Preparation of hydrogels by using of photoinitiated polymerization methods and the investigation of their mechanical properties

Photoinititated polymerization has been gaining interest in nowadays. The studies on the synthesis of hydrogels by using of photopolymerization technique has been increaded. In photopolymerized system, efficient polymerisation process requires the presence of a photoinitiator (PI), which is converted into reactive radicals upon exposure to a UV or visible light and photoinitiator is most important part of these formulations. Free radicals were created by PIs which can initiate polymerization to form crosslinked hydrogels. Furthermore PIs must have biocompatibility, solubility in water, and low toxity .In this study, the synthesis of hydrogels were achieved by the photopolymerization technique and the effect of photoinitiators on the photopolymerization was also investigated. The effects of monomer on the water uptake of hydrogels were determined .Different concentrations of polyethyleneglycol monoacrylate (PEGMA) and various molecular weights of polyethyleneglycol diacrylate (PEGDA) with thioxanthone derivative photoinitiators synthesised previously; (9-oxo-9H-Thioxanthen-2-yloxy)-acetic acid, (TXOCH2COOH), (9-oxo-9H-Thioxanthen-2-yloxy)-sodium acetate (TXOCH2COO-Na+), (9-oxo-9H-Thioxanthen-2-ylsulfonyl)-acetic acid (TXSCH2COOH), (9-oxo-9H-Thioxanthen-2-ylsulfonyl)-sodium acetate (TXSCH2COO-Na+) and a commercial type I. photoinitiator; 4-(2- hydroxide ethoxy)phenyl-(2- hydroxide -2-propile) were used for formulations to form hydrogel. Formulations were irradiated with medium mercury lamp until gellation occurs in air atmosphere.In the following step, the swelling behaviour of hydrogels were determined in aqueous and alkali media. The effect of different diacrylates on the gelation time and swelling behaviour of hydrogels were investigated. The surface morphology of hydrogels were obtained by Scanning Electrom Microscopy (SEM). To study the kinetics of hydrogels , Photo-DSC was employed. Various light intensities were used and heat flow of polymerization , rate of polymerization and converision percentages of monomer to polymer were calculated.In this work, the swelling percentages of hydrogels were found very high and the remarkable increase was determined at the pH: 13 value of medium.Key words: Hydrogels, Photopolymerisation, Photoinitiator, Photo-DSC, SEM