Search results for "polymers"

Specific features of the interfacial tension in the case of phase separated solutions of random copolymers

2000

Abstract Phase diagrams (cloud point curves, critical points, tie lines for constant critical composition) and interfacial tensions as a function of temperature were measured for solutions of two random copolymers: poly(dimethylsiloxane- ran -methylphenylsiloxane) [I] and poly(styrene- ran -acrylonitrile) [II]. Acetone and anisole served as solvents for I and toluene for II; all solutions exhibit UCSTs between 300 and 310 K. The phase separation behavior can be well modeled if one accounts for the molecular and chemical non-uniformities of the random copolymers used in this study. The interfacial tensions σ differ most markedly from that of comparable homopolymer solutions in their correlat…

Synthesis and characterization of optically active 2,4-disubstituted-2-oxazolines and their polymerization

1994

Four different optically active 2,4-disubstituted-2-oxazolines were synthesized and characterized. Cationic polymerization of these oxazolines were studied. Three of the oxazolines could be polymerized using methyl trifluoromethanesulfonate as initiator. S-(–)-2-Phenyl-4-isopropyl-2-oxazoline could not be polymerized under the conditions used.

From Polymers to Functional Biomaterials.

2017

Polypept(o)ides: Hybrid Systems Based on Polypeptides and Polypeptoids.

2015

Polypept(o)ides combine the multifunctionality and intrinsic stimuli-responsiveness of synthetic polypeptides with the "stealth"-like properties of the polypeptoid polysarcosine (poly(N-methyl glycine)). This class of block copolymers can be synthesized by sequential ring opening polymerization of α-amino acid N-carboxy-anhydrides (NCAs) and correspondingly of the N-substituted glycine N-carboxyanhydride (NNCA). The resulting block copolymers are characterized by Poisson-like molecular weight distributions, full end group integrity, and dispersities below 1.2. While polysarcosine may be able to tackle the currently arising issues regarding the gold standard PEG, including storage diseases i…

Composition, distribution, and sources of polycyclic aromatic hydrocarbons in sediments of the gulf of Milazzo (Mediterranean Sea, Italy)

2014

This article describes the characterization of Polycyclic Aromatic Hydrocarbons (PAHs) in sediments of Milazzo Gulf (Italy) located in front of an oil refinery and a power plant. The investigated area is characterized by urban and industrial activities. The sixteen PAHs identified by the USEPA, as requiring priority monitoring, and other non USEPA listed PAHs, namely perylene and some methyl derivatives, were investigated The total PAHs concentrations, expressed as ∑ 19 PAH ranges from 5.6–7402 μg/Kg d.w., with a mean value of 492 μg/Kg d.w. The concentrations of PAHs found in 64 out of 67 samples were lower than the effect range low (ERL = 2460 μg/Kg) concentration, while the remaining sam…

On the factors governing the pressure dependence of the viscosity of moderately concentrated polymer solutions

1982

Viscosity measurements were carried out as a function of pressure and temperature with solutions of polystyrene in eight (endothermal) θ-solvents at the respective critical composition by means of a Searle-type apparatus. A rolling-ball viscometer was used for the investigation of the pure solvents. In all cases the viscosity coefficient increases in a more or less exponential manner when the pressure is raised. For θ-conditions, the volumes of activation of the solutions exceed that of the pure solvent by typically 10–15%. The exact amount of this extra efffect stemming from the presence of the polymer and its variation with temperature can be qualitatively correlated with the heats of mix…

Rheology of Sodium Hyaluronate Saline Solutions for Ophthalmic Use

2007

The aim of this work was to investigate the rheological properties of different saline solutions of sodium hyaluronate (NaHA) with special interest for medical applications. The experimental results were compared with literature data for commercial ophthalmic viscosurgical devices (OVDs) used in cataract surgery. We offer some tools to tailor the rheological behavior of OVDs for different purposes. We have investigated to which extent surgical requirements can be fulfilled by adjusting either the molecular weight of NaHA or its concentration, parameters that are in some respects equivalent but not in others. Furthermore, we demonstrate that moduli and complex viscosities of NaHA saline solu…

Morphology and thermal behavior of dicyanate ester-polyetherimide semi-IPNS cured at different conditions

2000

A high-temperature thermosetting bisphenol-A dicyanate, BADCy was modified with polyetherimide, PEI, at various compositions. Phase separation and rheokinetics through curing were studied by optical microscopy, dynamic and isothermal differential scanning calorimetry, and rheological measurements. The PEI phase separated at the early stages of curing, well before gelation, and did not affect the polycyclotrimerization kinetics. The phase structure and thermal properties of the final network were investigated as a function of the PEI content and cure temperature. For this purpose, dynamic mechanical analysis, scanning electron microscopy studies, and thermogravimetrical analysis were carried…

Influence of water, temperature and sucrose on dynamics in glassy starch-based products studied by low field 1H NMR

2009

Abstract In this study, the influence of both water content and temperature on the mobility of glassy starch-based matrices (starch alone or mixed with sucrose at the ratio 0% to 20% db) were studied using time domain 1 H NMR. The 2nd moment M 2 , and transversal relaxation time T 2 ∗ were used to study the molecular mobility of the rigid and mobile fraction of the NMR signal, respectively. The molecular mobility of the protons constituting the samples increased with water content (up to 13% wb) at all temperatures. For a given water content, both rigid and mobile protons exhibited a lower mobility in the presence of sucrose. When mobility characteristic parameters, M 2 second moment values…

Stereoselective Metabolic Activation of Dibenzo[a,l]Pyrene in the Human Mammary Carcinoma Cell Line MCF-7 Results in Formation of (-)-antiand (+)-syn…

1996

Abstract Dibenzo[a,l]pyrene (DB[a,l]P) is an important polycyclic aromatic hydrocarbon because of possible human exposure and its exceptionally high carcinogenicity in rodents. We examined the metabolism of DB[a,l]P and the formation of DB[a,l]P-DNA adducts in the human mammary carcinoma cell line (MCF-7). Analysis of the DNA adducts by 33P-postlabeling, immobilized boronate chromatography, HPLC and TLC demonstrated that DB[a,l]P is stereoselectively metabolized to specific optical isomers of DB[a,l]P-11,12-diol-13,14-epoxide (DB[a,l]PDE). The major anti-DB[a,l]PDE adduct formed in DB[a,l]P-treated MCF-7 cells resulted from reaction of (-)-anti-DB[a,l]PDE with DNA whereas the two major syn-…