Structural studies of radiation‐crosslinked poly(ethylene oxide)

Abstract

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.

Sorption of Hydrophobic Compounds by Modified Poly(ethylene oxide) Networks

“…b) ref. [11] tions contaminated with dyes, even at low concentrations of the polymer flocculates (0.035-0.1 wt.-%). The binding (absorption) of hydrophobic organic compounds such as sodium picrate and bromophenol blue is strongly enhanced by the covalently-bound lipophilic quaternary ammonium cations in the networks.…”

“…The length between crosslinks in the PEO gels (network density) varies depending on the irradiation dose (c-rays). [11,12] It is well recognized that a higher network density causes slower diffusion of the solvent within the three dimensional structure of the polyether, while a lightly crosslinked polymer absorbs much larger quantities of water or organic solvent. [12] Therefore, the PEO-based networks were prepared by low irradiation doses.…”

Ethylene Oxide Polymers

“…The resulting polymer network exhibits hydrogel properties of high water capacity (81,82). Studies of the cross-linking mechanism and structure of the cross-linked polymer indicate that a complex network of cross-linked chains of varying lengths is present (83)(84)(85)(86). When the cross-linking is performed in solution, the cross-links can be both intermolecular and intramolecular; the overall structure of the cross-linked polymer is the combined result of chain scission, intramolecular bonding, and intermolecular bonding.…”

Crosslinked poly(ethylene oxide) for drug release systems

“…In our earlier work (Ref. 13) we have studied the structure and the thermal behaviour of freeze-dried high molecular weight PEO gels, obtained by 7-irradiation of 2 % aqueous solutions at different doses. The crosslink density (density of the effective network, v,) was calculated from the storage modulus, E', according to the theory of rubber elasticity (Ref.…”