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Classical concepts on polymer crystallization are under revision, due to the demands made by a wealth of new information acquired from experiments and computer simulations that explore the time-resolved molecular details of the crystallization process. A brief summary of the classical ideas and the contrasting new results is presented here.
The equilibrium state of polymer single crystals is considered by explicitly taking into account the amorphous fraction formed by loops and tails of the chains. Using ideal chain statistics, a general expression for the free energy excess of the amorphous part is derived. I show that tight loops and close reentries are favored under experimental conditions for under-cooling of polymer single...
We review how the nucleation mechanism of polymer crystallization could be assigned to intramolecular processes and what are the preliminary benefits for understanding some fundamental crystallization behaviors. The speculative concept of molecular nucleation and the theoretical model of intramolecular nucleation have been elucidated in a broad context of classical nucleation theory. The...
Kinetic theory of crystal nucleation is proposed for flexible chain polymers subjected to flow deformation with transient molecular deformation and orientation. Significant transient effects in the kinetics of oriented nucleation are expected in melt processing involving high deformation rates, like in high-speed melt spinning.
We performed depolarized light scattering (DPLS) and polarized optical microscope (POM) measurements on the structure formation process or the crystallization process of isotactic polystyrene (iPS) under shear flow below and above the nominal melting temperature Tm. It was found in the DPLS measurements that an anisotropic oriented structure on a μm scale was formed even above the nominal...
The ordering process and glass transition of poly(ethylene terephthalate) (PET) in oriented glassy states have been investigated using real time X-ray scattering experiment with synchrotron radiation sources and (temperature modulated) differential scanning calorimetry. The time evolution of the X-ray scattering patterns observed during the isothermal annealing process could well be reproduced...
In this article, the role of chain entanglement on the formation of flowinduced crystallization precursor structure in polymer melts was discussed. In particular, recent experimental findings from in-situ rheo-X-ray studies and ex-situ microscopic examinations were described: (1) the shish arise from the stretched chain segments in the entanglement network of the high molecular weight species;...
The full dissolution and crystallization of PA6 in water and PA4.6 in water and ethanol under pressure are described. Dissolution of PA6 in water is very fast and effective: it is completed during heating at 5°C/min in a DSC without stirring. It drastically lowers subsequent crystallization and melting temperatures. The maximum depression of the crystallization and melting temperatures is...
Crystallization of low molecular weight polyethylene from concentrated solutions has been studied using small angle neutron scattering (SANS). The detection sensitivity of the volume fraction degree of crystallinity is estimated to be 10-5, allowing for measuring the structure and kinetics during the very early stages of crystal growth. SANS spectra for both the early and late stages of crystallization...
We present microscopy investigations on the morphology of crystals of poly-2-vinylpyridine-polyethyleneoxid diblock copolymers (P2V P - PEO) in thin films with thicknesses below and above the thickness of a single lamella. For crystallisation temperatures above 45°C, nucleation is highly unlikely. Thus, the resulting morphologies represent essentially single crystals,...
This chapter deals with the crystallization behavior of long frustrated alkyl groups as part of side chain polymers. Results from crystallization experiments on poly(n-octadecylmethacrylate) [PODMA] homopolymers with different molecular weight and on microphase-separated poly(styrene-block-octadecylmethacrylate) block copolymers [P(S-b-ODMA] by calorimetry and scattering techniques are presented.
Recent results on the crystallization of block copolymers with more than one crystallizable block are reviewed. The effect that each block has on the nucleation, crystallization kinetics and location of thermal transitions of the other blocks has been considered in detail. Depending on the thermodynamic repulsion between the blocks, the initial melt morphology in weakly segregated double...
The interlamellar domain of semicrystalline polyethylene is studied by means of off-lattice Metropolis Monte Carlo simulations using a realistic united atom force field with inclusion of torsional contributions. Both structural as well as thermal and mechanical properties are discussed for systems with the {201} crystal plane parallel to the interface. In so doing, important data is obtained...
In semi-crystalline polymers, a range of morphologies can be obtained in which a chain may traverse the amorphous region between the crystals or fold back into the crystals leading to adjacent or non-adjacent re-entry, depending on the molecular architecture and crystallization conditions. This causes topological variations on the crystal surface and the occurrence of an interphase between...
Even if many efforts have been spent on the explanation of the mechanisms involved during the polymer crystallization in typical industrial processing conditions, they are still only partially understood. Up to now, due to the remarkable experimental difficulties, in literature only few systematic works have been focused on the effect of high cooling rates and/or solidification pressure on...
The deformation behavior of semicrystalline polymers associated with polymorphic transformations under tensile deformation is discussed in the case of isotactic polypropylene (iPP). The mechanical properties and polymorphic transformations occurring during plastic deformation of iPP samples with variable stereoregularity, containing only rr stereo-defects, are presented. Thermoplastic materials...
In-situ observation of polymer crystallization with atomic force microscopy is rapidly becoming a standard method, providing an increasing wealth of real-space information on the growth process at the molecular scale. Here, in-situ studies of dendritic thin film growth are extended to polyethylene, and the conditions for the onset of flat-on crystal growth and dendritic growth are given....
Crystallization behaviours are characterized with the nucleation and crystal growth rates, which are strongly dependent on temperature and molecular weight in polymeric materials. Their rates show the bell-shape temperature dependence with maximum rates. The maximum rates are characteristic intrinsic values in polymer crystallization mechanism. Temperature and molecular weight dependencies...
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