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Polymer Aggregates (polymer + aggregate)
Selected AbstractsAcid-labile, thermoresponsive (meth)acrylamide polymers with pendant cyclic acetal moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2008Xiao-Nan Huang Abstract Acid-labile, thermoresponsive polymers with pendant six-membered cyclic acetal groups were prepared by radical polymerization of two monomers, N -(2,2-dimethyl-1,3-dioxan-5-yl) methacrylamide (NDMM) and N -(2,2-dimethyl-1,3-dioxan-5-yl) acrylamide (NDMA). The aqueous solution properties of the polymers, PNDMM and PNDMA, were studied by turbidimetry, 1H NMR, fluorescence, and DSC measurements. It is found that both polymers show sensitive and reversible phase transitions with distinct lower critical solution temperatures (LCST). Below their LCSTs, there are still some polymer aggregates as evidenced by measurements of pyrene excitation spectra and urea effects on the cloud points (CP) of polymers. The salting effect of six inorganic sodium salts on the phase transition behavior of PNDMM was investigated by turbidimetric approach. The salting-out to salting-in effect is in the order of SO42, > F, > Cl, > Br, > I, > SCN,, following the Hofmeister's series. pH-dependent hydrolysis of PNDMM and PNDMA was studied by turbidimetric and 1H NMR methods. They are both pH-sensitive and their hydrolysis rates significantly increase with decreasing pH value. The CP of PNDMM gradually increases with the acid-triggered hydrolysis of the acetal groups and the hydrolyzed polymer with , 30% hydrolysis degree does not show thermally induced phase transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4332,4343, 2008 [source] Roles of rhenium diimine complexes as metal-ion probes and photosensitizers in functional polyurethanesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2003Ching Sum Hui Abstract Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge-transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12,14 Å and 10,3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708,1715, 2003 [source] Single-Line EPR Spectra from Radicals Encapsulated in Aggregates of Amphiphilic Block Copolymers with Hydrophobic Dendritic Pendants in WaterMACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2006Kana Tamano Abstract Summary: A water-insoluble organic 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical is solubilized in aqueous solutions of aggregates of amphiphilic block copolymers with hydrophobic dendritic pendants. The number (100,200) of DPPH molecules solubilized in an aggregate, which is evaluated from UV-visible absorption spectra, is in agreement with that of the DPPH radicals determined from electron paramagnetic resonance (EPR) spectroscopy. The DPPH radicals are stably solubilized without decomposition in the polymer aggregates. The radicals exhibit a single-line EPR absorption, which is narrowed by the interspin interaction, and indicates the assembly formation of DPPH radicals in polymer aggregates. These results suggest the effective utilization of the DPPH radical as a spin-probe indicator in aqueous solutions. When DPPH is solubilized in aqueous solutions of NaAMPS- b -G2(n3), the polymer solutions become purple colored, which is characteristic of the DPPH radical. [source] Rheology of polyurethane solutions with different solventsPOLYMER INTERNATIONAL, Issue 1 2002L de Vasconcelos Abstract Hard segment hydrogen bonding interactions in a particular polyurethane segmented copolymer have been analysed through a viscometric approach to determine the behaviour of polyurethane solutions with different solvent compositions. Analysis of log,,spversus log c[,] master curves (solely comprising dilute and semidilute regimes) showed that these systems could be differentiated by the slope of the first part of the curve (dilute regime), the characteristic reduced concentration c*[,], and the slope of the second part of the curve (semidilute regime), differences which were related to a possible occurrence of polymer aggregates. Experiments with solutions in the concentrated regime, at different temperatures, were used to relate non-Newtonian behaviour to hydrogen bonding. © 2001 Society of Chemical Industry [source] | ||||||||||