Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-02-14
2003-01-07
Dawson, Robert (Department: 1772)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S474400, C525S431000
Reexamination Certificate
active
06503632
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel polydialkylsiloxane/polyamide copolymer, a process for producing the same, and to various materials such as ophthalmic materials such as contact lenses and intraocular lenses, medical materials such as antithrombotic materials, and a variety of cosmetic compositions or electronic materials formed with the copolymer.
BACKGROUND ART
Siloxane polymers typified by polydimethylsiloxane have excellent biocompatibility, gas permeability, and other functions, and their various uses in the medical field have been awaited, some of which have been brought into practice. However, conventional siloxane polymers have a problem in strength and therefore their uses are limited.
Under the circumstances, polymers having both an alkylamide group excellent in strength, particularly an aramid segment such as an aromatic polyamide (aramid), and a siloxane segment excellent in biocompatibility and the like are now under development.
For example, there has been proposed a complexed polymer formed by copolymerizing a siloxane polymer with aramid (Japanese Patent Application Laid-Open No. Hei 1-12384), and there have been disclosed that this polymer serves as an excellent biocompatible material (Japanese Patent Application Laid-Open No. Hei 2-203863 and Japanese Patent Application Laid-Open No. Hei 5-285216) and that this polymer can be utilized as a contact lens material (Japanese Patent Application Laid-Open No. Hei 6-313864).
According to the production method of the siloxane/aramid copolymers, such copolymers appear to be a material in which at least dozens of percentages of free amino groups remain at its ends. Moreover, since the aramid segment of the siloxane/aramid copolymer dissolves in a limited variety of solvent systems, the biocompatibility test which is carried out on each of these copolymers provides nothing but the evaluation results of the film molded therefrom according to the solvent casting method in which a solvent such as N,N-dimethylacetamide (hereinafter, abbreviated as DMAc), dimethylformamide (hereinafter, abbreviated as DMF), or the like is employed.
Generally, a molded article obtained according to the solvent casting method is made almost free from solvent by being subjected to a solvent-removing treatment comprised of heating the article to the glass transition temperature of the polymer or higher and lowering the pressure. However, when a solvent like DMF or DMAc having a high polarity and a relatively high boiling point is employed, removing the solvent to such an extent as is considered to be non-problematic in terms of the use as a medical material is extremely difficult. Therefore, for use as a medical material, it would be desirable that a copolymer is heat-moldable without using a solvent, and the copolymer is required to have a sufficient thermal stability.
However, the heretofore suggested complexed polydialkylsiloxane/polyamide copolymer formed by block-copolymerizing a siloxane polymer with aramid has a problem that, when heated to a certain temperature to evaporate the solvent completely or examine its fluidity upon heating after having been molded by the solvent casting method, it turns pale yellow and further browns. In addition, there is a problem that, due to crosslinking reaction, an attempt to dissolve the heat-dried copolymer in the same solvent again will result in failure. Furthermore, it has come to be known that there is a problem that heating the copolymer to high temperatures causes its liquid siloxane component to decompose and elute. Therefore, when heat-molding such polymer, sufficient care must be taken over the temperature control, heating time and the like. Further, such polymer is inapplicable to ophthalmic or medical materials, for not only is such polymer difficult to heat-mold, but also heat treatment for removing the solvent inevitably incorporated therein is arduous.
Surface and Interface Analysis, Vol. 10, p416-423 (1987) and Surface and Interface Analysis, Vol. 13, p233-236 (1998) report that plasma irradiation is carried out to render the surface of a contact lens made of an acrylate polymer having a siloxane side chain hydrophilic. Polymer Journal, Vol. 42, p841-847 (1985) also reports that a silicone rubber contact lens is subjected to plasma irradiation thereby to make its surface hydrophilic. However, there exists a problem that, even after such treatment, it is difficult for the lens to retain its hydrophilicity over a long period of time and that adhesion of protein onto the lens surface becomes considerable.
In Polymer Journal, Vol. 20, p485-491 (1988), it is reported that, as can be understood from the fact that the gas permeability of polydimethylsiloxane is not adversely affected even if it is subjected to electron beam irradiation at a dose of 80 Mrad, electron beam irradiation at a dose of 80 Mrad or so does not cause neither crosslinking nor decomposition in the chemical structure. On the other hand, in Adhesion, Vol. 34 p201-209 (1991), it is reported that, as a result of the swellability (solubility) test made on polydimethylsiloxane irradiated with an electron beam, polydimethylsiloxane was completely dissolved at 20 KGy (=2 Mrad) or less and that crosslinking was observed at 50 KGy (=5 Mrad) or more. The publication also says that such electron beam irradiation raises the storage modulus (G′) and loss modulus (G″).
These publications referred only to energy beam irradiation of siloxane polymers, and none of them touched on improvements in physical properties resulting from energy beam irradiation of a molded article of the polydialkylsiloxane/polyamide copolymer.
The above-mentioned polydialkylsiloxane/polyamide copolymer is what is constituted of siloxane chains into which, mainly for supplementing strength-related drawbacks of a siloxane polymer, aramid segments have been introduced as multi blocks. As compared to a molded article which is exclusively made of a siloxane polymer, its molded article fabricated by the solvent casting or heat-molding method has a largely improved strength as it is, which is due to the interaction between the aramid segments. However, with respect to the influence the aramid segment to siloxane segment ratio of the polydialkylsiloxane/polyamide copolymer exerts, its strength owing to aramid and such functions as oxygen permeability and biocompatibility due to siloxane are in a trade-off relation. Therefore, when aiming. for a still higher, well-balanced performance, its physical properties need to be improved not by varying the ratio but by other means.
A polyamide, due to its amide bonding, shows relatively good hydrophilicity. However, it has been known that, when a polyamide is complexed with a siloxane-type polymer as in the case of a polydialkylsiloxane/polyamide copolymer, the resulting material will be highly hydrophobic, which is because the mobility of its siloxane segments at the molecular level is good and thus the surface of the material is covered by the siloxane segments. Although not all the medical materials are required to be hydrophilic and whether hydrophilicity is a requisite or not depends on the intended use, for example, contact lens materials need to be hydrophilic in view of not only a good fit to the eye but also the prevention of a lens from, as a result of a long-time wear, clinging to the cornea of the eyeball. To give an example, silicone elastomer contact lenses have once been put into practical use, which resulted in failure because their hydrophilicity was insufficient.
Thus, for expanding the uses of a molded article of a highly hydrophobic polydialkylsiloxane/polyamide copolymer, it is necessary to impart hydrophilicity to the surface thereof. However, nothing has been heretofore proposed to improve the hydrophilicity of polydialkylsiloxane/polyamide copolymer molded articles.
On the contrary, copolymers having a phosphorylcholine derivative group have been studied from various aspect because of their excellent contamination resistance, hydrophilicity, and biocompatibil
Akashi Mitsuru
Hayashi Akio
Hosotani Ryuzo
Shiino Daijiro
Sonoda Kensaku
Darby & Darby
Dawson Robert
Feely Michael J
NOF Corporation
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