Search results for "opening"

Polymerizations of Cyclic Esters Catalyzed by Titanium Complexes Having Chalcogen-Bridged Chelating Diaryloxo Ligands

2002

A series of titanium complexes having tellurium-bridged chelating bis(aryloxo) ligands, [TiX2{2,2‘-Te(4-Me-6-tBu-C6H2O)2}]2 (5:  X = Cl; 6:  X = OiPr), catalyzed the ring-opening polymerization of cyclic esters such as e-caprolactone, δ-valerolactone, and l-lactide. The strong dependence of polymerizations on the solvent was observed in this catalytic system. When the polymerizations of e-caprolactone and l-lactide were carried out in toluene at 100 °C, tellurium-bridged bis(aryloxo)titanium complex 5 was found to give polymers with rather broad molecular weight distribution due to back-biting. When the polymerizations of e-caprolactone and l-lactide was carried out in anisole or in dioxane…

Polymerization of ε-caprolactone using heterobimetallic lanthanocene complexes

1997

The chiral heterobimetallic complexes Li[Ln(η 5 :η 1 -C 5 R 4 1 SiMe 2 NCH 2 CH 2 R 2 ) 2 ] (ln= Y, Lu; C 5 R 4 1 = C 5 Me 4 , C 5 H 4 , 3-C 5 H 3 tBu; R 2 = OMe, NMe 2 ) have been found to polymerize e-caprolactone to give a polymer of high molecular weight (M n > 20000) and moderate polydispersity (M w /M n < 2). Failure to observe a correlation between monomer/initiator ratio and molecular weight suggest a polymerization mechanism different from a pseudo-anionic mechanism

Introducing PeptoPlexes: Polylysine-block-Polysarcosine Based Polyplexes for Transfection of HEK 293T Cells

2014

A series of well-defined polypeptide-polypeptoid block copolymers based on the body's own amino acids sarcosine and lysine are prepared by ring opening polymerization of N-carboxyanhydrides. Block lengths were varied between 200-300 for the shielding polysarcosine block and 20-70 for the complexing polylysine block. Dispersity indexes ranged from 1.05 to 1.18. Polylysine is polymerized with benzyloxycarbonyl as well as trifluoroacetyl protecting groups at the ϵ-amine group and optimized deprotection protocols for both groups are reported. The obtained block ionomers are used to complex pDNA resulting in the formation of polyplexes (PeptoPlexes). The PeptoPlexes can be successfully applied i…

Synthesis and characterization of bisalkylated polysarcosine-based lipopolymers

2019

The use of PEGylated lipids for the synthesis of stealth liposomes and lipid formulations for nucleic acid delivery has promoted the development of nanoparticle based drugs for cancer therapy, and chronic diseases. Moreover, several other nanomedicines based on these materials have advanced into clinical trails. This enormous success, however, has recently been compromised by the occurrence of immune responses towards PEG, which render pharmacokinetics and can substantially reduce the therapeutic efficiency of drugs. Therefore, alternatives for PEGylated lipids with comparable or even identical solution properties are required. In this work, we report the synthesis of polysarcosine based li…

Monofunctional metathesis polymers via sacrificial diblock copolymers.

2006

1983

Synthese a partir de l'hexahydro-1,5,5a,6,9,9a benzodioxepinne-2,4. Polymerisation en masse en un produit incolore, cireux (Tg=−11°C)

1991

Polyfunctional chloroformates were applied to the polymerization of 2-phenyl-2-oxazoline and 2-methyl-2-oxazoline. The use of a trifunctional initiator, viz. the chloroformate of 2,2-bis(hydroxymethyl)-1-butanol, led to three-arm star polymers of 2-oxazolines. Two macromolecular initiators, viz. poly(ethylene oxide) with two chloroformate end groups (α-chloroformyl-ω-chloroformyloxypoly(oxyethylene)) with number-average molar masses 350 g/mol ≤ Mn ≤ 6000 g/mol and α-chloroformyl-ω-methoxypoly(oxyethylene) with Mn = 350 and 750 g/mol were applied for the synthesis of poly(2-oxazoline)-block-poly(ethylene oxide)-block-poly(2-oxazoline) and poly(2-oxazoline)-block-poly(ethylene oxide) copolyme…

An Efficient Method for Controlled Propylene Oxide Polymerization: The Significance of Bimetallic Activation in Aluminum Lewis Acids

2009

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic c…

2018

Ring-opening metathesis (ROM) of various unsaturated, constrained bicyclic ring systems has been investigated with the use of commercial ruthenium-based catalysts. Starting from various cyclodienes, the corresponding derived bicyclic lactone, lactam, and isoxazoline derivatives were submitted to ROM under ethenolysis. These functionalized, strained bicyclic systems afforded novel highly-functionalized diolefinated heterocyclic scaffolds in ROM reactions with stereocontrol, through the conservation of the configuration of the stereogenic centers of the starting compounds.

Prese urbane. Studi di enunciazioni cittadine

2017

Distinguished and diverse theorists such as Benveniste, Barthes, De Certeau and Lotman have each approached the city in different ways. But while several key differences exist between them, their points of view intertwine around the concept of urban enunciation and intersect at differing points. In this study, the positions of these authors will be presented, compared and elaborated upon and the categories of linguistic enunciation of urban space will be set out, drawing from a vision of translation between languages that frequently leads, as is so often the case in Semiotics, to productive analytical models. The linguistic signs of the city will also be illustrated by examples of "short fo…