Studies of fluoropolymers for use in opthalmic applications

• Main Author: Jonsen, Karen
• Published: Kingston University 1995
• Subjects: 668.4; Chemistry
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260100

The contact lens is an undoubtedly important optical correction medium for many visual defects. Materials used in contact lens applications must exhibit specific properties which are determined by the physiological conditions of the eye. Polymethyl methacrylate became a popular hard lens material because of its toughness, excellent optical clarity, acceptable surface properties, and biocompatibility. Its rigidity and virtual impermeability to oxygen led to the development of alternative materials such as rigid gas permeable contact lenses of which fluoropolymers have long been considered as desirable materials. As an introduction to this thesis, the eye and its defects are discussed briefly with methods for their correction. A concise review of the property requirements of a contact lens precedes a detailed discussion of the history and development of contact lenses and their materials. Perfluoropolymers, well known for their extraordinary resistance to chemical and thermal attack, and low surface energy deterring deposition, have potential utility in ophthalmic applications due to their oxygen permeability and biocompatibility. Partially fluorinated hydrocarbon materials are also promising, among which are fluoroacrylates and fluoromethacrylates related to polymethyl methacrylate. A range of simple fluoroacrylates and fluoromethacrylates with increasing fluoroalkyl side chain length were synthesised alone and together with methyl methacrylate in various formulations to assess their structural-property relationship. Reaction kinetics were studied using differential scanning calorimetry to determine optimum polymerisation conditions, and gel permeation chromatography was used to evaluate reactivity ratios and hence the distribution of the different components throughout the polymer chain. As experienced with past and present contact lens materials, it became apparent that to acquire desired properties, for example high oxygen permeability, a compromise had to be made with other properties, for example low wettability. This problem has constantly plagued the experts working in this field, and looks as if it will continue to do so for some time. In conclusion, the polymers investigated were discovered to be only suitable as contact lens materials as components in formulations with other monomers providing the necessary balance of properties.