Search results for "molar mass distribution"
showing 10 items of 115 documents
Convenient Access to α‐Amino‐ω‐Hydroxyl Heterobifunctional PEG and PPO via a Sacrificial Hexahydro‐Triazine Star Strategy
2019
The anionic ring opening polymerizations of ethylene oxide (EO) and propylene oxide (PO) are performed by using 1,3,5-triethanol hexahydro-1,3,5-triazine (TrAz) as a "sacrificial" trifunctional initiator. Well-defined three-arm star polymers are obtained with a narrow molecular weight distribution (M w /M n < 1.1). Molecular weights range from 3-15 kg mol-1 . Since these star polymers possess an acid-labile hexahydro-triazine core, acidic hydrolysis leads to cleavage of the arms. This gives access to well-defined α-amino-ω-hydroxyl heterobifunctional poly(ethylene glycol) (PEG) and poly(propylene oxide) (PPO) in the molecular weight range of 1-5 kg mol-1 and low dispersity M w /M n < 1.1. T…
Secondary structure of peptides. 4:13C-Nmr CP/MAS investigation of solid oligo- and poly(L-alanines)
1983
Primary and tertiary amine-initiated polymerizations of L-alanine-N-carboxyanhydride (L-Ala-NCA) were conducted at 20 or 100°C in a variety of solvents. The 75.5-MHz 13C-nmr CP/MAS spectra of the resulting poly(L-alanines) revealed that all samples contain both α-helix and pleated-sheet structures. Depending on the reaction conditions the α-helix content varied between ca. 1 and 99%. Reprecipitation from aprotic nonsolvents does not change the α-helix/β-sheet ratio, indicating that this ratio is thermodynamically controlled. Since relatively large amounts of oligopeptides of degree of polymerization (DP) 4–6 can be extracted by means of acetic acid, it is concluded that (a) most poly(L-alan…
1988
Synthese par alkylation reductrice de l'anthracene par des electrophiles bifonctionnels comme le dibromo-1,3 propane. Le polymere du titre est un precurseur du polymere redox polyanthrylenetrimethylene
Über die bestimmung der strömungsdispersion zur ermittlung von molekulargewichtsverteilungen mit der gelchromatographie
1974
Die Kenntnis der axialen Dispersion ist eine notwendige Voraussetzung zur Ermittlung von Molekulargewichtsverteilungen aus der gelchromatographischen Elutionskurve. Die vorliegende Arbeit beschaftigt sich mit der Bestimmung der axialen Dispersion unter Verwendung monodisperser Polymerer. Abschliesend wird ein Verfahren vorgeschlagen, welches aus der gelchromatographischen Elutionskurve von Proben mit bekannter Molekulargewichtsverteilung die Dispersion naherungsweise zu ermitteln gestattet. The knowledge of the axial dispersion is necessary for the determination of molecular weight distributions from gel permeation chromatography elution diagrams. This work deal with the determination of th…
Molar Mass Distribution and Size of Hydroxyethyl Starch Fractions Obtained by Continuous Polymer Fractionation
2002
By the use of continuous polymer fractionation (CPF) the initial polymer can be separated into fractions of different molar masses, which makes it possible to obtain hydroxyethyl starch (HES) fractions tailor-made for specific application. Two samples of HES (HES A and HES B) were fractionated by means of CPF. By size-exclusion chromatography-multi-angle laser light-scattering-differential refractive index (SEC/ MALLS/DRI) measurements it was shown that CPF is able to remove the low-molar-mass components and to adjust the samples to various desired molar masses with lower polydispersities than the original samples. In terms of the weight-average mean molar mass M w , the sol fractions have …
Über die bestimmung des zahlenmittels des molekulargewichts von polyoxymethylenen. 36. Mitt. Über polyoxymethylene
1968
Die Bestimmung des Zahlenmittels des Molekulargewichts (Mn) von Polyoxymethylenen durch Osmose, durch Kryoskopie, durch chemische und infrarotspektroskopische Endgruppenbestimmung und durch andere Methoden wird diskutiert. Osmotische Messungen in Phenol bei 90°C gelangen mit Cellophanmembranen besser als mit Glasmembranen. Kryoskopische Messungen nach RAST in Campher ergaben nur in Gegenwart eines Antioxydans zuverlassige Ergebnisse. Zur Endgruppenanalyse wurde vor allem die infrarotspektroskopische Bestimmung von Acetatgruppen weiterentwickelt; zur Auswertung wurde die Intensitat der Carbonylbande bei 5,70 μ in Beziehung gesetzt zu der CH2-Bande bei 6,8 μ und eine Eichung mit Hilfe des Chr…
General Kinetic Analysis and Comparison of Molecular Weight Distributions for Various Mechanisms of Activity Exchange in Living Polymerizations
1997
The molecular weight distributions in many living (e.g. anionic, group transfer, cationic, and radical) polymerizations strongly depend on the dynamics of various equilibria between chain ends of d...
Synthesis of linear and three-arm star tert-chlorine-telechelic polyisobutylenes by a two-step conventional laboratory process
1997
A two-step conventional laboratory process was developed for the synthesis of mono- and difunctional linear and three-arm star tert-chlorine-telechelic polyisobutylenes (PIB) with desired molecular weights (MW) and narrow molecular weight distribution (MWD) by living carbocationic polymerization (LCCP). This polymerization method applies easy to handle operations and chemicals. LCCP of isobutylene (IB), was carried out in CH2Cl2 as solvent and with BCl3 as coinitiator in the first step to obtain soluble low MW PIB prepolymer with narrow MWD. This was followed by addition of hexane, TiCl4 and additional monomer in the second step to prepare PIBs with desired MW and narrow MWD in practically …
The calculation of the number-average degree of polymerization starting from intrinsic viscosity and overall rate
1962
The relation between the intrinsic viscosity [η] and the number-average degree of polymerization Pn is a function of the molecular weight distribution of the polymer. In a polymer in which the termination of polymer radicals occurs partly by combination of two growing chains, this molecular weight distribution depends on number and extent of additional reactions such as chain transfer; i.e., it is variable. Therefore Pn of such polymers cannot be obtained from intrinsic viscosity measurements by means of an equation of the type [η] = KPna. A new method is proposed which allows the evaluation of Pn in these cases, without necessity of osmotic (or related) measurements or fractionation. The v…
Synthesis and Characterization of Isotactic Poly(1-hexene)/Branched Polyethylene Multiblock Copolymer via Chain Shuttling Polymerization Technique
2018
Understanding from the underlying mechanism of chain shuttling polymerization (CSP) is limited due to scarceness of successful reports and incompetence of traditional characterization techniques to distinguish blocky structures. Here, a simple synthesis approach for production of an isotactic poly(1-hexene)/branched polyethylene multiblock copolymer from a 1-hexene monomer is presented. Resulting copolymers can be easily characterized because of their solubility in most organic solvents. This novel blocky architecture is synthesized using ansa-ethylenebis(1-η5-indenyl)zirconium dichloride and α-diimine nickel(II) bromide catalysts. While the former participates in 1,2-enchainment of monomer…