Search results for "Ethylene"

Influence of plasticizers suggests role of topology in polymer solidification at high cooling rates

2012

Although solidification in processing deter- mines short- and long-term properties, methods for under- standing polymer crystallization mostly rely on real time experiments. Their evidences being drawn on time scales farther apart with respect to those experienced in process- ing. Nor significant outcomes have been so far drawn with approaches mimicking the typical processing times, the Continuous Cooling Transformation methods. Use of these techniques has indeed been limited to a heuristic interpretation of the structure developed under extreme solidification conditions without suggesting alternative routes to the understanding or even clues to the many open questions on polymer crystalliz…

Hyperbranched-linear-hyperbranched ABA-type block copolymers based on poly(ethylene oxide) and polyglycerol

2009

BACKGROUND: Until recently, hyperbranched polymers were thought to be ill-defined materials that were not useful as building blocks for well-defined complex polymer architectures. It is a current challenge to develop strategies that offer rapid access to well-defined hyperbranched block copolymers. RESULTS: A convenient three-step protocol for the synthesis of double-hydrophilic hyperbranched–linear–hyperbranched ABA-type triblock copolymers based on poly(ethylene oxide) (PEO) and hyperbranched polyglycerol (hbPG) is presented. The Bola-type polymers exhibiting an aliphatic polyether structure were prepared from a linear (lin) linPG-b-PEO-b-linPG precursor triblock. The materials exhibit lo…

1982

The stress relaxation behaviour after compression yielding of two semicrystalline polymers, a low density polyethylene and an isotactic polypropylene, is investigated. Data taken at several strains, reached with different sample loading rates, are considered. Master curves are obtained by means of dimensionless stress and time measures, similar to those recently adopted for some amorphous polymers. Die Spannungsrelaxation nach Druckbeanspruchung wurde an zwei semikristallinen Polymeren, Polyethylen neidriger Dichte und isotaktischem Polypropylen, untersucht. Die bei unterschiedlichen Deformationen, welche mit unterschiedlichen Beanspruchungsgeschwindigkeiten erreicht wurdern, erhaltenen Erg…

The role of the disposition of the recycled polymer on the properties of films for greenhouses coverage

2010

Multilayer films, by using postconsumer materials in the central layer, i.e., multilayer composition: virgin polyethylene/postconsumer polymer/virgin polyethylene, allows to get a film for greenhouses coverage with good mechanical properties and photo-oxidation resistance, similar to that of the films made from virgin material and certainly better than the photo-oxidation resistance of the film made melt blending the virgin polyethylene and the postconsumer polymer. Moreover, the disposition of the postconsumer polymer containing oxygenated groups only in the central layer determines a significant slowdown of the photo-oxidation process of the multilayer film although faster than of the pri…

Characterization of a fiber reinforced semirigid liquid crystalline polymer

1997

In this work, samples of a semirigid Liquid crystalline polymer reinforced with carbon and glass fibers has been characterized. Semirigid liquid crystalline polymers (LCPs) show some advantages with respect to rigid LCPs: in particular lower processing temperatures, and better compatibility with flexible thermoplastics, but also some disadvantages: lower mechanical properties and poor thermomechanical resistance. Both properties can be improved by adding inorganic fillers. Although elastic modulus and tensile strength of the glass fiber filled LCP improve remarkably with increasing the filler content, the same properties for the carbon fiber-filled samples do not increase with increasing ti…

Composites of ethylene-vinyl acetate copolymers with modified magnesium hydroxide-thermo-oxidative ageing

2014

Flame retardant composites must perform their protective roles permanently, also under conditions of intermittent or long-term exposure to sunlight, moisture or increased temperature. The aim of our work was characterization of the thermo-oxidative ageing (90 °C) and the changes in flammability of ethylene-vinyl acetate copolymer composites with 40 and 60 wt.% of magnesium hydroxide. The neat polymer and its composites were investigated for their thermal (DSC) and structural (FTIR) characteristics as well as their density, melt flow index, tensile properties and combustibility during ageing test. As FTIR results identified the different carbonyl groups in copolymer were created, the highest…

Solution Properties of Polysarcosine: From Absolute and Relative Molar Mass Determinations to Complement Activation

2018

Polysarcosine (pSar) was one of the first polymers synthesized in a controlled living manner, but it was only recently when it was reconsidered as a promising alternative for poly(ethylene glycol) (PEG) in biomedical applications. Despite receiving more and more attention, very little is known about the solution properties of pSar, such as coil dimensions and thermodynamic interactions. In this article, we report on these properties of pSar with degrees of polymerization 50 < X-n < 400 that were prepared by controlled living ring-opening polymerization. The polymers are characterized by gel permeation chromatography (GPC), MALDI-TOF mass spectrometry, dynamic and static light scattering (SL…

Effect of irradiation temperature and dose rate on the mechanical tensile behaviour of low density polyethylene

1993

Abstract The effect of ageing due to gamma radiation, at various dose rates and temperatures, on the mechanical tensile behaviour of low density polyethylene is studied. In order to detect synergistic effects, tensile tests on samples subjected to thermal treatment corresponding to the same temperature for the same time as for the irradiation tests have also been performed. The results indicate a generalized decrease of the elongation at break, with brittleness of the material for the most severe ageing treatments. For modulus values, an increase is observed for particular experimental conditions. These results are related to morphological and structural modifications induced in the polymer…

Amphiphilic poly(ether urethanes) carrying associative terpyridine side groups with controlled spacing

2021

The rational design of transiently crosslinked polymer gels requires a profound understanding of how molecular and topological factors determine the mechanical and dynamic material properties. To refine so-far established structure–property relations, complementary and versatile model sytems are still a crucial prerequisiste. In this study, the synthesis of a metallo-supramolecular associating terpyridine-diol (referred to as sticker) and its incorporation into poly(ethylene glycol) (pEG) based polyurethanes (PU) with strictly alternating vs. random sequences and variable sticker spacings is described. Synergetic effects resulting from the proximity of multiple neighboring urethane and stic…

Hydrogen-Bonded Aggregates of Oligoaramide−Poly(ethylene glycol) Block Copolymers

2010

Rod−coil copolymers with an oligomeric rod aggregate on a nanometer length scale, which is important for many applications like e.g. organic photovoltaics. However, this aggregation behavior and the driving forces such as hydrogen bonding and π−π interactions, as well as the role of side groups, are not yet fully understood. Here, we investigated these noncovalent interactions in oligo(p-benzamide)−poly(ethylene glycol) (OPBA−PEG) copolymers using solid-state NMR supported by wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and polarization optical microscopy (POM). It was found that longer OPBAs form layered β-sheet-like aggregates and that these are stabilized …