Search results for "polymerization"

Cover Picture: Nanostructuring with a Crosslinkable Discotic Material (Small 8/2007)

2007

Low-fouling, mixed-charge poly-L-lysine polymers with anionic oligopeptide side-chains

2018

Biosensors and biomedical devices require antifouling surfaces to prevent the non-specific adhesion of proteins or cells, for example, when aiming to detect circulating cancer biomarkers in complex natural media (e.g., in blood plasma or serum). A mixed-charge polymer was prepared by the coupling of a cationic polyelectrolyte and an anionic oligopeptide through a modified "grafting-to" method. The poly-l-lysine (PLL) backbone was modified with different percentages (y%) of maleimide-NHS ester chains (PLL-mal(y%), from 13% to 26%), to produce cationic polymers with specific grafting densities, obtaining a mixed-charge polymer. The anionic oligopeptide structure (CEEEEE) included one cysteine…

Following ionic activity by electrochemistry during the polymerase chain reaction

2009

The most commonly used technique for gene detection is the polymerase chain reaction (PCR). PCR is associated with alterations in ionic activity because inorganic pyrophosphate (PPi) and inorganic phosphate (Pi) ions are produced during nucleotide polymerization. To maintain electro-neutrality, magnesium, potassium, and ammonium ions are bound to DNA. Deoxynucleotides are also bound to DNA during PCR. Some authors have described DNA itself as an electrically conducting polymer formed by base stapling with the formation of extensive Pi systems. In the current study, alterations in electrical conductivity determined experimentally during PCR are reported, and a model explaining the observed c…

Photoimaging through in-Situ Photopolymerization of Heterobifunctional Mesogenic Compounds in Liquid Crystalline State

2007

A series of heterobifunctional mesogenic biphenyl esters having two different polymerizable groups, i.e., acryl and diacetylene groups, were synthesized and their thermal behaviors and polymerization investigated. All compounds showed enantiotropic transitions. Under POM, highly birefringent focal-conic fan textures appeared on heating and cooling from the isotropic melt. Compounds 6−8 having a butyl spacer between a biphenyl and a diacetylene group exhibited LC phases even at room temperature. The X-ray diffractograms of compounds 6−8 showed a set of reflections in the small-angle region. They consisted of more than three sharp diffraction peaks with d spacings in the ratio of 1:1/2:1/3, s…

Isostructural potassium and thallium salts of sterically crowded triazenes: a structural and computational study.

2008

Because of their similar cationic radii, potassium and thallium(I) compounds are usually regarded as closely related. Homologous molecular species containing either K(+) or Tl(+) are very rare, however. We have synthesized potassium and thallium salts MN3RR' derived from the biphenyl- or terphenyl-substituted triazenes Tph2N3H (1a), Dmp(Mph)N3H (1b), Dmp(Tph)N3H (1c), and (Me4Ter)2N3H (1d) (Dmp=2,6-Mes 2C6H3 with Mes=2,4,6-Me3C6H2; Me4Ter=2,6-(3,5-Me2C6H3)2C6H3; Mph=2-MesC6H4; Tph=2-TripC6H4 with Trip=2,4,6-(i)Pr3C6H2). The potassium complexes 2a- d were obtained in almost quantitative yield from the reaction of 1a- d with potassium metal in n-heptane. Metalation of 1a- d with TlOEt afforde…

Characterization of melt-polymerized polycarbonate: preparative fractionation, branching distribution and simulation

2001

Melt-polymerized bisphenol-A polycarbonate materials characterized by a low degree of branching were fractionated according to molecular weight by the continuous polymer fractionation (CPF) method. The distribution of two types of end-groups and in-chain salicylate moieties arising from thermal rearrangement reactions were assessed across the molecular weight distribution by analysis of the fractions. Experimentally determined branching densities of the fractions agreed well with a molecular simulation based on a random sampling polycondensation model. Both simulation and experiments showed that the branching density increases with molecular weight in the experimentally accessible range. (C…

Electronic Properties of Mixed-Valence Manganates:  The Role of Mn Substitutional Defects

2002

Single-phase perovskites in the solid solution series La0.7+yA0.3-yMn1-xMxO3 (with 0.00 ≤ x ≤ 0.10; A = Sr2+, M = Cu2+, Zn2+, Sc3+, Cr3+, Co3+, and Ga3+; A = Ba2+, M = Cu2+, Zn2+, and Sc3+) have been prepared via the acetic acid solutions freeze-drying method. This soft procedure makes possible strict stoichiometric control, and the synthetic variables allow one to maintain a constant proportion of Mn4+ (ca. 32%) in the 47 compounds prepared. In this way, the concentration of cationic vacancies at A and B sites is practically negligible in all cases. X-ray powder diffraction patterns corresponding to the 47 compounds have been completely indexed with rhombohedral perovskite cells. The cryst…

Controlled radical polymerization of styrene in miniemulsion polymerization using reversible addition fragmentation chain transfer

2003

Abstract Miniemulsion polymerizations of styrene in the presence of two reversible addition–fragmentation chain-transfer (RAFT) agents were studied. The rates were significantly retarded by the presence of a RAFT agents S -(thiobenzoyl)thioglycolic acid, 1 , or dithiobenzoic acid 1-phenylethyl ester, 2 . Control in miniemulsion polymerization is not as good as for bulk polymerizations. The miniemulsions could also be stabilized against Ostwald ripening by a polymer terminated by a dithiobenzoic moiety. In this case, the polymerization was not controlled because of the generation of renucleated particles. To cite this article: I. Uzulina et al., C. R. Chimie 6 (2003).

Polymere ester von säuren des phosphors, 4. Polymerisation des 2-äthoxy-2-oxo-4,5-dihydro-1,3,2-dioxaphosphorins

1976

Die ringoffnende Polymerisation des 2-Athoxy-2-oxo-4,5-dihydro-1,3,2-dioxaphosphorins (1) mit Alkoholaten als Initiatoren, ist durch folgende Merkmale gekennzeichnet: (a) Zur Polymerisation sind Temperaturen von uber 100°C und Reaktionszeiten von vielen Tagen erforderlich. (b) Es stellt sich ein Polymerisations-Depolymerisations-Gleichgewicht ein. Fur 125°C liegt der maximale Umsatz bei der Polymerisation in Substanz bei 70%. (c) Die Polymerisationsenthalpie hat den Wert 0±12,6 kJ mol—1 (0±3 kcal mol—1). (d) Es werden nur Oligomere gebildet. Die Ausbeute an Substanz mit Pn > 5 liegt um 3%. Die Oligomeren mit Pn = 1 bis 5 werden durch Dunnschichtchromatographie getrennt und durch Massenspekt…

Cationic and Zwitterionic Polymerizable Surfactants:  Quaternary Ammonium Dialkyl Maleates. 1. Synthesis and Characterization

1999

Cationic and zwitterionic reactive dialkyl maleates with different hydrophobic chain lengths (R = C10H21, C12H25, C16H33, and C18H37), and some similar surfactants without double bonds were synthesized with an aim to use them as stabilizers in the batch and seeded emulsion copolymerization of styrene and butyl acrylate (part 2 of this series). Surfactants are obtained in a three-step synthesis, starting from ring opening of maleic anhydride, followed by O alkylation with an aminoalkyl compound, and finishing with quaternization of the amino group in the hydrophilic part of the molecule. The chemical structure of surfactants was confirmed by 1H NMR. Melting points and critical micelle concen…