Investigation of the solvent absorption characteristics of various copolymer gels and controlled release studies for naproxen sodium

In this thesis, 6 different kinds of copolymer gels based on N-vinylimidazole (VIm) were synthesized. Stearyl methacrylate (SM) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (METAC) were used as comonomer. While pH-sensitive p(VIm) and METAC series hydrogels exhibited hydrophilic character, pH and temperature-sensitive SM series displayed both hydrophilic and hydrophobic. The p(V-co-SM15) gel, which has the most hydrophobic character among the copolymers, was quaternized with 1-bromohexadecane (BHD) to enhance its hydrophobic character. Instrumental characterization of the gels were made with Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy dispersive spectrometry (EDS), thermogravimetric analyzer (TGA). Swelling behaviors were investigated in water and some organic solvents depending on the gel characters. The temperature and pH sensitivity of the gels were determined by repeating the swelling experiments in water at different temperatures and pHs. Besides the water and chloroform release behavior of SM gels, the effect of polarity index and partition coefficient of the solvents on swelling behavior was also investigated. While the equilibrium swelling ratio of p(VIm) was 3.37 gwater/ggel at pH 6.2 and 25°C, value of this ratio for SM and METAC gels were within the range of 0.56-1.60 and 5.53-6.80 gwater/ggel, respectively. SM gels exhibited the highest equilibrium swelling ratio in chloroform. The equilibrium swelling ratio of p(V-co-SM15) (5.44 gCHL/ggel) was increased to 6.50 gCHL/ggel by post quaternization. The presence of SM also caused temperature sensitivity. p(V-ko-SM15-Q), the most hydrophobic gel, was determined to be the most temperature sensitive gel with the 200% change in the maximum swelling ratio at the transition from 6°C to 50°C. It was noted that the equilibrium swelling ratio for all gels decreases with increasing pH, and the presence of comonomer decreases the pH sensitivity. It was also observed that as the hydrophobic character of the SM gels increased, the water release rate increased, and the chloroform release rate decreased. Naproxen-sodium (NS) release studies were carried out at 37°C at pH 1.2 and 7.4, and release kinetics of the gels were investigated. At its own pH of NS solution, p(V-co-METAC15) hydrogel had highest adsorption capacity value (Q=231.50 mgNS/ggel). The Q values of SM series (Q values varying between 17.65-35.06 mgNS/ggel) were increased to the range of 52.43-88.28 mgNS/ggel by means of changing the NS-polymer interaction mechanism (by loading at pH 3). For all gels, it was found that NS was released more slowly at pH 1.2 compared to pH 7.4, and the presence of hydrophobic monomer decreased the release rate of NS at all pHs. SM gels loaded with NS at pH 3 release NS faster than their counterparts loaded at its own pH of NS solution. NS release profiles of all gels fitted the Korsmeyer-Peppas release pattern, and n values of the model were determined between 0.5-1.