Search results for "MOLA"

Branched versus linear polyisoprene: Fractionation and phase behavior

2007

Abstract Branched polyisoprene (PI) was prepared from PI-macromonomers. Linear byproducts of the synthesized polymer were removed by means of inverse spin fractionation, using the solvent cyclohexane (CH) and the precipitant acetone (AC). A well-defined fraction (Mw = 17.5 kg/mol, Mw/Mn = 1.8) of the branched polyisoprene obtained in this manner was used to determine different phase diagrams with branched and/or linear PI in the mixed solvent CH/AC at 25 °C. For comparable molar masses of the polymers the two-phase area is smallest for the branched PI and slightly larger for the linear PI; in the case of the unfractionated original sample of the branched polymer one observes a pronounced pe…

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…

1976

Polyoctenylenes and polydodecenylenes prepared by the methathesis reaction exhibit a bimodal molecular weight distribution. The low molecular weight fraction consists of cyclic oligomers, the high molecular weight fraction is assumed to contain linear polymers. The distribution of cyclic oligomers together with the polymer material indicates a ring-chain equilibrium. The slope of the plot log Kx (molar cyclization equilibrium constant) vs. log x (degree of polymerization) is close to −2,5 as predicted by the Jacobson and Stockmayer theory for unstrained macrocycles. Polyoctenylene und Polydodecenylene, dargestellt mit Hilfe der Metathese-Reaktion, weisen eine bimodale Molekulargewichtsverte…

Streulichtmessungen an polymerlösungen zur bestimmung der verteilungsbreite des Molekulargewichtes

1978

By increasing the experimental accuracy of the classical light scattering technique it became possible to determine the width U = Mw/Mn − 1 of the molecular weight distribution of polymers. For this purpose a very stable laser and a lock-in-amplifier were used allowing an accuracy of 0,2–0,3% in the scattering intensity. The numerical evaluation of the polydispersity is done by a Gaus-Newton procedure analysing the small curvature of the reciprocal scattering function. In an appropriate molecular weight range U is obtained with an error between 0,01 and 0,1 depending on the width of the molecular weight distribution of the sample tested.

Polymerisation von äthylenoxid mit dem kaliumalkoholat von 4-benzolazo-benzylalkohol. I. Der anionische polymerisationsmechanismus

1966

Athylenoxid last sich mit dem Kaliumalkoholat von 4-Benzolazo-benzylalkohol polymerisieren. Dabei erhalten die Polyathylenoxide eine zusatzliche UV-Absorption, die auf covalent eingebaute C6H5NNC6H4(p) CH2O-Gruppen zuruckzufuhren ist. Wenn der ubliche Mechanismus der anionischen Polymerisation gilt, sollte jedes Polyathylenoxidmolekul eine besonders absorbierende Endgruppe enthalten. Fraktioniert man die mit dem Alkoholat hergestellten Polyathylenoxide, so ist die Extinktion bei gleicher Polymerkonzentration nicht wie erwartet um so groser, je kleiner das Molekulargewicht ist. Bestimmt man ferner quantitativ den Gehalt an C6H5NNC6H4(p) CH2O-Gruppen in Polyathylenoxidfraktionen und nimmt ein…

1982

p-Cresol and eight oligo[(hydroxyphenylene)methylene] compounds 1b–e and 4a–d could be esterified with good yields with acryloyl chloride or propionyl chloride, respectively, in the presence of triethylamine. The simple and multiple acrylates and propionates were characterized by determination of their molar masses, elemental analyses, hydrogenation of the CC double bonds in the acrylate groups, and by their IR- and UV-spectra. No steric hindrance could be ascertained. Acrylates with more than three phenolic units in their molecules were found to have a range of melting, whereas all the propionates possess sharp melting points. This can be explained by polymerization of the acrylates which …

Second-order NLO main-chain polymers by polymerization of poled monomers

1993

A new method of preparing oriented NLO main chain polymers is presented. We synthesized NLO-monomers that consist of donor acceptor substituted tolane molecules that can be poled in the low molar mass state. In the oriented polar state these monomers can be chemically linked using a thermally activated polyaddition reaction. This reaction links the donor head of one monomer to the acceptor tail of the next hibiting bulk noncentrosymmetry with the average direction of the molecular dipoles parallel to the aligning field.

Die zweifache unterdrückung der polymerisation einiger bis(methacrylsäureester) mittels radikalischer additionsreaktionen

1973

Aus Hydrochinon, Resorcin, Dihydroxydiphenylen und Dihydroxynaphthalinen wurden mit Methacrylsaurechlorid Bis(methacrylsaureester) hergestellt. Setzte man diese in siedendem Benzol mit groser Verdunnung gelosten Ester dem Angriff von Radikalen aus α.α′-Azoisobuttersauredinitril (Primarradikale) aus, dessen Uberschus in Beziehung zum Ester mindestens zwanzigfach molar war, so erhielt man mittels saulenchromatographischer Trennung Verbindungen, bei denen je olefinische Doppelbindung zwei Primarradikale addiert waren (unterdruckte Polymerisation). Die Struktur dieser Produkte wurde mittels Elementaranalyse, Molekulargewichtsbestimmung, IR- und 1H-NMR-Spektren bewiesen. Demnach kann die Polymer…

1990

Taking into account the dependency on molar mass of the viscometric interaction parameter B, the modified Stockmayer-Fixman-Burchard equation ([η]/M1/2) = KΘ + C″ · A2 · M1/2 is obtained. It relates the intrinsic viscosity, [η], to the second virial coefficient, A2, and to the unperturbed dimensions parameter, KΘ, with C″ being a constant. Hereupon, KΘ can be determined from [η] and A2 data of any binary (solvent/polymer) and/or ternary (solvent 1/solvent 2/polymer) system, BPS and/or TPS. Because of the scarcity of reliable sets of [η] and A2 values mostly for TPS, the application of the above equation to obtain KΘ coefficients rests limited. This limitation can be surmounted by an A2 eval…

1986

In order to graft methacrylonitrile onto preformed networks containing thermolabile azo groups, the monomer was used to swell the networks and then the temperature raised to the decomposition temperature for the azo groups. The unusually high grafting efficiencies yields (e) achieved are explained in terms of both the differences in the reactivities of the primary radicals formed and side reactions, which lead to additional grafting sites. As an aid to understand the dependence of monomer conversion on that of the initiator a kinetic model is discussed, which involves the consideration of the polymerization taking place both in the homogeneous phase and within the polymer pearls, which can …