Search results for "Copolymer"
showing 10 items of 1003 documents
Peculiar mechanism of solubilization of a sparingly water soluble drug into polymeric micelles. Kinetic and equilibrium studies.
2012
Complementary kinetic and equilibrium studies on the solubilization process of the sparingly water soluble tamoxifen (TAM) drug in polymeric aqueous solutions have been performed by using the spectrophotometric method. In particular, the amphiphilic copolymers obtained by derivatization of polymeric chain of poly(N-2-hydroxyethyl)-dl-aspartamide, PHEA, with poly(ethylene glycol)s, PEG (2000 or 5000 Da), and/or hexadecylamine chain, C16, namely PHEA-PEG2000-C16, PHEA-PEG5000-C16, PHEA-C16, have been employed. Preliminary to the kinetic and equilibrium data quantitative treatment, the molar absorption coefficient of TAM in polymeric micelle aqueous solution has been determined. By these studi…
Thermodynamics of Surfactant, Block Copolymer and Their Mixtures in Water: The Role of the Isothermal Calorimetry
2009
The thermodynamics of conventional surfactants, block copolymers and their mixtures in water was described to the light of the enthalpy function. The two methodologies, i.e. the van't Hoff approach and the isothermal calorimetry, used to determine the enthalpy of micellization of pure surfactants and block copolymers were described. The van't Hoff method was critically discussed. The aqueous copolymer+surfactant mixtures were analyzed by means of the isothermal titration calorimetry and the enthalpy of transfer of the copolymer from the water to the aqueous surfactant solutions. Thermodynamic models were presented to show the procedure to extract straightforward molecular insights from the …
Recycling of compatibilized and uncompatibilized nylon/polypropylene blends
2001
The recycling of compatibilized and uncompatibilized nylon6/polypropylene blends has been carried out by repetitive extrusions. The change of the properties of the blends is a function not only of the number of reprocessing steps but also of the type of compatibilizer. The worsening of the mechanical properties is small and, indeed, some improvement can be observed after one or two extrusion steps for some blends. It is hypothesised that the decrease of the molecular weight, the typical effect occurring during this thermomechanical treatment, is counterbalanced and overcome by the possible formation of new copolymers that act as bridges between the two phases. This behaviour is displayed by…
Synthesis of PP-LCP graft copolymers and their compatibilizing activity for PP/LCP blends
1998
The aim of this work was the synthesis of new graft copolymers consisting of polypropylene (PP) backbones and liquid crystalline polymer (LCP) branches, to be used as compatibilizing agents for PP/LCP blends. The PP-g-LCP copolymers have been prepared by polycondensation of the monomers of a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2), that is, sebacic acid (S), 4,4′-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the mole ratio of 1 : 1 : 2, carried out in the presence of appropriate amounts of a commercial acrylic-acid-functionalized polypropylene (PPAA). The polycondensation products, referred to as COPP50 and COPP70, having a calculated PPAA concentration of 50 and…
Reduction of the interfacial tension between ‘immiscible’ polymers: to which phase one should add a compatibilizer
2001
Abstract The reduction of interfacial tension σ between polyethylene oxide (PEO) and polypropylene oxide (PPO) by either a triblock copolymer EO–PO–EO or a diblock copolymer styrene–EO was studied by means of the pendant drop method from 70 to 120°C. Time independent data correspond to stationary states and do not represent equilibrium information. The addition of the compatibilizer to the PPO phase is approximately twice as efficient as the addition to the PEO phase for both block copolymers. Knowing the concentration dependence of σ for one of the coexisting phases it is possible to forecast the effects resulting from the addition of the other phase by means of model considerations based …
Effect of the Orientation on the Properties of Compatibilized Polypropylene/Liquid Crystal Polymer Blends
1999
Abstract Blends of polypropylene and a semirigid liquid crystal polymer have been compatibilized with an acrylic acid modified polypropylene and with an ad-hoc synthesized graft copolymer made from polypropylene and from the monomers of the liquid crystal polymer. The two compatibilizers improve the adhesion and the mechanical properties of the two incompatible phases. The two compatibilizers give about the same results. The effect of the compatibilization improve also the orientation of the liquid crystalline polymer particles and the mechanical properties.
Structure, morphology and crystallization of a random ethylene-propylene copolymer
2003
The structure, morphology, and crystallization behavior of a random ethylene–propylene copolymer, containing 2 wt % ethylene sequences, are analyzed and compared with those of a plain polypropylene sample by means of optical and scanning microscopy, wide-angle X-ray scattering, and calorimetry. For the copolymer, different polymorphs (α, γ and smectic modifications) and morphologies can be obtained through changes in the crystallization and annealing conditions. The analysis of the structural results suggests that the γ phase of isotactic polypropylene can be generated for high molecular mass samples with drastic decreases in the undercooling. The spherulite growth rate (G) data, in conjunc…
Use of PP-g-OXA in the Compatibilization of PP/LCP Blends
1999
Abstract Adding small amounts of liquid crystalline polymers (LCP) to flexible thermoplastic matrices (FTP) allows to enhance the mechanical and thermomechanical properties. Therefore it is possible to obtain materials with new properties only by simple mixing. A strong shortcoming is the incompatibility between LCP and FTP that leads to materials with very poor properties unusable for commercial pourposes. The presence of a compatibilizer is therefore required. Oxazoline functionality is known to be highly reactive toward many other functional groups and then oxazoline functionalized polymers can be efficiently used as compatibilizer precursors. In this work the compatibilizazion of polypr…
On the mechanism of compatibilization of polyolefin/liquid crystalline polymer blends with graft copolymers
2000
The compatibilization mechanism of some compatibilizers for blends of polyolefins with a liquid crystalline polymer (LCP) was studied. Polyethylene (PE) and polypropylene (PP) were blended with a semirigid LCP (SBH) in a batch mixer, either with and without compatibilizers. The latter were two commercially available samples of functionalized polyolefins, that is, a PE-g-MA (HDM) and a PP-g-AA (Polybond 1001) copolymer and some purposely synthesized PE-g-LCP and PP-g-LCP copolymers. Microtomed films of the binary and the ternary blends were annealed at 240°C on the hot stage of a polarizing microscope and the changes undergone by their morphology were recorded as a function of time. The resu…
Synthesis and characterization of redox-sensitive polyurethanes based on L-glutathione oxidized and poly(ether ester) triblock copolymers
2021
Abstract Segmented polyurethanes, based on PCL-PEG-PCL copolymers, 1,4-diisocyanatobutane and l -glutathione oxidized, used as chain extender, were synthetized. Three different reactions conditions were investigated using three different copolymers having ɛ-CL/polyethylene glycol molar ratios equal to 12, 24 and 36 and three different reaction conditions. As investigated by size exclusion chromatography analyses and quantification of l -glutathione, the polymerization and the extension phase's efficiency depended on the ɛ-CL/PEG ratio and the extension phase's operating temperature. Three selected polyurethanes were characterized by spectroscopic, differential scanning calorimetry (DSC) and…