Search results for "Molar mass"
showing 9 items of 239 documents
The initial stages of the heterogeneous degradation of alkali cellulose by oxygen in relation to the morphology of native cotton cellulose
2007
Treatment of cotton cellulose with sodium hydroxide solutions of varying concentration over extended periods in the absence of oxygen markedly decreases the intrinsic viscosity of both the cellulose in cuoxam and its cellulose trinitrate derivative (CTN) in acetone. Light-scattering measurements show that the molecular weight does not change while the radius of gyration decreases and the second virial coefficient increases. The narrow molecular weight distribution of the native cotton is still maintained. Mild oxidation first causes the intrinsic viscosity to increase. At more prolonged oxidation times the viscosity decreases. These results are interpreted by an intramolecular cross-linking…
Absolutes Molekulargewicht und Molekulargewichtsverteilung von nativer, unbelichteter Baumwollcellulose
1965
An ausgereifter Cellulose einer noch geschlossenen Baumwollkapsel wurde das Molekulargewicht nach der Lichtstreuungsmethode bestimmt. Danach besitzt die native, unbelichtete Baumwollcellulose einen Polymerisationsgrad von Pw = 12500 ±10%. Der Wertsteht in guter Ubereinstimmung mit den Polymerisationsgraden, die am selben Praparat und in fruheren kinetischen Arbeiten an nativer Cellulose aus den gemessenen STAUDINGER-Indices mit der Eichbeziehung [η] = 4,46·P0,76 erhalten wurden. Ferner wurde am gleichen Praparat die Molekulargewichtsverteilung ermittelt. Eine Gegenuberstellung mit der Verteilung einer Baumwollcellulose bei 18% Umsatz zeigt, das der Polymerisationsgrad der Sekundarwandcellul…
Untersuchungen zum oxidativen abbau nativer cellulose. I. Das anfangsstadium des heterogenen abbaus von alkalicellulose aus baumwolle und eine bezieh…
1973
Behandlung nativer Baumwollcellulose mit NaOH verschiedener Konzentration uber langere Zeiten unter Reinstickstoff vermindert den STAUDINGER-Index der Cellulose in CUOXAM und des daraus hergestellten Cellulosetrinitrats (CTN) in Aceton um einen erheblichen Betrag. Lichtstreuungsmessungen zeigen, das wahrend dieses Prozesses das Molekulargewicht erhalten bleibt, wahrend der Tragheitsradius abnimmt und der 2. Virialkoeffizient zunimmt. Die enge Molekulargewichtsverteilung des nativen Produkts bleibt hierbei erhalten. Schwache Sauerstoffzufuhr erhoht zunachst die Viskositat, um sie erst bei langerem Abbau zu erniedrigen. Diese Phanomene werden folgendermasen gedeutet : Die Cellulosemolekule li…
Highly Syndiotactic or Isotactic Polyhydroxyalkanoates by Ligand-Controlled Yttrium-Catalyzed Stereoselective Ring-Opening Polymerization of Function…
2017
International audience; Reported herein is the first stereoselective controlled ROP of a specific family of racemic functional β-lactones, namely 4-alkoxymethylene-β-propiolactones (BPL(OR) s). This process is catalyzed by an yttrium complex stabilized by a nonchiral tetradentate amino alkoxy bisphenolate ligand _ONOO(R'2) ₍2-) , which features both a good activity and a high degree of control over the molar masses of the resulting functional poly(3-hydroxyalkanoate)s. A simple modification of the R' substituents in ortho and para position on the ligand platform allows for a complete reversal from virtually pure syndioselectivity (Ps up to 0.91 with R'=cumyl) to very high isoselectivity (Pi…
Tailored electrospun nanofibrous polycaprolactone/gelatin scaffolds into an acid hydrolytic solvent system
2018
[EN] Blended nanofibrous scaffolds based on polycaprolactone (PCL) and gelatin (Ge) were successfully prepared. A formic/acetic acid (1:1) mixture was used to dissolve PCL/Ge blends from 100/0 to 20/80 %wt in steps of 10 %wt. The hydrolysis of the PCL diluted in the formic/acetic acid mixture was considered as a method for tailoring the surface morphology and physicochemical features of the nanofibrous PCL/Ge scaffolds as a function of the dissolution time. The fibre diameter remained in the nanoscale range for all the studied scaffolds, which is crucial to mimic the extra-cellular matrix size. The reduction of the intrinsic viscosity, molar mass and hydrodynamic radius found for the PCL mo…
Transfers of small analytes in a multiphasic stirred fruit yoghurt model
2007
International audience; The transfer of small analytes in a multiphasic stirred fruit yoghurt model, made of a pectin gel aimed to mimic fruit pieces and of a dairy gel done with milk acidified by glucono-δ-lactone hydrolysis, have been studied. The concentration gradients between the pectin gel and the dairy gel were the driving force for the migration of small analytes (i.e. water, protons and colorants). Water migrated from the dairy to the pectin gel, causing modifications in the water content of both gels and an equilibration of their water activity at 0.938±0.003. Inversely, protons migrated from the pectin to the dairy gel. These changes in composition of both gels being likely to ha…
Titanium (IV) chloride complexes with salen ligands supported on magnesium carrier: Synthesis and use in ethylene polymerization
2009
The magnesium support with the formula MgCl 2 (THF) 0.32 (Et 2 AlCl) 0.36 was used for immobilization of salen complexes of titanium [Ti(salen)Cl 2 , Ti(salen(O-Me) 2 )Cl 2 ]. The effects of the catalyst composition (i.e. type of titanium complex and type of activator), polymerization temperature, polymerization time, and the effect of comonomer (1-octene) on the activity of the obtained supported catalysts, on the polymer characteristics (molecular weight, molecular weight distribution, melting point), and on the polymer morphology were studied. The findings were compared to those obtained for corresponding unsupported systems. Catalysts immobilization results in considerable changes in ca…
Titanium and Vanadium Catalysts with 2-Hydroxyphenyloxazoline and Oxazine Ligands for Ethylene-Norbornene (co)Polymerization
2019
A series of titanium and vanadium complexes with oxazoline 2-(4,5-dihydro-1,3-oxazol-2-yl)phenol (L1), 2-(4-methyl-4,5-dihydro-1,3-oxazol-2-yl)phenol (L2), and oxazine 2-(5,6-dihydro-4H-1,3-oxazin-2-yl)phenol (L3) ligands were synthesized, and their structures were determined by NMR and MS methods as (L)2MtCl2. The vanadium complexes were found to be highly active in ethylene (7300 kgPE/(molV·
Reactive Compatibilization of PBT/EVA Blends with an Ethylene-Acrylic Acid Copolymer and a Low Molar Mass Bis-Oxazoline
2004
Polyesters and polyolefins form highly incompatible blends with poor properties and gross morphology that hinder any practical applications. In this work, the possibility to compatibilize an incompatible blend of poly(butylene terephthalate) (PBT) with ethylene vinyl acetate (EVA) by adding a bis-oxazoline compound, 2,2'-(1,3-phenylene)-bis(2-oxazoline) (PBO), and an ethylene acrylic acid copolymer (EAA) as compatibilizer precursors has been studied. The results indicate that the binary uncompatibilized blends show poor mechanical properties and a bad morphology with scarce adhesion between the phases. The situation is only slightly improved when the EAA is added while the best performance …