Search results for "polymerization"

New Self-Assembling Polyaspartamide-Based Brush Copolymers Obtained by Atom Transfer Radical Polymerization

2009

A simple and efficient method for the synthesis of polyaspartamide-based brush copolymers using Atom Transfer Radical Polymerization (ATRP) is here presented. The syntheses were performed by using two subsequent steps. In the first step the macroinitiator was obtained by the conjugation of a proper number of 2-bromoisobutyryl bromide (BIB) residues to the R, -poly(N-2-hydroxyethyl)-D,L-aspartamide (PHEA) side chains, obtaining the PHEA-BIB copolymer. PHEA-BIB copolymer was used as “multi-functional macroinitiator” for the polymerization via ATRP of hydrophilic methacrylic monomers, such as methacrylic acid (MA), obtaining PHEA-IB-poly(MA) copolymer, sodium methacrylate (MANa+), obtaining PH…

Novel water-swellable beads based on an acryloylated polyaspartamide

2001

Spherical polymeric microparticles have been prepared by a reverse-phase suspension polymerization technique. The starting polymer was α,β-poly (N-2-hydroxyethyl)-dl-aspartamide (PHEA) partially functionalised with glycidylmethacrylate (GMA) in order to introduce reactive vinyl groups in the side chain. The PHEA–GMA copolymer obtained (PHG) was cross-linked in a mixture of water/hexane–carbon tetrachloride in the presence of sorbitan trioleate (Span 85) as surfactant and ammonium persulfate/N,N,N′,N′-tetramethylethylenediamine as initiator system. The reaction was also carried out in the presence of N,N′-dimethylacrylamide as comonomer or N,N′-ethylenebisacrylamide as a cross-linking agent.…

Design, Synthesis and Evaluation of Enzyme-Responsive Fluorogenic Probes Based on Pyridine-Flanked Diketopyrrolopyrrole Dyes

2020

The ever-growing demand for fluorogenic dyes usable in the rapid construction of analyte-responsive fluorescent probes, has recently contributed to a revival of interest in the chemistry of diketopyrrolopyrrole (DPP) pigments. In this context, we have explored the potential of symmetrical and unsymmetrical DPP derivatives bearing two or one 4-pyridyl substituents acting as optically tunable group(s). The unique fluorogenic behavior of these molecules, closely linked to N-substitution/charge state of their pyridine unit (i.e., neutral pyridine or cationic pyridinium), has been used to design DPP-based fluorescent probes for detection of hypoxia-related redox enzymes and penicillin G acylase …

Novel pathways for the preparation of mesoporous MCM-41 materials: control of porosity and morphology

1999

Two novel synthesis routes for the preparation of mesoporous MCM-41 materials are introduced. Both methods use tetra-n-alkoxysilanes such as tetraethoxysilane (TEOS) or tetra-n-propoxysilane (TPS) as a silica source which are added to an aqueous solution of a cationic surfactant in the presence of ammonia as catalyst. In this study, n-alkyltrimethylammonium bromides and n-alkylpyridinium chlorides were employed as templates. The addition of an alcohol (e.g. ethanol or isopropanol) leads to a homogeneous system which allows the formation of spherical MCM-41 particles. The main advantages of these methods are short reaction times, excellent reproducibility and easy preparation of large batche…

1989

The reaction kinetics for the group transfer polymerization (GTP) of tert-butyl methacrylate (TBMA) using a silyl ketene acetal initiator and a nucleophilic catalyst are investigated. The reaction is shown to be of first order in both monomer and catalyst concentrations. The “livingness” of this system appears to be influenced by the reaction temperature. At temperatures above −20°C, deactivation is observed, with its severity increasing with increasing temperature. This deactivation is attributed to a depletion of catalyst by side reactions. It was demonstrated that reactivation is made possible by the addition of more catalyst. This result is in contrast to the anionic polymerization of T…

Kinetischer nachweis zweier arten von ionenpaaren bei der anionischen polymerisation von styrol in tetrahydropyran

1967

Die durch Na-Naphthalin angeregte Polymerisation des Styrols in THP wurde im Temperaturbereich von -40 bis +50°C kinctisch verfolgt. Die Geschwindigkeitskonstante kw(±) der uber das lonenpaar erfolgenden Polymerisation wurde gemessen, indem die elektrolytische Dissoziation durch Zusatz von Tetraphenylbornatrium unterdruckt wurde. Oberhalb von 20°C ergibt sich bei Auftragung nach ARRHENIUS eine Gerade, aus welcher Aktivierungsenergie Ec und Frequenzfaktor Ac des Kontaktionenpaares zu berechnen sind. Diese Parameter stimmen in guter Naherung mit den E- und A- Werten uberein, die in sehr schwach polaren Losungsmitteln fur die anionische Polymerisation erhalten werden. Unterhalb von +20°C weich…

1981

The anionic polymerization of tert-butyl methacrylate (TBMA) in tetrahydrofuran, using Na+ and Cs+ as counterions proceeds without side reactions even at room temperature. The resulting molecular weight distributions are nearly monodisperse (Mw/Mn ⩽ 1,01). The rate constants for the propagation of ion pairs were measured in the range from + 15 to −100°C. The Arrhenius plots are linear, but different for the two counterions, resulting in the following numerical values for the frequency exponent A and the activation energy Ea: A = 8,5 and Ea = 7,2 kcal/mol = 30 kJ/mol for Na+; A = 9,5 and Ea = 5,6 kcal/mol = 23 kJ/mol for Cs+. The difference between the counterions, which is in contrast to th…

ELECTROCHEMICALLY ASSISTED ATOM TRANSFER RADICAL GRAFT COPOLYMERIZATION. PRELIMINARY STUDIES

2012

Atom transfer radical polymerization (ATRP) is a versatile technique for exerting precise control over polymer molecular weights, molecular weight distributions, and complex architectures. It has been recently shown that an externally applied electrochemical potential can reversibly activate the copper catalyst for this process by a one-electron reduction of an initially added air-stable cubric species (Cu(II)/Ligand) [1-2]. In particular Gennaro and co-authors have shown that the polymerization kinetic can be changed modulating the external potential [1-2]. In the last years, an increasing interest has been devoted to synthesis of graft copolymers obtained from commercial polymers for inco…

On thermal behaviour of DMC catalysts for ring opening polymerization of epoxides

2016

Abstract The thermoanalytical studies of two types of the double metal cyanide catalysts were carried out. The identity of the catalysts was characterized by an elemental analysis and FTIR. The thermoanalytical examinations performed with the use of TG-DSC, EGA-FTIR, EGA-MS shed new light on views of the bonding of the ligands in the DMC. The chemical justification of the processes responsible for the TG/DSC steps was proposed. Several organic ligand complexing states were found in both types of catalysts. The ligand-DMC bondings were decomposing stepwise in relatively low temperature ranges, which could suggest their negligible role at catalytic reaction being performed usually at higher t…

Overexpression of a cell wall enzyme reduces xyloglucan depolymerization and softening of transgenic tomato fruits.

2010

Xyloglucan xyloglucosyltransferase/endohydrolase (XTHs: EC 2.4.1.207 and/or EC 3.2.1.151) has been proposed to have a dual role integrating newly secreted xyloglucan chains into an existing wall-bound xyloglucan and restructuring existing cell wall material by catalyzing transglucosylation between previously wall bound xyloglucan molecules. In this work we generated transgenic tomatoes with altered levels of an XTH gene. These transgenic fruits showed significant overexpression of the XTH proteins in comparison with the wild type. Specific XET activity was approximately 4.33 fold higher in the transgenic fruits compared with the wild type fruits, although in both cases the activity decrease…