Search results for "polymers"
showing 10 items of 3567 documents
ALTMET Polymerization of Amino Acid-Based Monomers Targeting Controlled Drug Release
2016
Giving the imminent necessity of a new generation of biodegradable and biocompatible polymers prepared from feedstock, the synthesis of a potentially biodegradable amino acid-based copolymer by the alternating diene metathesis (ALTMET) strategy is herein presented. The reaction was tailored to minimize isomerization and deactivation of ruthenium catalysts by intramolecular coordination with the amide carbonyl group of the amino-acid-based monomer. Alternated l-lysine–phosphoester copolymers with molar masses higher than 18 000 g/mol were obtained using Hoveyda–Grubbs second-generation and Umicore M2 catalysts. The copolymer was further used to prepare nanoparticles loaded with rifampicin (u…
Hyperbranched Poly(ethylene glycol) Copolymers: Absolute Values of the Molar Mass, Properties in Dilute Solution, and Hydrodynamic Homology
2015
Hyperbranched poly(ethylene glycol) copolymers were synthesized by random anionic ring-opening multibranching copolymerization of ethylene oxide with glycidol as a branching agent, leading to poly(ethylene glycol) structure with glycerol branching points. Extending the available range of molar masses by novel synthesis strategies, a limited extent of control over the degree of polymerization was achieved by variation of the solvent in this copolymerization. Generally, absolute molar mass characterization of hyperbranched polymers still represents an unresolved challenge. A series of the hyperbranched poly(ethylene glycol)-co-(glycerol) copolymers (hbPEGs) of a wide range of molar masses (14…
Reactive compatibilization of PA6/LDPE blends with an ethylene–acrylic acid copolymer and a low molar mass bis-oxazoline
2003
Abstract A sample of polyamide-6 (PA) was blended with low density polyethylene (LDPE) in the 80/20 wt/wt ratio, either without and with 2 phr of an ethylene–acrylic acid copolymer (EAA), Which was known to behave as a compatibilizer precursor, and the effect of the addition of small amounts (0.2 or 0.35 phr) of a fourth component, 2,2′-(1,3-phenylene)-bis(2-oxazoline) (PBO), was investigated. The reactions of PBO with EAA, PA and their blends were studied by recording as a function of time the torque applied to the blending apparatuses and by studying the solubility behavior of the products in formic acid. The PALDPE blends were prepared in a co-rotating twin screw extruder and were charac…
Continuous polymer fractionation of poly(methyl vinyl ether) and a new Kuhn-Mark-Houwink relation
1995
Continuous polymer fractionation (CPF) — a new large-scale method — was applied to the technical poly(methyl vinyl ether) (PVME) using toluence as solvent and petroleum ether as non-solvent. Two different devices served as fractionation apparatus, namely a column packed with glass beads and a set of mixer-settler extractors. Advantages and draw-backs of these devices are discussed. The experiments yielded numerous PVME fractions, varying in molar mass from 22 to 87 kg/mol and in molecular non-uniformity U = (M¯w/Mn) – 1 from 0,25 to 0,41 according to gel-permeation chromatography as compared with ca. U = 1,30 for the starting material. The following Kuhn-Mark-Houwink relation was establishe…
Phase equilibria and interfacial tension between coexisting phases for the system water/2-propanol/poly(acrylic acid)
1995
The cloud point curve, tie-lines and interfacial tensions were measured for solutions of 50 mol-% neutralized (counter-ion Na ○+ ) poly(acrylic acid) (molar mass M w = 9 700 g/mol; polydispersity index M w /M n = 2,0) in the mixed solvent water/2-propanol at 30°C. Due to the non-uniformity of the polymer, the end-points of the tie-lines are not situated on the cloud-point curve. The interfacial tension σ, determined by means of the spinning drop method, increases in sigmoidal manner with R tl , the length of the tie-line, expressed in terms of weight fractions. An evaluation of these data in a double-logarithmic plot of σ.M -0,5 versus R tl yields a critical exponent of 4,23 as compared wit…
Apparent Molar Mass of a Polyelectrolyte in an Organic Solvent in the Low Ionic Strength Limit As Revealed by Light Scattering
2013
The apparent molar mass of a partially quaternized poly-2-vinylpyridines (degree of quaternization 4.3% < Q < 35%) in 1-propanol is measured by light scattering at low ionic strength (10–6 M < cs < 10–3 M) as a function of polyion repeat unit concentration (7 × 10–5 monomol/L < cm,p < 4 × 10–2 monomol/L). No dialysis was applied prior to measurements. The apparent molar mass under “salt-free” conditions is smaller than the true molar mass by an order of magnitude, while approaching the true value at higher ionic strength. Concomitant data on the dependence of scattering intensity on scattering wave vector show that the dilute polyelectrolyte solutions are strongly correlated. A recent theor…
1995
About 340 g of a cycloaliphatic ionene (see formula given in the introduction) were fractionated by a continuous countercurrent extraction method (CPF). The efficiency of the separation was checked by viscometry and gel permeation chromatography (GPC). Ten different fractions with number average molecular masses between 16 000 and 29 000 D were obtained and their glass transition temperatures T g determined by differential scanning calorimetry (DSC) for their bromide and tetrafluoroborate salts. No molecular weight dependence of T g was found, in contrast to recently reported results with aliphatic ionenes, where - in case of the bromide - T g increases with rising molecular weight.
Reduction of Polymerization Shrinkage Stress and Marginal Microleakage Using Soft-Start Polymerization
2003
Purpose: This study evaluated the influence of a soft-start light-curing exposure on polymerization shrinkage stress and marginal integrity of adhesive restorations. Materials and Methods: Six resin-based composites (Pertac II, Tetric Ceram, Definite, Surefil, Solitaire, and Visio-Molar) were adhesively bonded to a cylindrical cavity (n = 9 per material/light) in a photoelastic material. Visible light-curing was applied using either the standard polymerization mode (800 mW/cm2 exposure duration 40 s) of the curing light (Elipar TriLight, 3M ESPE) or the exponential mode from the same device (ramp-curing: 150 mW/cm2 to 800 mW/cm2 within the first 15 s of a total curing time of 40 s). Polymer…
Nebenreaktionen der radikalisch ausgelösten Cyclisierung von 2,2′-Methylen-bis(4-methyl-1,2-phenylen)-dimethacrylat
1979
2,2′-Methylene-bis(4-methyl-1,2-phenylene) dimethacrylate (1) was reacted with an excess of 2,2′-azoiso-butyronitrile (mole ratio 1:15) highly diluted in boiling benzene. The reaction products were separated by column chromatography. It was found that the 1-cyano-1-methylethyl radical induced the cyclization of 1 to yield the product of a head to tail addition (2) in 55% yield. In addition, the product of a head to head addition (3) was isolated in 4% yield. 35% of 1 reacted in the same way as it has already been observed as suppression of polymerization in the case of p-tolyl methacrylate to give the products 4 and 5. The structures of the products were confirmed by elemental analyses, by …