Stress polymer

Type of stress Polymers ductile at 25°C and at 1 min strain rate... 

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

A. Popov, N. Rapoport, and G. Zaikov, Oxidation of Stressed Polymers, Gordon and Breach, London, p. 336 (1991). 

In their pioneering experiment, Zhurkov et al. [96] determined that the IR-frequency shift Av in a stressed polymer is approximately linear with the applied... 

Popov A, Rapoport N, Zaikov GE (1991) Oxidation of stressed polymers, Gordon and Breach Sci Publ New York London Tokyo, p 335... 

At least two different techniques are available to compress an emulsion at a given osmotic pressure H. One technique consists of introducing the emulsion into a semipermeable dialysis bag and to immerse it into a large reservoir filled with a stressing polymer solution. This latter sets the osmotic pressure H. The permeability of the dialysis membrane is such that only solvent molecules from the continuous phase and surfactant are exchanged across the membrane until the osmotic pressure in the emulsion becomes equal to that of the reservoir. The dialysis bag is then removed and the droplet volume fraction at equilibrium is measured. 

What changes occur in a stress polymer after the yield point ... 

Radiation-induced decomposition, 5,6-dihydrothymine, 930 Radiation stress, polymers, 685 Radical polymerization dialkyl peroxides, 707 peroxycarboxylic esters, 697 Radicals... 

Wool, R. P. Measurements of Infrared Frequency Shifts in Stressed Polymers, preprint... 

Shen, D. Y., Hsu, S. L. Vibrational Spectroscopic Characterization of Rigid Rod Polymers. III. Microstructural Changes in Stressed Polymers, Polymer... 

Jacobson K (1999) Oxidation of stressed polymers as studied by chemiluminescence. PhD Thesis, Royal Inst of Technology, Stockholm... 

When subjected to an applied stress, polymers may deform by either or both of two fundamentally different atomistic mechanisms. The lengths and angles of the chemical bonds connecting the atoms may distort, moving the atoms to new positions of greater internal energy. This is a small motion and occurs very quickly, requiring only 10 [-12] seconds [25],... 

ESC is mostly a surface-initiated failure of multiaxially stressed polymers in contact with surface-active substances. These surface-active substances do not cause chemical degradation of the polymer, but rather accelerate the process of macroscopic brittle-crack failure. Crazing and cracking may occur when a polymer under multiaxial stresses is in contact with a medium. A combination of external and/or internal stresses in a component may be involved. 

Zhurkov et al. used light scattering and low angle X-ray scattering (LAXS) to study the time-dependent formation of microcracks or cavities in stressed polymers. The concentrations of microcavities were found to be as high as 10 - 10 cm , uniformly distributed throughout the specimen, thougji more numerous close to the specimen surface. 

In spite of the difficulty of establishing direct correlations between macroscopic fracture phenomena and microscopical molecular fracture phenomena, the large amoimt of work carried out in recent years on the application of ESR and other techniques to molecular events in stressed polsmers has brou t us much closer to success. In particular it can now be stated in broad terms but vrith some confidence just how far the breakage of molecules within a stressed polymer contributes to macroscopic deformation and failure in any particular case. Work will no doubt continue with a view to reconciling even more closely the microscopical and macroscopic descriptions of fracture phenomena. 

In amorphous state, solid polymers retain the disorder characteristic for liquids, except that the molecular movement in amorphous solid state is restrained. The movement of one molecule versus the other is absent, and some typical liquid properties such as flow are absent. At low stress, polymers display elastic properties, reverting to a certain extent to the initial shape in a relaxation process. However, they can be irreversibly deformed upon application of appropriate force. The deformation and flow of polymers is very important for practical purposes and is studied by a branch of science known as rheology (see e.g. [1]). The combination of mechanical force and increased temperature are commonly applied for polymer molding for their practical applications. The polymers that can be made to soften and take a desired shape by the application of heat and pressure are known as thermoplasts, and most linear polymers have thermoplastic properties. 

Reviews on the analysis of polymers and polymer products have recently appeared (184-187). Typical applications are covered for analysis of raw materials for coatings (188-191) and determination of volatile components of commercial polymers (192). Mass spectrometry of thermally treated polymers (193) and of stressed polymers are treated (194) with instrumental and experimental details given in more detail than in corresponding journal references. 

When polymer molecules are completely dissolved in solution, the solution behaves as a liquid. Liquids, for example, continuously deform in response to a continuously applied stress. Polymers can also form gels, which do not behave as liquids. The individual polymer chains in a gel form a continuous network within the liquid phase. The network is maintained by chemical or physical interactions between polymer ehains these interactions may involve covalent cross-links, hydrogen bonds, or physical entanglement of the molecules. The network restricts the response of the gel to an applied stress. As a result, the mechanieal properties of a gel are qualitatively different from the mechanical properties of a fluid. 

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