Low polydispersity poly-hema compositions

#This invention relates to poly-HEMA compositions having a specific molecular weight range and polydispersity. Methods for making contact lenses from said poly-HEMA and the contact lenses made thereof are also disclosed.

#Contact lenses have been used commercially to improve vision since the 1950s. Most current contact lenses are made of hydrogels formed by polymerizing hydrophilic monomers such as HEMA and vinylpyrrolidone in the presence of a minor amount of a crosslinking agent. The polymerization of the monomers results in shrinkage which may be as much as 20% by volume.

#Prepolymers having backbones of PVA and reactive groups of acrylic groups have been disclosed. The reactive prepolymer is dissolved in water, and crosslinked inside a mold by irradiation with UV light to form a contact lens. The shrinkage during cure is small, but the hydrogels thus produced exhibits mechanical properties that may prove marginal for contact lens use.

#FIG. 1 shows Hansen Solubility Parameter spheres for the compositions made in the Examples.

#The present invention relates to compositions comprising poly-HEMA having a peak molecular weight between about 25,000 and about 100,000, preferably between 25,000 and 80,000 and a polydispersity of less than about 2 to less than about 3.8 respectively and covalently bonded thereon, at least one cross-linkable functional group.

#The present invention further relates to low polydispersity poly-HEMA suitable for making the crosslinkable prepolymers of the present invention, processes for functionalizing and purifying said poly-HEMA to form said crosslinkable prepolymers, viscous solutions made from said crosslinkable prepolymers, hydrogels made from said viscous solutions and articles made from said crosslinkable polymers, hydrogels and viscous solutions. Still further, the present invention relates to processes for making said viscous solutions, hydrogels and articles. Preferred articles include medical devices, and specifically contact lenses.

#We have discovered that the undesirable shrinkage, expansion and related problems possessed by poly-HEMA hydrogels may be overcome by producing hydrogels from a crosslinkable prepolymer having a relatively low molecular weight and low polydispersity. We have also discovered that poly-HEMA having a relatively low molecular weight and low polydispersity can be prepared by new practical methods and have useful applications in themselves. In addition, the poly-HEMA of the present invention can be converted into crosslinkable prepolymers useful for making a number of articles, including hydrophilic coatings and contact lenses with improved mechanical properties. Finally the crosslinkable prepolymers of the present invention permit the production of high precision molded articles.