TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen T1 - High molecular weight poly(l-lactide) via ring-opening polymerization with bismuth subsalicylate-The role of cocatalysts N2 - The catalytic potential of bismuth subsalicylate (BiSub), a commercial drug, for ring-opening polymerization (ROP) of L-lactide was explored by variation of co-catalyst and polymerization time. Various monofunctional phenols or carboxylic acids, aromatic ortho-hydroxy acids and diphenols were examined as potential co-catalysts. 2,2´-Dihydroxybiphenyl proved to be the most successful co-catalyst yielding weight average molecular weights (uncorrected Mw values up to 185 000) after optimization of reaction time and temperature. Prolonged heating (>1-2h) depending on catalyst concentration) caused thermal degradation. In polymerization experiments with various commercial Bi(III) salts a better alternative to BiSub was not found. By means of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry a couple of unusual and unexpected transesterification reactions were discovered. Finally, the effectiveness of several antioxidants and potential catalyst poisons was explored, and triphenylphosphine was found to be an effective catalyst poison. KW - Polylactide KW - MALDI-TOF MS KW - Ring-opening polymerization KW - Bismuth PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-519513 DO - https://doi.org/10.1002/app.50394 SN - 0021-8995 VL - 138 IS - 19 SP - 50394 PB - Wiley AN - OPUS4-51951 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Meyer, A. T1 - High Tm linear poly(L-lactide)s prepared via alcohol-initiated ROPs of L-lactide N2 - Alcohol-initiated ROPs of L-lactide were performed in bulk at 160 °C for 72 h with variation of the catalyst or with variation of the initiator (aliphatic alcohols). Spontaneous crystallization was only observed when cyclic Sn(II) compounds were used as a catalyst. Regardless of initiator, high melting crystallites with melting temperatures (Tm) of 189–193 °C were obtained in almost all experiments with Sn(II) 2,2′-dioxybiphenyl (SnBiph) as catalyst, even when the time was shortened to 24 h. These HTm poly(lactide)s represent the thermodynamically most stable form of poly(L-lactide). Regardless of the reaction conditions, such high melting crystallites were never obtained when Sn(II) 2-ethylhexanoate (SnOct2) was used as catalyst. SAXS measurements evidenced that formation of HTm poly(L-lactide) involves growth of the crystallite thickness, but chemical modification of the crystallite surface (smoothing) seems to be of greater importance. A hypothesis, why the “surface smoothing” is more effective for crystallites of linear chains than for crystallites composed of cycles is discussed. KW - Polylactide KW - MALDI-TOF MS KW - Ring-opening polymerization PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-524330 DO - https://doi.org/10.1039/d1ra01990b VL - 11 IS - 23 SP - 14093 EP - 14102 PB - Royal Society of Chemistry AN - OPUS4-52433 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen T1 - ROP of L-lactide and ε-caprolactone catalyzed by tin(ii) andtin(iv) acetates–switching from COOH terminated linear chains to cycles N2 - The catalytic potential of tin(II)acetate, tin(IV)acetate, dibutyltin-bis-acetate and dioctyl tin-bis-acetate was compared based on polymerizations of L-lactide conducted in bulk at 160 or 130°C. With SnAc2 low-Lac/Cat ratios (15/1–50/1) were studied and linear chains having one acetate and one carboxyl end group almost free of cyclics were obtained. Higher monomer/catalyst ratios and lower temperatures favored formation of cycles that reached weight average molecular weights (Mw's) between 100,000 and 2,500,000. SnAc4 yielded mixtures of cycles and linear species under all reaction conditions. Dibutyltin- and dioctyl tin bis-acetate yielded cyclic polylactides under most reaction conditions with Mw's in the range of 20,000–80,000. Ring-opening polymerizations performed with ε-caprolactone showed similar trends, but the formation of COOH-terminated linear chains was significantly more favored compared to analogous experiments with lactide. The reactivity of the acetate catalysts decreased in the following order: SnAc2> SnAc4>Bu2SnAc2~Oct2SnAc2 KW - Polylactide KW - MALDI-TOF MS KW - Catalyst KW - Ring-opening polymerization KW - Tin acetates PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-521923 DO - https://doi.org/10.1002/pol.20200866 VL - 59 IS - 5 SP - 439 EP - 450 PB - Wiley Online Library AN - OPUS4-52192 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lauer, Franziska A1 - Seifert, Stephan A1 - Kneipp, Janina A1 - Weidner, Steffen T1 - Simplifying the Preparation of Pollen Grains for MALDI-TOF MS Classification N2 - Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) is a well-implemented analytical technique for the investigation of complex biological samples. In MS, the sample preparation strategy is decisive for the success of the measurements. Here, sample preparation processes and target materials for the investigation of different pollen grains are compared. A reduced and optimized sample preparation process prior to MALDI-TOF measurement is presented using conductive carbon tape as target. The application of conductive tape yields in enhanced absolute signal intensities and mass spectral pattern information, which leads to a clear separation in subsequent pattern analysis. The results will be used to improve the taxonomic differentiation and identification, and might be useful for the development of a simple routine method to identify pollen based on mass spectrometry. KW - PCA KW - MALDI-TOF MS KW - Conductive carbon tape KW - Pollen KW - Sample pretreatment PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-392885 UR - http://www.mdpi.com/1422-0067/18/3/543/ DO - https://doi.org/10.3390/ijms18030543 SN - 1422-0067 VL - 18 IS - 3 SP - 543 EP - 554 PB - MDPI AG CY - Basel, Switzerland AN - OPUS4-39288 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Scheliga, F. T1 - Cyclic Polylactides via Simultaneous Ring-Opening Polymerization and Polycondensation Catalyzed by Dibutyltin Mercaptides N2 - L-Lactide is polymerized in bulk at 160 8C either with dibutyltin bis(benzylmercaptide) (SnSBzl), dibutyltin bis(benzothiazole 2-mercaptide) (SnMBT), or with dibutyltin bis(pentafluorothiophenolate) (SnSPF) as catalysts. SnSBzl yields linear polylactides having benzylthio-ester end groups in addition to cyclic polylactides, whereas SnMBT and SnSPF mainly or exclusively yield cyclic polylactides. This finding, together with model reactions, indicates that the SnS catalysts promote a combined ring-opening polymerization and polycondensation process including end-to-end cyclization. SnMBT caused slight racemization (3%–5%), when used at 160 8C. With SnSPF optically pure cyclic poly(L-lactide)s with high-molecular weights can be prepared at 160 8C. KW - Cyclopolymerization KW - Catalysts KW - MALDI-TOF MS KW - Polyester KW - Ring-opening polymerization PY - 2017 DO - https://doi.org/10.1002/pola.28762 VL - 55 IS - 22 SP - 3767 EP - 3775 PB - Wiley Periodicals AN - OPUS4-42600 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. A1 - Weidner, Steffen A1 - Scheliga, F. ED - Shaplov, A. T1 - Cyclization and dispersity of polyesters N2 - Two classes of polyesters were prepared by irreversible polycondensations. The dependence of the dispersities on the experimental parameters such as synthetic method, chemical structure, molecular weight and initial monomer concentration was determined. At first it was demonstrated that it is essential for a correct calculation of Mn and Mw to include all oligomers down to the dimers in the evaluation of SEC curves. Furthermore, it was demonstrated for poly(e-caprolactone)s and polylactides that reversible polycondensations and ring-opening polymerizations with equilibration yield identical products. Finally, the dependence of the dispersity on various experimental Parameters was determined for equilibrated poly(e-caprolactone)s and polylactides. KW - Irreversible polycondensation KW - Polycaprolactone KW - Polylactide KW - Dispersity KW - MALDI-TOF MS PY - 2017 DO - https://doi.org/10.1002/masy.201600169 SN - 1022-1360 SN - 1521-3900 VL - 375 IS - 1 SP - Article 1600169, 1 EP - 6 PB - Wiley-VCH AN - OPUS4-42407 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wessig, P. A1 - Schulze, T. A1 - Pfennig, A. A1 - Weidner, Steffen A1 - Prentzel, S. A1 - Schlaad, H. T1 - Thiol–ene polymerization of oligospiroketal rods N2 - 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. KW - Oligospiroketals KW - Polymerization KW - MALDI-TOF MS PY - 2017 DO - https://doi.org/10.1039/C7PY01569K SN - 1759-9954 SN - 1759-9962 VL - 8 IS - 44 SP - 6879 EP - 6885 PB - Royal Society of Chemistry AN - OPUS4-42685 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Kricheldorf, H. R. T1 - Spirocyclic bisphenoxides of Ge, Zr, and Sn as catalysts for ring-expansion polymerizations of L- and meso-lactide N2 - Spirocyclic phenoxides of germanium, zirconium, and tin were prepared from 2,20-dihydroxybiphenyl and 2,20-dihydroxy-1,10-binaphthyl. Ring-expansion polymerizations of L-lactide are mainly studied at 160 or 180 °C. The reactivity of the catalysts increases in the order: Zr < Ge < Sn. Regardless of catalyst, the weight-average molecular weights (Mw) never exceed 50,000 g mol−1. The resulting poly(L-lactide)s are optically pure and have a cyclic architecture. Decreasing temperature and time favor Formation of even-numbered cycles, and at 102 ° cyclics, almost free of odd-numbered rings are obtained. Analogous polymerizations of meso-lactide give similar results >120 °C, but different results at 100 or 80 °C. Surprisingly, bell-shaped narrow molecular weight distributions are obtained <140 °C, resembling the pattern of living polymerizations found for alcohol-initiated polymerizations. An unusual transesterification mechanism yielding narrow distributions of odd-numbered cycles is discovered too. KW - Cyclization KW - Polylactides KW - MALDI-TOF MS KW - Ring-opening polymerization KW - Spirocyclic PY - 2018 DO - https://doi.org/10.1002/pola.29259 SN - 0887-624X SN - 1099-0518 VL - 56 IS - 24 SP - 2730 EP - 2738 PB - Wiley Periodicals AN - OPUS4-46498 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Diehn, Sabrina A1 - Zimmermann, B. A1 - Bagcioglu, M. A1 - Seifert, Stephan A1 - Kohler, A. A1 - Ohlson, M. A1 - Fjellheim, S. A1 - Weidner, Steffen A1 - Kneipp, Janina T1 - Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) shows adaption of grass pollen composition N2 - MALDI time-of-flight mass spectrometry (MALDI-TOF MS) has become a widely used tool for the classification of biological samples. The complex chemical composition of pollen grains leads to highly specific, fingerprint-like mass spectra, with respect to the pollen species. Beyond the species-specific composition, the variances in pollen chemistry can be hierarchically structured, including the level of different populations, of environmental conditions or different genotypes. We demonstrate here the sensitivity of MALDI-TOF MS regarding the adaption of the chemical composition of three Poaceae (grass) pollen for different populations of parent plants by analyzing the mass spectra with partial least squares discriminant analysis (PLS-DA) and principal component analysis (PCA). Thereby, variances in species, population and specific growth conditions of the plants were observed simultaneously. In particular, the chemical pattern revealed by the MALDI spectra enabled discrimination of the different populations of one species. Specifically, the role of environmental changes and their effect on the pollen chemistry of three different grass species is discussed. Analysis of the Group formation within the respective populations showed a varying influence of plant genotype on the classification, depending on the species, and permits conclusions regarding the respective rigidity or plasticity towards environmental changes. KW - Pollen KW - MALDI-TOF MS KW - Classification KW - Partial least square discriminant analysis (PLS-DA) KW - Principal component analysis (PCA) PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-465294 DO - https://doi.org/10.1038/s41598-018-34800-1 SN - 2045-2322 VL - 8 IS - 1 SP - 16591, 1 EP - 11 PB - Nature AN - OPUS4-46529 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kricheldorf, H. R. A1 - Weidner, Steffen A1 - Scheliga, F. T1 - About formation of cycles in Sn(II) octanoate-catalyzed polymerizations of lactides N2 - At first, formation of cycles in commercial poly(Llactide)s is discussed and compared with benzyl alcoholinitiated polymerizations performed in this work. This comparison was extended to polymerizations initiated with 4-cyanophenol and pentafluorothiophenol which yielded cyclic polylactides via end-biting. The initiator/catalyst ratio and the acidity of the initiator were found to be decisive for the extent of cyclization. Further polymerizations of L-lactide were performed with various diphenols as initiators/co-catalysts. With most diphenols, cyclic polylactides were the main reaction products. Yet, only catechols yielded even-numbered cycles as main reaction products, a result which proves that their combination with SnOct2 catalyzed a ring-expansion polymerization (REP). The influence of temperature, time, co-catalyst, and catalyst concentrations was studied. Four different transesterification reactions yielding cycles were identified. For the cyclic poly(L-lactide)s weight average molecular weights (Mw’s) up to 120,000 were obtained, but 1H NMR end group analyses indicated that the extent of cyclization was slightly below 100%. The influence of various parameters like structure of Initiator and catalyst and temperature on the formation of cyclic poly(Llactide)s has been investigated. Depending on the chosen conditions, the course of the polymerization can be varied from a process yielding exclusively linear polylactides to mainly cyclic polylactides. Three different reaction pathways for cyclization reactions have been identified. KW - Cyclization KW - MALDI-TOF MS KW - Polyester KW - Ring-opening polymerization KW - Transesterification PY - 2018 DO - https://doi.org/10.1002/pola.29077 SN - 0887-624X VL - 56 IS - 17 SP - 1915 EP - 1925 PB - Wiley Periodicals Inc. AN - OPUS4-46052 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -