Search results for "copolymer"
showing 10 items of 1003 documents
Surface reconstruction of the lamellar morphology in a symmetric poly(styrene-block-butadiene-block-methyl methacrylate) triblock copolymer: A tappin…
1996
The surface morphology of a symmetric poly(styrene-block-butadiene-block-methyl methacrylate) triblock copolymer (PS-b-PB-b-PMMA) with 6 wt % PB has been investigated by tapping mode scanning force microscopy (SFM). The results are compared to the bulk morphology as determined by transmission electron microscopy (TEM). In solvent-cast films PS/PMMA lamellae are formed, which are oriented nearly perpendicular to the free surface. Like in the bulk, also at the free film surface polybutadiene spheres are located at the lamellar PS/PMMA interface. However, contrary to the bulk, the surface morphology includes a large number of defects such as curved lamellar and disclinations, and the lamellar …
The Unique Versatility of the Double Metal Cyanide (DMC) Catalyst: Introducing Siloxane Segments to Polypropylene Oxide by Ring-Opening Copolymerizat…
2020
The combination of hydrophobic polydimethylsiloxane (PDMS) blocks with hydrophilic polyether segments plays a key role for silicone surfactants. Capitalizing on the double metal cyanide (DMC) catalyst, the direct (i.e., statistical) copolymerization of cyclic siloxanes and epoxides is shown to be feasible. The solvent-free one-pot copolymerization of hexamethylcyclotrisiloxane and propylene oxide results in the formation of gradient propylene oxide (PPO)-PDMS copolymers. Copolymers with up to 46% siloxane content with low dispersities (Ð < 1.2) are obtained in the molecular weight range of 2100-2900 g mol-1 . The polymerization kinetics are investigated by pressure monitoring and in situ 1 …
HPMA Based Amphiphilic Copolymers Mediate Central Nervous Effects of Domperidone
2011
In this study we give evidence that domperidone encapsulated into amphiphilic p(HPMA)-co-p(laurylmethacrylate) (LMA) copolymer aggregates is able to cross the blood-brain barrier, since it affected motor behaviour in animals, which is a sensitive measure for CNS actions. Carefully designed copolymers based on the clinically approved p(HPMA) were selected and synthesized by a combination of controlled radical polymerization and post-polymerization modification. The hydrodynamic radii (R(h) ) of amphiphilic p(HPMA)-co-p(LMA) alone and loaded with domperidone were determined by fluorescence correlation spectroscopy.
Copolymers of ethylene with monoalkenyl- and monoalkenyl(siloxy)silsesquioxane (POSS) comonomers – Synthesis and characterization
2017
Abstract The hybrid ethylene/POSS copolymers were obtained using the rac -Et(Ind) 2 ZrCl 2 catalyst activated by MAO. A series of monoalkenyl- and monoalkenyl(siloxy)silsesquioxanes derivatives with different structures of reactive alkenyl substituent and types of non-reactive groups attached to the T 8 POSS cage was used as comonomers. The kind and concentration of the POSS comonomer in the reaction feed as well as extended reaction time were found to strongly influence the catalyst efficiency and incorporation of POSS units into polymer chains. The comonomer reactivity was significantly dependent on the length of the alkenyl reactive substituent in the POSS molecule and it was highest for…
Characterization of blends with polyamide 6 and ethylene acrylic acid copolymers at different acrylic acid content
2002
In this work the morphological, calorimetric, rheological and mechanical behaviour and fourier transmission infrared analysis of blends made with polyamide 6 (PA6) and ethylene acrylic acid copolymers (EAA) containing different amount of acrylic acid were investigated. The results observed from the sample characterizations evidenced as acrylic acid cause a compatibilizing effect between polyethylene and polyamide components with modifications of blends morphology and mechanical behaviour. These effects are enhanced with increase of the acrylic acid content in the copolymer and they were attributed generally to hydrogen bond interactions among the acrylic acid group and the functional groups…
Adsorption Active Diblock Copolymers as Universal Agents for Unusual Barrier-Free Transitions in Stimuli-Responsive Brushes
2021
We reconsider a recently proposed design for smart responsive brushes, which is based on a conformational transition in very dilutely embedded block copolymers with a surface active block (Qi et al., Macromolecules 53, 5326, 2020). Under certain conditions, the transition acquires an unusual character: it remains very sharp, but the barrier separating the adsorbed and desorbed states disappears completely. We show that these features are very robust with respect to changing almost all system parameters: the lengths of the inert and active blocks of the minority chain, the brush length, its density, and its polydispersity. The only relevant condition is that the inert block of the minority c…
Recycling of degraded polyethylene: Blends with nylon 6
1992
Abstract Recycled polyethylene can be used for blending with nylon to obtain blends with mechanical properties better than those of blends with virgin polyethylene. Moreover, the mechanical properties of these blends are very close to and, in some cases, better than those of the pure nylon and those of blends made with functionalized polyolefines. The carbonyl groups of the photo-oxidized polyethylene react with amino end-groups of nylon 6, giving rise to graft copolymers which act as interfacial agents between the two incompatible phases. Large degrees of photo-oxidation of the polyethylene and intense mixing improve the properties of the blends.
PET/PEN Blends of Industrial Interest as Barrier Materials. Part I. Many-Scale Molecular Modeling of PET/PEN Blends
2006
Mesoscale molecular simulations, based on parameters obtained through atomistic molecular dynamics and Monte Carlo calculations, have been used for modeling and predicting the behavior of PET/PEN blends. Different simulations have been performed in order to study and compare pure homopolymer blends with blends characterized by the presence of PET/PEN block copolymers acting as compatibilizer. A many-scale molecular modeling strategy was devised to evaluate PET/PEN blend characteristics, simulate phase segregation in pure PET/PEN blends, and demonstrate the improvement of miscibility due to the presence of the transesterification reaction products. The behavior of distribution densities and …
Endocytotic uptake of HPMA-based polymers by different cancer cells: impact of extracellular acidosis and hypoxia.
2017
Daniel G&uuml;ndel,1 Mareli Allmeroth,2 Sarah Reime,1 Rudolf Zentel,2 Oliver Thews1 1Institute of Physiology, Martin Luther University Halle-Wittenberg, Halle (Saale), 2Institute of Organic Chemistry, Johannes Gutenberg-University, Mainz, Germany Background: Polymeric nanoparticles allow to selectively transport chemotherapeutic drugs to the tumor tissue. These nanocarriers have to be taken up into the cells to release the drug. In addition, tumors often show pathological metabolic characteristics (hypoxia and acidosis) which might affect the polymer endocytosis.Materials and methods: Six different N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer structures (homopolymer as well as…
HPMA-based block copolymers promote differential drug delivery kinetics for hydrophobic and amphiphilic molecules.
2015
Abstract We describe a method how polymeric nanoparticles stabilized with (2-hydroxypropyl)methacrylamide (HPMA)-based block copolymers are used as drug delivery systems for a fast release of hydrophobic and a controlled release of an amphiphilic molecule. The versatile method of the miniemulsion solvent-evaporation technique was used to prepare polystyrene (PS) as well as poly-d/l-lactide (PDLLA) nanoparticles. Covalently bound or physically adsorbed fluorescent dyes labeled the particles’ core and their block copolymer corona. Confocal laser scanning microscopy (CLSM) in combination with flow cytometry measurements were applied to demonstrate the burst release of a fluorescent hydrophobic…