Investigation of the synthesis, characterization and usage of PMMA-co-PHEMA, PMMA-co-PnBMA veandPnBMA-co-PHEMA copolymers as lens material

Researches have carried out to make the most suitable types for contact lens use and to develop the synthesis and physical properties of materials that have applications in biomedical fields. Various combinations of monomers can alter the physical and chemical properties of these materials. In this study, polymethylmethacrylate (PMMA), polyhydroxyethylmethacrylate (PHEMA) and poly(n-butylmethacrylate) (PnBMA) homopolymers, which are thought to have lens material potential, were used in different combinations and compositions. Random copolymers of PMMA-co-PHEMA (PMMA/PHEMA: 1/1; 1/2; 2/1), PMMA-co-PnBMA (PMMA/PnBMA: 1/1; 1/2; 2/1) and PnBMA-co- PHEMA (PnBMA/PHEMA: 1/1; 1/2; 2/1) were synthesized by conventional radical method using AIBN azo initiator. Characterization of these copolymers was performed using Reduced Full Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), Gel Permeability Chromatography (GPC), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA). The UV-VIS measurements of the copolymers prepared in film form were made depending on the wavelength (325-700 nm), and the refractive indices (RI) in the optical region were calculated. Equilibrium water content(EWC) of the copolymers was determined by gravimetric method (24 hours and 48 hours later), and oxygen permeability (Dk) values were calculated. By comparing the FTIR spectra of homopolymers and copolymers, copolymerization formation was observed at the molecular level. According to GPC results, the polymerization was successfully achieved. Glass transition temperatures (Tg) were found from DSC thermograms and it was determined that copolymer structures were formed. TGA results show that the copolymers are thermally stable up to high temperature values. Visible area optical transmittance was found to be quite high in all samples. It was concluded that copolymers need additional chemicals to provide protection against UVA rays due to their high UVA (325-400 nm) permeability. The RI values were found to be compatible with those found in the literature for lens materials. The very low EWC values of PMMA-co-PnBMA copolymers showed that these copolymers cannot be used as contact lens material. When all the results obtained are evaluated, it is suggested that it would be more accurate to use PMMA-co-PnBMA copolymers as bone cement and dental composite resin, but if it is to be used as contact lens material, it is recommended to form new copolymers with some water-retaining additional monomers. In PnBMA-co-PHEMA copolymers, it was observed that EWC value increased when PHEMA ratio increased (1/1 ,1/2) after 24 hours, while EWC value decreased when PnBMA ratio (1/1 , 2/1) increased. While the visible region optical transmittance of PnBMA-co-PHEMA copolymers is measured lower than the other samples, the highest optical transmittance belongs to (1/1) sample in this group. The best results in terms of moisture retention (EWC) and oxygen permeability were obtained for PnBMA-co-PHEMA copolymers. It has been found that the UVA (325-400 nm) transmittance of PnBMA-co-PHEMA copolymers is lower than the other two copolymers, but as high as the others for use as contact lens material. Thus, besides investigating the suitability of using copolymers of different compositions as lens materials, the effect of the composition on their optical properties was also investigated. In addition to these, tensile tests of PMMA-co-PnBMA copolymers on film forms were performed and the mechanical properties of the films were investigated. Mechanical testing could not be performed because the films of PMMA-co-PHEMA and PnBMA-co-PHEMA copolymers are brittle.