Search results for "medium"

Saccharomyces eubayanusandSaccharomyces uvarumassociated with the fermentation ofAraucaria araucanaseeds in Patagonia

2014

Mudai is a traditional fermented beverage, made from the seeds of the Araucaria araucana tree by Mapuche communities. The main goal of the present study was to identify and characterize the yeast microbiota responsible of Mudai fermentation as well as from A. araucana seeds and bark from different locations in Northern Patagonia. Only Hanseniaspora uvarum and a commercial bakery strain of Saccharomyces cerevisiae were isolated from Mudai and all Saccharomyces isolates recovered from A. araucana seed and bark samples belonged to the cryotolerant species Saccharomyces eubayanus and Saccharomyces uvarum. These two species were already reported in Nothofagus trees from Patagonia; however, this …

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…

1992

Semi-IPN's of different composition, based on linear poly(methyl vinyl ether) (PVME) and crosslinked polystyrene are studied using stress and birefringence measurements in simple elongation. From quasistatic stress-strain experiments at constant T(experiment)-Tg, it can be deduced that the stress results only from the deformation of the polystyrene network, while the PVME chains do not contribute to the macroscopic stress. The concentration dependence of the network modulus is adequately described by the rubber elastic theories

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…

Study of the Curing Process of DGEBA Epoxy Resin Through Structural Investigation

2015

In this work, a multi-scale approach with different analytical methods is applied to study the curing process and the structural properties of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin. This monomer, thermally cured using 4,4′-diaminodiphenilsulfone (DDS) as hardener, is analyzed after 10, 45, 90, and 120 min of reaction time at 180 °C to obtain information on samples with different cross-linking densities. Samples are also characterized after extraction in acetone in order to obtain structural information on the insoluble parts. For this purpose, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), solid-state nuclear magnetic resonance (ss-NMR),…

Design and synthesis of biobased epoxy thermosets from biorenewable resources

2017

International audience; Biobased diepoxy synthons derived from isoeugenol, eugenol or resorcinol (DGE-isoEu, DGE-Eu and DGER, respectively) have been used as epoxy monomers in replacement of the diglycidyl ether of bisphenol A (DGEBA). Their curing with six different biobased anhydride hardeners leads to fully biobased epoxy thermosets. These materials exhibit interesting thermal and mechanical properties comparable to those obtained with conventional petrosourced DGEBA-based epoxy resins cured in similar conditions. In particular, a high Tg in the range of 90–130 °C and instantaneous moduli higher than 4.3 GPa have been recorded. These good performances are very encouraging, making these n…

Synthesis of AB and ABA block copolymers as compatibilizers in nylon 6/polycarbonate blends

1996

Nylon 6 (Ny6) and Bisphenol A polycarbonate (PC) are immiscible and form biphasic blends. To improve the compatibility of Ny6 and PC several ABA and AB Ny6/PC block copolymers were synthesized, and their compatibilizing behavior on the blends were tested. Block copolymers were prepared by reacting monoamino- or diamino-terminated Ny6 homopolymers with high molecular weight PC at 130°C in anhydrous DMSO. The reaction of diamino- and monoamino-terminated Ny6 with polycarbonate produces block copolymers of the type PC-Ny6-PC (ABA) and PC-Ny6 (AB), respectively, plus a certain amount of unconverted PC degradated to lower molecular weights. To separate the block copolymer from the unconverted PC…

Evaluation of Ligno Boost™ softwood kraft lignin epoxidation as an approach for its application in cured epoxy resins

2018

Abstract In this study, modification of LignoBoost™ softwood kraft lignin with epichlorhydrin in water-organic solvents media was realized. Lignin-based epoxy resins were obtained by two ways: acetone extraction of glycidylated lignin or glycidylation of the acetone soluble lignin fraction. The effect of glycidylation regimes on the yields of acetone soluble fractions, their functional composition and physical-chemical characteristics was investigated using wet chemistry methods, FTIR spectroscopy, size exclusion chromatography (SEC) and differential scanning calorimetry (DSC). The positive effect of the biphasic phase transfer catalytic system – KOH/quaternary ammonium salt – on glycidylat…

Dielectric spectroscopy of novel thiol-ene/epoxy thermosets obtained from allyl-modified hyperbranched poly (ethyleneimine) and diglycidylether of bi…

2019

[EN] Dielectric Thermal Analysis (DETA) of a series of new thermoset obtained by click chemistry was performed. The new thermosets were obtained by a dual-curing process consisting in a first photochemical thiol-ene, followed by a thermal thiol-epoxy starting from an allyl-terminated hyperbranched poly(ethyleneimine) (HBPEI) and different proportions of diglycidylether of bisphenol A (DGEBA) and the corresponding stoichiometric proportions of pentaerythritol tetrakis (3-mercaptopropionate, PETMP). The dielectric behaviour was obtained experimentally supressing the conductive effects. Two sub-Tg intramolecular non-cooperative gamma and beta relaxations and an intermolecular cooperative alpha…

Metal complexes of an amine bisphenol with a thiophene side-arm

2010

Dioxomolybdenum(VI) and oxotungsten(VI) complexes with a new amine bisphenol ligand (H2L) are reported. The ligand which carries a neutral nitrogen atom, two phenolic oxygen atoms and a thiophene side-arm was synthesized by a simple one-pot Mannich reaction. Further reaction with [MoO2(acac)2] yielded a monomeric molybdenum complex [MoO2(L)(MeOH)] (2a) or a dimeric complex [Mo2O2(μ-O)2(L)2] (2b), depending on the reaction conditions. The reaction with a tungsten trisglycolate [W(eg)3] led to the formation of a monomeric compound [WO(eg)(L)] (3). In these complexes, the potentially tetradentate amine bisphenolate dianion coordinates as a tridentate O,N,O donor while the sulfur side-arm donor…