Search results for "MACRO"
showing 10 items of 3471 documents
Amphiphilic Polyethers of Controlled Chain Architecture
2003
The amphiphilic polymers, polymers which contain in their macromolecules both hydrophilic and hydrophobic units1, are the base for valuable materials due to their diversified interaction with liquids. So they may act as emulsifiers, compatibilizers, “smart” materials (responding to external stimuli)2 and many others. In order to control their properties, the hydrophilic — hydrophobic balance in the macromolecules has to be controlled. This balance depends not only upon the constitution of the chain repeating units, but also upon the art of their distribution in the chains (copolymers of controlled unit sequences), the chain topology, the size of the chains and many others. So a careful engi…
Kinetics and Mechanisms in the Anionic Polymerization of Methacrylic Esters
1987
Under appropriate conditions the anionic polymerization of methacrylates proceeds in an ideal manner leading to polymers with narrow molecular weight distributions. From the kinetics of polymerization and from the microstructure of the polymers the existence of different active species is concluded, the most important one being a peripherally solvated contact ion pair. Depending on polymerization conditions two different modes of monomer addition can occur. Homo- and copolymerization experiments show that the influence of the ester group is mainly given by electronic effects. In non- polar solvents the polymerization of tert.-butyl methacrylate (in contrast to methyl methacrylate) leads to …
Supramolecular Polymers in Aqueous Media
2016
This review discusses one-dimensional supramolecular polymers that form in aqueous media. First, naturally occurring supramolecular polymers are described, in particular, amyloid fibrils, actin filaments, and microtubules. Their structural, thermodynamic, kinetic, and nanomechanical properties are highlighted, as well as their importance for the advancement of biologically inspired supramolecular polymer materials. Second, five classes of synthetic supramolecular polymers are described: systems based on (1) hydrogen-bond motifs, (2) large π-conjugated surfaces, (3) host-guest interactions, (4) peptides, and (5) DNA. We focus on recent studies that address key challenges in the field, provid…
Function of biomolecules as a probe for studying the effects of organic co-solvents on their conformations
1980
Abstract Conformation changes associated with the function of biomolecules can bring out variations of the extent and specific structure of their hydrophobic areas exposed to solvent, with consequent local rearrangements of the solvent. This is one of the channels through which the solvent exerts its role in the functional equilibria of biomolecules. The function of biological macromolecules in perturbed aqueous solvent can therefore be a suitable probe for studying the response of macromolecule-solvent systems to perturbations caused by organic co-solvents. We shall discussed the effects that the presence of some monohydric alcohols and some amides in the aqueous medium have on some thermo…
Copolymers sensitive to temperature and pH in water and in water+oil mixtures: A DSC, ITC and volumetric study
2011
Block copolymer micelles are receiving an increasing interest because of the variety of structures and the possibilities to tune them by changing external and internal parameters achieving the desired properties for a specific purpose. We have investigated the acid/base behavior, self-assembling and solubilization ability towards polar oils of star-like copolymers named Tetronics. They are composed of branched four-arms each one consisting of two blocks made of EO and PO units linked to the diethylenediamine group, which confers pH response ability. The copolymers T1107 and T90R4 were studied with a sequential and reverse architecture. The thermodynamics of the acid/base equilibrium was stu…
Introduction to the microsymposium and on the modulation of thermodynamic parameters relative to biomolecule-solvent interactions
1980
Abstract As a result of introducing a macromolecule in a solvent, changes in the structures of both solute and solvent are generally found. In this specific meaning we refer here to ‘relaxation phenomena’. The discussion will either concern or keep in a view the case of biomolecules and to which extent these changes are involved in their thermodynamic stability or functional structure: Dr. Ben-Naim will discuss hydrophobic interactions and structural changes in the solvent; Dr. Wen will focus on thermodynamic properties of aqueous solutions on hydrophobic solutes; Dr. Cordone, Dr. Fornili and myself shall discuss results of experiments concerning solutes on several types(proteins, polynucle…
Reversible swelling of polyanion/polycation multilayer films in solutions of different ionic strength
1996
Immersion of consecutively adsorbed polyanion/polycation multilayer films in solutions of different ionic strength causes reversible thickness changes. Swelling of the films up to 18% was observed after soaking the films in aqueous solutions of NaCl at concentrations up to 1.0 mol/l. X-ray reflectivity clearly shows that the thickness changes are reversible within experimental error and that the films seem to get smoother after several cycles of immersion in salt solutions and in pure water. The extent of swelling depends on the internal film structure, namely on the number of polyanion/polycation interfaces in a film of a given thickness. Interestingly, the swelling levels off at salt conc…
Viscosimetric investigation of the interaction between sodium dodecylsulfate micelles and a polymer drug carrier
1993
Abstract The viscosities of aqueous sodium dodecyl sulfate solutions with and without α,β-poly( N -hydroxyethyl)- dl -aspartamide (PHEA), at 15, 25 and 35°C are reported. The viscosities of SDS and of PHEA aqueous solutions are discussed in terms of the parameter D [D = ( η η 0 − 1)/φ] describing the non-ideal behavior of SDS micelles and of PHEA macromolecules. The viscosities of SDS plus PHEA aqueous solutions, discussed in terms of the parameter F [ F = η rel ( PHEA ) + η rel ( SDS ) − η rel ( SDS + PHEA )] M , demonstrate the occurrence of interactions between SDS micelles and the PHEA macromolecule. Both D and F are scarcely influenced by temperature variation.
Polymerization of Mono- and Bi-functional Diacetylene Derivatives in Monolayers at the Gas-Water Interface
1979
The spreading and polymerization behaviour of long chain acids and phospholipid analogues containing diacetylene groups is described. Especially the polymerization in monolayers is followed spectroscopically with a new device used in connection with a commercial UV spectrometer. The polymerization is topochemically controlled. Sonification of the phospholipid analogues in water results in the formation of liposomes with multilayered membranes. Polymerization of the liposomes in water forms aqueous solutions of polymer vesicles.
Conformational analysis of α,β-poly(N-hydroxyethyl)-dl-aspartamide (PHEA) and α,β-polyasparthydrazide (PAHy) polymers in aqueous solution
1998
Abstract α,β-Poly(N-hydroxyethyl)- dl -aspartamide (PHEA) and α,β-polyasparthydrazide (PAHy) are synthetic polymers previously studied for biomedical applications. We report here the results of a small-angle X-ray scattering analysis carried out on these two macromolecules in aqueous solution. The data obtained indicate that the two polymers assume remarkably different conformations in aqueous solution, although the backbone is supposed to be the same for the two chains. PHEA can be represented by a random coil conformation, whereas PAHy can be described in terms of an elliptical cylinder characterized by an almost planar structural arrangement with the backbone refolded on itself in a fash…