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- 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)
Organisationseinheit der BAM
For the development of selective and sensitive chemical sensors, we have developed a new family of poly(etherphosphoramide) polymers. These polymers were obtained with satisfactory yields by nucleophilic aromatic polycondensation using isosorbide as green resources, and bisphenol A with two novel difluoro phosphinothioic amide monomers. Unprecedented, the thiophosphorylated aminoheterocycles monomers, functionalized with two heterocyclic amine, N-methylpiperazine and morpholine were successfully obtained by nucleophilic substitution reaction of P(S)–Cl compound. The resulting polymers were characterized by different analytical techniques (NMR, MALDI–ToF MS, GPC, DSC, and ATG). The resulting partially green polymers, having tertiary phosphine sulfide with P–N side chain functionalities along the main chain of polymers are the sensitive film at the surface of a gold electrode for the impedimetric detection of Cd, Ni, Pb and Hg. The bio-based poly(etherphosphoramide) functionalized with N-methylpiperazine modified sensor showed better analytical performance
than petrochemical based polymers for the detection of Ni2+. A detection limit of 50 pM was obtained which is very low compared to the previously published electrochemical sensors for nickel detection.
The preparation and characterization of poly(ionic liquid)s (PILs) bearing a polystyrene backbone via reversible addition fragmentation chain transfer (RAFT) polymerization and their photolithographic patterning on silicon wafers is reported. The controlled radical polymerization of the styrenic ionic liquid (IL) monomers ([BVBIM]X, X = Cl− or Tf2N−) by RAFT polymerization is investigated in detail. We provide a general synthetic tool to access this class of PILs with controlled molecular weight and relatively narrow molecular weight distribution (2000 g mol−1 ≤ Mn ≤ 10 000 g mol−1 with dispersities between 1.4 and 1.3 for p([BVBIM]Cl); 2100 g mol−1 ≤ MP ≤ 14 000 g mol−1 for p([BVBIM]Tf2N)). More importantly, we provide an in-depth characterization of the PILs and demonstrate a detailed mass spectrometric analysis via matrix-assisted laser desorption ionization (MALDI) as well as – for the first time for PILs – electrospray ionization mass spectrometry (ESI-MS). Importantly, p([BVBIM]Cl) and p([DMVBIM]Tf2N) were photochemically patterned on silicon wafers. Therefore, a RAFT agent carrying a photoactive group based on ortho-quinodimethane chemistry – more precisely photoenol chemistry – was photochemically linked for subsequent controlled radical polymerization of [BVBIM]Cl and [DMVBIM]Tf2N. The successful spatially-resolved photografting is evidenced by surface-sensitive characterization methods such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The presented method allows for the functionalization of diverse surfaces with poly(ionic liquid)s.
Isosorbide, succinyl chloride and isophthaloyl chloride are polycondensed under various reaction conditions. The heating in bulk with or without catalysts as well in an aromatic solvent without catalyst, and polycondensation with the addition of pyridine only yield low molar mass copolyesters. However, heating in chlorobenzene with addition of SnCl2 or ZnCl2 produces satisfactory molar masses. The number average molecular weights (Mn) of most copolyesters fall into the range of 7000–15,000 Da with polydispersities (PD) in the range of 3–9. The MALDI-TOF mass spectra almost exclusively displayed peaks of cyclics indicating that the chain growth was mainly limited by cyclization and not by side reactions, stoichiometric imbalance or incomplete conversion. The glass-transition temperatures increased with the content of isophthalic acid from 75 to 180 °C and the thermo-stabilities also followed this trend.
Efficient Cu-catalyzed 1,3-dipolar cycloaddition reactions have been used to prepare two series of three regioisomers of G-1 and G-2 poly(triazole-pyridine) dendrons. The G-1 and G-2 dendrons consist of branched yet conformationally pre-organized 2,6-bis(phenyl/pyridyl-1,2,3-triazol-4-yl)pyridine (BPTP) monomeric and trimeric cores, respectively, carrying one focal and either two or four peripheral alkyl side chains. In the solid state, the conformation and supramolecular organization were studied by means of a single crystal X-ray structure analysis of one derivative. At the liquidsolid interface, the self-assembly behavior was investigated by scanning tunneling microscopy (STM) on graphite surfaces. Based on the observed supramolecular organization, it appears that the subtle balance between conformational preferences inherent in the dendritic backbone on the one side and the adsorption and packing of the alkyl side chains on the graphite substrate on the other side dictate the overall structure formation in 2D.
In the present study the incorporation of iron into an organic polymer, composed of formamidine subunits [R–N=C(H)–NH–R], has been examined. The catalytic ability of the recyclable material was investigated in the iron-catalyzed formation of C–C bonds. After optimization of the reaction conditions, excellent yields and chemoselectivities were feasible.
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.
L-Lactide was polymerized in bulk at 140 °C with three different cyclic tin catalysts and the time was varied from 1 d up to 14 d. The MALDI TOF spectra confirmed the formation of cyclic polylactides (PLAs) and displayed a characteristic change of peak intensity distribution with formation of a “saw tooth pattern”. This pattern confirms a previous hypothesis that cyclic PLAs tend to form crystallites with extended ring conformation and relatively smooth surface. This type of crystallites is formed under thermodynamic control by transesterification on the surface of the crystallites. In this way PLAs with extraordinarily high melting temperatures (Tm's up to 200.6 °C) and extraordinarily high melting enthalpy were obtained (ΔHm's up to 105 J g−1). These ΔHm values require a revision of the maximum ΔHm value calculated in the literature for ideal PLA crystals.