History polymer

Bastiaansen C.W.M., H.E.H. Meyer, and P.J. Lemstra. 1990. Memory effects in poly-ethylenes influence of processing and crystallization history. Polymer 31 1435-1440. 

Carraher CE Jr (2005) General topics silica aerogels-properties and uses. Polymer News, 30(12), 386-388 Carraher CE Jr (2005) Silica aerogels - synthesis and history. Polymer News, 30 62-64 Pajonk GM (2003) Some applications of silica aerogels. Colloid and Polymer Science, 281 637—651 Akimov YK (2003) Fields of Application of Aerogels (Review) Instruments and Experimental Techniques (Translation of Pribory i Tekhnika Eksperimenta), 46 287-299... 

The Deformation History. Polymer dynamics can be investigated by SANS via special phenomena such as demixtion observed by X-rays or crystallization. A more direct way is simply to observe a sample mechanically displaced out of equilibrium. A classical approach used in other techniques is a steady deformation, characterised by a constant rate of deformation s = 1/L dL/dt, where L is a distance. The investigation in time is related to the dependence on s. Other procedures involve time-dependent deformation histories, which relate to the actual time typical cases are a periodic deformation, e.g. oscillatory, and a stepstrain deformation. A time analysis is then needed. In the case of a periodic deformation, one can divide the period 2nj into small intervals of phase v /, i / -I- A , within which is measured. In the case of... 

IC1 Ichihara, S., Komatsu, A., and Hata, T., Thermodynamic studies on the glass transition and the glassy state of polymers. 11. Enthalpies and specific heats of polystyrene glasses of different thermal histories, Polym. J., 2,644, 1971. 

Figure 11.1 The stress-strain time relation obtained from creep. (Reproduced from Turner, S. (1966) The strain response of plastics to complex stress histories. Polym. Eng. Sci., 6, 306. Copyright (1966) Society of Plastics Engineers.)...

Turner, S. (1966) The strain response of plastics to complex stress histories. Polym. Eng. Sci., 6, 306. 

Menezes, E. V., Graessley, W. W. Nonlinear rheological behavior of polymer systems for several shear-flow histories. /. Polym. Sci., Polym. Phys. (1982) 20, pp. 1817-1833... 

Coarse-grained models have a longstanding history in polymer science. Long-chain molecules share many common mesoscopic characteristics which are independent of the atomistic stmcture of the chemical repeat units [4, 5 and 6]. The self-similar stmcture [7, 8, 9 and 10] on large length scales is only characterized by a single length scale, the chain extension R. 

Our purpose in this introduction is not to trace the history of polymer chemistry beyond the sketchy version above, instead, the objective is to introduce the concept of polymer chains which is the cornerstone of all polymer chemistry. In the next few sections we shall introduce some of the categories of chains, some of the reactions that produce them, and some aspects of isomerism which multiply their possibilities. A common feature of all of the synthetic polymerization reactions is the random nature of the polymerization steps. Likewise, the twists and turns the molecule can undergo along the backbone of the chain produce shapes which are only describable as averages. As a consequence of these considerations, another important part of this chapter is an introduction to some of the statistical concepts which also play a central role in polymer chemistry. 

To provide a rational framework in terms of which the student can become familiar with these concepts, we shall organize our discussion of the crystal-liquid transition in terms of thermodynamic, kinetic, and structural perspectives. Likewise, we shall discuss the glass-liquid transition in terms of thermodynamic and mechanistic principles. Every now and then, however, to impart a little flavor of the real world, we shall make reference to such complications as the prior history of the sample, which can also play a role in the solid behavior of a polymer. 

Monte Carlo (MC) techniques for molecular simulations have a long and rich history, and have been used to a great extent in studying the chemical physics of polymers. The majority of molecular modeling studies today do not involve the use of MC methods however, the sampling capabiUty provided by MC methods has gained some popularity among computational chemists as a result of various studies (95—97). Relevant concepts of MC are summarized herein. 

Modem synthetic polymers are the subject of increasing research by conservation scientists. Not only does their frequent use in conservation treatments require a better understanding of their long term stabiUty, but also many objects, including those in collections of contemporary art and in history and technology museums, are made out of these new materials. 

Many industrially important fluids cannot be described in simple terms. Viscoelastic fluids are prominent offenders. These fluids exhibit memory, flowing when subjected to a stress, but recovering part of their deformation when the stress is removed. Polymer melts and flour dough are typical examples. Both the shear stresses and the normal stresses depend on the history of the fluid. Even the simplest constitutive equations are complex, as exemplified by the Oldroyd expression for shear stress at low shear rates ... 

Poly(viaylidene fluoride) [24937-79-9] is the addition polymer of 1,1-difluoroethene [73-38-7], commonly known as vinylidene fluoride and abbreviated VDF or VF2. The formula of the repeat unit in the polymer is —CH2—CF2—. The preferred acronym for the polymer is PVDF, but the abbreviation PVF2 is also frequently used. The history and development of poly(vinyhdene fluoride) technology has been reviewed (1 3). 

Polymer Composition. The piopeities of foamed plastics aie influenced both by the foam stmctuie and, to a gieatei extent, by the piopeities of the parent polymer. The polymer phase description must include the additives present in that phase as well. The condition or state of the polymer phase (orientation, crystallinity, previous thermal history), as well as its chemical composition, determines the properties of that phase. The polymer state and cell geometry are intimately related because they are determined by common forces exerted during the expansion and stabilization of the foam. 

Some representative backbone stmctures of PQs and PPQs and their T data are given in Table 1. As in other amorphous polymers, the Ts of PQs and PPQs are controlled essentially by the chemical stmcture, molecular weight, and thermal history. Several synthetic routes have been investigated to increase the T and also to improve the processibiUty of PPQ (71). Some properties of PPQ based on 2,3-di(3,4-diaminophenyl)quinoxaline and those of l,l-dichloro-2,2-bis(3,4-diaminophenyl)ethylene are summarized in Table 2. 

The first polymer with a polymethylene stmcture was synthesized by von Pechmann in 1898 from diazomethane (1). Since then, there have been four milestones in the history of PE polymers as commercial plastics. 

The polymer is exposed to an extensive heat history in this process. Early work on transesterification technology was troubled by thermal—oxidative limitations of the polymer, especially in the presence of the catalyst. More recent work on catalyst systems, more reactive carbonates, and modified processes have improved the process to the point where color and decomposition can be suppressed. One of the key requirements for the transesterification process is the use of clean starting materials. Methods for purification of both BPA and diphenyl carbonate have been developed. 

Master curves can also be constmcted for crystalline polymers, but the shift factor is usually not the same as the one calculated from the WLF equation. An additional vertical shift factor is usually required. This factor is a function of temperature, partly because the modulus changes as the degree of crystaHiuity changes with temperature. Because crystaHiuity is dependent on aging and thermal history, vertical factors and crystalline polymer master curves tend to have poor reproducibiUty. 

A crystalline or semicrystalline state in polymers can be induced by thermal changes from a melt or from a glass, by strain, by organic vapors, or by Hquid solvents (40). Polymer crystallization can also be induced by compressed (or supercritical) gases, such as CO2 (41). The plasticization of a polymer by CO2 can increase the polymer segmental motions so that crystallization is kinetically possible. Because the amount of gas (or fluid) sorbed into the polymer is a dkect function of the pressure, the rate and extent of crystallization may be controUed by controlling the supercritical fluid pressure. As a result of this abiHty to induce crystallization, a history effect may be introduced into polymers. This can be an important consideration for polymer processing and gas permeation membranes. 

The chemical and physical properties of cellulose depend ia large measure on the spatial arrangements of the molecules. Therefore, cellulose stmctures have been studied iatensively, and the resulting information has been important ia helping to understand many other polymers. Despite the extent of work, however, there are stiU many controversies on the most important details. The source of the cellulose and its history of treatment both affect the stmcture at several levels. Much of the iadustrial processiag to which cellulose is subjected is iatended to alter the stmcture at various levels ia order to obtain desired properties. 

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