditions (i.e., crystallization is only a function of temperature), the multiple melting behavior of these semicrystalline polymers may be designated as being the result of one of the following reasons: the presence of two (or more) crystal modifications, 13,15 the presence of two (or more) crystalline morphologies, 28 the presence of two populations of crystal lamellae of different thicknesses, 35,38,40,[43][44][45] and the simultaneous melting, recrystallization, and remelting of the lamellae initially formed at the crystallization conditions. 22,34,37,39,42,46 Among these models, simultaneous meltingrecrystallization-remelting and the dual-lamellar population models seem to receive much attention in explaining the multiple melting behavior in various semicrystalline polymers that do not exhibit multiple crystal modifications upon crystallizing at the crystallization conditions studied. The simultaneous melting-recrystallization-remelting model first proposed by Holdsworth and Turner-Jones 22 hypothesizes that the primary lamellae formed at the crystallization temperature (T c ) undergo a partial melting process that gives rise to an observation of the lowmelting endotherm (usually observed at ca.…”

Blends of polycarbonate and acrylic polymers: Crystallization of polycarbonate

“…Furthermore, the progressive addition of subsidiary lamellae along a dominant one also leads to a progressive decrease of the long spacing. 46 With the presence of more acrylic polymer in the system the time required to reach the equilibrium long spacing increases. This is because the amorphous component reduces the crystal growth rate.…”