Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (168) (entfernen)
Referierte Publikation
- ja (168) (entfernen)
Schlagworte
- MALDI-TOF MS (55)
- Polylactide (40)
- Cyclization (26)
- MALDI (16)
- Polycondensation (15)
- Ring-opening polymerization (15)
- Polymerization (8)
- MALDI TOF MS (7)
- Crystallization (6)
- Pollen (6)
- Ring-expansion polymerization (6)
- Transesterification (6)
- Catalyst (5)
- Crystalinity (5)
- Isosorbide (5)
- Lactide (5)
- Mass spectrometry (5)
- Polyester (5)
- Polymere (5)
- Polymers (5)
- Catalysts (4)
- Ionization (4)
- MALDI Massenspektrometrie (4)
- MALDI-TOF mass spectrometry (4)
- Polyesters (4)
- Bismuth (3)
- Imaging (3)
- Liquid chromatography (3)
- Polylactides (3)
- ROPPOC (3)
- Ring opening polymerization (3)
- SEC (3)
- Small-angle X-ray scattering (3)
- Adsorption (2)
- Amphiphiles (2)
- Biobased polymers (2)
- Biodegradable (2)
- Blends (2)
- Block copolymers (2)
- Catechol (2)
- Chromatographie (2)
- Coupling methods (2)
- Crosslinking (2)
- Crystals (2)
- Cyclic (2)
- Cyclopolymerization (2)
- Dispersity (2)
- Epsilon-caprolactone (2)
- FTIR (2)
- Field-flow fractionation (2)
- ICP-MS (2)
- Kopplung (2)
- MALDI mass spectrometry (2)
- MALDI-TOF-MS (2)
- MS/MS (2)
- Macrocycles (2)
- Massenspektrometrie (2)
- Multivariate statistics (2)
- Polyglycolide (2)
- Polymer (2)
- Polymerisation (2)
- Polystyrene (2)
- Polyurethane (2)
- Polyurethanes (2)
- Reversible addition fragmentation chain transfer (RAFT) (2)
- Ring-opening Polymerization (2)
- SAXS (2)
- Sample preparation (2)
- Silver nanoparticles (2)
- Synthesis (2)
- Thermal degradation (2)
- Tin catalysts (2)
- 2-oxazoline (1)
- A4F (1)
- AET (1)
- AFM (1)
- Adhesion promotion (1)
- Alternating co-poly(ether pyridine)s (1)
- Amphiphilic polymers (1)
- Annealing (1)
- Application (1)
- Aromatic organic compounds, (1)
- Aromatic pollutants (1)
- Artificial weathering (1)
- Aryl iodides (1)
- Asymmetric flow filed-flow fractionation (1)
- Asymmetrical flow field flow fractionation (AF4) (1)
- Attenuated total reflectance-Fourier transorm infrared spectroscopy (1)
- Biodegradability (1)
- Biodegradable polyesters (1)
- Biopolymers (1)
- Biosourced isosorbide (1)
- Blockcopolymer (1)
- CRM (1)
- Caco-2 cells (1)
- Caesium (1)
- Capillary electrophoresis (1)
- Capillary electrophoresis (CE) (1)
- Carbon fiberepoxy resin laminates (1)
- Carboxyl group (1)
- Catalytic ability (1)
- Cationic ring opening polymerization (1)
- Cationization (1)
- Chain scission (1)
- Chemical reduction of functional groups (1)
- Chromatography (1)
- Classification (1)
- Click chemistry (1)
- Conductive carbon tape (1)
- Conjugated oligomers (1)
- Controlled radical polymerization (1)
- Conversion (1)
- Copolyester (1)
- Copolymer composition (1)
- Copolymer sequence (1)
- Copolymeranalytik (1)
- Copolymerization (1)
- Cotton effect (1)
- Coupling (1)
- Cyclics (1)
- Cyclisation (1)
- Cycloaddition (1)
- Cycloparaphenylenes (1)
- DCTB (1)
- Degradation (1)
- Dendrimers (1)
- Dendrons (1)
- Dried droplet (1)
- Droplet (1)
- Dynamic light scattering (1)
- ESI (1)
- ESI-Massenspektrometrie (1)
- Electron paramagnetic resonance study (1)
- Electrospray (1)
- Electrospray ionization (1)
- Electrospray ionization (ESI) (1)
- Epsilon-Caprolactone (1)
- Epsilon-caprolactone (e-CL) (1)
- Europium (1)
- Foldamers (1)
- Fractionation of polymers (1)
- Fragmentierung (1)
- Friction (1)
- Ft-IR (1)
- Functionalized graphene nanoribbons (1)
- Fundamentals (1)
- Glycodendrimers (1)
- Glycolide (1)
- Gradient chromatography (1)
- Gradient elution (1)
- Gradient elution liquid chromatography (GELC) (1)
- Graphene monomers (1)
- Graphene nanoribbons (1)
- Graphene wires (1)
- Green chemistry (1)
- Hafnium (1)
- Heavy metals (1)
- Hexabenzocoronene (1)
- Hierarchical cluster analysis (1)
- Hierarchical self-assembly (1)
- High performance liquid chromatography (1)
- Host–guest systems (1)
- Humidity (1)
- Hybrid nanoparticles (1)
- Hydrolytic degradation (1)
- Hyphenated techniques (1)
- Imaging MS (1)
- In situ EXAFS (1)
- In situ SAXS/WAXS (1)
- In vitro digestion (1)
- Inductively coupled plasma-mass spectrometry (1)
- Inlet ionization (1)
- Intrinsic viscosity (1)
- Ion mobility (1)
- Ionization mass spectrometry (1)
- Iron oxide nanoparticles (1)
- Irreversible polycondensation (1)
- Isophthalic acid (1)
- Isotope dilution analysis (1)
- Jacobsen-Stockmayer theory (1)
- Kopplungsmethoden (1)
- L-lactide (1)
- LC-MS coupling (1)
- Lactides (1)
- Lacunary Keggin ion (1)
- Lanthanide ions (1)
- Laser-induced redox reactions (1)
- Layer topography (1)
- Lead ions (1)
- Light scattering (LS) (1)
- Liquid adsorption chromatography (1)
- Liquid adsorption chromatography at critical conditions (1)
- Liquid chromatography at critical conditions (1)
- Liquid chromatography under critical conditions (LCCC) (1)
- MALDI Imaging MS (1)
- MALDI TOF Massenspektrometrie (1)
- MALDI TOF mass spectrometry (1)
- MALDI-TOF (1)
- MALDI-TOF MS/MS (1)
- MOF (1)
- Mass Spectrometry (1)
- Mass spectrometry imaging (1)
- Materials Chemistry (1)
- Matrices (1)
- Matrix segregation (1)
- Matrix-assisted ionization ion mobility spectrometry mass spectrometry (1)
- Matrix-assisted laser desorption (1)
- Matrix-assisted laser desorption/ionization (1)
- Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) (1)
- Matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (1)
- Mechanism (1)
- Mechanism of polymerization (1)
- Mega-dalton (1)
- Metal ion complexation (1)
- Metal ion-intradendrimer complexes (1)
- Metal triflates (1)
- Microwave (1)
- Moisture (1)
- Molar mass determination (1)
- Molar mass distribution (1)
- Molecular masses (1)
- Molecular recognition (1)
- Morphology (1)
- Multicyclic polymers (1)
- Multivariate Statistics (1)
- Multivariate analyses (1)
- N-vinyl pyrrolidone (1)
- Nanolithography (1)
- Nanoparticle (1)
- Nanoparticles (1)
- Nanoparticles with same nominal diameter (1)
- Networks (1)
- Oligoazobenzene (1)
- Oligospiroketals (1)
- On-surface polymerization (1)
- Organic Chemistry (1)
- PCA (1)
- PET (1)
- Partial least square discriminant analysis (PLS-DA) (1)
- Pentafluoropyridine (1)
- Phenolic acid (1)
- Phenolic compounds (1)
- Phenyleneethynylenes (1)
- Phosphonate esters (1)
- Photoligation (1)
- Photooxidation (1)
- Photoswitchable (1)
- Plasma (1)
- Plasma modification (1)
- Pollen grains (1)
- Poly(ether-phosphoramide)s sulfides (1)
- Poly(ethylene glycol) (1)
- Poly(ethylene terephthalate) (1)
- Polyaddition (1)
- Polycaprolactone (1)
- Polycarbonate-co-dimethylsiloxane copolymer (1)
- Polycondensations (1)
- Polyelectrolytes (1)
- Polyethylene oxide (1)
- Polyforamidine (1)
- Polykondensation (1)
- Polymer MALDI (1)
- Polymer blends (1)
- Polymer film (1)
- Polymer reference materials (1)
- Polymerization mechanisms (1)
- Polymers and Plastics (1)
- Polyoxometalates (1)
- Polysarcosine (1)
- Principal component analysis (1)
- Principal component analysis (PCA) (1)
- Quantification (1)
- ROMP (1)
- Raman (1)
- Renewable resources (1)
- Reversible addition/fragmentation chain transfer (RAFT) (1)
- Ring opening polymerization (ROP) (1)
- Ring-opening Polymerisation (1)
- Ring-opening polymerizations (1)
- Salicylate (1)
- Sample loss (1)
- Sample pretreatment (1)
- Self-assembly (1)
- Semi-interpenetrating networks (1)
- Silica gel modification (1)
- Size exclusion chromatography (1)
- Size exclusion chromatography (SEC) (1)
- Size-exclusion chromatography (1)
- Sn catalysts (1)
- Soft ionization mass spectrometry (ESI, MALDI) (1)
- Software (1)
- Solvent-free (1)
- Sonoga (1)
- Sorption isotherm (1)
- Sorption mechanism (1)
- Speciation (1)
- Spirocyclic (1)
- Stereocomplex (1)
- Succinic acid (1)
- Sulfobetaines (1)
- Supramolecular chemistry (1)
- Surface coating (1)
- TPU (1)
- Target plate material (1)
- Telechelic polyesters (1)
- Thermo-desorption (1)
- Thermochemistry (1)
- Thin polymer layers (1)
- Tin acetates (1)
- Tin(II)octanoate (1)
- Toxicity (1)
- Triazenes (1)
- Two-dimensional off-line coupling (1)
- Two-dimensional-liquid chromatography (2D-LC) (1)
- UPLC (1)
- UV degradation (1)
- UV radiation (1)
- Ultraschallfalle (1)
- Universal calibration (1)
- Vacuum ionization (1)
- Water-soluble polymers (1)
- X-ray photoelectron spectroscopy (1)
- Zinc catalyst (1)
- a2 + b3 polycondensation (1)
- cyclization (1)
- dispersity (1)
- mass spectra (1)
- mass spectrometry (1)
- polycondensation (1)
- polyesters (1)
- polyionic liquids (1)
- reversible addition fragmentation chain transfer (RAFT) polymerization (1)
- ring-expansion polymerization (1)
- surface modification (1)
Organisationseinheit der BAM
- 6 Materialchemie (73)
- 6.3 Strukturanalytik (73)
- 1 Analytische Chemie; Referenzmaterialien (5)
- 1.2 Biophotonik (2)
- 1.7 Organische Spuren- und Lebensmittelanalytik (2)
- 6.6 Physik und chemische Analytik der Polymere (2)
- 7 Bauwerkssicherheit (2)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (2)
- 1.0 Abteilungsleitung und andere (1)
- 1.3 Instrumentelle Analytik (1)
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 with two cyclic catalysts − 2,2-dibutyl-2-stanna-1,3-dithiolane (DSTL) and 2-stanna-1,3-dioxa-4,5,6,7-dibenzepane (SnBiph). The monomer/initiator ratio, temperature (140 – 180 °C) and time (1–––4 days) were varied. The MALDI TOF mass spectra exclusively displayed peaks of cyclic polyglycolide (PGA) and revealed an unusual “saw-tooth pattern” in the mass range below m/z 2 500 suggesting formation of extended ring crystallites. The DSC measurements indicated increasing crystallinity with higher temperature and longer time, and after annealing for 4 d at 160 °C a hitherto unknown and unexpected glass transition was found in the temperature range of 170–185 °C. Linear PGAs prepared by means of metal alkoxides under identical conditions did not show the afore-mentioned features of the cyclic PGAs, neither in the mass spectra nor in the DSC measurements. All PGAs were also characterized by SAXS measurements, which revealed relatively small L-values suggesting formation of thin crystallites in all cases with little influence of the reaction conditions.
Ring-opening polymerizations (ROPs) of l-lactide (LA) were performed with ethyl l-lactate or 11-bromoundecanol as initiators (In) and tin(II) ethyl hexanoate (SnOct2) as catalyst (Cat) using four different LA/In ratios (20/1, 40/1, 60/1, and 100/1). One series of ROPs was conducted in bulk at 120 °C, yielding PLAs with low dispersities (Ð ~ 1.2–1.4), and a second series was conducted in bulk at 160 °C, yielding higher dispersities (Ð ~ 1.3–1.9). Samples from both series were annealed for 1 or 14 days at 140 °C in the presence of SnOct2. Both polycondensation and disproportionation reactions occurred, so that all four samples tended to form the same type of molar mass distribution below 10,000 Da, regardless of their initially different number average molar masses (Mn). Both initiators gave nearly identical results. The thermodynamic control of all reversible transesterification processes favored the formation of crystallites composed of chains with a Mn around 3500–3700, corresponding to a crystal thickness of 10–13 nm.
Solvent-free sample preparation offers some advantages over solvent-based techniques, such as improved accuracy, reproducibility and sensitivity, for matrix-assisted laser desorption/ionization (MALDI) analysis. However, little or no information is available on the application of solvent-free techniques for the MALDI analysis of polymer blends. Solvent-free sample preparation by ball milling was applied with varying sample-to-matrix ratios for MALDI time-of-flight mass spectrometry analysis of various polymers, including polystyrenes, poly(methyl methacrylate)s and poly(ethylene glycol)s. The peak intensity ratios were compared with those obtained after using the conventional dried droplet sample preparation method. In addition, solvent-assisted milling was also applied to improve sample homogeneities.
Depending on the sample preparation method used, different peak intensity ratios were found, showing varying degrees of suppression of the signal intensities of higher mass polymers. Ball milling for up to 30 min was required to achieve constant intensity ratios indicating homogeneous mixtures. The use of wet-assisted grinding to improve the homogeneity of the blends was found to be disadvantageous as it caused partial degradation and mass-dependent segregation of the polymers in the vials.The results clearly show that solvent-free sample preparation must be carefully considered when applied to synthetic polymer blends, as it may cause additional problems with regard to homogeneity and stability of the blends.
With 2,2-dibutyl-2-stanna-1,3-dithiolane (DSTL) and 2-stanna-1,3-dioxa-4,5,6,7-dibenzoxepane (SnBiPh) as catalysts ring-expansion polymerizations (REP) were performed either in 2 M solution using three different solvents and two different temperatures or in bulk at 140 and 120 ◦C. A kinetically controlled rapid REP up to weight average molecular masses (Mẃs) above 300 000 was followed by a slower degradation of the molecular masses at 140 ◦C, but not at 120 ◦C Furthermore, a low molecular mass cyclic poly(L-lactide) (cPLA) with a Mn around 16 000 was prepared by polymerization in dilute solution and used as starting material for ring-ring equilibration at 140 ◦C in 2 M solutions. Again, a decrease of the molecular mass was detectable, suggesting that the equilibrium Mn is below 5 000. The degradation of the molecular masses via RRE was surprisingly more effective in solid cyclic PLA than in solution, and a specific transesterification mechanism involving loops on the surface of crystallites is proposed. This degradation favored the formation of extended-ring crystallites, which were detectable by a “saw-tooth pattern” in their MALDI mass spectra.
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 usefulness of seven different Tin catalysts, Bismuth subsalicylate and Titan tetra(ethoxide) for the polycondensation of ethyl L-lactate (ELA) was examined at 150 °C/6 d. Dibutyltin bis(phenoxides) proved to be particularly effective. Despite the low reactivity of ELA, weight average molecular masses (Mw) up to 12 500 were found along with partial crystallization. Furthermore, polylactides (PLAs) of similar molecular masses were prepared via ELA-initiated ROPs of L-lactide by means of the four most effective polycondensation catalysts. The crystalline linear PLAs were annealed at 140 or 160 °C in the presence of these catalysts. The consequences of the transesterification reactions in the solid PLAs were studied by means of matrix-assisted laser desorption/ionization (MALDI TOF) mass spectrometry, gel permeation chromatography (GPC) and small-angle X-ray scattering (SAXS). The results indicate that polycondensation and formation of cycles proceed in the solid state via formation of loops on the surface of the crystallites. In summary, five different transesterification reactions are required to explain all results.
Alcohol-initiated ring-opening polymerizations (ROP) of L-lactide (LA) were studied in solution at 70 °C, whereupon the nature of the alcohol, the LA/initiator ratio, the LA/SnOct2 ratio and the time were varied. In contrast to literature, neat SnOct2 is catalytically active in THF and several aromatic but donor solvents, such as 1,3-dioxolane, dimethylformamide (DMF) or N-methyl pyrrolidone (NMP), strongly reduce the activity of SnOct2. In agreement with literature, no cycles were formed by neat SnOct2 at 70 °C in toluene, whereas almost complete cyclization occurs at 115 °C. This finding is attributed to strongly reduced mobility of the initially formed linear chains having one Sn-O-CH and one anhydride end group. Due to better solvation and enhanced mobility cyclization occurs in THF at 70 °C.
Ring-opening polymerizations of l-lactide are studied in bulk at 140 or 160 °C with zinc n-hexanoate, zinc 4-chlorothiophenolate, and zinc pentafluoro thiophenolate (ZnSPF) as catalysts. The reactivity increases in the given order.
With all three catalysts a high fraction of cycles is obtained only at polymerization (annealing) times around 7 d. With ZnSPF weight average molecular weights (Mw) up to 178 000, a Tm around 199 °C and a 𝚫Hm around 99 J g−1 were achieved. The samples annealed for 4 or 7 d also display a saw tooth pattern of the mass peak distribution in the matrix-assisted laser desorption/ionization time of flight spectra indicating transesterification reactions across the surface of extended ring crystals. This process optimizes the thermodynamical properties of the crystalline cyclic polylactides and is responsible for the high Tm and 𝚫Hm values.
1-Hydroxymethylnaphtalene (HMN) or 11-bromoundecanol (BUND) were used as initiators and Sn(II) 2-ethylhexanoate (SnOct2) as catalyst for ROPs of L-Lactide (LA) at 115 °C in bulk or in 4 M and 2M solutions in toluene. The LA/In ratio, the LA/Cat ratio and the time were varied. The matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectra exclusively displayed peaks of linear chains, when the ROPs were conducted in bulk. But in contrast to reports in the literature, mixtures of linear and cyclic poly(L-lactide) (PLA), were obtained, when the ROPs were performed in solution. The intensity distribution of the mass peaks of cyclic PLAs displayed a “saw-tooth pattern” after annealing in contrast to the mass peak distribution of the liner chains. This new phenomenon indicated that cyclic PLAs and linear PLAs crystallized in separate crystals from the same reaction mixture. This conclusion was confirmed by fractionated crystallization from 2 M solution, which confirmed that the cyclic PLAs nucleate and crystallize faster than the linear chains.