Order-disorder transitions 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... 

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. 

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-... 

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. 

As we will see in Chapter 11, it is usual to describe interactions in polymers using the Flory interaction parameter x, which varies as the inverse of the temperature. Thus if x is relatively small it is possible to form a single phase at temperatures below the degradation point of the polymer. Then, as you cool and X gets larger, the system phase-separates. The temperature or value of x at which this occurs, the order-disorder transition, varies with composition and it is possible to... 

Hydrogenated SBCs are often used to modify polyolefins such as polypropylene, polybutylene and polyethylene. One of the unique characteristics of strongly phase-separated block copolymers such as high molecular weight (>50 000) SEBS and SEPS is their response to shear in the melt. These polymers retain their phase-separated structure well above the Tg of the polystyrene because their order-disorder transition temperatures are above processing temperatures. This phase separation strongly inhibits flow in the absence of shear resulting in infinite viscosity at zero shear rates. The application of shear... 

Order-disorder, or rod-to-coil , transitions in dilute solution have been reported for polydiacetylenes (2, 5-11), polysilylenes (12-15), and alkyl-substituted polythiophenes (16). The interpretation of the experimental observations has been the subject of considerable controversy with respect to whether the observations represent a single-polymer-molecule phenomenon or a many-chain aggregation or precipitation process (3-16). Our own experimental evidence (12, 13) and that of others (5-8, 10, 16) weigh heavily in favor of the single-chain interpretation. In our theoretical interpretation, we will assume that the order-disorder transitions observed in dilute pol-ysilylene solutions represent equilibrium, single-chain phenomena. 

In this chapter, the theory of conformation-dependent polymer-solvent interactions, which was developed in detail by Schweizer (20-22) for soluble TT-conjugated polymers, will be used to explain both qualitatively and quantitatively a large body of observations on the polysilylenes (23, 24). The same theory has been used recently to interpret qualitatively order-disorder phenomena and the electronic thermochromism of TT-conjugated-polymer solutions and films (25, 26). The study presented in this chapter represents part of an ongoing effort to understand in a unified fashion both the optical properties (27-30) and order-disorder transitions (20-24) of flexible, conjugated-polymer solutions. 

Breadth of Phase Transition. The abruptness or width of the coexistence region of the order-disorder transition has also been estimated theoretically. For a monodisperse solution of a relatively high molecular weight polymer, an intrinsic coexistence region, ATc, exists because of standard flnite-size fluctuation effects. Numerical calculations yield the result (22)... 

Order-Disorder Transitions. General Features, Experimental data are summarized in Table II, and representative thermochromic behaviors are shown in Figure 2. For the dialkyl-substituted polysilylenes the transition is very sharp, with a barely discernible coexistence region and an approximate isosbestic point. On the other hand, the asymmetrically substituted polymers, except poly(n-dodecylmethylsilylene), display very smooth behavior only in n-hexane solution and a broad but clearly discernible transition in dilute toluene solution. The transition width (ATc) in toluene solution was taken to be the interval between departure from the extrapolated, smooth, high-temperature behavior and the onset of peak absorption wavelength saturation at low temperature. The transition temperature (Tq) is defined arbitrarily as the midpoint of this region. 

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