Binary Copolymer Synthesis And Properties Of Hydrogel Soft Contact Lens Materials

N-vinylpyrrolidone(NVP) and 2-hydroxyethyl methacrylate(HEMA) have many applications because of their excellent performance. NVP-co-HEMA copolymer hydrogels have been widely studied and used as soft contact lens and controlled-releasing materials in foreign countrys. On the contrary, we are behind in their studies and uses, and we don't have our own contact lens brand on sale in the market. This paper studied the synthesis and performance of the copolymer hydrogels basically and systematically based under this situation.The mechanical performance of the hydrogel material improved when MMA, EMA and BMA is added. Through the experiments, we can find that the HEMA-co-EMA hydrogel is bettet than others in mechanical and water-absorbing performance.Due to its special molecular structure, the NVP can improve the hydrogel's water-content. The results of the uni-factor experiments and perpendicular experiments show their best synthesizing craft as followed: NVP(20%Wt), initiator(0.1%Wt), crosslinker(0.2%Wt), reacting 16 hours under 80癈.From the converting ratio, we can know the reaction of NVP-co-HEMA is a typical free radical copolymerization. Its making-up can be calculated by Mayo-Lewis formula.Water in hydrogels existing in "bound-water" and "free-water". The DSC diagrams show that the "bound-water" is principally brought in by HEMA and NVP increase the "free-water" content.Hydrogel's swelling processes are divided into diffusion processes and relaxation processes, the "overshooting" phenomenon will occur if diffusion process is predominant. Swelling temperature, copolymer's constitution and ion concentration in solution can effect hydrogel's swelling process. The experiments demonstrated that these hydrogels' swelling processes are according with their swelling kinetic formula.