The structural characteristics of aqueous micelles composed of amphiphilic cyclic poly(n-butyl acrylate-b-ethylene oxide) (cyclic PBA-b-PEO) or a linear analogue (i.e., linear poly(n-butyl acrylate-b-ethylene oxide-b-n-butyl acrylate) (linear PBA-b-PEO-b-PBA)) were examined for the first time using synchrotron X-ray scattering techniques and quantitative data analysis. The scattering data were analyzed using a variety of methodologies in a comprehensive complementary manner. These analyses provided details of the structural information about the micelles. Both micelles were found to consist of a core and a fuzzy shell; however, the cyclic block copolymer had a strong tendency to form micelles with core and shell parts that were more compact and dense than the corresponding parts of the linear block copolymer micelles. The PBA block of the cyclic copolymer was found to form a hydrophobic core with a density that exceeded the density of the homopolymer in the bulk state. The structural differences originated primarily from the topological difference between the cyclic and linear block copolymers. The elimination of the chain end groups (which introduced entropy and increased the excess excluded volume) from the amphiphilic block copolymer yielded more stable dense micelles in solution.

Linear and cyclic amphiphilic block copolymers consisting of poly(ethylene oxide) (PEO) as the hydrophilic segment and poly(methyl acrylate) or poly(ethyl acrylate) as the hydrophobic segments were synthesized and self-assembled to form flower-like micelles. The micelles from linear (methyl acrylate)12(ethylene oxide)73(methyl acrylate)12 (Mn = 1000-3200-1000, l-MOM) showed a cloud point (Tc) at 46 °C by the transmittance of the micellar solution, whereas that of cyclic (methyl acrylate)30(ethylene oxide)79 (Mn = 2600-3500, c-MO) increased to 72 °C, as previously reported. DLS showed comparable diameters (l-MOM, 14 nm; c-MO, 12 nm) and Tc values (l-MOM, 48 °C; c-MO, 75 °C). For the investigation of the difference in Tc and the phase transition mechanism based on the polymer topology, NMR relaxometry was performed to determine the spin-lattice (T1) and spin-spin (T2) relaxation times. A decrease in T2 of the PEO segment in both l-MOM and c-MO was observed above Tc, suggesting that slow large-scale motions, such as the detachment of a chain end from the core, bridging, and interpenetration of the micelles, were inhibited. T1 of the PEO segment in l-MOM continuously increased in the experimental temperature range, indicating that the segment is hydrated even above its Tc. On the other hand, that of c-MO reached a ceiling above its Tc, likely due to the prevention of the rotation of the PEO main chain bonds caused by dehydration. Similar results were obtained for linear (ethyl acrylate)8(ethylene oxide)79(ethyl acrylate)8 (Mn = 800-3500-800, l-EOE) and its cyclic (ethyl acrylate)15(ethylene oxide)78 (Mn = 1500-3400, c-EO).

The phase diagram of the La--S-O system at 1073 K was established with the vacuum seal technique. Six phases exist at this temperature: La.,Oa (B-type), LaS.,, La2Sa, La202SO4, La20.,S and La20.,S2. The thermodynamic functions for the reaction La.,O2SO4 = La203 + SO., + 1/2 O2 were determined by using the emf method at temperatures from 1123 to 1373 K. The mechanisms of the oxidation reactions in the La--S--O system under different partial pressures of oxygen (--4.4 < log Po~ < --0.7) were also investigated by means of DTA, TG and powder X-ray diffractometry.Many phases have been reported to exist in the La-S-O system at high temperatures, e.g. La2Os, LaS2, La2Sz, La202SQ, La202S, LazO2S2, La2(SOa)z etc. La203 has five polymorphs [1-4]: A-type (hexagonal), B-type (monoclinic), C-type (cubic), H-type (hexagonal at high temperature) and X-type (structure unknown). The temperature range of stability for each La203 other than the B-type has been already established [5]. Three polymorphs of La2S3 [6][7][8] are known: c~-phase, fi-phase and 7-phase. Stable fi-La2Sa exists at temperatures between 923 and 1623 K. Recently, discovered Lal0Sl~O with a tetragonal structure and reported that this compound forms a solid solution with p-La2S3. LaS2 with a cubic structure has been synthesized by Flahaut et aL [13] and orthorhombic LaS2 has been reported by Dugue et al. [14] and Benazeth et aL [15].The thermodynamic data on the formation of Laz03 in the range of temperature from 298 to 1200 K and those for La2S3 from 298 to 2400 K have been compiled by Barin et al. [16,17], and those for La202S have been reported by Laptev et al. [18]. Moreover, thermodynamic studies on the La2OzSO4-La2(SO~)z and La203-La,,O2SOa systems have been carried out by Kellogg [19] and Grizik et aL [4], respectively. Wendlandt et aL [20,21] investigated the thermal decomposition of La2(SO4)a 9 9 H20.In the present paper, the phase relations in the La-S -O system at 1073 K were investigated by using the vacuum seal technique, and the thermodynamic functions for the reaction La202SO4 = La203 + SO~ + 1/20~ were estimated by the emf method using calcia-stabilized zirconia. Further, the mechanisms of the reactions of oxidation for each compound existing in the La-S-O system were studied under different partial pressures of oxygen by means of DTA, TG and powder X-ray diffraction.