Order-disorder polymers

In another study Milehev and Landau [27] investigated in detail the transition from a disordered state of a polydisperse polymer melt to an ordered (liquid erystalline) state, whieh oeeurs in systems of GM when the ehains are eonsidered as semiflexible. It turns out that in two dimensions this order-disorder transition is a eontinuous seeond-order transformation whereas in 3d the simulational results show a diseontinuous first-order transformation. Comprehensive finite-size analysis [27] has established... 

Using the so-called "block copolymers (a block of Na A-monomers at one end is covalently bonded to a block of Nb B-monomers) one can also realize the analogy of order-disorder phenomena in metallic alloys with polymers one observes transitions from the disordered melt to mesophases with various types of long range order (lamellar, hexagonal, cubic, etc ). We shall not consider these phenomena here further, however... 

In the second section a classification of the different kinds of polymorphism in polymers is made on the basis of idealized structural models and upon consideration of limiting models of the order-disorder phenomena which may occur at the molecular level. The determination of structural models and degree of order can be made appropriately through diffraction experiments. Polymorphism in polymers is, here, discussed only with reference to cases and models, for which long-range positional order is preserved at least in one dimension. 

Hashimoto T., Order disorder transition in block copolymers. Thermoplastic Elastomers A Comprehensive Review (Legge N.R., Holden G., and Schroeder H.E., eds.), Hanser Publishers, Munich, 1987. Bianchi U. and Pedemonte E., Morphology of styrene butadiene styrene copolymer. Polymer, 11, 268, 1970. 

Transition Temperature. The order-disorder transition temperature mid-point T is also determined both by the environment - salinity, pH value, and the nature of the ions in solution, and the structure of the polymer - charge, pyruvate, succinate and acetate content. Most published work describes the low salinity behaviour of such polymers, and has shown that for xanthan, the transition temperature exceeds 100 C as the salinity exceeds about 1 per cent sodium chloride (10). 

Liquid-solid transitions in suspensions are especially complicated to study since they are accompanied by additional phenomena such as order-disorder transition of particulates [98,106,107], anisotropy [108], particle-particle interactions [109], Brownian motion, and sedimentation-particle convection [109], Furthermore, the size, size distribution, and shape of the filler particles strongly influence the rheological properties [108,110]. More comprehensive reviews on the rheology of suspensions and rubber modified polymer melts were presented by Metzner [111] and Masuda et al. [112], respectively. 

As the temperature is decreased, the chains become increasingly rigid zc then approaches 1 if we assume that there is only one fully ordered crystalline structure and Zconf for the liquid becomes smaller than 1. This means that, at this level of approximation, the disordered state becomes less favorable than the crystalline ground state. A first-order disorder-order phase transition is expected to occur under these conditions. Flory interpreted this phase transition as the spontaneous crystallization of bulk semiflexible polymers [12], However, since the intermolecular anisotropic repulsion essential in the Onsager model is not considered in the calculation, only the short-range intramolecular interaction is responsible for this phase transition. 

An A-B diblock copolymer is a polymer consisting of a sequence of A-type monomers chemically joined to a sequence of B-type monomers. Even a small amount of incompatibility (difference in interactions) between monomers A and monomers B can induce phase transitions. However, A-homopolymer and B-homopolymer are chemically joined in a diblock therefore a system of diblocks cannot undergo a macroscopic phase separation. Instead a number of order-disorder phase transitions take place in the system between the isotropic phase and spatially ordered phases in which A-rich and B-rich domains, of the size of a diblock copolymer, are periodically arranged in lamellar, hexagonal, body-centered cubic (bcc), and the double gyroid structures. The covalent bond joining the blocks rests at the interface between A-rich and B-rich domains. 

Indeed, in the world of tomorrow we can expect new aspects of polymer solids to extend the conventional and successful structure ideas of this century. These, of course, were the recognition as molecular identities of the chains of repeating chemical monomers. The circumstances of those entities have resulted in interesting concepts of solubilities, viscosity, and other mechanics, and especially thermodynamic limitations m mutual solubility or comparability of polymer mixtures. But we have known for decades that even homogeneous regular chain polymers such as Carothers polyesters and polyamides formed solids with manifold imperfections and irregularities, such as order-disorder crystal configurations.(22,23)... 

Information on the morphology of polymers is revealed by techniques such as powder X-ray diffraction (PXRD), which is often called wide-angle X-ray scattering (WAXS) by polymer scientists, and small-angle X-ray scattering (SAXS). The crystallites exist in a polymer sample below the melting temperature T, an order-disorder transition, above which a viscous melt is formed. 

ORDER-DISORDER THEORY AND APPLICATIONS. Phase transitions in binary liquid solutions, gas condensations, order-disorder transitions in alloys, ferromagnetism, antiferromagnetism, ferroelectncity, anti-ferroelectricity, localized absorptions, helix-coil transitions in biological polymers and the one-dimensional growth of linear colloidal aggregates are all examples of transitions between an ordered and a disordered state. 

Marx, P. and Dole, M. Specific heat of synthetic high polymers. V. A. study of the order-disorder transition in polytetrafluoroethylene. J. Am. Chem. Soc. 17, 4771 (1955)... 

Hashimoto, T. (1985). Time resolved small-angle X-ray scattering studies on kinetics and molecular dynamics of order-disorder transition of block polymers. In Physical optics of dynamic phenomena and processes in macromolecular systems, (ed. B. Sedlacek), p. 106. Walter de Gruyter, Berlin. 

Hashimoto, T. (1996). Order-disorder transition in block polymers. In Thermoplastic elastomers, (ed. G. Holden, N. R. Legge, R. P. Qurik and H. E. Schroeder), p. 430. Hanser, Munich. 

There are a few polymers where reversible transitions have been discovered in the solid state. Furukawa, McCoskey and King (1952) and Marx and Dole (1955) studied calorimetrically the room temperature order-disorder transitions in polytetra-... 

From this point of view, polypeptides containing photochromic units in the side chains are quite special polymers. They can exist in ordered or disordered conformations, and photoisomerization of their photochromic side chains can produce order = disorder conformational changes. These photostimulated structural variations, such as random coil a-helix, take place as highly cooperative transitions therefore photochromic polypeptides actually work as amplifiers and transducers of the primary photochemical events occurring in the photosensitive side chains. 

Much experimental work has appeared in the literature concerning the microphase separation of miktoarm star polymers. The issue of interest is the influence of the branched architectures on the microdomain morphology and on the static and dynamic characteristics of the order-disorder transition, the ultimate goal being the understanding of the structure-properties relation for these complex materials in order to design polymers for special applications. 

Macromolecular conformations and reversible order-disorder and disorder-order transitions are highly sensitive to solvent, temperature, pressure, pH, water activity, and metal ions. Polyanions are distinguished from neutral molecules by their sensitivity to electrolytes. Whereas synthetic polymers do not normally dissolve or disperse spontaneously, some polysaccharides may do so in water (hydration), given their strong hydrophilicity. 

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