Search results for "Como"
showing 10 items of 1565 documents
Solubilization by polysoaps
1994
The aqueous solubilization power of several series of micellar homopolymers and copolymers (''polysoaps'') is investigated. Using five insoluble or poorly water-soluble dyes, comparisons of the capacities are made with respect to the influence of structural variables such as the polymer backbone, the polymer geometry, the comonomer content, and the charge of the hydrophilic group. Some guidelines for polysoap structures suited for efficient solubilization are established. Noteworthy is that the solubilization capacities of the polysoaps are neither linked to the ability to reduce the surface tension of water, nor to the polarity of the solubilization sites deduced from spectroscopic probes.
α,ω-Functionalized poly-N-isopropylacrylamides: controlling the surface activity for vesicle adsorption by temperature
2003
The synthesis of alpha,omega-end-functionalized copolymers of N-isopropylacrylamide and N-(3-dimethylaminopropyl)acrylamide was performed. Monomer ratios of 100:0, 96:4, and 81:19 were investigated. The lower critical solution temperature (LCST) of these polymers was determined by cloud-point measurements and by microcalorimetric measurements. The LCST increased from 32 over 37 to 47 degrees C as the hydrophobicity increased with increasing amount of comonomer N-(3-dimethylaminopropyl)acrylamide. The polymers could successfully be adsorbed onto gold surfaces. Finally, vesicle adsorption onto these self-assembled polymer films on flat gold surfaces was investigated as the vesicle solution te…
One-Step Block Copolymer Synthesis versus Sequential Monomer Addition: A Fundamental Study Reveals That One Methyl Group Makes a Difference
2018
Block copolymers of polyisoprene and polystyrene are key materials for polymer nanostructures as well as for several commercially established thermoplastic elastomers. In a combined experimental and kinetic Monte Carlo simulation study, the direct (i.e., statistical) living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in nonpolar media was investigated on a fundamental level. In situ 1H NMR spectroscopy enabled to directly monitor gradient formation during the copolymerization and to determine the nature of the gradient. In addition, a precise comparison with the established copolymerization of isoprene and styrene (I/S) was possible. Statistical copolymer…
Impact of Amino-Functionalization on the Response of Poly(ethylene glycol) (PEG) to External Stimuli
2022
It is shown that amino-functionalization of poly(ethylene glycol) (PEG) with the comonomer N,N-diethyl glycidyl amine (DEGA) triggers the emergence of extraordinary stimuli responsiveness and phase behavior of PEG. In dependence of the solution pH, tapered PEG-co-PDEGA exhibits a highly cooperative two-step inverse phase transition with respect to temperature. The polymer forms dispersed metastable nanoglobules in the medically relevant temperature range around human body temperature. Independently, cloud points can be adjusted between 40 and 90 °C via the pH of the solution. Changing the polymer architecture to a block structure, in pronounced contrast, the polymer exhibits a gradual growt…
Polymeric amphiphiles with hydrophilic main chain spacers: Studies in monolayers and Langmuir-Blodgett multilayers
1988
A methacrylic lipid was polymerized to form an amphiphilic homopolymer and random copolymers with various levels of acrylic acid comonomers. The behavior of these polymeric lipids was investigated in monolayers at the air-water interface and in Langmuir-Blodgett multilayers on polymer foil supports. The acrylic acid acts as a hydrophilic spacer along the polymer backbone, and improves the ability of the polymer to self-organize into highly ordered monolayers and ultimately LB multilayers. It is shown that the quality and stability of the multilayers increase substantially with the increase in comonomer content.
Functional Group Distribution and Gradient Structure Resulting from the Living Anionic Copolymerization of Styrene and para-But-3-enyl Styrene
2014
The functional group distribution along the polymer backbone resulting from the living anionic copolymerization of styrene (S) and para-but-3-enyl styrene (pBuS) was investigated in cyclohexane at room temperature. A variety of copolymers with different comonomer contents x(S) = 0–0.84 have been synthesized with molecular weight dispersities Mw/Mn ≤1.12. All polymers have been characterized in detail by 1H NMR spectroscopy, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). A detailed understanding of the monomer sequence distribution during the copolymerization was achieved by real-time 1H NMR spectroscopy. This technique permits us to determine the changing …
Hyperbranched Poly(propylene oxide): A Multifunctional Backbone-Thermoresponsive Polyether Polyol Copolymer
2012
Backbone-thermoresponsive hyperbranched poly(propylene oxide)-based polyether polyols have been synthesized by anionic ring-opening copolymerization of glycidol and propylene oxide. The number of functional hydroxyl end groups and the lower critical solution temperature (LCST) can be readily adjusted by varying the comonomer ratio. Molecular weights in the range of 1200-2000 g/mol were achieved. Hyperbranched polyether polyols with LCST values between 24 and 83 °C can be obtained in a convenient one-step reaction.
Ferrocene-Containing Multifunctional Polyethers: Monomer Sequence Monitoring via Quantitative 13C NMR Spectroscopy in Bulk
2014
Ferrocenyl glycidyl ether (fcGE) and allyl glycidyl ether (AGE) are copolymerized via living anionic ring-opening polymerization to generate polyfunctional copolymers with molecular weights up to 40 300 g/mol and low molecular weight dispersities (Mw/Mn < 1.18). Copolymerizations were carried out in bulk at 100 °C and unexpectedly found to proceed without any isomerization of the allyl double bonds. The copolymerization behavior of fcGE and AGE was monitored by in situ quantitative 13C NMR kinetic measurements in bulk, evidencing the formation of random copolymers under these conditions, showing no gradient of comonomer incorporation. The redox-active behavior of the copolymers and homopoly…
Poly(carbonate) copolymers with a tailored number of hydroxyl groups from glycidyl ethers and CO2
2014
Functional poly(carbonate)s with multiple hydroxyl functionalities have been prepared by copolymerization of carbon dioxide (CO2) with glycidyl methyl ether (GME) and benzyl glycidyl ether (BGE) in various ratios, using a diethylzinc–pyrogallol catalyst system. Subsequent catalytic hydrogenation was employed for removal of the benzyl protecting groups at the polymer backbone. A series of copolymers with varying comonomer fractions from 0 to 100% was obtained. The copolymers possessed a broad range of molecular weights from 9000 to 30 000 g mol−1 and showed polydispersities Mw/Mn between 2.4 and 3.6. The materials were characterized via1H and 13C NMR, SEC and differential scanning calorimetr…
Crystalline CO2 -Based Aliphatic Polycarbonates with Long Alkyl Chains
2018
Carbon dioxide (CO2 ) is an easily available, renewable carbon source and can be utilized as a comonomer in the catalytic ring-opening polymerization of epoxides to generate aliphatic polycarbonates. Dodecyl glycidyl ether (DDGE) is copolymerized with CO2 and propylene oxide (PO) to obtain aliphatic poly(dodecyl glycidyl ether carbonate) and poly(propylene carbonate-co-dodecyl glycidyl ether carbonate) copolymers, respectively. The polymerization proceeds at 30 °C and high CO2 pressure utilizing the established binary catalytic system (R,R)-Co(salen)Cl/[PPN]Cl. The copolymers with varying DDGE:PO ratios are characterized via NMR, FT-IR spectroscopy, and SEC, exhibiting high molecular weight…