Isothermal thickening and thinning processes in low molecular weight poly(ethylene oxide) fractions crystallized from the melt: 2. Crystals involving more than one fold

Liquidlike Morphological Transformations in Monolamellar Polymer Crystals

“…Consequently, polymer crystals represent metastable states [3] with a significant degree of disorder, mainly characterized by the degree of chain folding. Thus, such imperfect crystals are thermodynamically driven towards states of higher degrees of order [6][7][8][9][10][11][12][13][14][15]. However, the corresponding relaxation processes in the crystalline state are usually extremely slow and rather localized because the long sequence of connected segments is not very mobile.…”

“…Hence, annealing polymer crystals at elevated temperatures but below the melting point may result in faster improvement of the crystalline order. Therefore, the morphology of a polymer crystal does not only depend on the rate at which it was created (i.e., the crystallization temperature) but also, and sometimes most importantly, on the thermal treatment (e.g., the storage conditions) after the "primary" crystallization process.Previous studies have clearly demonstrated that the thickness of crystalline polymer lamellae depends on the crystallization temperature [16,17] and can increase when the crystals are annealed below the melting point (lamellar thickening) [6][7][8][9][12][13][14][15]]. An additional indication for the relaxation of nonequilibrium states comes from calorimetry curves showing a double melting peak [9,[12][13][14][15] which is related to melting of highly folded states and recrystallizing in less folded states which then finally melt again at higher temperatures.…”

“…An additional indication for the relaxation of nonequilibrium states comes from calorimetry curves showing a double melting peak [9,[12][13][14][15] which is related to melting of highly folded states and recrystallizing in less folded states which then finally melt again at higher temperatures. However, the actual pathways taken by such relaxations have never been observed in real space.…”

Isothermal crystallization kinetics of PEO in poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymers. I. Effect of the soft-block length

“…Recently, Strobl et al 18 reported that the Hoffman-Weeks method is not suitable for a syndiotactic-polypropylene (s-PP) copolymer because the crystals of s-PP and its copolymer keep their thickness constant during the isothermal crystallization process. For PEO, the crystallization mechanism is obviously different from that of s-PP; the isothermal thickening process was observed through time-resolved synchrotron small-angle X-ray scattering, DSC, and TEM experiments by Cheng et al 19,20 Furthermore, the Hoffman-Weeks method was used to obtain the T m o of copolymers by many researchers; we would like to use the HoffmanWeeks method to deal with our own experimental results. In the Hoffman-Weeks equation, the growth rate is nucleation-controlled at low supercooling and diffusion-controlled at high supercooling.…”

Defect orientation on the chain folded surfaces of two-arm poly(ethylene oxide) lamellar crystals

“…The IF chain crystals have also been observed in unbranched alkanes having uniform molecular lengths 5,6) . During the past decade, we have made substantial efforts in studying the mechanism of IF crystal formation in LMW PEOs [7][8][9][10][11][12] . Several steps in understanding the molecular architecture effects have been investigated: molecular weight dependence 13) , chain end effects 14) , and defects at chain centers 15) .…”