Monomeric Vinyl Research Articles

Synthese und Biologische Untersuchungen von C(13)/C(13′)‐Bis(desmethyl)disorazol Z**

AbstractWir beschreiben hier die Totalsynthese des Makrodiolids C(13)/C(13′)‐Bis(desmethyl)disorazol Z über die Bildung des Makrozyklus durch eine doppelte inter‐/intramolekulare Stille‐Kreuzkupplung eines monomeren Vinylstannan/Vinyliodid Vorläufers. Der Schlüsselschritt in der Synthese dieses Vorläufers ist die stereoselektive Aldolreaktion eines formalen Evans Acetat‐Aldolprodukts mit Crotonaldehyd. Wie mitttels Röntgenkristallographie gezeigt werden konnte, ist der Bindungsmodus des C(13)/C(13′)‐Bis(desmethyl)disorazol Z an Tubulin praktisch identisch mit demjenigen des Naturstoffs Disorazol Z. Desgleichen unterdrückt das C(13)/C(13′)‐Bis(desmethyl)disorazol Z die Tubulinpolymerisation zumindest gleich stark wie das Disorazol Z und es hemmt das Zellwachstum offenbar sogar mit höherer Potenz.

Synthesis and Biological Evaluation of C(13)/C(13')-Bis(desmethyl)disorazole Z.

We describe the total synthesis of the macrodiolide C(13)/C(13')-bis(desmethyl)disorazole Z through double inter-/intramolecular Stille cross-coupling of a monomeric vinyl stannane/vinyl iodide precursor to form the macrocycle. The key step in the synthesis of this precursor was a stereoselective aldol reaction of a formal Evans acetate aldol product with crotonaldehyde. As demonstrated by X-ray crystallography, the binding mode of C(13)/C(13')-bis(desmethyl)disorazole Z to tubulin is virtually identical with that of the natural product disorazole Z. Likewise, C(13)/C(13')-bis(desmethyl)disorazole Z inhibits tubulin assembly with at least the same potency as disorazole Z and it appears to be a more potent cell growth inhibitor.

IR laser ablation of poly(vinyl chloride): Formation of monomer and deposition of nanofibres of chlorinated polyhydrocarbon

IR laser-induced ablation of poly(vinyl chloride) was examined under different irradiation conditions and its volatile and solid products were characterized by mass, infrared, UV and X-ray photoelectron spectroscopy, electron microscopy and thermogravimetry. It is demonstrated that the major component among the volatile products is monomeric vinyl chloride and that the process causes deposition of Cl-containing polymeric films. The proportion between the volatile and solid products as well as the nature of the deposited films at different laser fluences have been examined. We show that the deposited films incorporate less Cl atoms than poly(vinyl chloride) and that they initially contain conjugated C C bonds and incorporate nano-sized fibre and necklace features. The process represents the first example of thermal degradation of poly(vinyl chloride) into monomer and makes it possible to fabricate crosslinked Cl-containing intractable polymer films.

Fluorinated mesogen-jacketed liquid-crystalline polymers as surface-modifying agents: Design, synthesis and characterization

Monomers with semifluorinated tails on monomeric vinyl hydroquinone cores were synthesized and their polymerization behavior was examined. The resulting semifluorinated mesogen-jacketed liquid-crystalline polymers (MJLCPs) proved to form fairly hydrophobic surfaces with water contact angles of 110–118°. These polymers were studied for the role of the fluorinated groups on both liquid-crystalline (LC) behavior and surface properties. Initial surface stability studies showed that these fluorinated MJLCP surfaces are relatively more stable than comparable systems of side-chain fluorocarbon LC blocks. Our studies show that M(1), 2,5-bis[(10-perfluorohexyl-decanoyl)oxy]styrene, could not be homopolymerized, while M(2) incorporating benzoate groups, 2,5-bis[4-(10-perfluorohexyl-decanyloxy)benzyloxy]styrene, permitted facile homopolymerization and block copolymer preparation by stable free-radical polymerization. As determined by wide-angle X-ray diffraction, the SCN transition temperature of the block copolymer shifted to a higher temperature with an increase in the DP of M(2). NEXAFS studies showed no net orientation of the (CF2)n side chains towards the surface normal consistent with observed low order smectic phases, nevertheless pointed to the presence of fairly hydrophobic CF2-covered surfaces. The above evidence proved the materials are suitable for application as surface-modifying agents. Polarized optical micrograph of M(1) showing a mosaic texture due to a smectic mesophase obtained on slow cooling at 2 K min−1 from the isotropic phase.

Cyclization and Reduced Pendant Vinyl Group Reactivity during the Free-Radical Crosslinking Polymerization of 1,4-Divinylbenzene

Free-radical cross-linking polymerization of 1,4-divinylbenzene (1,4-DVB) has been investigated in toluene. The monomer concentration was less than 5 w/v%. Conversion of monomer and pendant vinyl groups, weight-average molecular weight M w , and intrinsic viscosity [η] of the polymers were measured as a function of the reaction time up to the onset of macrogelation. A kinetic model was used to calculate the extent of cyclization and reduced pendant reactivity from the experimental data. Fraction of pendant vinyls in cycles, number of multiple cross-linkages, and the reactivity ratio of pendant to monomeric vinyl were evaluated as a function of the polymerization temperature, initial concentrations of 1,4-DVB and the initiator as well as the amount of styrene as a comonomer. The results indicate that 30-60% of pendant vinyls are used by cyclization reactions and, on average, 100-800 multiple cross-linkages occur per one intermolecular cross-link formed. The average pendant reactivity for intermolecular links is 2-3 orders of magnitude lower than the monomeric vinyl reactivity. These results were found to be in accord with the observed weak M w dependence of [η] of the polymers and their stability against degradation by ultrasonic waves. The critical exponent γ suggests non-mean-field behavior in the vicinity of the gel point

Pendant vinyl group reactivity during the free-radical copolymerization of methyl methacrylate and ethylene glycol dimethacrylate

Methyl methacrylate-ethylene glycol dimethacrylate (MMA-EGDM) copolymerization has been investigated in toluene at a monomer concentration of 22 w/v %. The kinetic models developed recently along with the experimental conversion curve and gel point data provided the calculation of the average reactivity of pendant vinyl groups. It was found that the pendant vinyl reactivity for intermolecular links is much less than the monomeric vinyl reactivity and it decreases further as the EGDM concentration increases. At 5–15 mol % EGDM, the average pendant reactivity is 1–2 orders of magnitude lower than the monomeric vinyl reactivity. The reduced pendant reactivity is mainly responsible for the shift of the gel point towards higher conversions.

THE VISCOSITY OF VINYL ACETATE

The viscosity of monomeric vinyl acetate has been measured over a range of temperatures from 0° to 60 °C. Two equations were obtained which represent the results. The empirical equation is [Formula: see text], and a theoretical equation is given as [Formula: see text]. The characteristic frequency has been obtained from the relation [Formula: see text], where μ is the ratio between the latent heat of evaporation and the heat of cohesion, v was found to be 2.17 × 1012.

THE DENSITIES AND PARACHORS OF VINYL ACETATE AND ITS LIQUID POLYMERS

The density of monomeric vinyl acetate has been determined over a range of temperature. The parachor and Ramsay and Shield's constant have been obtained for the monomer and some liquid polymers. On the assumption that a liquid polymer may be considered as a solution of a dimer in the monomer, parachors were calculated from the mixture law.If Staudinger's formula be assumed for the dimer the calculated and observed parachors agree to within 1%.