Theses supervised by Elvan Yılmaz
13 theses · Eastern Mediterranean University
Grafting of Poly (4-Vinyl Pyridine) onto Chitin under Heterogeneous Conditions
Chitin gel beads were prepared, crushed into powder and grafted with poly(4- vinylpyridine) (P4VP) under nitrogen gas by using cerium ammonium nitrate(CAN) as a redox initiator under heterogeneous conditions in toluene. The effect of the amount of chitin, concentration of the monomer (4VP), amount of the initiator (CAN), reaction time and temperature on the grafting percent has been studied. The maximum grafting yield of poly (4-vinylpyridine) on to chitin beads was determined to be 380%. The optimum conditions were 0.10 g of chitin, 10 mL of (4VP) monomer, and 0.50 g of cerium ammonium nitrate (CAN) initiator at 60°C for one hour reaction time. The grafted samples were found to be soluble in aqueous acidic buffer solution (pH=1.2). The grafted and non grafted products were characterized by FTIR spectroscopy, SEM, DSC and C13 NMR analysis. Keywords: 4-vinylpyridine (4VP), chitin gel, redox initiated grafting.
Grafting of Poly [(2-Diethylamino)Ethyl Methacrylate] onto Chitosan
In this study, chitosan was grafted with poly[(2-diethyl amino)ethyl methacrylate] in homogeneous and heterogeneous systems by using potassium persulphate as the initiator. The effect of temperature, time, (2-diethyl amino)ethyl methacrylate concentration and the concentration of the initiator on the grafting yield was examined in aqueous acetic solution under nitrogen atmosphere. The maximum grafting percentage of poly[(2-diethyl amino)ethyl methacrylate] on to chitosan was found to be 180% under homogeneous conditions using 0.5 mL of monomer concentration with 1.00 g chitosan dissolved in 1.0mL of 0.10% (w/v) acetic acid solution, temperature at 70◦C and 4 hour reaction time. The products were precipitated in ethanol in the powder form. They were found to be water soluble which is an improvement over the dissolution properties of the parent molecule, namely chitosan. Chitosan tripolyphosphate gel beads which were chemically crosslinked by glutaraldehyde or ethylene glycol digylcidyl ether were used as solid substrates for grafting of poly[(2-diethyl amino)ethyl methacrylate] PDEAEM in a heterogeneous system at the optimum conditions determined for the homogeneous system. The maximum grafting yield was found to be in the range 40-50%. The swelling kinetics of the grafted beads was followed in acidic, neutral and basic buffer solutions. The experiments demonstrated 166-4811% swelling within 72 hours. The synthesized copolymers were characterized by using Fourier Transform Infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), and scanning electron microscopy (SEM). Keywords: graft copolymerization, natural polymer, chitosan, chitosan tripolyphosphate bead, (2-diethyl amino)ethyl methacrylate (DEAEM), water soluble polymer.
Preparation and characterization of porous chitosan tripolyphosphate gel bead
In this study, Chitosan TPP beads and Chitosan TPP beads in the presence of PEG was prepared. PEG was added to achieve porosity after the removal of the polymer. The samples were characterized by FTIR and SEM analysis. The swelling behaviour was followed in pH 1.2, 7, and 11 and their Fe3+ ion adsorption rate from aqueous solution was determined at pH 1.2. Beads prepared both in the presence and absence of PEG contained porosity. Chi-TPP porous beads prepared by PEG leaching method swelled more in aqueous media having a swelling ratio of about 3500% in acidic media, 350% in neutral media and 400% in basic media as compared with Chi-TPP beads with swelling ratio of 2000% in acidic media, 150% in neutral media and 200% in basic media. The beads served as effective adsorbents for Fe3+. The Chi-TPP PEG beads showed a better adsorption capacity for Fe3+ and better swelling behavior as a result of increased hydrophilicity due to PEG treatment. The adsorption behavior obeyed Langmuir model and the kinetics followed pseudo second order. Keywords: Chitosan, Polyethyleneglycol, Fe3+ adsorption.
Synthesis and Characterization of Poly[2-(diethylamino ethyl methacrylate)] Hydrogels
Poly[2-(diethylamino ethyl methacrylate)] (PDEAEM) and its ethylene glycol dimethacrylate (EGDMA) cross-linked hydrogels were synthesized by free radical polymerization. Chemical structure was characterized by FTIR spectroscopy. The morphology of the homopolymer and of the hydrogels was investigated by SEM analysis. Swelling properties of the EGDMA crosslinked hydrogels of PDEAEM were followed under acidic and neutral conditions. The results revealed weakly pH responsive swelling behaviour with equilibrium swelling capacity values of 50% in acidic medium and 30% in distilled water. The drug loading and delivery properties of the homopolymer and its hydrogels were investigated using ciprofloxacin HCl as the model compound. EGDMA crosslinked hydrogels of PDEAEM exhibited 35% CFX loading capacity at pH=4 in 72 h. A percent cumulative drug release value of 60 was obtained with the hydrogel that (DEAEM/EGDMA = 1:7.5 by mole) within 2 hours in acidic solution. Keywords: 2-(diethylamino ethyl methacrylate), ethylene glycol dimethacrylate, hydrogels, ciprofloxacin-HCl, potassium persulfate, free radical polymerization.
A Miscibility study on pullulan/poly (Ethylene Glycol) blends
Miscibility of pullulan and poly(ethylene glycol) in aqueous solution has been determined by dilute solution viscometry. Blends of different compositions (100/0, 80/20, 50/50, 20/80, 0/100) with respect to pullulan/poly(ethylene glycol) have been prepared. Huggins plots of each homopolymer and polymer blend have been determined in aqueous solution at 25, 30 and 40 0C temperatures. From the data obtained from Huggins plots the miscibility parameters Δb, α, and μ have been calculated. The miscibility of polymers in a ternary system is measured by these parameters which are related to the slope of the Huggins’s plot and the intrinsic viscosities of the polymers and the polymer mixtures. In addition to solution viscosity measurements, blend films were prepared by the solvent casting method and were tested by SEM and DSC analysis methods for the investigation of blend miscibility in the solid state. Moreover the molecular interactions between pullulan and PEG were studied by FTIR spectroscopy. Favorable interactions via H-bonding have been confirmed. The results have shown that pul/PEG blend with a blend composition of (80/20) is miscible in solution with positive miscibility parameter values for Δb, α, and μ respectively. DSC and SEM results indicate miscibility in the solid state as well. Keywords: Viscosity, Miscibility, polymer blends, Pulluan, Poly(ethylene glycol).
Synthesis and Characterization of Alginate/Poly (4-vinylpyridine) Hybrid System
Polyelectrolyte multilayer (PEC) films of sodium alginate and poly(4-vinylpyridine) were prepared by immersing the sodium alginate (Na-Alg) films into the poly(4vinylpyridine) (P4VP) in 0.1 M hydrochloric acid solution. Then, the multilayer films were formed by the alternating addition of Na-Alg and P4VP respectively. The morphology, topography and chemical structures of the PEC films and its precursors were investigated and characterized by SEM analysis, AFM and FTIR spectroscopy respectively. It was observed that the number of layers and the nature of the outer layer affect the physicochemical characteristics. The thermal properties of the PEC films were examined by thermogravimetric analysis (TGA). The onset of degradation for PEC-2, PEC-3, PEC-4 and PEC-5 is at 180°C, 195°C, 195°C and 200°C respectively. Na-Alg film, on the other hand, decomposes at 215°C while P4VP film gives its first decomposition temperature at 290°C. The crystallinity indexes were calculated by XRD analysis. Complexation reduces the crystallinity comparing with the parent membrane, Na-Alg. Crystallinity index of Na-Alg film is 0.49 whereas the values for PEC-2, PEC-3, PEC-4 and PEC-5 are 0.25, 0.36, 0.42 and 0.39 respectively. The hydrophilicity of the PEC films was examined by using contact angle measurement. When Na-Alg is the outer layer in the PEC, hydrophilicity is higher. Roughness of the film surfaces was characterized by AFM measurements. The solubility of the films was tested in different organic solvents and in aqueous solution of acidic and basic pH values. They are insoluble in water and up to pH=4.2 in acid buffer solution. The swelling properties of the PEC films were studied in acidic aqueous solution of pH value 1.2 and in water. The highest equilibrium % swelling values among the PEC films have been obtained as 215% and 155% for PEC-5, in water and acidic buffer respectively within an hour. The drug loading-release properties for the PEC were studied using ciprofloxacin HCl as a model drug. The three layer film PEC-3, which is composed of Na-Alg outer layer deposited on a P4VP/Na-Alg double layer, is characterized by the lowest roughness (Rq=16.3 nm) and the most hydrophilic surface with a contact angle value of 38.1° among all other films prepared. Its crystallinity index is 0.36, and starts to degrade at 195 °C. It exhibits 130-135% equilibrium swelling capacity in acid buffer and water respectively. PEC-3 is the film with the highest drug loading capacity and drug loading efficiency values of 3.51% and 87% respectively when the initial drug concentration is 12.5 ppm. A cumulative drug release of 65% is obtained from PEC 3 within 24 h in water when the initial concentration of the drug solution is 12.5 ppm. Several kinetic models including zero order, first order, Higuchi and Korsmeyer-Peppas were tested to understand the kinetics and mechanism of the drug release from the PEC films of Na-Alg and P4VP. The best fit was obtained with Higuchi's equation. Release mechanism was found to be Fickian according to the Korsmeyer-Peppas equation. Keywords: sodium alginate, poly(4-vinylpyridine), polyelectrolyte complex, multilayer, ciprofloxacin HCl, LbL
Synthesis and characterisation of chemically crosslinked chitosan citrate gels
Chitosan was modified using citric anhydride to produce film membranes via solvent evaporation. The films dissolved in acidic media which showed that crosslinking was not achieved, but it showed an appreciable amount of swelling (896%) as a result of the modification with maximum % swelling obtained by 1.0 g citric acid (CA):0.5g chitosan at pH 11 as compared with chitosan films with maximum swelling % of 314% at the same pH. N-protected chitosan was chemically crosslinked with a non-toxic crosslinker citric anhydride to obtain citrate esters and incorporate the carboxylic group onto chitosan. Products obtained did not dissolve in acidic media which confirms crosslinking and there was also a high % of swelling observed with the maximum %swelling of 875% by 1.0 g CA: 0.5g at pH 4. Characterisation was done using FTIR and C-13 NMR. Free amine content was determined by titration and the kinetic study revealed that both modified and citrate crosslinked chitosan samples obeyed pseudo 2nd order. The effect of time on crosslinking showed that as time increases crosslinking also increased. In this study, we were able to develop a pH sensitive gel that could find a wide range of applications. Keywords: Chemical Crosslinking, Citrate ester, Crosslinking Density
Preparation and characterization of phosphorylated chitosan films via graft copolymerization
Graft copolymerization of bis (2-methacryloyl oxy ethyl) acid phosphate (BAP) on to chitosan initiated by potassium per sulphate (KPS) under N2 atmosphere has been studied. The effect of polymer concentration, monomer concentration, polymerization temperature, initiator concentration and polymerization time on the grafting yield have been investigated. The copolymers were characterized by FTIR, SEM, DSC, and contact angle measurement. Swelling and dissolution behaviour of grafted polymer was followed in different buffer solutions (pH = 3, 7, and 11). Keywords: Chitosan, Phosphorylated Chitosan, Contact Angle, BAP
Grafting of poly (2-Hydroxyethyl Methacrylate) onto chitin beads
Chitin was grafted with poly(2-hydroxyrthyl methacrylate) poly(HEMA) by using ceric ammonium nitrate (CAN) as the initiator. The effect of temperature, time, concentration of the monomer (HEMA), the amount of chitin beads and the initiator (CAN) concentration on the grafting yield has been studied under nitrogen atmosphere. The optimum conditions for the grafting process were established. The maximum grafting percentage of poly(HEMA) on to non porous chitin was found to be 65%, while for porous chitin beads it was 515%. The optimum conditions were 0.1 g of porous chitin beads, 8 mL (3.3 Mol/L) HEMA monomer, 0.5 g (4.6×10-2 mol/L) of CAN initiator for three hour reaction time at 35 °C. The products were characterized by FT-IR, SEM, C13 NMR and XRD analysis. Swelling and dissolution behavior of the products were followed in different buffer solutions (pH = 1, 7 and 11). Keywords: 2-hydroxyethyl methacrylate (HEMA), chitin, graft copolymerization, hydrogel, chitin bead.
Pullulan/Poly(2-Hydroxyl Ethyl Methacrylate) Cryogels
Pullulan – polyHEMA cryogel systems were synthesized by using radical chain polymerisation with the aid of chemical crosslinkers. Pullulan- ECH-graftpolyHEMA cryogels and pullulan-ECH-graft-polyHEMA-EGDMA cryogels were prepared from various different concentrations of starting monomer; 2-hydroxy ethyl methacrylate (HEMA) and natural polymer; pullulan. For all the cryogel systems epichlorohydrin (EPC) was used as crosslinker and for some of them in addition to EPC , ethylene glycol dimethacrylate was used. For the initiation of polymerization, the redox couples of ammonium persulfate (APS) and N,N,N’,N;-tetramethelen diamine (TEMED) were used. Swelling characteristics of the cryogel systems were analysed in three different conditions; acidic, neutral and basic conditions at 25 ℃. The concentrations of monomers and crosslinkers were altered to synthesize different cryogels with different swelling characteristic features. In addition, scanning electron microscopy (SEM) and FT-IR spectroscopy analyses were used for structural and morphological characteristic features determination. Based on dynamic swelling tests, it was found that pullulan-ECH-graft-polyHEMA-EGDMA cryogels bears the highest equilibrium swelling capacity characteristics with 97 %. These cryogels has got the highest degree of porosity among all the other types of cryogels. Keywords: Pullulan- ECH-graft-polyHEMA cryogels, epichlorohydrin (EPC), ammonium persulfate (APS) and N,N,N’,N;-tetramethelen diamine (TEMED).
Cationic Pullulan via Poly(N-vinylimidazole) Grafting
In this thesis, the possibility of grafting poly N-Vinylimidazole (PNVI) onto pullulan was investigated under homogenous and heterogenous conditions using potassium persulphate (KPS) and cerium(IV) ammonium nitrate (CAN) as redox initiators. It was found out that grafting of PNVI onto pullulan was succesful under heterogeneous conditions using any one of the initiators, CAN or KPS. Pullulangraft- PNVI was obtained using 0.1000 g pullulan, 10 mL NVI , 0.5 g CAN at 60 C for one hour in 100 mL toluene under nitrogen atmosphere with a grafting yield of 103%. Another pullulan-graft-PNVI sample was obtained under similar conditions using 0.5 g KPS with 162% grafting yield. Aqueous homogeneous reaction medium was not suitable for PNVI grafting onto pullulan. Keywords: pullulan, graft copolymer, redox initiation, PNVI
Graft Copolymerization of Benzyl Methacrylate onto Alginates
Homopolymerization of benzyl methacrylate has been studied by UV initiation using 25 mg DMPA with 2.5 ml BzMA and 0.5, 2.5 mL hexane for different time intervals. The maximum conversion value 99% has been obtained. Homopolymerization reaction was carried out with and without photo initiator. It was found that without photo initiator polymerization does not occur. DMPA and benzophenone were the two photo initiators tested. DMPA was found to be more effective than benzophenone, in a homopolymerization system of 50 mg DMPA or bezophenone, 2.5 mL BzMA and 0.5 mL hexane irradiated for 15 minutes, conversion resulted 61% and 11.5% respectively. Without photo initiator no polymerization occurred. Alginic acid, sodium alginate and calcium alginate have been grafted with poly(benzyl methacrylate) by the UV-irradiation method. The heterogeneous system was placed in a LZC4 photo-reactor with 15 cm distance from UV lamps (in UVA region, 350 nm) and irradiated for several different intervals of time, at room temperature (25±1◦C) and fixed power (7670 μW/cm2). Effect of irradiation time, monomer concentration and photo initiator concentration on the grafting yield was studied at room temperature. The maximum grafting yield was obtained using 0.52 g sodium alginate with 2.5 mL BzMA and 25 mg DMPA at 15 min. It was found that most vulnerable polymer to benzyl methacrylate grafting among alginic acid, sodium alginate and calcium alginate is sodium alginate with the highest grafting yields under the same conditions with others. Keywords: Alginate, Benzyl methacrylate, Graft copolymer, Photopolymerization
Poly(N-hydroxyethyl acrylamide) / Chitosan Based Hydrogels
Poly(N-hydroxyethyl acrylamide) (polyHEAA) was grafted onto chitosan in aqueous acidic medium using potassium per sulphate initiator to obtain polymer surfaces with blood compatibility for potential biomedical applications such as blood contacting devices as artificial veins or devices to remove excess ions from the blood. The grafting parameters monomer concentration, crosslinker concentration, initiator concentration, processing time and temperature were changed to find out the effect of each parameter on the grafting yield (%G) and choose the best preparation parameters for the aimed purpose. Grafting yield values up to 600% were achieved. Thermally cross-linked products were obtained upon drying at 60°C overnight. Chemically cross-linked films were prepared using methylene bis acrylamide (MBA) and glutaraldehyde (GA) cross-linkers. The products were characterized by FTIR, XRD and SEM analyses. Blood compatibility and protein adsorption characteristics of the MBA crosslinked and poly (N-hydroxy ethyl acrylamide) grafted chitosans namely (chitosan-graft-polyHEAA;MBA) were investigated. Protein adsorption onto the film surfaces were about 10% human serum albumin (HSA) removal from aqueous solution, after 3 h contact, in vitro. Blood compatibility was evaluated with respect to activated prothrombin time (PT), activated partial thromboplastin time (APTT), and platelet adhesion. PT and APTT values remained within normal ranges after blood-polymer contact for 90 minutes, with chitosan-graft-polyHEAA films, in vitro. Examining chitosan-graft-MBA or chitosan-graft-(polyHEAA;MBA), and blank chitosan films caused higher PT and APTT values under similar experimental conditions with chitosan-graft-polyHEAA films, exhibiting blood anticoagulant activity. SEM images taken before and after contact with blood sample did not reveal iv any significant blood component adhesion on the chitosan-graft-(polyHEAA;MBA) film surface contrary to the observation made on the chitosan film. However, the blood components on the film surfaces were not identified. Glutaraldehyde crosslinked films (chitosan-graft-(polyHEAA;GA)) were prepared and tested as adsorbents for Fe3+ ion in solution. It was observed that crosslinking, swelling and polyHEAA grafting values acted together in determining the adsorption capacity. The highest adsorption capacity was found as 44.8 mg Fe /g adsorbent at pH=1.2, at room temperature from 500 ppm FeCl3 solution within 24 h contact by a sample with 586% grafting yield value. Keywords: biomaterial, chitosan, glutaraldehyde, grafting, hemocompatibility, hydrogel, methylene bis acrylamide, polyacrylamide.