Search results for " Plastics"

Dynamics of macromolecules grafted in spherical brushes under good solvent conditions

2013

Spherical polymer brushes have a structure intermediate between star polymers and polymer brushes on flat substrates, and are important building blocks of polymer nanoparticles. Molecular dynamics simulations are presented for isolated spherical polymer brushes under good solvent conditions, varying the grafting density as well as the chain length, using a coarse-grained bead-spring model of flexible chains. We complement previous work on the static properties of the same model by analyzing the chain dynamics, studying the motions of monomers in relation to their position along the grafted chains, and extract suitable relaxation times. A qualitative discussion in terms of the Rouse model is…

The use of master curves to describe the simultaneous effect of cooling rate and pressure on polymer crystallization

2003

In a previous work a master-curve approach was applied to experimental density data to explain isotactic polypropylene (iPP) behaviour under pressure and high cooling rates. Suitable samples were prepared by solidification from the melt under various cooling rate and pressure conditions with the help of a special apparatus based on a modified injection moulding machine. The approach here reported is more general than the case study previously shown, and is suitable to be applied to several materials and for different measures related to crystalline content. The proposed simple model is able to predict successfully the final polymer properties (density, micro-hardness, crystallinity) by supe…

Über eine Beziehung zwischen Verdünnunasentropie und Verdünnungsenthalpie in Lösungen von Polystyrol und Polymethylmethacrylat

1973

Durch Lichtstreuungsmessungen wurde der Entropieanteil und der Enthalpieanteil des 2. osmotischen Virialkoeffizienten (A2) von athermischen und exothermischen Losungen von Polystyrol (PS) und Polymethylmethacrylat (PMMA) bei 25°C und Normaldruck bestimmt. Zur Auffindung von athermischen und exothermischen Losungsmitteln fur diese Polymeren wurde die Temperaturabhangigkeit des STAUDINGERindex verwendet. Die ermittelten thermodynamischen Grosen A2, A2,S und A2,H ergeben zusammen mit fruheren Messungen eine beziehung, die nahezu unabhangig vom speziellen System ist. The second osmotic virial coefficient A2 and its entropic and enthalpic parts of athermal and exothermal solutions of polystyrene…

Molecular surfaces: An advantageous starting point for the description of composition-dependent viscosities applied to polymer solutions

1999

The viscosity of polymer/solvent systems is modeled as a function of composition under the premises that the dissipation of energy is taking place at the molecular interfaces and that the friction between solvent and solute varies with composition due to a change in the flow mechanism (drainage of coils). The simple expression obtained in this manner contains three system-specific parameters: a geometric factor γ, which accounts for the differences of the surface to volume ratios of the components; a hydrodynamic parameter α, which measures the friction between solute and solvent in the case of fully draining polymer coils; and β, which corrects for changes in the friction between unlike mo…

Mechanical properties of injection-molded binary blends of polyethylene with small additions of a liquid-crystalline polymer

2011

The results of the investigation of the mechanical properties of polyethylene (PE) blends with small (<3 wt %) additions of thermotropic liquid-crystalline polymers (LCPs) are reported. PE/LCP compositions with various LCP weight contents were obtained by thermoplastic mixing in a two-stage process. Short-term and long-term mechanical behavior of various PE/LCP compositions were analyzed. Data on the influence of LCP addition on the tensile elastic modulus [or Young's modulus (E)], stress at yield (σY), stress at break (σB), strain at yield, strain at break, and deformation at long-term (1000-h) tensile creep were obtained. The experimental results of the investigation show that even small …

Synthesis and activity of zirconocene catalysts supported on silica-type sol-gel carrier for ethylene polymerization

2001

Synthesis and activity of bis(cyclopentadienyl)zirconium dichloride catalyst supported on unconventional silica-type material obtained in sol-gel process and activated by organoaluminium co-catalyst were studied. The effect of support modification conditions (thermal dehydration and/or modification by organoaluminium compound) and a type of co-catalyst on an activity of the catalytic system in ethylene polymerization and properties of resulting polymers were investigated and compared with results obtained earlier for vanadium catalysts supported on mentioned sol-gel carrier. The most appropriate method of the sol-gel silica-type support preparation is thermal pre-treating (200°C) followed b…

Surface and bulk ordering in thin films of a symmetrical diblock copolymer

2013

Amphiphilic diblock copolymers have the ability to adapt their surface's molecular composition to the hydrophilicity of their environment. In the case of about equal volume fractions of the two polymer blocks, the bulk of these polymers is known to develop a laminar ordering. We report here our investigation of the relationship between bulk ordering and surface morphology/chemical composition in thin films of such an amphiphilic diblock copolymer. Upon annealing in vacuum, the expected lamella ordering in the bulk of the film is observed and we find the morphology of the film surface to be defined by the thickness of the as-deposited film: If the as-deposited thickness matches the height of…

Thermo- and photo-oxidative stability and improved processability of polyamide stabilized with a new functional additive

2005

During processing polyamides can undergo thermo-mechanical degradation due to the mechanical stress and to the high temperature applied to the melt. Degradation can occur also during the polyamides lifetime due to many driving forces, like temperature, ultraviolet radiations, etc. The mechanisms of degradation are not well understood and the stabilization with usual stabilizers, like phenol antioxidants, is not so efficient as for other classes of polymers. The aim of this work is the study of the effects of the addition of a new multifunctional additive on the processing and on the thermo- and photo-stabilization of polyamide-6. This additive is able to prevent the thermo-mechanical degrad…

New amphiphilic conjugates of mono- and bis(carboxy)-PEG(2,000) polymers with lipoamino acids as surface modifiers of colloidal drug carriers

2010

Interplay between Chain Collapse and Microphase Separation in Bottle-Brush Polymers with Two Types of Side Chains

2010

Conformations of a bottle-brush polymer with two types (A,B) of grafted side chains are studied by molecular dynamics simulations, using a coarse-grained bead−spring model with side chains of up to...