The byproduct was separated from the product-solution by vacuum filtration. The filtrate was concentrated, and the product was precipitated out by adding it to five times excess of diethyl ether. The product was separated by vacuum filtration to separate the ether soluble impurities from the product. The product so formed was purified by recrystallizing it from its solution in dichloromethane. The final purified product was dried under vacuum.

Figure 2

Synthesis of hydrogels. Because there are two reactive terminal hydroxyl groups in PEG, these macromers (PEGDA) contain two acrylate groups per molecule. Upon free-radical polymerization, these macromers form a cross-linked three-dimensional gel.

Again, both bulk- and solution-polymerization methods were tried for synthesizing the hydrogels. The solution polymerization in aqueous medium was comparatively faster than bulk polymerization. The polymerization of the acrylates was determined by the time presence of –H and –OH radicals in the H₂O molecules in the dispersed phase. This condition may be attributed to the release of –H and –OH free radicals from the water molecules, which helps in the initiation and propagation of polymerization. The PEG molecules further are capped with hydrophobic polymerizable units, thereby forming micelle-like structures in water. The effective concentration of the double bonds within the micelles increases, thereby increasing the rate of the propagation reaction in free-radical polymerization. The radical-termination reactions are diffusion-controlled and are retarded with the increase in viscosity of the medium, which restricts the segmental motion of the involved polymer radical. An increase in the propagation rate and a decrease in the termination rate results in a high polymerization rate and rapid gelation (29).