Gelation of poly(ethylene oxide) solutions by gamma radiation: Effects of molecular weight and irradiation conditions

Brederode, R. A. Van; Rodriguez, Ferdinand

doi:10.1002/app.1970.070140408

Cited by 15 publications

(2 citation statements)

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“…They form crystallites with increased conformational entropy thus decreasing the surface free energy and increasing the free energy of the crystalline region.m*21 On the other hand the processes of crosslinking and cleavage mutually compensate in their effect on the free energy of the amorphous regions. Melting ocam between temperatures T(4) and T (8) at which GJ4-8) becomes equal to the values of Gc(4)-Gc(8). The free energy differences remain constant between AG(4) and AG(8).…”

Section: Ag(4)mentioning

confidence: 99%

“…10) corresponding to AH/a(8)-AH/a(15) decrease. The decrease in AG at constant melting temperature is only possible when the free energies of the crystalline and the amorphous regions simultaneously increase: see curves Gc (8)(9)(10)(11)(12)(13)(14)(15) and G, (8)(9)(10)(11)(12)(13)(14)(15) in Figure 10. This can be explained by destructive processes taking place during the irradiation and melting.…”

Section: Ag(4)mentioning

confidence: 99%

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Structural studies of radiation‐crosslinked poly(ethylene oxide)

Minkova

Stamenova

Tsvetanov

et al. 1989

J Polym Sci B Polym Phys

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The structure and thermal behavior of freeze‐dried gels of radiation‐crosslinked high molecular weight poly(ethylene oxide) (PEO) were investigated by optical and electron microscopy, wide‐angle x‐ray scattering (WAXS), DTA, TGA, and thermomechanical analysis. The gels are highly porous with thin crystalline walls. Small spherulite and hedrite structures are observed on the walls. A model for gel formation in solution is suggested. A statistically homogenous chemical network is formed as a result of intrachain and interchain crosslinking. Simultaneous grafting of macromolecular fragments formed by chain scission also occurs. On increasing the irradiation dose from 1 to 15 Mrad, the degree of crystallinity determined by x‐ray diffraction and the total intensity of diffraction gradually decrease. The temperature and enthalpy of melting diminish steeply up to 5 Mrad, fall only slightly from 5 to 8 Mrad, and do not change from 8 to 15 Mrad. By comparing the x‐ray and DTA crystallinity values, this is shown to be due not only to reduced crystallinity at higher network density but also to Tree energy changes of entropic origin in crystalline and amorphous regions. Radiation chemical yields, G(‐units), for these dose ranges are 100, 38, and 0, respectively. Thermomechanical analysis was used to determine the elastic modulus of compression as a function of the dose absorbed, and the average molecular weight $ \bar M_{\rm c} $ of network chains was estimated. $ \bar M_{\rm c} $ decreases with doses up to 10 Mrad and does not change with further irradiation.

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Section: Ag(4)mentioning

confidence: 99%

Section: Ag(4)mentioning

confidence: 99%

Structural studies of radiation‐crosslinked poly(ethylene oxide)

Minkova

Stamenova

Tsvetanov

et al. 1989

J Polym Sci B Polym Phys

View full text Add to dashboard Cite

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Radiation Chemistry of Polymers

Hill

Whittaker

2004

Encyclopedia of Polymer Science and Technology

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Polymeric materials are exposed to high energy radiation either deliberately to alter their properties or inadvertently during their use in high dose environments. As a consequence, an understanding of how radiation modifies the polymer structure, and hence properties, is essential for many applications. In addition, the understanding of the degradation of polymers with light or heat can benefit from knowledge of the reaction pathways of radical and charged species formed on irradiation with high energy photons. This article aims to provide a broad overview of the fundamental processes occurring during radiolysis of polymers. This is achieved through a discussion of the interaction of high energy photons with matter, and the subsequent reactions of mainly radical intermediates. Polymers either cross‐link or degrade on exposure to radiation, and the final properties of the polymers depend critically on the balance of these two main reaction pathways. A number of examples are taken from the literature to illustrate how the tendency to undergo cross‐linking or main‐chain scission depends on the polymer structure. The overall yield of reactions can be greatly reduced by the introduction of aromatic groups into the polymer structure. On the other hand, yields can be increased by the inclusion of radiation‐sensitive groups such as sulfones. Similarly, the rates of reactions and the balance between cross‐linking and scission can depend sensitively on the radiolysis temperature. While this review focuses on a discussion of the reactions occurring on radiolysis in vacuo, the effect of the presence of dissolved oxygen on the reaction pathways is also discussed.

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Radiation Chemistry of Polymers

Hill

Whittaker

2016

Encyclopedia of Polymer Science and Technology

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Polymeric materials are exposed to high energy radiation either deliberately to alter their properties or inadvertently during their use in high dose environments. As a consequence, an understanding of how radiation modifies polymer structure, and hence properties, is essential for many applications. In addition, the understanding of the degradation of polymers with light or heat can benefit from knowledge of the reaction pathways of radical and charged species formed on irradiation with high energy photons. This article aims to provide a broad overview of the fundamental processes occurring during radiolysis of polymers. This is achieved through a discussion of the interaction of high energy photons with matter, and the subsequent reactions of mainly radical intermediates. Polymers either cross‐link or degrade on exposure to radiation, and the final properties of the polymers depend critically on the balance of these main reaction pathways. Examples are taken from the literature to illustrate how the tendency to undergo cross‐linking or main‐chain scission depends on the polymer structure. The overall yield of reactions can be greatly reduced by the introduction of aromatic groups into the polymer structure. On the other hand, yields can be increased by the inclusion of radiation‐sensitive groups such as sulfones. Similarly, the rates of reactions and the balance between cross‐linking and scission can depend sensitively on the radiolysis temperature. While this review focuses on a discussion of the reactions occurring on radiolysisin vacuo, the effect of the presence of dissolved oxygen on the reaction pathways is also briefly addressed.

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Gelation of poly(ethylene oxide) solutions by gamma radiation: Effects of molecular weight and irradiation conditions

Cited by 15 publications

References 4 publications

Structural studies of radiation‐crosslinked poly(ethylene oxide)

Structural studies of radiation‐crosslinked poly(ethylene oxide)

Radiation Chemistry of Polymers

Radiation Chemistry of Polymers

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