Filtern
Erscheinungsjahr
Dokumenttyp
Schlagworte
- MALDI-TOF MS (21)
- Polylactide (16)
- Crystalinity (5)
- Crystallization (4)
- Cyclization (3)
- MALDI TOF MS (3)
- Polyglycolide (3)
- Polymerization (3)
- Ring-expansion polymerization (3)
- Adsorption (2)
- Amphiphiles (2)
- Block copolymers (2)
- Crystals (2)
- Isosorbide (2)
- MALDI (2)
- Pollen (2)
- Polycondensation (2)
- Silver nanoparticles (2)
- Synthesis (2)
- Transesterification (2)
- Alternating co-poly(ether pyridine)s (1)
- Annealing (1)
- Aromatic organic compounds, (1)
- Aromatic pollutants (1)
- Biobased (1)
- Biobased polymers (1)
- Biodegradable (1)
- Biosourced isosorbide (1)
- Caco-2 cells (1)
- Catalysts (1)
- Catalytic ability (1)
- Classification (1)
- Cyclic (1)
- Cycloaddition (1)
- Cyclopolymerization (1)
- Dendrons (1)
- Dynamic light scattering (1)
- ESI (1)
- Electrospray ionization (1)
- Europium (1)
- FTIR (1)
- Fatigue biaxial (1)
- Field-flow fractionation (1)
- Functionalized graphene nanoribbons (1)
- Fundamentals (1)
- Gradient chromatography (1)
- Graphene monomers (1)
- Graphene nanoribbons (1)
- Graphene wires (1)
- Green chemistry (1)
- Hexabenzocoronene (1)
- High performance liquid chromatography (1)
- Hyphenated techniques (1)
- ICP-MS (1)
- In vitro digestion (1)
- Inductively coupled plasma-mass spectrometry (1)
- Inlet ionization (1)
- Ion mobility (1)
- Isophthalic acid (1)
- Isotope dilution analysis (1)
- Liquid adsorption chromatography at critical conditions (1)
- Liquid chromatography (1)
- Liquid chromatography at critical conditions (1)
- MALDI Massenspektrometrie (1)
- MALDI-TOF mass spectrometry (1)
- Matrices (1)
- Matrix-assisted ionization ion mobility spectrometry mass spectrometry (1)
- Matrix-assisted laser desorption/ionization (1)
- Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) (1)
- Mechanism of polymerization (1)
- Multivariate analyses (1)
- N-vinyl pyrrolidone (1)
- Oligospiroketals (1)
- On-surface polymerization (1)
- Partial least square discriminant analysis (PLS-DA) (1)
- Pentafluoropyridine (1)
- Phenolic compounds (1)
- Poly(ether-phosphoramide)s sulfides (1)
- Poly(ethylene glycol) (1)
- Polyesters (1)
- Polyforamidine (1)
- Polymer film (1)
- Polysarcosine (1)
- Principal component analysis (PCA) (1)
- ROPPOC (1)
- Raman (1)
- Renewable resources (1)
- Reversible addition fragmentation chain transfer (RAFT) (1)
- Reversible addition/fragmentation chain transfer (RAFT) (1)
- Ring-opening polymerization (1)
- SAXS (1)
- SEC (1)
- Semi-interpenetrating networks (1)
- Silica gel modification (1)
- Size-exclusion chromatography (1)
- Small-angle X-ray scattering (1)
- Sorption isotherm (1)
- Sorption mechanism (1)
- Speciation (1)
- Stereocomplex (1)
- Succinic acid (1)
- Vacuum ionization (1)
- mass spectrometry (1)
- polyionic liquids (1)
- reversible addition fragmentation chain transfer (RAFT) polymerization (1)
- ring-expansion polymerization (1)
- surface modification (1)
Organisationseinheit der BAM
A poly(L-lactide) with a trifluoroethyl ester end group and an average degree of polymerization (DP) of 50 was synthesized by ROP of L-lactide initiated with trifluoroethanol. Small-angle X-ray scattering (SAXS) in combination with differential scanning calorimetry (DSC) measurements revealed an average crystal thickness of 13 nm, corresponding to 45 repeat units. This suggests that most crystallites were formed by extended PLA chains, and both flat surfaces were covered by CF3 groups. The crystalline PLAs were annealed at 140 or 160 °C in the presence of two catalysts: tin(II) 2-ethylhexanoate, (SnOct2) or dibutyltin bis(pentafluorophenoxide) (BuSnPhF). The chemical reactions, such as polycondensation and cyclization, proceeded in the solid state and were monitored by matrix-assisted laser desorption/ionization time-offlight (MALDI TOF) mass spectrometry and gel permeation chromatography (GPC) measurements. Under optimal conditions a large fraction of linear chains was transformed into crystallites composed of extended cycles. Additionally, MALDI TOF MS analysis of GPC fractions from samples annealed for 28 or 42 days detected chain elongation of the linear species up to a factor of 20.
The nucleophilic thiol–ene (thia-Michael) reaction between molecular rods bearing terminal thiols and bis-maleimides was investigated. The molecular rods have oligospiroketal (OSK) and oligospirothioketal (OSTK) backbones. Contrary to the expectations, cyclic oligomers were always obtained instead of linear rigid-rod polymers. Replacing the OS(T)K rods with a flexible chain yielded polymeric products, suggesting that the OS(T)K structure is responsible for the formation of cyclic products. The reason for the preferred formation of cyclic products is due to the presence of folded conformations, which have already been described for articulated rods.
Polysarcosine (M-n = 3650-20 000 g mol(-1), D similar to 1.1) was synthesized from the air and moisture stable N-phenoxycarbonyl-N-methylglycine. Polymerization was achieved by in situ transformation of the urethane precursor into the corresponding N-methylglycine-N-carboxyanhydride, when in the presence of a non-nucleophilic tertiary amine base and a primary amine initiator.
The Na salt of chloroacetic acid is condensed in suspension. Furthermore,glycolic acid is condensed in bulk or in concentrated solution by means of SnCl2 or 4-toluene sulfonic acid (TSA) as catalysts. The temperatures are varied from 160 to 200°C and the time from 1 to 5 days. Low molar mass cyclic poly(glycolic acid) (PGA) is detected by means of matrix-assisted laser desorption ionization time-of-flight (MALDI TOF) mass spectrometry in most PGAs. A predominance of certain cycles having an even number of repeat units is observed suggesting a thermodynamically favored formation of extended-ring crystals. Extremely high melting temperatures (up to 237.5°C)and high melting enthalpies are found for polycondensations with TSA in 1,2-dichlorobenzene.
Glycolide was polymerized in bulk by means of four different ROPPOC catalysts: tin(II) 2-ethylhexanoate (SnOct2), dibutyltin bis(pentafluoro-phenoxide) (BuSnOPF),zinc biscaproate (ZnCap), and zinc bis(pentafluoro-phenyl sulfide) (ZnSPF). The temperature was varied between 110 and 180°C and the time between 3 h and 7 days. For the few polyglycolides (PGAs) that were soluble extremely high molecular masses were obtained. The MALDI TOF mass spectra had all a low signal-to-noise ration and displayed the peaks of cyclic PGAs with a“saw-tooth pattern ”indicating formation of extended-ring crystallites in the mass range below m/z 2500. The shape of DSC curves varied considerably with catalyst and reaction conditions, whereas the long-distance values measured by SAXS were small and varied little with the polymeriza-tion conditions.
Two kinds of cyclic poly(D- and L-lactide)s were synthesized, namely CI labeled samples mainly consisting of even-numbered cycles with low dispersity and CII, CIII or CIV-labeled ones consisting of equal amounts of even and odd-numbered cycles with high dispersity and igher molecular weights (Mw up to 300 000). Furthermore, linear poly L-lactide)s were prepared by initiation with ethanol and in both series the molecular weight was varied. The formation of stereocomplexes from cyclic poly(D-lactide)s and all kinds of poly L-lactide)s was performed in dichloromethane/toluene mixtures. The stereocomplexes crystallized from the reaction mixture were characterized in the virgin state and after annealing at 205 °C.
Stereocomplexes free of stereohomopolymers with crystallinities up to 80% were obtained from all experiments in yields ranging from 60 to 80%. Despite the high annealing temperature (maintained for 1 h), little transesterification was observed and the crystallinity slightly increased.
SnOct2 (Sn(II) 2-ethylhexanoate) catalyzed ROPs of L-lactide were performed in bulk with eight different alcohols as initiators. The time was varied between 1 h and 24 h for all initiators. For two initiators the temperature was also lowered to 115 ◦C. Even-numbered chains were predominantly formed in all polymerizations at short times, but the rate of transesterification (e.g. even/odd equilibration) and the molecular weight distribution were found to depend significantly on the nature of the initiator. Observed transesterification reactions also continued in solid poly (L-lactide), and with the most active initiator, almost total equilibration was achieved even at 130 ◦C. This means that all chains including those of the crystallites were involved in transesterification reactions proceeding across the flat surfaces of the crystallites. The more or less equilibrated crystalline polylactides were characterized by DSC and SAXS measurements with regard to their melting temperature (Tm), crystallinity and crystal thickness.
L-lactide (LA) was polymerized in toluene by means of neat tin(II) 2-ethylhexanoate (SnOct2). Concentration, time and temperature were varied. The isothermally crystallized polyLAs (PLA) were characterized in the virgin state with regard to topology, molar mass, melting temperature (Tm), crystal modification, high or low Tm morphology, crystallinity and crystal thickness. Even a small amount of solvent favored cyclization relative to polymerization in bulk, so that cyclic polylactides were obtained at 115 ◦C and even at 95 ◦C. At all temperatures the α-modification of PLA was obtained along with crystallinities up to 90%. With 6 M solution the high Tm morphology with Tm’s > 190 ◦C was obtained at 115 ◦C. The crystal thickness of crystallites grown from solution at 115 ◦C was on the average 10–20% higher than that of PLA polymerized in bulk. At a polymerization temperature of 75 ◦C cyclization was incomplete and fewer perfect crystallites were formed. A new hypothesis for the crystal growth of cyclic polyLAs is proposed.
A reversed phase high performance liquid chromatography coupled to an inductively coupled Plasma mass spectrometer (HPLC–ICP-MS) approach in combination with isotope dilution analysis (IDA) for the separation and parallel quantification of nanostructured and ionic silver (Ag) is presented. The main Focus of this work was the determination of the ionic Ag concentration. For a sufficient stabilization of the Ions without dissolving the nanoparticles (NPs), the eluent had to be initially optimized. The determined Ag ion concentration was in a good agreement with results obtained using ultrafiltration. Further, the mechanism of the NP separation in the HPLC column was investigated. Typical size exclusion effects were found by comparing results from columns with different pore sizes. Since the recovery rates decreased with increasing Ag NP size and large Ag NPs did not elute from the column, additional interactions of the particles with the stationary phase were assumed. Our results reveal that the presented method is not only applicable to Ag NPs, but also to gold and polystyrene NPs. Finally, IDA-HPLC-ICP-MS experiments in single particle mode were performed to determine the particle cut-off size. The comparison with conventional spICP-MS experiments resulted in a similar diameter and particle size distribution.
In the framework of the development of green analytical chemistry, a silica gel (SG) coated with a semi-penetrating network based on the partially biosourced poly(ethersulfone) is studied for a greener extraction process of aromatic organic pollutants. An optimized composition of the semi-penetrating network (80% of the linear polymer (LP): isosorbide-based poly(ethersulfone) and 20% cross-linking agent (XP) type bismaleimide) leads to a total adsorption of the selected aromatic pollutants, whatever their hydrophilicity. Adsorption characteristic, kinetics and isotherms of the SG-semi-INP LP80/XP20 for p-hydroxybenzoic acid and for toluic acid were studied. Langmuir model led to a better ftting of the adsorption isotherms; the adsorption of toluic acid is easier than that of p-hydroxybenzoic acid. 1/n values of benzoic acid was lower for SGsemi-INP LP80/XP20 compared to biochar and to cross-linked methacrylate resin, showing a higher adsorption efciency.