TY - JOUR A1 - Weidner, Steffen A1 - Kricheldorf, H. R. T1 - Matrix-assisted laser desorption/ionization behavior of neat linear and cyclic poly(L-lactide)s and their blends N2 - Numerous new tin catalysts that enable the synthesis of cyclic polylactides with broad variation in their molecular mass were recently developed. The abundance of cyclics in matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra is, however, frequently reported to greatly exceed that of linears. Thus, the MALDI ionization behavior of various end-capped linear poly(L-lactide)s and one cyclic poly(L-lactide) was investigated and compared. Neat compounds and various blends of cyclic and linear species were prepared and studied under identical conditions with regard to sample preparation and instrumental condition, except for the laser power. For this purpose, two different MALDI-TOF mass spectrometers were applied. Our results reveal that cyclics indeed show a slightly better ionization in MALDI, although their ionization as a neat compound seems to be less effective than that of linear polylactides. The ionization of most linear polylactides investigated does not depend on the end group structure. However, linear polylactides containing 12-bromododecyl end groups reveal an unexpected saturation effect that is not caused by fragmentation of the polymer or the end group, or by electronic saturation of the detector digitizer. Furthermore, polylactides with a 2-bromoethyl end group did not show such a saturation effect. An overestimation of cyclic species in MALDI-TOF mass spectra of poly(L-lactide)s must be considered, but the commonly assumed peak suppression of linear polymers in mixtures of both structures can be excluded. KW - Polylactide KW - MALDI-TOF MS KW - Blends KW - Ionization PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-504216 DO - https://doi.org/10.1002/rcm.8673 VL - 34 SP - e8673 PB - Wiley Online Libary AN - OPUS4-50421 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 poly(L-lactide)s via REP or ROPPOC of L-lactide N2 - A new kind of high melting (HTm) pol(L-lactide) was discovered when cyclic poly(L-lactide)s were prepared by ring-expansion polymerization with cyclic tin catalysts at 130–160 °C in bulk. By DSC measurements with 10 K min−1 melting temperatures (Tm) in the range of 190–196 °C were found. The WAXS and SAXS measurements evidenced that not a new crystal lattice but a well-ordered morphology and a higher perfection of the crystallites are responsible for the high Tm values and high crystallinities. Under identical reaction conditions SnOct2-catalyzed and alcohol-initiated ROPs do not yield these crystallites. Furthermore, it was found that the standard crystallites are kinetically favored upon rapid crystallization, whereas the high melting form of poly(L-lactide) is thermodynamically more stable. KW - Polylactide KW - MALDI-TOF MS KW - ROPPOC PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-507477 DO - https://doi.org/10.1039/c9py01908a VL - 11 IS - 12 SP - 2182 EP - 2193 PB - Royal Society of Chemistry AN - OPUS4-50747 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meyer, A. A1 - Weidner, Steffen A1 - Kricheldorf, H. T1 - Stereocomplexation of cyclic polylactides with each other and with linear poly(L-lactide)s N2 - 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. KW - Polylactide KW - MALDI-TOF MS KW - Stereocomplex KW - Cyclic PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-496693 DO - https://doi.org/10.1039/c9py01236b VL - 10 SP - 6191 EP - 6199 PB - Royal Society for Chemistry AN - OPUS4-49669 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 - Synthesis of cyclic polymers and flaws of the Jacobson–Stockmayer theory N2 - Cyclic poly(L-lactide)s were prepared by ring-opening polymerization combined with simultaneous polycondensation (ROPPOC) in bulk at 160 ° with dibutyltin bis(4-cyanophenoxide) as catalyst. It is demonstrated by MALDI TOF mass spectrometry and 1H NMR end group analyses that cycles are formed by endto-end cyclization in addition to “back-biting” transesterification. Formation of high molar mass cyclic poly L-lactide)s by means of several more reactive ROPPOC catalysts presented previously and in new experiments is discussed. These experimental results, together with theoretical arguments, prove that part of the Jacobson–Stockmayer theory is wrong. The critical monomer concentration, above which end-toend cyclization is seemingly impossible, does not exist and reversible like irreversible polycondensations can theoretically proceed up to 100% conversion, so that finally all reaction products will necessarily adopt a cyclic architecture. KW - Polylactide KW - MALDI-TOF MS KW - Cyclization PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-506419 DO - https://doi.org/10.1039/d0py00226g VL - 11 IS - 14 SP - 2595 EP - 2604 PB - Royal Society for Chemistry AN - OPUS4-50641 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 - Synthesis of cyclic poly(l-lactide) catalyzed by Bismuth salicylates-A combination of two drugs N2 - l‐lactide was polymerized in bulk at 160 or 180°C with mixtures of bismuth subsalicylate (BiSub) and salicylic (SA) as catalysts. The SA/Bi ratio and the monomer/Bi ratio were varied. The highest molecular weights (weight average, Mw) were achieved at a SA/Bi ratio of 1/1 (Mw up to 92 000 g mol−1). l‐Lactide was also polymerized with combinations of BiSub and silylated SA, and Mw values up to 120 000 g mol−1 were achieved at 180°C. MALDI‐TOF mass spectrometry and Mark‐Houwink‐Sakurada measurements proved that under optimized reaction conditions the resulting polylactides consist of cycles. KW - Polylactide KW - MALDI-TOF MS KW - Cyclization KW - Catalyst KW - Salicylate PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-488622 DO - https://doi.org/10.1002/pola.29473 SN - 0887-624X SN - 1099-0518 SP - 29473 PB - Wiley AN - OPUS4-48862 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Kricheldorf, H. R. T1 - Ring–Ring Equilibration in Solid, Even-Numbered Cyclic Poly(l-lactide)s and their Stereocomplexes N2 - Even-numbered cyclic poly(d-lactide) and poly(l-lactide) are prepared by ringexpansion polymerization. The cyclic pol(l-lactide) is annealed either at 120 or at 160 °C for several days. The progress of transesterification in the solid state is monitored by the formation of odd-numbered cycles via matrix-assisted laser desorption/ionization-time of flight mass spectrometry. The changes of the crystallinity are monitored by differential scanning calorimetry, wideand small-angle x-ray scattering (WAXS and SAXS) measurements. Despite total even-odd equilibration at 160 °C, the crystallinity of poly(l-lactide) is not reduced. Furthermore, the crystallinity of the stereocomplexes of both cyclic polylactides do not decrease or vanish, as expected, when a blocky or random stereosequence is formed by transesterification. This conclusion is confirmed by 13C NMR spectroscopy. These measurements demonstrate that transesterification is a ring–ring equilibration involving the loops on the surfaces of the lamellar crystallites thereby improving crystallinity and 3D packing of crystallites without significant broadening of the molecular weight distribution. KW - Polylactide KW - MALDI-TOF MS KW - Cyclization PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-506458 DO - https://doi.org/10.1002/macp.202000012 VL - 221 IS - 9 SP - 2000012 PB - Wiley-VCH Verlag AN - OPUS4-50645 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Steinkönig, J. A1 - Bloesser, F. R. A1 - Huber, B. A1 - Welle, A. A1 - Trouillet, V. A1 - Weidner, Steffen A1 - Barner, L. A1 - Roesky, P. W. A1 - Yuan, J. A1 - Goldmann, A. S. A1 - Barner-Kowollik, C. T1 - Controlled radical polymerization and in-depth mass-spectrometric characterization of poly(ionic liquid)s and their photopatterning on surfaces N2 - 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. KW - reversible addition fragmentation chain transfer (RAFT) polymerization KW - polyionic liquids KW - mass spectrometry KW - surface modification PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-355202 DO - https://doi.org/10.1039/C5PY01320H VL - 7 SP - 451 EP - 461 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-35520 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sötebier, Carina A1 - Bierkandt, Frank A1 - Rades, Steffi A1 - Jakubowski, Norbert A1 - Panne, Ulrich A1 - Weidner, Steffen T1 - Sample loss in asymmetric flow field-flow fractionation coupled to inductively coupled plasma-mass spectrometry of silver nanoparticles N2 - In this work, sample losses of silver nanoparticles (Ag NPs) in asymmetrical flow field-flow fractionation (AF4) have been systematically investigated with the main focus on instrumental conditions like focusing and cross-flow parameters as well as sample concentration and buffer composition. Special attention was drawn to the AF4 membrane. For monitoring possible silver depositions on the membrane, imaging laser ablation coupled to inductively coupled plasma mass spectrometry (LA-ICP-MS) was used. Our results show that the sample residue on the membrane was below 0.6% of the total injected amount and therefore could be almost completely avoided at low sample concentrations and optimized conditions. By investigation of the AF4 flows using inductively coupled plasma mass spectrometry (ICP-MS), we found the recovery rate in the detector flow under optimized conditions to be nearly 90%, while the cross-flow, slot-outlet flow and purge flow showed negligible amounts of under 0.5%. The analysis of an aqueous ionic Ag standard solution resulted in recovery rates of over 6% and the ionic Ag content in the sample was found to be nearly 8%. Therefore, we were able to indicate the ionic Ag content as the most important source of sample loss in this study. KW - Asymmetric flow filed-flow fractionation KW - ICP-MS KW - Nanoparticles KW - Sample loss KW - Quantification PY - 2015 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-336171 DO - https://doi.org/10.1039/c5ja00297d SN - 0267-9477 SN - 1364-5544 VL - 30 IS - 10 SP - 2214 EP - 2222 PB - Royal Society of Chemistry CY - London AN - OPUS4-33617 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 - Doriti, A. A1 - Brosnan, S. A1 - Weidner, Steffen A1 - Schlaad, H. T1 - Synthesis of polysarcosine from air and moisture stable N-phenoxycarbonyl-N-methylglycine assisted by tertiary amine base N2 - 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. KW - Polysarcosine KW - MALDI-TOF MS KW - Synthesis PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-359309 DO - https://doi.org/10.1039/c6py00221h SN - 1759-9954 SN - 1759-9962 VL - 7 IS - 18 SP - 3067 EP - 3070 AN - OPUS4-35930 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Wolff, D. A1 - Springer, J. T1 - Influence of Chirality on Phase Behaviour of Copolymers Containing Cholesterol as Mesogenic Group PY - 1996 SN - 1022-1352 SN - 1521-3935 VL - 197 SP - 1337 EP - 1348 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-11091 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zydziak, N. A1 - Konrad, W. A1 - Feist, F. A1 - Afonin, S. A1 - Weidner, Steffen A1 - Barner-Kowollik, C. T1 - Coding and decoding libraries of sequence-defined functional copolymers synthesized via photoligation N2 - Designing artificial macromolecules with absolute sequence order represents a considerable challenge. Here we report an advanced light-induced avenue to monodisperse sequencedefined functional linear macromolecules up to decamers via a unique photochemical approach. The versatility of the synthetic strategy—combining sequential and modular concepts—enables the synthesis of perfect macromolecules varying in chemical constitution and topology. Specific functions are placed at arbitrary positions along the chain via the successive addition of monomer units and blocks, leading to a library of functional homopolymers, alternating copolymers and block copolymers. The in-depth characterization of each sequence-defined chain confirms the precision nature of the macromolecules. Decoding of the functional information contained in the molecular structure is achieved via tandem mass spectrometry without recourse to their synthetic history, showing that the sequence information can be read.We submit that the presented photochemical strategy is a viable and advanced concept for coding individual monomer units along a macromolecular chain. KW - Photoligation KW - Copolymer sequence KW - MALDI-TOF MS/MS PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-391542 DO - https://doi.org/10.1038/ncomms13672 SN - 2041-1723 VL - 7 SP - Artikel Nr. 13672 AN - OPUS4-39154 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 - 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 - Meyer, A. T1 - Poly(L-lactide): Optimization of Melting Temperature and Melting Enthalpy N2 - Twice recrystallized L-lactide was polymerized with a dozen of different tin or bismuth catalysts in bulk at 160°C for 24 h and was annealed at 150°C afterwards. In two cases Tm values above 197.0°C were obtained. The parameters causing a scattering of the DSC data were studied and discussed. The samples prepared with SnCl2, 2,2-dibutyl-2-stanna-1,3-ditholane (DSTL) or cyclic tin(II) bisphenyldioxide (SnBiph) were subject to annealing programs with variation of time and temperatures, revealing that the Tm´s did not increase. However, an increase of Hm was achieved with maximum values in the range of 93-96 J g-1 corresponding to crystallinities off around 90%. Further studies were performed with once recrystallized L-lactide. Again, those samples directly crystallized from the polymerization process showed the highest Tm values. These data were compared with the equilibrium Tm0 and Hm0 data calculated by several research groups for perfect crystallites. A Tm0 of 213+/-2°C and a Hm0 of 106 J g-1 show the best agreement with the experimental data. The consequences of annealing for the thickness growth of crystallites are discussed on the basis of SAXS measurements. Finally, a comparison of cyclic and linear poly L-lactide)s is discussed. KW - Polylactide KW - MALDI-TOF MS KW - Transesterification PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-538656 DO - https://doi.org/10.1039/D1MA00957E SP - 1 EP - 10 PB - Royal Society for Chemistry AN - OPUS4-53865 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weidner, Steffen A1 - Meyer, A. A1 - Chatti, S. A1 - Kricheldorf, H. R. T1 - About the transformation of low Tm into high Tm poly(L-lactide)s by annealing under the influence of transesterification catalysts N2 - Cyclic polylactides were prepared in bulk at 170 °C, crystallized at 120 °C and then annealed at temperatures between 130 and 170 C with variation of catalyst, catalyst concentration and annealing time. The transformation of the initially formed low melting (LTm) crystallites, having melting temperatures (Tm) <180 °C into high melting (HTm) crystallites having Tm values > 189 °C was monitored by means of DSC measurements and characterized in selected cases by SAXS measurements. It was confirmed that the formation of HTm crystallites involves a significant growth of the thickness of the lamellar crystallites along with smoothing of their surface. Annealing at 170 °C for 1 d or longer causes thermal degradation with lowering of the molecular weights, a gradual transition of cyclic into linear chains and a moderate decrease of lamellar thickness. An unexpected result revealed by MALDI TOF mass spectrometry is a partial reorganization of the molecular weight distribution driven by a gain of crystallization enthalpy. KW - Polylactide KW - MALDI-TOF MS KW - Crystallization KW - Annealing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-521062 DO - https://doi.org/10.1039/d0ra10012a VL - 11 IS - 5 SP - 2872 EP - 2883 PB - Royal Society of Chemistry AN - OPUS4-52106 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 - Meyer, A. A1 - Weidner, Steffen T1 - High Tm Poly(l-lactide)s by Means of Bismuth Catalysts? N2 - One series of BiSub-catalyzed ring-opening polymerizations (ROPs) is per-formed at 160 °C for 3 days with addition of difunctional cocatalysts to find out, if poly(l-lactide) crystallizes directly from the reaction mixture. An analogous series is performed with monofunctional cocatalysts. High Tm crystal-lites (Tm > 190 °C) are obtained from all bifunctional cocatalysts, but not from all monofunctional ones. It is shown by means of SAXS measurements that the high Tm values are mainly a consequence of a transesterification–homogenization process across the lamellar surfaces resulting in thickness and smoothing of the surfaces. An unusual enthalpy-driven modification of the molecular weight distribution is found for samples that have crystallized during the polymerization. A third series of ROPs is performed at 170 °C for 2 h followed by annealing at 120 °C (2 h) to induce crystallization. Complete transformation of the resulting low Tm crystallites (Tm < 180 °C) into the high Tm crystallites by annealing at 170 °C for 1 d is not achieved, despite variation of the cocatalyst. KW - Polylactide KW - MALDI-TOF MS KW - Crystallization PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-522777 DO - https://doi.org/10.1002/macp.202100019 SN - 1022-1352 VL - 222 IS - 8 SP - 19 PB - Wiley AN - OPUS4-52277 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 - Kricheldorf, H. R. A1 - Scheliga, F. A1 - Weidner, Steffen T1 - What does conversion mean in polymer science? N2 - The definition of the term “conversion” is discussed for a variety of polymer syntheses. It is demonstrated that in contrast to organic and inorganic chemistry several different definitions are needed in polymer science. The influence of increasing conversion on structure and topology of homo- and Copolymers is illustrated. Chain-growth polymerizations, such as radical polymerization or living anionic polymerizations of vinyl monomers, condensative chain polymerization, two and three-dimensional step-growth polymerizations, ring–ring or chain–chain equilibration and chemical modification of polymers are considered. KW - Polymers KW - Polymerization KW - Conversion KW - Polycondensation PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-523597 DO - https://doi.org/10.1002/macp.202100010 VL - 222 IS - 8 SP - 10 PB - Wiley VCH AN - OPUS4-52359 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -