Search results for "Molar"

Reactivity Towards Acidic Protic Ligands of Cyclopalladated Di‐μ‐hydroxo Complexes

2008

The dinuclear hydroxo complexes [{Pd(μ-OH)(C∧N)}2] [C∧N = 2-(2-pyridyl)phenyl (Phpy) (I), 7,8-benzoquinolyl (Bzq) (II) and 2-(2-oxazolinyl)phenyl (Phox) (III)] react in a 1:2 molar ratio with a wide variety of protic electrophiles H(L∧L) bearing different sets of donor atoms (L∧L = O∧O or O∧N) to give the mononuclear neutral palladium(II) derivatives with the general formula [Pd(L∧L)(C∧N)] [O∧O = salicylaldehydate (sal) (1), acetylacetonate (acac) (2) and benzoylacetonate (bzac) (3); O∧N = N-phenylsalicylaldiminate (N-Phsal) (4), N-p-chlorophenylsalicylaldiminate (N-pClPhsal) (5), 2-pyrrolecarbaldeydate (2-pcal) (6), 8-hydroxyquinolinate (oxin) (7)]. Structural characterisation of complexes…

A green route to synthesize poly(lactic acid)-based macromonomers in scCO2 for biodegradable nanoparticle production

2014

Poly(lactic acid)-based macromonomers, aimed at biomedical applications and with well-defined average chain length, are produced through catalytic ring-opening polymerization of L,L-lactide co-initiated by a co-monomer bearing a double bond. Reactions have been carried out in supercritical carbon dioxide (scCO2) at different temperatures, ranging from 90 to 130 °C. The resulting oligomers have been characterized by different techniques (1H-NMR, 13CNMR, MALDI-TOF, ESI, GPC, FT-IR, TGA), which show that oligomers with narrower molecular weight distribution are produced at the lowest temperature. In addition, a significant reduction of the impact of the secondary reactions has been found at th…

On The Incompatibility of Dextran and Pullulan in Aqueous Solutions and Its Modeling

2012

Joint aqueous solutions of branched dextran and linear pullulan are investigated with respect to their phase separation. The experiments demonstrate that the polymers are – depending on the molar mass of dextran – incompatible in aqueous solutions despite their chemical similarity. This finding can be modeled on the basis of an approach accounting for chain connectivity and conformational relaxation of the components. According to these calculations, the polymers exhibit a miscibility gap in joint solutions despite the favorable interactions between them. Using information on the subsystems H2O/dextran and H2O/pullulan, the assumption of complete miscibility of the polysaccharides is requir…

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.