Transparent polymer hydrogels

Transparent polymer hydrogels have been studied for use as ophthalmic materials such as soft contact lenses (93). 

Polymerization of monomers in the absence of any other solvent is called bulk polymerization. Bulk polymerization of monomers, such as hydrox-yethyl methacrylate (or HEMA), leads to the production of a glassy, transparent polymer matrix that is very hard. When immersed in water, such a glassy matrix swells to become relatively soft and flexible. Although it allows the transfer of water and some low molecular weight solutes, this kind of swollen polymer matrix (i.e., hydrogel) is considered nonporous. The... 

Saito H, Sakurai A, Sakakibara M, Saga H (2003) Preparation and properties of transparent cellulose hydrogels. J Appl Polym Sci 90 3020-3025... 

Hu, X., Xiong, L., Wang, T., Lin, Z., Liu, X., Tong, Z., 2009. S5mthesis and dual response of ionic nanocomposite hydrogels with ultrahigh tensibiUty and transparence. Polymer 50, 1933-1938. 

The GGM-rich hemicelluloses, isolated from water-impregnated spruce chips by heat-fractionation [218], has been used as pre-polymers after modification with methacrylic functions [439]. Radical polymerization of the modified hemicelullose with 2-hydroxyethyl methacrylate in water yielded elastic, soft, transparent, and easily swollen hydrogels. 

Soft lenses are made of hydrophilic hydrogel polymers that contain 36-74% water. Other plastics and copolymers are added to alter the physical characteristics of the lens. The diameter is 10.5-15.5 mm and the thickness at the center 0.03-20 mm. Soft lenses can correct most optical defects, including myopia, hyperopia, and astigmatism. Bifocal lenses are also available. They can be colored with either transparent hnes or opaque patterns to change apparent eye color or to mask malformations of the cornea or iris. They are available for daily, weekly, and twice-weekly disposable nse, 1-3 months frequent replacement, and annual replacement. 

FIGURE 12.13 Change in opaqueness of electrode-supported hydrogel (transparent gel without CEP) upon growth of the conducting polymer component (dark green gel with CEP) within the gel network. 

The hydrogel used in this study has been the poly(2-hydroxy-ethylmethacrylate) obtained by a radical polymerization of the 2-hydroxyethylmethacrylate (HEMA) accomplished at 60 C for 2 hours using 0.5% by weight of ethyleneglycoldimethacrylate (EDMA) as cross-linking agent and 0.1% by weight of a,a -bisisobutyronitrile (AIBN) initiator. The polymer shows perfect transparency and is able to absorb and desorb water reversibly. ... 

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