Deformation of crystalline polymers

Note at proof Recently Gaylord et al. (Polymer, 25, 1577, 1984) have shown theoretically that elastic deformation of crystalline polymers is controlled by energetic interaction rather than by entropy. 

Structure and deformation of crystalline polymers. Rheology, 5 Chap. VI. New York Academic Press 1969. 

Pawlak A, Galeski A (2005) Plastic deformation of crystalline polymers the role of cavitation and crystal plasticity. Macromolecules 38 9688-9697 Peterlin A (1971) Molecular model of drawing polyethylene and polypropylene. J Mater Sci 6 490 Popli R, Mandelkem L (1987) Influence of structural and morphological factors on the mechanical properties of the polyethylenes. J Polym Sci B Polym Phys 25 441 Read D, Duckett R, Sweeny J, Mcleish T (1999) The chevron folding instability in thermoplastic elastomers and other layered material. J Phys D Appl Phys 32 2087-2099 Resconi L, Cavallo L, Fait A, Piemontesi F (2000) Selectivity in propene polymerization with metallocene catalysts. Chem Rev 100 1253... 

It is evident from the preceding discussion that many aspects of the deformation of crystalline polymers have yet to be understood on a molecular basis. A great deal of work remains to be done. However, progress has been made by focusing on the independent structural variables that define the crystalline states. 

The mechanisms associated with plastic deformation of crystalline polymers can be explained better on the basis of two examples of isotactic polypropylene subjected to drawing eind to plane strain compression in a channel die. The envisioned differences between defiarmation with and without cavitation are summarized in Figure 1.21. 

Figure 1.21. Mechanisms associated with plastic deformation of crystalline polymers explained by an example of isotactic polypropylene of molecular weight 3.1x10 [10]...

Pawlak A and Galeski A (2005) Plastic deformation of crystalline polymers The role of cavitation and crystal plasticity. Macromolecules 38 9688-9697. 

Peterlin A (1975) Plastic deformation of crystalline polymers, in Polymeric Materials (Ed. Baer E) American Society for Metals, Metals Park, Ohio, pp. 175-195. 

Table 1.1 and Figure 1.21 are from Macromolecules, Vol. 38, 2005, Authors Pawlak A and Galeski A, Title Plastic Deformation of Crystalline Polymers The Role of Cavitation and Crystal Plasticity, pp. 9688-9697, Copyright 2005, with permission from The American Chemical Society. 

The plastic deformation of such polymers is a major research area and has a triennial series of conferences entirely devoted to it. The process seems to be drastically different from that familiar from metals. A review some years ago (Young 1988) surveyed the available information about polyethylene the yield stress is linearly related to the fraction of crystallinity, and it increases sharply as the thickness... 

If the ordered, crystalline regions are cross sections of bundles of chains and the chains go from one bundle to the next (although not necessarily in the same plane), this is the older fringe-micelle model. If the emerging chains repeatedly fold buck and reenter the same bundle in this or a different plane, this is the folded-chain model. In either case the mechanical deformation behavior of such complex structures is varied and difficult to unravel unambiguously on a molecular or microscopic scale. In many respects the behavior of crystalline polymers is like that of two-ph ise systems as predicted by the fringed-micelle- model illustrated in Figure 7, in which there is a distinct crystalline phase embedded in an amorphous phase (134). 

Geil, P. H. Morphological Aspects of Deformation and Fracture of Crystalline Polymers, in Fracture Proce.sses in Polymer Solids (ed.) Rosen, B., p, 551, New York—London—Sydney, Interscience Publ. 1964... 

The break-up of crystallites and the reformation of the lamellar fragments into microfibrUs is the basis of a theory for the cold-drawing of isotropic semi-crystalline polymers due to Peterlin. " (See also Hosemann et and Robertson .) Both Peterlin and Hosemann assert that the main mechanism is the break-up of each crystallite into approximately twenty smaller units which lie like pearls on a string with their chain axes parallel to the IDD. Many aspects of these theories would seem to be relevant to the deformation of oriented polymers of modest draw ratios. 

Abstract The combination of nanomaterials and ordered deformable soft materials is emerging as an enabling system in nanoscience and nanotechnology. In this context, nanomaterial functionalized photoresponsive liquid crystalline polymers are very promising and versatile systems due to their dynamic function. Moreover, the unique characteristic of nanomaterials combined with the mechanical, self-organizing and stimuli-responsive properties of deformable liquid crystalline polymers opens up new and exciting possibilities. In this chapter, we present recent developments of photodeformable behaviors of liquid crystalline polymers functionalized with nanomaterials. The main emphasis revolves around how the physicochemical properties of different nanomaterials modulate the reversible photomechanical behaviors of liquid crystalline polymers and their potential application in devices such as optically controlled switches and soft actuators. 

Conventional low molar mass LCs as well as linear LC-polymers can be macroscopically ordered by external electric or magnetic fields, which is widely applied in optoelectronics in the case of low molar mass LCs. For LC-elastomers it is very important to know whether a macroscopic mechanical deformation of the polymer network influences the liquid crystalline side groups and whether a mechanical stress or strain produces similar effects as observed for conventional LCs by external fields. 

Thermoplasts are linear or weakly branched polymers. Their application temperature lies below the melting temperature in the case of crystalline polymers and below the glass transition temperature in the case of amorphous polymers. They are converted to an easily deformable plastic state on heating above these characteristic temperatures. This plastic state can be termed liquid with respect to the molecular order, or viscoelastic with respect to the rheological behavior. On cooling below the characteristic temperatures,... 

In the IR spectra of crystalline polymers, absorption bands often appear which are completely absent in amorphous polymers (Table 5-4). These bands lie mainly in the range 650-1500 cm" Consequently, they originate mainly from bond angle deformations, which are, in turn, affected by the macromolecular conformation. These bands in the IR spectrum thus relate primarily to the conformation of the individual macromolecules, and not to intermolecular interactions. However, macromolecules can crystallize into varying conformations, thereby giving rise to differing crystal modifications (see Section 5.3.1). These modifications can, in turn, coexist in one sample. To determine the degree of crystallinity from IR measurements, it is first necessary to ascertain whether all the crystalline contributions are included in the chosen band. 

J.M. Haudin, Plastic deformation of semicrystalline polymers, in Plastic Deformation of Amorphous and Semi-crystalline Materials, ed. by B. Escaig, C. G Sell (Les Editions de Physique, Paris, 1982), p. 291... 

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