Hydrogels and methods for their production

Details Hydrogels and methods for their production Hydrogels and methods for their production

2001-02-22

2003-05-06

Lovering, Richard D. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C516S099000, C522S009000, C522S033000, C522S175000, C522S183000, C522S904000, C522S905000, C524S916000, C525S329400, C525S936000

Reexamination Certificate

active

06559223

ABSTRACT:

§ 1. BACKGROUND
§ 1.1 Field of the Invention
The present invention relates to the field of polymers and, in particular, to polymerization, such as the photoinitiated polymerization of water soluble reactive monomers by radicals.
§ 1.2 Related Art
A first aspect of the present invention concerns polymerization and the cage effect. These topics are introduced in §§ 1.2.1 and 1.2.2, respectively, below. A second aspect of the present invention concerns hydrogels, which may be produced by the first aspect of the invention. Hydrogels are introduced in § 1.2.3 below.
§ 1.2.1 Photoinitiated Polymerization
The field of photointiated polymerizations is a subject of intense scientific and industrial study. Many applications such as photoresists, flexographic printing plates, photopolymerizable inks, coatings, and adhesives have been widely used. Yet many aspects of photopolymerization are incompletely understood and not subject to the utmost possibility of control.
Water-based photopolymerizations have a special advantage in protection of the environment. The development of water-soluble photoinitiators is under active development and new methods need to be created to control such photopolymerizations.
§ 1.2.2 The “Cage Effect”
The concept of the “cage effect” was introduced in 1934 to explain why the efficiency of I
2
photodissociation was less in solution than in the gas (Frank, J.; Rabinowitch, E.,
Trans. Faraday Soc.,
30, 120 (1934). This article is incorporated herein by reference.). Frank and Rabinowitch proposed that the solvent temporarily encapsulates the reactive iodide radical atoms in a solvent cage causing the radicals to remain as colliding neighbors before they either recombine or diffuse apart.
The cage effect has been widely used to explain many fundamental reaction phenomena; for example, magnetic isotope effects (Turro, N. J.,
J. Proc. Nat. Acad. Sci.,
80, 609 (1983). Lott, W. B.; Chagovetz, A. M.; Grissom, C. B.,
J. Am. Chem. Soc.,
117, 12194 (1995). These articles are incorporated herein by reference.), chemically induced dynamic nuclear polarization effects (Closs, G.,
J. Am. Chem. Soc.,
91, 4552 (1969). This article is incorporated herein by reference.), rate-viscosity correlations (Tanner, D. D.; Meintzer, C. P.; Tsai, E. C.; Oumar-Mahamat, H.,
J. Am. Chem. Soc.,
112, 7369 (1990). This article is incorporated herein by reference.), variations in products and yields as a function of the medium (Koenig, T.; Deinzer, M.; Hoobler, J. A.,
J. Am. Chem. Soc.,
93, 938 (1971). This article is incorporated herein by reference.) and variations in quantum yields as a function of the medium (Abram, I.; Milne, F.; Steel, C.,
J. Am. Chem. Soc.,
86, 745 (1969). This article is incorporated herein by reference.). The cage effect arising from solvent is important in explaining the kinetics including the initiation, propagation, and termination steps, of radical polymerization reactions. (Odian, G.,
Principles of Polymerization:
3
rd
ed., (Wiley-Interscience: New York, 1991). Bosch, P.; Mateo, J. L.; Serrano, J.,
J. Photochem. Photobiol. A,
103, 177 (1997). Tefera, N.; Weickert, G.; Westerterp, K. R.,
J. Appl. Polym. Sci.,
63, 1663 (1997). Wolff, E. -H. P.; Bos, A. N. R.,
Ind. Eng. Chem. Res.,
36, 1163 (1997). These works are incorporated herein by reference.)
Since supramolecular complexation became an intense field of study, cage effects have been one of the most important issues in this field. For example, cyclodextrin has been used as a cage in the study of photochemical reactions of dibenzyl ketones. (Rao, B. N.; Turro, N. J.; Ramamurthy, V.,
J. Org. Chem.,
51, 460 (1986). Rao, B. N.; Syamala, M. S.; Turro, N. J.; Ramamurthy, V.,
J. Org. Chem.,
52, 5517 (1987). These articles are incorporated herein by reference.) To make a long-lasting cage, people have tried to modify cage structures to cause more interactions between the host (cage) and the guest (radical pair). Among these are hydrophobic interactions in aqueous solutions.
Recently, many researchers have focused on the study of radical recombination in micelle systems. (Gould, I. R.; Zimmt, M. B.; Turro, N. J.; Baretz, B. H.; Lehr, G. F.,
J. Am. Chem. Soc.,
107, 4607 (1985). Wu, C.-H.; Jenks, W. S.; Koptyug, I. V.; Ghatlia, N. D.; Lipson, M.; Tarasov, V. F.; Turro, N. J.,
J. Am. Chem. Soc.,
115, 9583 (1993). These articles are incorporated herein by reference.) Turro et al. have investigated the effects of systematic changes in radical structure (hydrophobicity) and micelle structure. (Turro, N. J.; Wu, C.-H.,
J. Am. Chem. Soc.,
117, 11031 (1995). This article is incorporated herein by reference.)
§ 1.2.3 Hydrogels
Gels are chemically or physically cross-linked networks of polymers that can be swollen by liquids. Among the gels, a hydrogel is a network of hydrophilic polymers in which a large amount of water is present. Because of their relatively high biocompatibility, research on hydrogels has been focused on biomedical applications. (Peppas, N. A. e. a.,
Hydrogels in Medicine and Pharmacy; Properties and Applications
(CRC Press, Boca Raton, Fla., 1987) Vol. 3. This work is incorporated herein by reference.) Artificial skin (Chardack, W. N.; Brueske, D. A.; Santomauro, A. p.; Fazekas, G.,
Ann. Surg.,
155, 127 (1962). DeRossi, D.,
Polymer Gels
(Plenum Press New York, 1991). These works are incorporated herein by reference.) or contact lenses (Wichterle, O.; D., L.,
Nature,
185, 117, (1960). Wichterle, O.; D., L. U.S. Patent (1961). These works are incorporated herein by reference.) have a long history in the applications of the hydrogels. Recently, drug delivery system using hydrogels became a very fast growing research area. (Peppas, N. A.; Bures, P.; Leobandung, W.; Ichikawa, H.,
Eur. J. Pharma. Biopharm,
50, 27, (2000). This article is incorporated herein by reference.)
§ 1.2.3.1 Physical Hydrogels Differ from Covalently Crosslinked Hydrogels
In physical gels, a gelation occurs through van der Waals or hydrogen bonding or other noncovalent interactions between chains. (“Thermoreversible Gelation of Polymers and Biopolymers, by J. -M. Guenet, 1992, Academic Press. Incorporated herein by reference.) Physical gels require high cooperativity to be stable. For example, the energy involved in van der Waals interaction can be small compared to kT. Consequently, these gels can be reversible.
Most physical hydrogels are biopolymers, such as gelatin gels (Katz, J. R.; Derksen, J. C.; Bon, W. F.,
Rec. Trav. Chim. Pays
-
Bas,
50, 725, (1931). This article is incorporated herein by reference.) and polyssacharide gels (Anderson, N. S.; Campbell, J. W.; Harding, M. M.; Rees, D. A.; Samuel, J. w. B.,
J. Mol. Biol.,
45, 85, (1969). This article is incorporated herein by reference.). Gelatin gels (Petzron, I.; Djabourov, M.; Bosio, L.; Leblond, J.,
J. Polym. Sci. polym. Phys. Ed.,
28, 1823, (1990). This article is incorporated herein by reference.) consist of triple helices. Polysaccharide gels are known to be composed of double helices (Hermansson, A. M.,
Carbohydr. Polym.,
10, 163, (1989). This article is incorporated herein by reference.).
There are few examples of physical gels made by synthetic polymers. Poly(vinyl alcohol) (PVA) gels are probably the first system of this kind ever to be studied. (Sone, Y.; Hirabayashi, K.; Sakurada, I.,
Kobunshi Kagaku
10, 1, (1953). Kominami, T.; Naito, R.; Odanaka, H.,
Kobunshi Kogaku,
12, 218, (1955). These articles are incorporated herein by reference.) Very intensive studies of PVA gels have been performed (Peppas, N. A.; Merrill, E. W.,
J. Polym. Sci. Polym Chem. Ed.,
(1976). Finch, C. A.
PVA
-
Properties and Applications
(John Wiley & Sons: New York, 1973). These works are incorporated herein by reference.), including studies of chemically cross-linked PVA gels. (Takamura, T.; Takayarna, G.; Ukida, G.,
J. Appl. Polym. Sci.,
9, 3215, (1965). This article is incorporated herein by reference.) Physical gels are generally “weaker” than chemical gels. For example, the physical cross-linking of a gel can be destroyed by adding large a

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