Synthesis of silicone magnetic fluid for use in eye surgery
Section snippets
Background
The anterior segment of the eye is bounded by cornea and lens–iris diaphragm, and contains the aqueous humor. The posterior segment begins behind the lens–iris diaphragm and includes, from inside outwards: the vitreous (gel/fluid), retina (neurosensory tissue), and choroid (heavily vascular). The retinal photoreceptors are supported by the choroid. The retina and choroid stay attached to each other with a suction pump which keeps the subretinal space dry.
Retinal detachment is a major cause of
Preparation of magnetic fluids
Critical to the success of these magnetic fluids is the development of the steric stabilizers, which must prevent the coagulation of the metal particles. Block copolymers are now recognized to be more efficient than homopolymers as dispersion stabilizers. The “anchor” block is designed to strongly adsorb onto the particle surface, and the “tail” block extends outward into the polydimethylsiloxane (PDMS) fluid preventing aggregation of the particles (Fig. 6). Cyano groups have an established
Reagents
Dichloromethane (Baxter) was washed twice with concentrated sulfuric acid, then with water until neutral. Subsequently, it was pre-dried with anhydrous magnesium sulfate and distilled from phosphorus pentoxide. Hexamethylcyclotrisiloxane (General Electric Co.) was stirred over calcium hydride powder at 80°C for 12 h, then distilled into a dry flask where it was diluted with anhydrous dichloromethane. Tetrahydrofuran (E.M. 99.5%), Triethylene glycol dimethyl ether (TEGDME, Aldrich, 99%) were
Results
Initials samples of triblock copolymers with block lengths of 2.5 k–2.5 k–2.5 k, 4 k–4 k–4 k, and 8 k–8 k–8 k g/mol have been prepared and characterized. Equilibration of DxCN(x=3–5) with dilithium diphenylsilanediolate as both catalyst and chain stopper was followed by NMR and GPC by sampling the reaction mixture at different reaction times. The macroinitiators were generally heated at 100°C for 48 h to allow the mixture to reach equilibrium. PCPMS macroinitiators are soluble in THF,
Conclusion
Nitrile containing triblock copolymers have been developed as stabilizers for silicone magnetic fluids (PDMS-b-PCPMS-b-PDMS)s has been successfully prepared by living polymerization of D3 using lithium silanolate ended poly (3-cyanopropyl) methylsiloxane macroinitiators. The macroinitiators were prepared by equilibration of mixtures of (3-cyanopropyl)methylcyclosiloxanes and dilithium diphenylsilanediolate, and the molecular weight of the macroinitators was controlled by the ratio of monomer to
Acknowledgements
The authors wish to thank Dr. S. Charles for evaluation of silicone magnetic particle fluids, Drs. R. Stratton, T. Rice and K. Olsen for editorial advice, Dr. S. Davis for DSC, Dr. Q. Ji for GPC, MR. T. Glass for quantitative NMR, Mr. M. Price for graphics, and Dow Corning for materials.
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