Bulunan: 156 Adet 0.002 sn
Koleksiyon [20]
Tam Metin [2]
Yayın Türü [7]
Yazar [20]
Yayın Yılı [20]
Konu Başlıkları [20]
Yayıncı [20]
Yayın Dili [2]
Dergi Adı [20]
Free radical crosslinking copolymerization. Gelation behavior of macromonomeric azoinitiators versus macrocrosslinkers

Yıldız, Ufuk | Hazer, Baki

Article | 1998 | Macromolecular Chemistry and Physics199 ( 2 ) , pp.163 - 168

In order to evaluate the gelation behavior of macromonomeric azoinitiators (MIMs), the free radical polymerization of MIM and macrocrosslinkers (MCRs) have been compared. MIMs were synthesized by the reaction between 4,4'-dicyano-4,4'-azovaleryl chloride and poly(ethylene glycol)s PEG-400, -1000, -1500, -2000 and 4-vinylbenzyl chloride. MCRs were obtained by vinylation of both hydroxyl ends of PEG samples with 4-vinylbenzyl chloride. Bulk copolymerization of styrene with MIMs or MCRs in the concentration range between 2.91 and 31.50 wt.-% at 70°C for 3 h gave PSt-PEG networks. The gelation behavior of MIM was remarkably different fr . . .om that of MCR. In each case, gel fractions and swelling ratios of the gels depend on the molecular weights of the PEG sequences. Critical minimum concentrations for the onset of gelation were determined as 5, 8, 10 and 10 wt.-% for MIMs containing PEG units with molecular weight 400, 1000, 1500 and 2000, and 6, 12, 18 and 19 wt.-% for MCRs containing PEG units with the same molecular weights as above. Below those concentrations no network is formed. The critical minimum values for the onset of gelation were also obtained from homo- and copolymerization of partially vinylized MIMs with styrene Daha fazlası Daha az

Synthesis of a new macroperoxy initiator with methyl methacrylate and t-butyl peroxy ester by atom transfer radical polymerization and copolymerization with conventional vinyl monomers

Öztürk, Temel | Yılmaz-Savaşkan, Sevil | Hazer, Baki

Article | 2008 | Journal of Macromolecular Science, Part A: Pure and Applied Chemistry45 ( 10 ) , pp.811 - 820

In this study, we present the synthesis of poly-MMA macroperoxy initiators obtained by the ATRP of MMA with bromo methyl benzyl t-butyl peroxy ester (t-BuBP) as an initiator, and CuX (X:Br or Cl)/2,2'-bipyridine (bpy) as a catalyst system at 0, 20, 30 and 40C. The peroxygen groups do not decompose during the ATRP reaction, because low reaction temperatures used for the ATRP reaction are not enough to decompose them. The peroxygen groups of poly-PMMA macroperoxy initiators can lead them to react with a monomer by using appropriate reaction conditions to obtain the block or graft copolymers. For this purpose, poly-MMA macroperoxy init . . .iators were used to synthesize poly(MMA-b-S) block copolymers with S and used for graft copolymerization of polybutadiene (PBd) and natural rubber (RSS-3) to obtain crosslinked poly(MMA-g-PBd) and poly(MMA-g-RSS-3) graft copolymers. Swelling ratio values of the crosslinked graft copolymers in CHCl3 were calculated. The characterizations of the polymers were achieved by FT-IR, 1H-NMR, GPC, DSC, SEM, and the fractional precipitation () techniques. The reaction schemes were also performed using the HYPERCHEM 7.5 program. The mechanical properties of the products were investigated Daha fazlası Daha az

Soft tissue response to the presence of polypropylene-g-poly(ethylene glycol) comb-type graft copolymers containing gold nanoparticles

Hazer, Derya Burcu | Hazer, Baki | Dinçer, Nazmiye

Article | 2011 | Journal of Biomedicine and Biotechnology2011 , pp.811 - 820

Solution electrospinning of polypropylene-based fibers and their application in catalysis

Berber, Emine | Horzum, Nesrin | Hazer, Baki | Demir, Mustafa M.

Article | 2016 | Fibers and Polymers17 ( 5 ) , pp.760 - 768

Since the dissolution of polyolefins is a chronic problem, melt processing has been tacitly accepted as an obligation. In this work, polypropylene (PP) was modified on molecular level incorporating poly(ethylene glycol) (PEG) as graft segment (PP-g-PEG) in a range of 6 to 9 mol%. Gold nanoparticles were nucleated in the presence of the copolymer chains via redox reaction. The dissolution of the amphiphilic comb-type graft copolymers containing gold nanoparticles (80 nm in diameter) was achieved in toluene and successfully electrospun from its solution. The diameter of composite fibers was in the range from 0.3 to 2.5 µm. The design . . .of the structurally organized copolymer fiber mats provided a support medium for the nanoparticles enhancing the active surface area for the catalytic applications. The resulting composite fibers exhibited rapid catalytic reduction of methylene blue (MB) dye in the presence of sodium borohydride (NaBH4) compared to corresponding composite cast film. © 2016, The Korean Fiber Society and Springer Science+Business Media Dordrecht Daha fazlası Daha az

Synthesis and characterization of the novel thermoresponsive conjugates based on Poly(3-hydroxy alkanoates)

Toraman, Tuğba | Hazer, Baki

Article | 2014 | Journal of Polymers and the Environment22 ( 2 ) , pp.159 - 166

Novel thermoresponsive polymer conjugates based on microbial polyesters and poly-N-isopropyl acryl amide, PNIPAM, have been reported. The unsaturated poly-3-hydroxy alkanoates, poly (3-hydroxy undecenoate), PHU, and 1:1 mixture of 10-undecenoic acid and soy oil acids, PHU-Sy, were brominated by using bromine in the dark, at room temperature. Brominated PHAs were transformed to macro reversible addition-fragmentation chain transfer (RAFT) agents via the substitution reaction with potassium ethyl xanthate. RAFT polymerization of N-isopropyl acryl amide, NIPAM, was initiated by the PHA-derivative containing xanthate pendant groups in o . . .rder to obtain brush type PHA-g-PNIPAM thermo responsive amphiphilic graft copolymers. The water uptake of the PHU-g-PNIPAM and PHU-Sy-g-PNIPAM amphiphilic graft copolymers changed from 50 % to completely soluble in water. Structural and thermal characterization of the novel conjugates were carried out by using 1H NMR, GPC, DSC and TGA techniques. Graphical Abstract: [Figure not available: see fulltext.] © 2014 Springer Science+Business Media New York Daha fazlası Daha az

One-step synthesis of triarm block copolymers via simultaneous reversible-addition fragmentation chain transfer and ring-opening polymerization

Öztürk, Temel | Göktaş, Melahat | Hazer, Baki

Article | 2010 | Journal of Applied Polymer Science117 ( 3 ) , pp.1638 - 1645

One-step synthesis of star copolymers by reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerization (ROP) by using a novel dual initiator is reported. Triarm block copolymers comprising one polystyrene (or polyacrylamide) arm and two poly(b-butyrolactone) arms were synthesized in one-step by simultaneous RAFT polymerization of styrene (St) (or acrylamide, designated as AAm) and ROP of b-butyrolactone (BL) in the presence of a novel trifunctional initiator, 1,2-propanediol ethyl xanthogenate (RAFT-ROP agent). This dual initiator was obtained through the reaction of 3-chloro-1,2- propanediol with the potas . . .sium salt of ethyl xanthogenate. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the one-step polymerization reaction were evaluated. The characterization of the products was achieved using Fourier-transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance (1HNMR),13C-nuclear magnetic resonance ( 13C-NMR), Gas chromatography-mass spectrometry (GC-MS), gel-permeation chromatography (GPC), thermogravimetric analysis (TGA), and fractional precipitation (c) techniques. VC 2010 Wiley Periodicals, Inc Daha fazlası Daha az

Reactions of anionic living polymers with bromomethyl-functionalized benzoyl peroxides

Hazer, Baki | Hirao, Akira | Volga, Cüneyt

Article | 1999 | Macromolecular Chemistry and Physics200 ( 1 ) , pp.71 - 76

In order to synthesize benzoyl peroxide functionalized polystyrene (PSt), polyisoprene (PI) and poly(methyl methacrylate) (PMMA), anionic living PSt, PI, and PMMA were allowed to react with an excess amount of 4-(bromomethyl)benzoyl tert-butyl peroxide (BMtB) or bis[3,5-bis(bromomethyl)benzoyl] peroxide (BDBP) in tetrahydrofuran (THF) at -78°C. The results indicate that coupling reactions leading to dimers are significant during the reaction. Dimer formation was avoided when the living polystyrene was modified to the alcoholate anion by reaction with ethylene oxide (EO). © Wiley-VCH Verlag GmbH, 1999.

The efficacy of silver-embedded polypropylene-grafted polyethylene glycol-coated ventricular catheters on prevention of shunt catheter infection in rats

Hazer, Derya Burcu | Mut, Melike | Dinçer, Nazmiye | Sarıbaş, Zeynep | Hazer, Baki | Özgen, Tunçalp

Article | 2012 | Child's Nervous System28 ( 6 ) , pp.839 - 846

Purpose: Catheter-related infection is a major complication of ventriculoperitoneal shunt in children. The aim of this study is to determine inflammatory response and the efficacy of polypropylene-grafted polyethylene glycol (PP-g- PEG) copolymer and silver nanoparticle-embedded PP-g- PEG (Ag-PP-g-PEG) polymer-coated ventricular catheters on the prevention of catheter-related infections on a new experimental model of ventriculoperitoneal shunt in rats. Methods: Thirty six Wistar albino rats were divided into six groups: group 1, unprocessed sterile silicone catheterembedded group; group 2, sterile PP-g-PEG-coated catheter group; gro . . .up 3, sterile Ag-PP-g-PEG-coated catheter group; group 4, infected unprocessed catheter group; group 5, infected PP-g-PEG-coated catheter group; and group 6, infected Ag-PP-g-PEG-coated catheter group, respectively. In all groups, 1-cm piece of designated catheters were placed into the cisterna magna. In groups 4, 5, and 6, all rats were infected with 0.2 mL of 10×106 colony forming units (CFU)/mL Staphylococcus epidermidis colonies before the catheters were placed. Thirty days after implantation, bacterial colonization in cerebrospinal fluid and on catheter pieces with inflammatory reaction in the brain parenchyma was analyzed quantitatively. Results: Sterile and infected Ag-PP-g-PEG-covered groups revealed significantly lower bacteria colony count on the catheter surface (ANOVA, 0±0, p<0.001; 1.08±0.18, p< 0.05, respectively). There was moderate inflammatory response in the parenchyma in group 4, but in groups 5 and 6, it was similar to that of the sterile group (ANOVA, 16.33± 3.02, p<0.001; 4.00±0.68, p<0.001, respectively). Conclusions: The PP-g-PEG, especially Ag-PP-g-PEG polymer-coated ventricular catheters are more effective in preventing the catheter-related infection and created the least inflammatory reaction in the periventricular parenchyma. © Springer-Verlag 2012 Daha fazlası Daha az

Dispersion polymerization of styrene and methyl methacrylate initiated by macromonomeric azoinitiator

Yıldız, Ufuk | Hazer, Baki

Article | 1999 | Angewandte Makromolekulare Chemie265 , pp.16 - 19

The free radical dispersion polymerization of styrene (St) and methyl methacrylate (MMA) initiated by poly(oxyethylene) (PEO) macroazoinimer (MIM-400) in water/ethanol, was investigated at three different temperatures (50, 60 and 80°C) for seven polymerization times (3, 6, 9, 12, 24, 36 and 48 h). PSt-PEO and PMMA-PEO networks were obtained. In each case, polymer gel fractions depend on the polymerization temperature and polymerization time. With the same initial concentration of MIM-400, maximum gel fraction was found at 80 wt.-% with St copolymerization while 100 wt.-% in case of copolymerization with MMA at 80°C for 48 h. © Wiley . . .-VCH Verlag GmbH, 1999 Daha fazlası Daha az

Soybean oil based polylactic acid membranes: Synthesis and degradation characteristics

Aydın Tığlı, R. Seda | Akyol, Elvan | Hazer, Baki

Article | 2018 | Journal of Polymers and the Environment26 ( 3 ) , pp.1262 - 1271

Controlling the degradation parameters is one of the main challenges of preparing appropriate biomaterials for biomedical applications. In this study, the effect of soybean oil inclusion on hydrolytic degradation of polylactic acid (PLA) was investigated both in vitro and in vivo. PLA/oil membranes were prepared by using polymeric soybean oil (PSO), epoxidized soybean oil and soybean oil (SOYA) with their varied concentrations. Degradation of membranes was performed in vitro for 8 weeks period and in vivo for 4 weeks period. Weight loss, changes in molecular weight, thermal properties and morphological changes were studied during de . . .gradation. SOYA blended PLA membranes show the lowest degradation rates by bulk degradation after 4 weeks in vitro, followed by surface erosion for the first week. Approximately twofold high percentage weight losses of all membranes were obtained after 4 weeks of degradation in vivo in comparison with in vitro data. The significant weight loss, molecular weight loss and thermal property change for PSO blended membranes were determined during in vivo degradation which highlights the increase of degradation rate by bulk degradation. Drastic morphological changes were observed on surface of degraded membranes in vivo with large pores, cracks, fissures and large cavities. © 2017, Springer Science+Business Media New York Daha fazlası Daha az

Simple production experiment of poly (3-hydroxy butyrate) for science laboratories and its importance for science process skills of prospective teachers

Koray, Özlem | Köksal, Mustafa Serdar | Hazer, Baki


Poly (3-hydroxybutyrate), PHB, is a biocompatible and biodegradable polymer accumulated in microorganism cells as a reserve material. PHB production in biotechnology laboratories has been carried out by using expensive instruments such as autoclave, a large thermostatted shaker, a freeze dryer, and an automatic refrigerated centrifuge. A very simple method of PHB production with Alcaligenes eutrophus for use in science teaching freshman laboratory is reported in this article. The study was conducted with 6 prospective elementary teachers. An ordinary glass 1 L jar, a 4L pressure cooker and thermostate for aquariums were used in ferm . . .entation process of the bacterium in nutrient solution containing table sugar as a substrate. In conclusion, the thermal and characterization data confirmed the PHB structure. Science Process Skills are investigated in this study. Qaulitative method was used to acquire data and analyze the science process skills experienced by the students in the experiment. The article discusses on development of some science process skills during the experimental process and gives suggestions for future use and research Daha fazlası Daha az

An electrochemical biosensor for direct detection of DNA using polystyrene-g-soya oil-g-imidazole graft copolymer

Koçak, İzzet | Şanal, Timur | Hazer, Baki

Article | 2017 | Journal of Solid State Electrochemistry21 ( 5 ) , pp.1397 - 1405

A label-free electrochemical DNA biosensor was developed through the attachment of polystyrene-g-soya oil-g-imidazole graft copolymer (PS-PSyIm) onto modified graphene oxide (GO) electrodeposited on glassy carbon electrode (GC). GC/GO electrode was initially functionalised via electrochemical reduction of 4-nitrobenzene diazonium salt, followed by the electrochemical reduction of NO2 to NH2. Subsequent to the electrochemical deposition of gold nanoparticles on modified surface, the attachment of the PS-PSyIm graft copolymer on the resulting electrode was achieved. The interaction of PS-PSyIm with DNA at the bare glassy carbon electr . . .ode was studied by cyclic voltammetry technique, and it was found that interaction predominantly takes place through intercalation mode. The selectivity of developed DNA biosensor was also explored by DPV on the basis of considering hybridisation event with non-complementary, one-base mismatched DNA and complementary target DNA sequence. Large decrease in the peak current was found upon the addition of complementary target DNA. The sensitivity of the developed DNA biosensor was also investigated, and detection limit was found to be 1.20 nmol L-1. © 2017, Springer-Verlag Berlin Heidelberg Daha fazlası Daha az

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