Search results for "Oxide"
showing 10 items of 6424 documents
Double-Hydrophilic Linear-Hyperbranched Block Copolymers Based on Poly(ethylene oxide) and Poly(glycerol)
2008
A convenient 4-step (2-pot) approach for the synthesis of biocompatible, double hydrophilic linear-hyperbranched block copolymers based on poly(ethylene oxide) (PEO) and poly(glycerol) (PG) is described. The polymers consisting exclusively of an aliphatic polyether structure were prepared from linear PEO-b-(l-PG) precursor block copolymers, obtained via anionic polymerization of ethylene oxide and subsequently ethoxyethyl glycidyl ether (EEGE). In order to generate initiating functionalities for glycidol, the protected hydroxyl groups of the P(EEGE) block were recovered by hydrolysis with hydrochloric acid. Partial deprotonation of the linear poly(glycerol) block with cesium hydroxide permi…
Water-Soluble Poly(vinylferrocene)-b-Poly(ethylene oxide) Diblock and Miktoarm Star Polymers
2012
We describe the synthesis of water-soluble diblock and miktoarm star polymers consisting of poly(vinylferrocene) (PVFc) and poly(ethylene oxide) (PEO) blocks. First, end-functionalized poly(vinylferrocene) was generated by end-capping the living carbanionic PVFc chains with benzyl glycidyl ether (BGE) or ethoxy ethyl glycidyl ether (EEGE). Acidic hydrolysis of the EEGE-terminated PVFc partially oxidized the PVFc backbone. However, the dihydroxyl end-functional PVFc was obtained in quantitative yields by hydrogenolysis of the BGE-terminated PVFc. A series of block copolymers and AB2 miktoarm star copolymers was obtained in a second polymerization step, utilizing the respective end-functional…
Topology-Dependent Swichability of Peptide Secondary Structures in Bioconjugates with Complex Architectures
2013
Peptide sequences, which exhibit a reversible pH-responsive coil to α-helix secondary structure transition, are conjugated to polymer precursors to yield linear AB and graft ABA peptide-poly(ethylene oxide) conjugates. While the PEO B-block is comparable, the conjugates differ in topologies of the peptide bearing A-blocks. The influences of topology on the structure transitions in the peptide segments are investigated, comparing linear AB-bioconjugates with graft ABA-bioconjugates having multiple peptide segments combined in star or pom-pom topologies.
“Clickable PEG” via anionic copolymerization of ethylene oxide and glycidyl propargyl ether
2017
A straight forward synthesis of poly(ethylene glycol) (PEG) with multiple alkyne groups distributed along the polymer chain is introduced. Direct access to clickable PEG is achieved by the monomer-activated anionic ring-opening copolymerization (AROP) of ethylene oxide (EO) with glycidyl propargyl ether (GPgE). Notably for successful polymerization no protection of the alkyne unit is required owing to the mild reaction conditions. Defined PEG-co-PGPgE and PGPgE (co)polymers with PDIs of 1.18–1.60 and molecular weights of Mn = 3000–9500 g mol−1 were prepared. In situ1H NMR kinetic studies revealed remarkably disparate reactivity ratios of rEO = 14.8 and rGPgE = 0.076, representing a pronounc…
PEO/CHCl3. Crystallinity of the Polymer and Vapor Pressure of the Solvent. Equilibrium and Nonequilibrium Phenomena
2003
Vapor pressures were measured for the system CHCl3/PEO 1000 (PEO stands for poly(ethylene oxide) and 1000 for Mw in kg/mol) at 25 °C as a function of the weight fraction w of the polymer by means of a combination of headspace sampling and gas chromatography. The establishment of thermodynamic equilibria was assisted by employing thin polymer films. The degrees of crystallinity α of the pure PEO and of the solid polymer contained in the mixtures were determined via DSC. An analogous degree of polymer insolubility β was calculated from the vapor pressures measured in this composition range. The experiments demonstrate that both quantities and their concentration dependence are markedly affect…
Chemoenzymatic synthesis of a poly(hydroquinone)
1999
Chemoenzymatic synthesis of a poly(hydroquinone) was achieved by enzymatic oxidative polymerization of 4-hydroxyphenyl benzoate, followed by alkaline hydrolysis of the resulting polymer. The polymerization of 4-hydroxyphenyl benzoate was performed using a peroxidase and hydrogen peroxide as catalyst and oxidizing agent, respectively, in an aqueous organic solvent. Soybean peroxidase afforded the polymer in good yields. IR analysis of the polymer showed the formation of the polymer consisting of a mixture of phenylene and oxyphenylene units. By alkaline hydrolysis of the resulting polymer, benzoate moiety was completely removed to give poly(hydroquinone).
Rapid Synthesis and MALDI-ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers
2009
Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well-defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5-8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30000g · …
Hyperbranched Polyglycerols with Elevated Molecular Weights: A Facile Two-Step Synthesis Protocol Based on Polyglycerol Macroinitiators
2009
Hyperbranched polyglycerol (PG) is established as one of the few hyperbranched polymers that offer the possibility to control molecular weight up to Mn = 6000 g/mol. This work introduces a facile 2-step strategy that relies on the use of a low molecular weight PG (Mn = 500 and 1000 g/mol) as a macroinitiator for the slow addition of glycidol, permitting to overcome previous limitations concerning molecular weights and molecular weight control. A systematic investigation of the effect of the degree of deprotonation on the control of the polymerization reaction has been carried out. A series of hyperbranched PGs with molecular weights up to Mn = 24000 g/mol has been obtained under fully contr…
Functional PEG-based polymers with reactive groups via anionic ROP of tailor-made epoxides
2012
In this review article functional epoxide monomers that are suitable for controlled ring-opening polymerization (ROP) are discussed. Functional epoxides possess reactive groups, which either are directly accessible or carry suitable protective groups that can be removed in a facile one-step reaction after polymerization. The methods used to obtain linear, functional aliphatic polyethers rely on living polymerization techniques for the synthesis of well-defined structures. Materials properties, such as thermo-responsive behavior in combination with different functional groups that can be addressed selectively, render these novel materials interesting for a variety of applications.
A road less traveled to functional polymers: epoxide termination in living carbanionic polymer synthesis.
2010
Functional polymers possess tremendous potential both in academia and in industry. In particular, oxiranes offer manifold possibilities for the introduction of single hydroxyl or multiple orthogonal functionalities in carbanionic polymerization. Here, we present a brief overview of the fascinating possibilities arising from the employment of common as well as individually designed epoxide derivatives for the synthesis of end-functional polymers. Continuous flow techniques can be utilized for the rapid generation and screening of precisely defined hydroxyl-modified polymers. The utilization of functionalized polymers as precursors for the formation of complex macromolecular architectures (e.…