2-hydroxethyl methacrylate

Hydrogels, ie, gelatin and agar, have been known for a long time. In the late nineteenth century, Herschel proposed the use of jelly materials on the cornea for the correction of vision (108). In 1960, the use of synthetic hydrogels for contact lenses was proposed and several U.S. patents were obtained for the invention of cross-linked hydrophilic polymers, eg, systems based on 2-hydroxethyl methacrylate [868-77-9] (HEMA) (5) (109—112). 

Cross-linked pre-polymers having fractionalized molecular weights between 35,000 and 70,000 daltons with polydispersity indexes of less than 3.4 have been prepared by the free radical addition of 2-hydroxethyl methacrylate, HEMA, with 2% methacrylic acid or glycerol methacrylate. Once crosslinked, these materials are particularly useful as contact lenses because of their limited shrinkage and expansion. 

Preparation of Poly(2-Hydroxethyl Methacrylate-co-Methacrylic Acid) (poly-HEMA)... 

A 5-liter stainless steel reactor was charged with ethanol (1911.6 g), 2-hydroxethyl methacrylate (1056.6 g), dodecyl mercaptan (3.00 g), and methacrylic acid (21.00 g)... 

TABLE 1. Fractionalization effectiveness for poly(2-hydroxethyl methacrylate-co-methacrylic acid) using selected extraction solvents. 

L. Kanerva, R. Jolanki, T. Leino, T. Estlander, Occupational allergic contact dermatitis from 2-hydroxethyl methacrylate and ethylene glycol dimethacrylate in a modified acrylic structural adhesive, Contact Dermat. 33 (1995) 84—89. 

Of particular concern in these studies has been the presence of 2 hydroxethyl methacrylate (HEMA). This has been shown experimentally to be able to diffuse through the pulp chamber when released from a bonding agent placed beneath a composite resin (Hamid and Hume 1997). Thickness made a difference to the rate of diffusion, but even relatively thick layers of dentin (i.e., in the range 3.4—3.6 mm) were not sufficient to eliminate it completely. Another finding of significance was that diffusion of HEMA was much more rapid in teeth that had been severely affected by caries. In other words, the reason that tooth repair is needed clinically, caries, turns out to be responsible for affecting dentine permeability adversely, and opens the way for potentially harmful monomers to reach the pulp. 

Figure 9 Relative intensities of characteristic negative ion fragments from HEMA-EMA copolymers (see text) plotted as function of bulk composition. Error bars in (A) represent the largest spread of values for any measurement those in (B) and (C) represent the spread of values for all repeated measurements. (Reproduced with permission from Briggs D and Ratner BD (1988) A semi-quantitative SIMS analysis of the surfaces of random ethyl methacrylate hydroxethyl methacrylate copolymer films. Polymer Communications 29 6-8 Butterworths.)...

Fig. 9. Scanning electron micrograph illustrating the expulsion of 1 jam polystyrene seed particles from 4.2 ym poly(methyl methacrylate (73 %)/hydroxethyl methacrylate (20 %)/ethylene glycol dimethacrylate (7 %)) particles.

Poly(2-hydroxethyl methaciylate-co-glycerol methacrylate) was also prepared having a molecular weight of 41,000 daltons with a PDI of 2.80. 

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