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Temperature (°C) 45 40 35 30 25 20 PLGA/PEG/PLGA ITA-PLGA/PEG/PLGA-ITA white viscous suspension suspension white gel white viscous cloudy gel cloudy viscous cloudy viscous amber sol amber sol 15 0 5 10 15 20 25 Concentration (w% ) white gel amber viscous cloudy gel amber viscous amber gel amber gel Fig. 2: The sol-gel transition phase diagram of the triblock copolymers PLGA-PEG-PLGA and ITA-PLGA-PEG-PLGA-ITA The diagram demonstrates three basic areas - sol, gel and suspension (precipitate). The phase diagram of PLGA-PEG-PLGA shows the critical gel concentration (CGC) of 19.2 w% and the critical gelation temperature (CGT) of 34.5 °C. For the next study, the solution of 23 %wt was used because of forming the amber hydrogel at around 37°C. As for the copolymer modified by ITA, CGC and CGT were determined to be 15.3 w% and 25.0 °C, respectively. The values were shifted below the curves of the polymer without the itaconic acid which pointed that the presence of hydrophilic –COOH groups causes better interaction between the polymer and water molecules. Therefore, CGC and CGT were observed to be lower than those of the copolymer without ITA. The change from sol to gel, which occurred by increasing the temperature, was not sharp. At the temperature much lower than the critical gel temperature; unimers, individual micelles, and grouped micelles coexisted in the sol state (Fig. 2 amber sol). The unimer fraction decreased with the temperature increasing (Fig. 2 amber viscous). At the same time, the grouped micelle size grew rapidly resulting in sol-gel transition (Fig. 2 amber gel). The aggregation and packing interactions between micelles increased to form denser gel with the raising temperature (Fig. 2 cloudy viscous state, cloudy gel). When the temperature was further raised, the hydrophobic chains in the micelle core shrank tightly. Also, the hydrophilic PEG block underwent dehydration and the second gel-sol transition arisen (Fig. 2 white viscous state, white gel, suspension). The over shrunk micelle groups precipitated in water and the solution separated into two phases of water and precipitated polymer (Fig. 2 precipitation) [8]. Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 220
Each micelle has a hydrophobic core and a hydrophilic shell, and can move relatively freely without any bridging connection between the micelles. Sol-gel transition occurs when the total volume of micelles fraction is larger than the maximum packing fraction volume [8]. The degradation behavior of PLGA-PEG-PLGA was investigated. Four samples of the copolymer in 0.7 ml of the phosphate buffer (pH 7.4) were placed into the incubator at 37 °C (the normal temperature of a human body). The samples were taken out and lyophilized after 3, 5, 7 and 10 days. The rest of the copolymer was analyzed by GPC. The decrease in the molecular weight during these periods can be seen in Fig. 2. After 3, 5 and 7 days two phases in the vials can be observed, the copolymer gel and the buffer. The total dissolving of the copolymer occurred after 10 days when the measured molecular weight (Mn) was found to be 4170 (Tab. 1). Tab. 1: The change of the molecular weight and the polydispersity during the degradation in the phosphatic buffer (pH 7.4, 37 °C) Time (day) Molecular weight Polydispersity 0 6010 1.21 3 5840 1.23 5 5220 1.31 7 4770 1.33 10 4170 1.35 The change of polydispersity (D) was related to the change of Mn. Mn decreased while D increased with the growing number of the shorter copolymer chains. Molecular weight 6500 6000 5500 5000 4500 4000 3500 0 2 4 6 8 10 12 Time (day) Fig. 3: The change of the molecular weight (Mn)● and the polydispersity (D)∆ after 0, 3, 5, 7, and 10 days. Sborník soutěže Studentské tvůrčí činnosti Student 2006 a doktorské soutěže O cenu děkana 2005 a 2006 Sekce DSP 2006, strana 221 1,36 1,34 1,32 1,30 1,28 1,26 1,24 1,22 1,20 Polydispersity
Page 1 and 2: PRODUCTION OF SELECTED SECONDARY ME
Page 3 and 4: containing ampicillin, IPTG and x-g
Page 5 and 6: THE SIMPLE METHOD FOR THE RECOGNITI
Page 7 and 8: Figure 1 Negative-ion mode MALDI-TO
Page 9 and 10: Table 1 Evaluation of negative-ion
Page 11 and 12: Fig. 1: Scheme of the hydride gener
Page 13 and 14: [4] H. Matusiewicz, M. Kopras, J. A
Page 15 and 16: - are hypotriglyceridemic; - exhibi
Page 17 and 18: HYDROPHOBIZED SODIUM HYALURONATE IN
Page 19 and 20: spectrophotometer (AMINCO-Bowman, S
Page 21 and 22: Hyaluronate derivatives showed with
Page 23: copolymers were additionally functi
Page 27 and 28: STUDY OF THE COPPER(II) IONS NON-ST
Page 29 and 30: CuSO4, Cu(ClO4)2 and Cu2P2O7 of the
Page 31 and 32: total flux [mol.m -2 ] 0.7 0.65 0.6
Page 33 and 34: number of free radicals is very low
Page 35 and 36: Differences can be caused by severa
Page 37 and 38: MEASUREMENT OF THERMOPHYSICAL PROPE
Page 39 and 40: The typical time responses of tempe
Page 41 and 42: Figure 4 illustrates the typical de
Page 43 and 44: sodium sulphate and filtered to a 5
Page 45 and 46: Compare all tested evening primrose
Page 47 and 48: IMPROVED FLUORIMETRIC DETERMINATION
Page 49 and 50: Al F i 80 70 60 50 40 30 20 10 0 0
Page 51 and 52: F i 60 50 40 30 20 10 Data UCL LCL
Page 53 and 54: PHYSICAL-CHEMICAL ASPECTS OF PAINT
Page 55 and 56: Finally, the solubility parameter o
Page 57 and 58: Study of the influence of different
Page 59 and 60: Fig.1: Chemical structures of pI ma
Page 61 and 62: Identification of pI markers - Firs

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