Search results for "Tributi"

Star poly(2-ethyl-2-oxazoline)s-synthesis and thermosensitivity

2011

A series of star-shaped poly(2-ethyl-2-oxazoline)s was prepared by cationic polymerization. The polymerization was initiated by dipentaerythrityl hexakis(4-nitrobenzene sulfonate) and a tosylated hyperbranched polymer of glycidol. The polymerization proceeded in a controlled manner. The star structure of the products was determined by nuclear magnetic resonance. The molar mass distributions that were measured by gel permeation chromatography with multiangle laser light scattering were narrow, and the experimental values of the molar masses were close to those predicted. The very compact structure of the polymers obtained (compared with the linear counterparts) confirmed the star formation. …

Molecular characterization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide derivatives as potential self-assembling copolymers forming polymeric micelles

2003

A family of graft copolymers derivatives obtained from α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) have been studied as potential self-assembling macromolecules forming stable polymeric micelles at low critical micellar concentration. These polymers are obtained grafting on PHEA poly(ethylene glycol) (PEG) (Mw 5000 g/mol) (PHEA–PEG), hexadecylamine (PHEA–C16) or both moieties (PHEA–PEG–C16). The PHEA derivatives were characterised by a multi-angle light scattering (MALS) photometer on line to a size exclusion chromatography system in obtaining the molar mass distribution of the polymers. In addition, to investigate the capacity to form micellar aggregates in aqueous medium the MALS pho…

Fluorescence Correlation Spectroscopy in Dilute Polymer Solutions: Effects of Molar Mass Dispersity and the Type of Fluorescent Labeling

2015

Fluorescence correlation spectroscopy (FCS) has become an important tool in polymer science. Among various other applications the method is often applied to measure the hydrodynamic radius and the degree of fluorescent labeling of polymers in dilute solutions. Here we show that such measurements can be strongly affected by the molar mass dispersity of the studied polymers and the way of labeling. As model systems we used polystyrene and poly(methyl methacrylate) synthesized by atom transfer radical polymerization or free-radical polymerization. Thus, the polymers were either end-labeled bearing one fluorophore per chain or side-labeled with a number of fluorophores per chain proportional to…

1996

An iterative, approximative procedure is presented, to calibrate the determination of molar masses of polymers with gel-permeation chromatography, additionally using viscometry, and transformations, according to Benoit's concept of universal calibration, even if only polymers with broad molar mass distribution are available. The calculated (intermediate) values of the average molar masses from each step of iteration converge to final values. With at least two fractions of the polymers to be analyzed, and with measured intrinsic viscosities of the fractions, a calibration curve of gel-permeation chromatography and Mark-Houwink's constants can be determined. Assumptions for the use of the cal…

Polymer-polymer interaction, in the presence of a solvent as measured by viscometry

2001

Dilute solution viscometry experiments have been carried out in five ternary polymer systems solvent(1)/polymer(2)/polymer(3). Values of the specific viscosity of polymer (3) in a ‘binary solvent’ formed by polymer(2) + solvent(1) have been used to determine the compatibility of the polymer blends. Krigbaum and Wall formalism has been used to predict compatibility which relies on an interaction parameter that depends on the concentration, weight fraction and molar mass of each polymer. To reduce the dependences and to clarify the criterion of compatibility, a parameter independent of polymer (3) composition and molar mass has been deduced. This parameter shows the same behaviour with polyme…

Films of Halloysite Nanotubes Sandwiched between Two Layers of Biopolymer: From the Morphology to the Dielectric, Thermal, Transparency, and Wettabil…

2011

This study focused on the preparation and characterization of films based on biopolymers (hydroxypropylcellulose and low methoxyl pectin) and halloysite nanotubes (HNTs). The morphology is strongly dependent on the polymer nature. In particular, we observed a sandwich-like structure composed of two hydroxypropylcellulose layers incorporating the HNTs and a homogeneous distribution of the nanotubes into the low methoxyl pectin matrix. The different mesoscopic properties were invoked to explain the dielectric, thermal, and wettability properties of the corresponding films. Nanocomposites obtained by combining materials from renewable resources and HNTs is a challenging task in view of designi…

The Efficiency of Polymer Fractionation at Lower Critical Solution Temperatures

1978

The efficiency of a single fractionation step (i.e. of the partition of a given polymer sample between the coexisting phases which form when its solution demixes) is governed by the variation of the mass ratio of the individual P-mers with chain length. These dependences have been measured for the system dimethoxymethane/diethylether/ polystyrene which exhibits lower critical solution temperatures by means of the Baker-Williams method and by means of g.p.c. Their comparison with the results of previous investigation on systems showing upper critical solution temperatures reveals no thermodynamic differences in the aptitude of upper and lower critical solution temperatures for fractionation …

Polydispersity Effects on Interpenetration in Compressed Brushes

2019

We study the effect of polydispersity on the compression and interpenetration properties of two opposing polymer brushes by numerical self-consistent field approach and by analytical theory. Polydispersity is represented by an experimentally relevant Schulz–Zimm chain-length distribution. We focus on three different polydispersities representing sharp, moderate, and extremely wide chain length distributions and derive approximate analytical expressions for the pressure–separation curves, Π(D). We study the brush interpenetration and quantify it in terms of the overlap integral, Γ, representing the number of interbrush contacts, and interpenetration length, δ. For the case of moderate densit…

Basic kinetic model for the reaction yielding linear polyurethanes. II

1995

On the basis of the gradual polyaddition kinetic model developed earlier, an attempt was made to provide a generalized mathematical model for the set of reactions yielding linear polyurethanes. The model is a system of first-order ordinary differential equations. It was assumed at the present stage of this model that the rate constants for the reaction considered do not change. The model developed was then solved numerically. Average molecular weight of the polymer and composition data for oligomers were calculated for a constant volume batch reactor and varied process parameters. The GPC method, which was tested for model urethane oligomers, was employed to verify the model developed. The …

Molecular Weight Distribution of Hyperbranched Polymers Generated by Self-Condensing Vinyl Polymerization in Presence of a Multifunctional Initiator

1999

The molecular weight distribution (MWD) is derived for polymers generated by self-condensing vinyl polymerization (SCVP) of a monomer having a vinyl and an initiator group (“inimer”) in the presence of a multifunctional initiator. If the monomer is added slowly to the initiator solution (semi-batch process), this leads to hyperbranched polymers with a multifunctional core. If monomer and initiator are mixed simultaneously (batch process), even at vinyl group conversions as high as 99%, the total MWD consists of polymers which have grown via reactions between inimer molecules (i.e., the normal SCVP process) and those which have reacted with the initiator. Consequently, the weight distributio…