Search results for " Plastic"
showing 10 items of 3463 documents
Continuous fractionation of poly[(dimethylimino)decamethylene bromide] and molecular weight dependence of the glass transition
1995
30 g of the ionene poly[(dimethylimino)decamethylene bromide] were fractionated by a continuous counter-current extraction method (CPF) using ethylene glycol monoethyl ether as the solvent and diisopropyl ether as the non-solvent component. The efficiency of the separation was checked by viscometry and gel-permeation chromatography (GPC) measurements. Eight fractions of different molar mass were prepared for differential scanning calorimetry (DSC) experiments. With bromide as counter-ion, the glass transition temperature of the ionene increases from ca. 60 to 85°C as the intrinsic viscosity of this material (in 0,4 M aqueous solutions of KBr at 25°C) rises from ca. 14 to 22 mL/g. When bromi…
Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N-isopropylacrylamide)
2003
The interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (M w = 1 600 kg/mol) poly(N-isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, T cp decreases steadily with rising polymer concentration up to 10 wt.-%. The application of shear supports phase separation and reduces T cp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected wit…
Mark-Houwink Parameters of Biosynthetic Poly(γ-glutamic acid) in Aqueous Solution
2001
A combined viscosity–light scattering–gel permeation chromatography (GPC) study was carried out on bacterially produced poly(γ-glutamic acid) (PGGA). PGGA samples with weight-average molecular weights ranging from 8×104 up to 8×105 g·mol–1 dissolved in phosphate buffer at 0.13 M ionic strength were used. It was found that the Mark–Houwink relation is acceptably obeyed, giving K and a values of 1.84×10–6 dL·g–1 and 1.16, respectively. As expected, GPC analysis showed that PGGA does not follow the universal calibration plot and that deviations can not be avoided by modifying the ionic strength.
Synthesis of Water-Soluble Copolymers Carrying Long-Chain (C12 to C30 ) Aliphatic Moieties
2011
Water-soluble copolymers from mono-1-alkyl itaconates and N-vinyl-2-pyrrolidone are synthesized and characterized. Themono-1-alkyl itaconates are prepared from itaconic anhydride and the related alcohol: 1-dodecanol, 1-octadecanol, 1-docosanol, and 1-triacontanol. The mono-1-triacontyl itaconate is synthesized fromplant growth regulator policosanols extracted from Agave fourcrouydes, where 1-triacontanol is the major product. The reactivity ratios, calculated according to the Mao-Huglin method for copolymerizations conducted to medium-high conversions, indicate a tendency toward alternation for all copolymerization reactions. Water solubility of copolymers is provided as a function of copol…
Towards the Generation of Self-Healing Materials by Means of a Reversible Photo-induced Approach
2011
Photo-induced reversibility as a tool for self-healing: a reversible photo-induced dendritic macromonomer was synthesized and proven to form networks with different features depending on the crosslinking conditions. While networks formed from aqueous systems exhibited a reversible change in their crosslinking degree, networks generated in bulk underwent fully reversibility. The latter was then exploited for generating self-healing materials by means of a photo-induced treatment.
Functionalization of Crosslinked Vesicles by Co-Self-Assembly of a Gelable Diblock Copolymer and Mercaptosilane
2008
Herein, a convenient and general method to simultaneously fix and functionalize polymeric vesicles with sulphydryl groups by the co-self-assembly of poly(ethylene oxide)-block-poly[3-(triethoxysilyl)propyl methacrylate] (PEO-b-PTESPMA) and 3-mercaptopropyltrialkoxysilane in an aqueous solution is reported. The presence of sulphydryl groups across the vesicle membrane has been confirmed by using an energy-filtered technique during TEM analysis and by capturing Au nanoparticles.
Double-Shell Vesicles, Strings of Vesicles and Filaments Found in Crosslinked Micellar Solutions of Poly(1,2-butadiene)-block-poly(ethylene oxide) Di…
2001
Micellar structures of amphiphilic poly(1,2-butadiene)-block-poly(ethylene oxide) diblock copolymers have been crosslinked in aqueous solution by γ-irradiation. By transmission electron microscopy (TEM) of neganively stained specimen it is shown that the precominant structures present are sopolymer sesicles (which appear to be double latered. These fived vesules are stable with respect to their share and can be transferred from water into a good solvent for blue filbeks, such as tetrahydrofuran, this demonstrating the effectiveness of the crosslinking. In addition to the resicles a small number of flexible cylindrichl/filimented structures sequentially fused vesicles/strings of vesicles and…
Structural Characterization of Zirconia Nanoparticles Prepared by Microwave-Hydrothermal Synthesis
2009
Nanocrystalline zirconia powders have been prepared by microwave-hydrothermal synthesis starting from aqueous solution of ZrOCl2·8H2O. Results of investigations on the aqueous suspension stability of the washed zirconia nanopowders by dynamic light scattering showed that the suspension, constituted by superaggregates of nanoparticles (131 ± 10 nm), was stable up to 15 days. Nanopowders were investigated by means of transmission electron microscopy and small angle x-ray scattering measurements which proved that the zirconia nanopowder is constituted by small primary nanoparticles of ca. 8 nm that agglomerate forming bigger aggregates of 50 ± 1 nm.
Membranes Directly Prepared from Solutions of Unsubstituted Cellulose
2005
Summary: Starting from 5 wt.-% solutions of a prehydrolysis kraft pulp ( = 135 kg · mol−1) in the mixed solvent (dimethylacetamide + 7 wt.-% LiCl) we have prepared cellulose membranes on different supports according to the phase inversion process using above all acetone (AC) and 2-propanol as precipitants. In this context we have studied the phase behavior of the quasiternary system (DMAc+LiCl)/AC/cellulose. The obtained membranes are mechanically stable and in their mechanical and separation properties on the whole comparable to membranes consisting of regenerated cellulose. With respect to gas separation the ideal selectivity of CO2 in combination with N2 and O2 turns out to be opposite f…
Micelles of Polysoaps: The Role of Bridging Interactions
1996
Polysoaps, hydrophilic polymers incorporating amphiphilic monomers, form intrachain micelles in aqueous media. The micelles are similar to those formed by monomeric amphiphiles but are also endowed with a swollen, starlike corona formed by the spacer chains joining the amphiphiles. Long polysoaps form strings comprising many intrachain micelles. Exchange of amphiphiles between such micelles may give rise to bridging attraction, resulting in the adoption of a collapsed configuration in which the swollen micelles are close packed into a spherical globule. Upon addition of free amphiphiles, this structure unravels in a highly nonlinear fashion. Titration by surfactants, and the resulting swell…