Search results for "Melting point"

Polymerization of mono- and multilayer forming diacetylenes

1977

Heptadeca-2,4-diine-1-ol and Heptadeca-2,4-diine-1-acid were synthesized and their polymerization behaviour in the solid state was investigated. Both compounds polymerize thermally below the melting point and photochemically under the action of uv-light to form polymers via 1,4-addition to the conjugated triple bonds with a backbone of conjugated double-and triple-bonds. The photoresponse spectra resemble the absorption spectra exhibiting maxima of photoreactivity in the absorption band of the conjugated triple bonds of the monomers.

Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride

1980

Nylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x-ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high-modulus fibers after subsequent crystallization. Also, t…

Rheological characterization of polycaprolactam anionically synthesized in the presence of lithium chloride

1980

Melt viscosity and dynamic-mechanical data are reported for samples obtained by anionic polymerization of caprolactam, in the presence of LiCl. The full body of results is essentially in line with those previously reported relative to mixtures of inorganic salts and commercial nylon 6, In particular a drastic-decrease of the melting point and of the rate of crystallization is confirmed as well as an increase of the glass transition temperature and of the melt viscosity. Some quantitative differences exist, which may be attributed to the different molecular weight distribution in the polymers employed in the present work.

Crystallization kinetics of LDPE/Ny6 blends

1988

The crystallization behaviour of low density polyethylene/nylon 6 blends has been investigated as a function of the composition. The melting points of the polymers are almost uninfluenced by the presence of the other homopolymers except for blends with a nylon content of 75–90%. Blends with 10% nylon content do not exhibit the crystallization peak during the cooling step probably because of the low concentration and high viscosity of the low density polyethylene matrix. The crystallinity degree of the polyethylene is independent of the composition, while some variations are shown by the polyamide. Finally the rate of nucleation is strongly affected by the composition, in particular for the …

1989

A series of combined main-chain side-group liquid-crystalline polymers was synthesized by melt polycondensation from trans-1,4-cyclohexanedicarboxylic acid, chloro-1,4-phenylene diacetate and 6-(4-methoxy-4′-biphenylyloxy)hexyl-1,4-phenylene diacetate. These polyesters combine the features of rigid-rod main-chain LC-polymers and of side-group LC-polymers. Polymers with small fractions of mesogenic side-groups (5 and 10 mol-%) have lower melting points than the parent polymer poly(chloro-1,4-phenylene 1,4-cyclohexanedicarboxylate) but are still liquid crystalline up to their decomposition at T ≥ 400°C. In polymers with larger fractions of mesogenic side-groups (50 and 100 mol-%) partial isom…

Thermomechanical Properties of Radiation-Modified Polyethylene/Ethylene-Propylene-Diene Copolymer/Liquid-Crystalline Copolyester Blends

1999

Radiation-modified blends of high-density polyethylene (PE) with ethylene-propylene-diene copolymer (EPDM; 10-65 wt.%) and thermotropic liquid-crystalline polymer (LCP; 10 wt.%) were investigated. The LCP was a liquid-crystalline copolyester of 40% poly(ethylene terephthalate) with 60% 4-hydroxybenzoic acid. The constituents were blended using a circular extruder, the specimens were prepared by compression molding and irradiated by 60Co γ-radiation up to 200 kGy. Mechanical, thermal, and morphological properties in wide temperature range were investigated for the irradiated and non-irradiated specimens. The effects of irradiation on the thermomechanical behaviour of the PE matrix are discus…

Studies on electron-beam irradiation and plastic deformation of medical-grade ultra-high molecular weight polyethylene

2011

Abstract Separated and combined electron-beam irradiation and plastic deformation effects on the structures of ultra-high molecular weight polyethylene (UHMWPE) were studied. It was found that the concentration of carbonyl (ketones, esters and peresters), hydroxyl and vinyl groups increases with the growing dose of adsorbed electrons. It also tends to exhibit a slight increase in the melting point and crystallinity of the samples. A mechanical stress in the polymer was found to accelerate radiation-induced degradation. It was concluded that each of the factors studied (i.e. electron beam sterilization and plastic deformation) had a different impact on the polymer structure. The change in th…

Guest-Induced Folding and Self-Assembly of Conformationally Adaptive Macrocycles into Nanosheets and Nanotubes

2017

A conformationally adaptive macrocycle is presented, namely zorb[4]arene, which exists in multiple conformations in the uncomplexed state. The binding cavity of zorb[4]arene is concealed, either due to a collapsed conformation or by self-inclusion. The zorb[4]arene with long alkyl chains manifests itself with surprisingly low melting point and thus exist as an oil at room temperature. Binding of a guest molecule induces the folding and conformational rigidity of zorb[4]arene and leads to well-defined three-dimensional structures, which can further self-assemble into nanosheets or nanotubes upon solvent evaporation, depending on guest molecules and the conformations they can induce.

Über die synthese von oligophenylenes mit einer o-verknüpfung. 10. Mitteilung

1960

Es werden zwei Wege zur Darstellung von Oligophenylenen mit einer o-Winkelung beschrieben. Als Ausgangssubstanzen dienen der Mono-enolather des Cyclohexandion (1,2) bzw. Cyclohexenoxyd. Die Darstellung des Mono-enolathylathers des Cyclohexandion (1,2) wird beschrieben. Durch Oxydation nach OPPENAUER mit Chinon als Wasserstoffacceptor konnen die als Zwischenprodukte der Oligophenylene erhaltenen Cyclohexanolderivate in 90%iger Ausbeute in die benotigten Ketone ubergefuhrt werden. Folgende o-gewinkelten Oligophenylene wurden synthetisiert : o-Terphenyl; 2o2-Quater-phenyl ; 32, 43-Dimethyl-2o2-quaterphenyl ; 3o2-Quinquiphenyl ; 12, 23-Dimethyl-3o2-quinquiphenyl ; 12, 23, 42, 53-Tetramethyl-3o2…

Über die stereospezifische polymerisation von styrol mit natriumorganischen verbindungen

1958

Es wird uber die Herstellung von kristallisierbaren Polystyrolen durch Polymerisation von Styrol mit natriumorganischen Verbindungen bei niedrigen Temperaturen berichtet. Anteile der Polymeren sind rontgenkristallin und haben Schmelzpunkte von uber 200°C. Dieser kristallisierbare Anteil nimmt mit fallender Polymerisationstemperatur zu. Bei konstanter Polymerisationtemperatur fallen die Viskositatszahlen der Polymeren mit steigender Katalysatorkonzentration. It is reported on the preparation of cristallizable polystyrenes by means of polymerisation of styrene with sodiumorganic compounds under low temperatures. X-ray diffraction shows the cristallinity of the polymers having melting points o…