Ali Usanmaz

The effect of preparation conditions of acrylic denture base materials on the level of residual monomer, mechanical properties and water absorption

OBJECTIVES AND METHODS The curing of several commercial powder/liquid mixtures of acrylic denture base materials was carried out at different temperatures and curing times. The levels of residual monomer, tensile strength, percentage elongation before break and water absorption were measured. RESULTS AND CONCLUSION It was found that the level of residual monomer determined by gas-liquid chromatography decreased with curing time and temperature increase. At the same time, the tensile strength was improved and water absorption decreased.

Polymerization of N-Vinylcaprolactam and Characterization of Poly(N-Vinylcaprolactam)

Poly(N-vinylcaprolactam), PNVCL, is a nonionic, nontoxic, water soluble, thermally sensitive and biocompatible polymer. It contains hydrophilic carboxylic and amide groups with hydrophobic carbon-carbon backbone suitable for biomedical applications. In this study, N-vinylcaprolactam was polymerized by free radical polymerization at 50, 60 and 70°C. The synthesized polymers were white powder, soluble in water and common organic solvents. The percent conversion vs. time plot is almost linear up to about 60% conversion without induction period. The activation energy of polymerization was calculated as 108.4 kJ/mol from the Arrhenius plot. FTIR and NMR results showed that polymerization takes place by opening of carbon-carbon double bond without any change in the caprolactam ring. Polymer was characterized by FTIR, 1H-NMR and 13C -NMR, DSC, TGA and XRD techniques. The DSC thermogram of monomer has shown a melting point at 37.3°C. The polymer has Tg value at 1.8°C and softening temperature at 68.8°C. It was determined from the X-Ray powder pattern that the polymerization proceed in the b-crystallographic axis direction.

Characteristics and release profiles of MPEG-PCL-MPEG microspheres containing immunoglobulin G

Polyester-polyether type block copolymers have attracted attention in the area of drug delivery systems with their capability in providing a broad range of amphiphilic characteristics. The aim of the present work was to prepare and characterize immunoglobulin G (IgG) loaded methoxy poly(ethylene glycol)-poly(ɛ-caprolactone)-methoxy poly(ethylene glycol) (MPEG-PCL-MPEG) microspheres as potential carrier for therapeutic monoclonal antibodies used in clinics. MPEG-PCL-MPEG triblock copolymer was synthesized by ring-opening polymerization of ɛ-caprolactone initiated by MPEG and then characterized. Microspheres were prepared by double emulsion-solvent evaporation method and their properties were compared with those of PCL microspheres. Microspheres had spherical shape with a mean particle size around 6 μm. MPEG-PCL-MPEG microspheres had higher encapsulation efficiency than PCL microspheres. After 90 days of release, 30±2% and 57±3% of the bioactivity of IgG released from non-irradiated PCL and MPEG-PCL-MPEG microspheres were protected, respectively. Presence of MPEG in microspheres provided more controlled IgG release rate and protected IgG from denaturation during γ-irradiation (20±3% and 49±2% for PCL and MPEG-PCL-MPEG microspheres, respectively). In vitro cytotoxicity tests revealed that both MPEG-PCL-MPEG and PCL microspheres had no toxic effect on cells. This study showed that MPEG-PCL-MPEG microspheres are promising delivery systems for therapeutic monoclonal antibodies.

Synthesis and Characterization of Poly(allyl methacrylate) Obtained by Free Radical Initiator

Allyl methacrylate was polymerized in CCl4 solution by α,α′‐azoisobutyronitrile at 50, 60, and 70°C. The kinetic curves were auto‐accelarated types at 60 and 70°C, but almost linear at 50°C. Arrhenius activation energy was 77.5 kJ/mol. The polymer was insoluble in common organic solvents. It was characterized by FT‐IR, NMR, DSC, TGA and XPS methods. About 98–99% of allyl side groups were remained as pendant even after completion of the polymerization. The spectroscopic and thermal results showed that polymerization is not a cyclopolymerization type, but may have end group cyclization. The high molecular weight is the main cause of a polymer being insoluble even in the early stage of the polymerization. Molecular weight of 1.1×106 for a soluble polymer fraction was measured by light scattering method. The Tg of polymer was 94°C, and after curing at 150–200°C, increased to 211°C. The thermal pyrolysis of polymer at about 350°C gave an anhydride by linkage type degradation, and side group cyclization. The XPS analysis showed the presence of radical fragments of AIBN (initiator) and CCl4 (solvent) associated with oligomers.

Synthesis and Characterization of 2-Hydroxyethyl Methacrylate (HEMA) and Methyl Methacrylate (MMA) Copolymer Used as Biomaterial

A series of poly(methyl methacrylate-co-hydroxyethyl methacrylate) (PMMA-co-PHEMA), copolymers were synthesized by an emulsion polymerization technique. Copolymer compositions were determined by FT-IR and 1H-NMR spectroscopy. It was found that comonomer ratios used in the recipes were comparable within the actual copolymers. Glass transition temperatures (Tg) of PMMA-co-PHEMA copolymers were varied from 119°C to 100°C by increasing HEMA content. Thermogravimetric analysis showed that the copolymers were stable up to 330°C. High intrinsic viscosity values of copolymer resulted in ductile solution-cast films. The hydrophilicity of the films was analyzed by water uptake measurements.

Comparative study on mechanical, thermal, viscoelastic and rheological properties of vulcanised EPDM rubber

Abstract In this study, mechanical, thermal and rheological properties of vulcanised ethylene propylene diene monomer (EPDM) rubber containing different amounts of vulcanising agent, filler, paraffinic oil and stearic acid were compared. Moreover, reaction rate constant of the curing reaction has been calculated from the results of the rheological tests, and relative change of rate constant with the change of additives was studied by a new method. Thermal gravimetric analysis with in situ Fourier transform infrared (FTIR) spectra was taken, and the thermal degradation of the EPDM rubber was observed for varying amounts of vulcanising agent and filler content. Although the vulcanising agent improved the mechanical properties of the EPDM initially, a further increase in the vulcanising agents deteriorated the mechanical properties. Attenuated total reflectance FTIR spectrum confirmed the decrease in the relative degree of cross-linking with the increase in the vulcanising agent content to 10 h−1. Moreover, attenuated total reflectance FTIR spectra reaffirmed that cross-linking density increases with carbon black content. In situ FTIR spectra showed that the thermo-oxidative stability increased with the increase in filler content.

Thermal and mechanical properties of poly(methyl methacrylate) used as dental base material

The thermal and mechanical properties of poly(methyl methacrylate) prepared at different curing times were studied using DSC, TGA, tensile, and three-point bending test methods. The molecular weights of the polymer samples were determined from the viscosity measurements. The curing time applied for two different commercial materials, manufactured for dental use, ranged from 15 to 180 min. The samples cured for 15 and 20 min were soluble in chloroform completely, but the others were partially soluble. The insoluble fraction increased with curing time but the molecular weight of the soluble fraction remained constant. DSC thermograms showed further curing of the samples cured for 15 and 20 min. After curing for 180 min and/or annealing at room temperature for about 13 months, the samples were completely crosslinked. The characteristic values obtained from the tensile and the three-point bending tests were similar for samples cured at different times.

Degradation of Poly(2-hydroxyethyl methacrylate) Obtained by Radiation in Aqueous Solution

The degradation of poly(hydroxyethyl methacrylate), PHEMA obtained by γ -radiation induced polymerization of HEMA in aqueous solution, was studied. The polymer was a gel type and insoluble in common organic solvents. The DSC thermogram of the polymer gave a Tg value at 88.2°C and an endothermic peak showed further polymerization or crosslinking at 110–160°C. The degradation observed in TGA was a depolymerization type. However, the FT-IR of TGA fragments showed no monomer, which was degraded further. The degradation of monomer was studied by the GC-MS method. Similar results were also observed.

Thermal Degradation of Poly(Allyl Methacrylate) by Mass Spectroscopy and TGA

Allyl methacrylate, AMA was polymerized in CCl4 solution by α,α′‐azoisobutyronitrile at 50°C. The thermal degradation mechanism of PAMA was characterized by MS, TGA‐FT‐IR and FT‐IR‐ATR methods. The mass spectrum and TGA thermogram showed two stage degradation. The first stage of degradation was mostly linkage type degradation for the fragmentation of pendant allyl groups at 225–350°C. In the second stage, at 395–515°C, the degradation is random scission and depolymerization types. This was also supported by direct thermal pyrolysis of polymer under vacuum. The degradation fragments of MS and TGA were in agreement. In the degradation process, monomer degraded further to CO, CO2, allyl and ether groups. No strong monomer peak was observed in mass spectrum.

Radiation-induced and electroinitiated polymerization of allylbenzene

Abstract Radiation-induced and electroinitiated polymerization of allylbenzene has been investigated. Radiation-induced polymerization at room temperature was found to give mainly dimers and trimers with a maximum yield of 5%. Electroinitiated polymerization of the monomer yielded insoluble polymer films on the surface of the anode together with low molecular weight polymers in the bulk solution. The effects of temperature and monomer concentration on the rate of electroinitiated polymerization were also studied. The decrease in monomer concentration during electroinitiated polymerization was studied by taking cyclic voltammograms of the electrolysis solution. An apparent activation energy of 5.5 kJ mol −1 was found for the electroinitiated polymerization. The polymers were characterized by taking infra-red and nuclear magnetic resonance spectra. The polymerization proceeds via double bond addition of monomer together with isomerization of allylbenzene into β-methylstyrene.