Search results for: Steffen M. Weidner

Items from 1 to 20 out of 36 results

article

Toward understanding the ionization mechanism of matrix‐assisted ionization using mass spectrometry experiment and theory

Chuping Lee, Ellen D. Inutan, Jien Lian Chen, Mutanu M. Mukeku, more

Rapid Communications in Mass Spectrometry > 35 > S1 > n/a - n/a

Rationale Matrix‐assisted ionization (MAI) mass spectrometry does not require voltages, a laser beam, or added heat to initiate ionization, but it is strongly dependent on the choice of matrix and the vacuum conditions. High charge state distributions of nonvolatile analyte ions produced by MAI suggest that the ionization mechanism may be similar to that of electrospray ionization (ESI), but different...

article

Matrix‐assisted laser desorption/ionization behavior of neat linear and cyclic poly(L‐lactide)s and their blends

Steffen M. Weidner, Hans R. Kricheldorf

Rapid Communications in Mass Spectrometry > 34 > S2 > n/a - n/a

Rationale 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...

article

The Ring‐Opening Polymerization–Polycondensation (ROPPOC) Approach to Cyclic Polymers

Hans R. Kricheldorf, Steffen M. Weidner

Macromolecular Rapid Communications > 41 > 14 > n/a - n/a

A new concept called ring‐opening polymerization–polycondensation (ROPPOC) is presented and discussed. This synthetic strategy is based on the intermediate formation of chains having two end groups that can react with each other. The ROPPOC syntheses are subdivided into three groups according to the nature of the chain ends: two ionic end groups, one ionic and one covalent chain end, and a combination...

article

Ring–Ring Equilibration in Solid, Even‐Numbered Cyclic Poly(l‐lactide)s and their Stereocomplexes

Steffen M. Weidner, Andreas Meyer, Hans R. Kricheldorf

Macromolecular Chemistry and Physics > 221 > 9 > n/a - n/a

Even‐numbered cyclic poly(d‐lactide) and poly(l‐lactide) are prepared by ring‐expansion 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...

article

Poly(2‐oxazoline)s Based on Phenolic Acids

Nils Lüdecke, Steffen M. Weidner, Helmut Schlaad

Macromolecular Rapid Communications > 41 > 1 > n/a - n/a

A series of phenolic‐acid‐based 2‐oxazoline monomers with methoxy‐substituted phenyl and cinnamyl side chains is synthesized and polymerized in a microwave reactor at 140 °C using methyl tosylate as the initiator. The obtained poly(2‐oxazoline)s are characterized by NMR spectroscopy, MALDI‐TOF mass spectrometry, and size‐exclusion chromatography (SEC). Kinetic studies reveal that the microwave‐assisted...

article

SnOct₂-Catalyzed Syntheses of Cyclic Poly(l-lactide)s with Catechol as Low-Toxic Co-catalyst

Hans R. Kricheldorf, Steffen M. Weidner

Journal of Polymers and the Environment > 2019 > 27 > 12 > 2697-2706

Polymerizations of l-lactide in bulk at 160 or 180 °C were performed with 1/1 mixtures of catechol (CA) or 4-tert-butylcatechol (BuCA) and tin(II)-2-ethylhexanoate (SnOct₂) as catalysts and a variation of the Lac/Cat ratio. Weight average molar masses (Mw) up to 170,000 g mol⁻¹ were obtained with CA and up to 120,000 g mol⁻¹ with BuCA. The cyclic structure of the resulting poly(l-lactide)s was proven...

article

Fundamental Studies of New Ionization Technologies and Insights from IMS-MS

Sarah Trimpin, Ellen D. Inutan, Santosh Karki, Efstathios A. Elia, more

Journal of The American Society for Mass Spectrometry > 2019 > 30 > 6 > 1133-1147

Exceptional ion mobility spectrometry mass spectrometry (IMS-MS) developments by von Helden, Jarrold, and Clemmer provided technology that gives a view of chemical/biological compositions previously not achievable. The ionization method of choice used with IMS-MS has been electrospray ionization (ESI). In this special issue contribution, we focus on fundamentals of heretofore unprecedented means for...

article

Transesterification in Alcohol‐Initiated ROPs of l‐ and meso‐Lactide Catalyzed by Sn(II) and Sn(IV) Compounds at Low Temperatures

Steffen M. Weidner, Hans R. Kricheldorf

Macromolecular Chemistry and Physics > 219 > 24 > n/a - n/a

The purpose of this study is to shed more light on the transesterification processes in alcohol‐initiated and tin(II) 2‐ethylhexanoate (SnOct₂)‐catalyzed polymerizations of lactides at low or moderate temperatures. Ethanol‐initiated polymerizations are conducted in concentrated solutions at 80 °C and a strong dependence of even/odd equilibration on the alcohol/Sn ratio. Around or above 120 °C cyclization...

article

Cyclic Poly(l‐lactide) via Ring‐Expansion Polymerization by Means of Dibutyltin 4‐Tert‐Butylcatecholate

Hans R. Kricheldorf, Steffen M. Weidner, Felix Scheliga

Macromolecular Chemistry and Physics > 218 > 22 > n/a - n/a

Five new catalysts are prepared from dibutyltin oxide and catechol (HCa), 2,3‐dihydroxynaphthalene (NaCa), 4‐tert‐butyl catechol (BuCa), 4‐cyano catechol (CyCa), and 4‐benzoyl catechol (BzCa), but only BuCa gives useful results. When benzyl alcohol is used as an initiator, linear chains having benzyl ester end groups are formed in a slow polymerization process. In contrast to cyclic or noncyclic dibutyltin...

article

Cyclization and Dispersity of Polyesters

Hans R. Kricheldorf, Steffen M. Weidner, Felix Scheliga

Macromolecular Symposia > 375 > 1 > n/a - n/a

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 M_n and M_w to include all oligomers down to the dimers in the evaluation...

article

Transesterification in the Solid State of Cyclic and Linear Poly(l‐lactide)s

Steffen M. Weidner, Hans R. Kricheldorf

Macromolecular Chemistry and Physics > 218 > 14 > n/a - n/a

Poly(l‐lactide)s are synthesized and annealed at 120 °C and changes of the molecular weight distribution (MWD) are monitored by matrix‐assited laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. For example, benzyl alcohol+SnOct₂ causes equilibration of odd‐ and even‐numbered chains and the final goal of the transesterification is the most probable distribution. The underlying...

article

The Role of Transesterification in SnOct₂‐Catalyzed Polymerizations of Lactides

Steffen M. Weidner, Hans R. Kricheldorf

Macromolecular Chemistry and Physics > 218 > 3 > n/a - n/a

l‐lactide or meso‐lactide are polymerized either at 120 °C where the polymerization process of l‐lactide is accompanied by crystallization, or at 180 °C where poly(l‐lactide) remains in the molten state. Polymerizations at 120 °C initially yield even‐numbered chains (with respect to lactic acid units) having relatively low dispersity, but the fraction of odd‐numbered chains increases with time and...

article

Separation and quantification of silver nanoparticles and silver ions using reversed phase high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry in combination with isotope dilution analysis

Carina A. Sötebier, Steffen M. Weidner, Norbert Jakubowski, Ulrich Panne, more

Journal of Chromatography A > 2016 > 1468 > C > 102-108

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...

article

Dispersities of Polyesters of Various Diphenols Prepared by Irreversible Polycondensations

Hans R. Kricheldorf, Steffen M. Weidner

Macromolecular Chemistry and Physics > 217 > 12 > 1361 - 1369

Polyesters of bisphenol‐A, bisphenol‐P, catechol, and sebacic acid are prepared and different synthetic methods are compared. The diphenols are condensed with sebacoyl chloride either in dichloromethane/pyridine or in refluxing chlorobenzene without HCl‐acceptor. Furthermore, bisphenol‐A acetate is polycondensed with sebacic acid in bulk. All experiments are worked up so that fractionation is avoided...

article

Cyclization and dispersity of poly(alkylene isophthalate)s

Steffen M. Weidner, Hans R. Kricheldorf, Felix Scheliga

Journal of Polymer Science Part A: Polymer Chemistry > 54 > 1 > 197 - 208

Poly(alkylene isophthalate)s were prepared by different methods, either in solution or in bulk. The SEC measurements were evaluated in such a way that all oligomers were included. In solution (monomer conc. 0.1–0.7 mol/L) large fractions of rings were formed and high dispersities (up to 12) were obtained, which disagree with theoretical predictions. Polycondensations in bulk did neither generate cyclics...

article

Multicyclic Polyesters of Trimesic Acid and Alkanediols and the Theory of Network Formation

Hans R. Kricheldorf, Steffen M. Weidner, Mohammed Lahcini

Macromolecular Chemistry and Physics > 216 > 21 > 2095 - 2106

Trimesoyl chloride is polycondensed with various α,Ώ‐alkanediols in dichloromethane at different concentrations using equifunctional feed ratios. As evidenced by MALDI‐TOF (matrix assisted laser desorption/ionization‐time of flight) mass spectrometry the soluble reaction products mainly consist of perfect multicyclic oligomers and polymers. The solphase extracted from the gels also consists of perfect...

article

Matrix-Assisted Ionization-Ion Mobility Spectrometry-Mass Spectrometry: Selective Analysis of a Europium–PEG Complex in a Crude Mixture

Joshua L. Fischer, Corinne A. Lutomski, Tarick J. El-Baba, Buddhima N. Siriwardena-Mahanama, more

Journal of The American Society for Mass Spectrometry > 2015 > 26 > 12 > 2086-2095

The analytical utility of a new and simple to use ionization method, matrix-assisted ionization (MAI), coupled with ion mobility spectrometry (IMS) and mass spectrometry (MS) is used to characterize a 2-armed europium(III)-containing poly(ethylene glycol) (Eu-PEG) complex directly from a crude sample. MAI was used with the matrix 1,2-dicyanobenzene, which affords low chemical background relative to...

article

Taxonomic relationships of pollens from matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry data using multivariate statistics

Stephan Seifert, Steffen M. Weidner, Ulrich Panne, Janina Kneipp

Rapid Communications in Mass Spectrometry > 29 > 12 > 1145 - 1154

RationaleMatrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) has been suggested as a promising tool for the investigation of pollen, but the usefulness of this approach for classification and identification of pollen species has to be proven by an application to samples of varying taxonomic relations. MethodMALDI‐MS in combination with hierarchical cluster analysis (HCA) and principal...

article

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometric imaging of synthetic polymer sample spots prepared using ionic liquid matrices

Stefan J. Gabriel, Dietmar Pfeifer, Clemens Schwarzinger, Ulrich Panne, more

Rapid Communications in Mass Spectrometry > 28 > 5 > 489 - 498

RATIONALEPolymer sample spots for matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) prepared by the dried‐droplet method often reveal ring formation accompanied by possible segregation of matrix and sample molecules as well as of the polymer homologs itself. Since the majority of sample spots are prepared by this simple and fast method, a matrix or sample...

article

Matrix Segregation as the Major Cause for Sample Inhomogeneity in MALDI Dried Droplet Spots

Stefan J. Gabriel, Clemens Schwarzinger, Bettina Schwarzinger, Ulrich Panne, more

Journal of The American Society for Mass Spectrometry > 2014 > 25 > 8 > 1356-1363

The segregation in dried droplet MALDI sample spots was analyzed with regard to the matrix-to-sample ratio using optical microscopy, MALDI imaging mass spectrometry (MALDI MSI) and IR imaging spectroscopy. In this context, different polymer/matrix/solvent systems usually applied in the analysis of synthetic polymers were investigated. The use of typical matrix concentrations (10 mg mL⁻¹) in almost...

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Search results for: Steffen M. Weidner

Toward understanding the ionization mechanism of matrix‐assisted ionization using mass spectrometry experiment and theory

Matrix‐assisted laser desorption/ionization behavior of neat linear and cyclic poly(L‐lactide)s and their blends

The Ring‐Opening Polymerization–Polycondensation (ROPPOC) Approach to Cyclic Polymers

Ring–Ring Equilibration in Solid, Even‐Numbered Cyclic Poly(l‐lactide)s and their Stereocomplexes

Poly(2‐oxazoline)s Based on Phenolic Acids

SnOct₂-Catalyzed Syntheses of Cyclic Poly(l-lactide)s with Catechol as Low-Toxic Co-catalyst

Fundamental Studies of New Ionization Technologies and Insights from IMS-MS

Transesterification in Alcohol‐Initiated ROPs of l‐ and meso‐Lactide Catalyzed by Sn(II) and Sn(IV) Compounds at Low Temperatures

Cyclic Poly(l‐lactide) via Ring‐Expansion Polymerization by Means of Dibutyltin 4‐Tert‐Butylcatecholate

Cyclization and Dispersity of Polyesters

Transesterification in the Solid State of Cyclic and Linear Poly(l‐lactide)s

The Role of Transesterification in SnOct₂‐Catalyzed Polymerizations of Lactides

Separation and quantification of silver nanoparticles and silver ions using reversed phase high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry in combination with isotope dilution analysis

Dispersities of Polyesters of Various Diphenols Prepared by Irreversible Polycondensations

Cyclization and dispersity of poly(alkylene isophthalate)s

Multicyclic Polyesters of Trimesic Acid and Alkanediols and the Theory of Network Formation

Matrix-Assisted Ionization-Ion Mobility Spectrometry-Mass Spectrometry: Selective Analysis of a Europium–PEG Complex in a Crude Mixture

Taxonomic relationships of pollens from matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry data using multivariate statistics

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometric imaging of synthetic polymer sample spots prepared using ionic liquid matrices

Matrix Segregation as the Major Cause for Sample Inhomogeneity in MALDI Dried Droplet Spots

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