Sarah Crotty

A strong cationic Brønsted acid, [H(OEt2)2][Al{OC(CF3)3}4], as an efficient initiator for the cationic ring-opening polymerization of 2-alkyl-2-oxazolines

In this contribution, the cationic ring-opening polymerization (CROP) and copolymerization of 2-ethyl-2-oxazoline and 2-tert-butyl-2-oxazoline using a strong cationic Bronsted acid, [H(OEt2)2][Al{OC(CF3)3}4], as an initiator are described. First, various poly(2-ethyl-2-oxazoline) (PEtOx) samples are prepared and the living/controlled character of the reaction is demonstrated. We could show that the microwave-assisted CROP of EtOx using this initiator system proceeds faster if compared to classical initiators such as methyl tosylate. These results were then extended to the CROP of poly(2-tert-butyl-2-oxazoline) (PtButOx) and to PEtOx/PtButOx random and block copolymers of different compositions. The resulting materials were characterized using spectroscopic (1H-NMR, FT-IR), chromatographic (SEC), and thermoanalytic techniques (DSC, TGA). Although samples containing more than 13 wt% PtButOx were insoluble in common organic solvents, thermogravimetric (TGA, DSC), spectroscopic (IR), scattering methods (wide-angle X-ray scattering, WAXS), and SEC in hexafluoro-iso-propanol (HFIP) hinted at the successful formation of block copolymers. In particular, WAXS revealed increasing crystallinity for samples containing higher weight fractions of PtButOx.

Molecular and Structural Characterization of Hybrid Poly(ethylene oxide)–Polyhedral Oligomeric Silesquioxanes Star-Shaped Macromolecules

Octafunctionalized spherosilsesquioxanes (Q8M8(H)), decorated with Si-H functions, could be used to design, by coupling via hydrosilylation with α-methoxy-ω-undecenyl poly(ethylene oxide)s (PEOs), organic-inorganic nanocomposite structures. (1)H, (13)C, and (29)Si NMR; size exclusion chromatography; and Fourier transfrom infrared spectroscopy were used to follow the grafting reaction and determine the molar mass and the functionality of the different species. Hybrid star-shaped poly(ethylene oxide)s of precise molar mass and functionality could be isolated by fractional precipitation of the raw reaction product. Absolute molar masses of the purified star-shaped PEOs, calculated with the assumption of a functionality of 8, were comparable when measured by light scattering in methanol and by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Small-angle X-ray scattering was employed to determine their molecular and structural characteristics, representing the versatility and innovative aspect to this study. Both differential scanning calorimetry and optical microscopy were utilized to elaborate and analyze the thermal properties and crystallization, respectively, of the hybrid stars. Further ongoing work is being carried out currently to investigate and foresee the use of longer PEO branches onto the core.

Star-shaped poly(2-ethyl-2-oxazoline) featuring a porphyrin core: synthesis and metal complexation

Abstract We demonstrate the synthesis of star-shaped poly(2-ethyl-2-oxazoline) featuring a porphyrin core starting from alkyne-functionalized porphyrin ([TPP-TB]4) and azide-functionalized poly(2-ethyl-2-oxazoline) (PEtOx-N3) via copper-catalyzed azide-alkyne cycloaddition (CuAAC). The porphyrin core was further utilized for the complexation of either copper or iron within the central cavity. The obtained materials were investigated using a combination of nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, size-exclusion chromatography, and matrix assisted laser desorption/ionization time-of-flight mass spectrometry. In the case of copper, the inclusion of the metal ion was achieved in a one-pot reaction during the CuAAC reaction for attaching the PEtOx-N3 arms.

Abundance correction for mass discrimination effects in polymer mass spectra: Mass discrimination effects in polymer mass spectra

RATIONALE Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is frequently used to analyze homo- and copolymers, i.e. for computing copolymer fingerprints. However, the oligomer abundances are influenced by mass discrimination, i.e. mass- and composition-dependent ionization. We have developed a computational method to correct the abundance bias caused by the mass discrimination. METHODS MALDI-TOFMS in combination with computational methods was used to investigate three random copolymers with different ratios of styrene and isoprene. Furthermore, equimolar high- and low-mass styrene and isoprene homopolymers (2500 and 4200 Da) were mixed and also analyzed by MALDI-TOFMS. The abundances of both copolymers and homopolymers were corrected for mass discrimination effects with our new method. RESULTS The novel computational method was integrated into the existing COCONUT software. The method was demonstrated using the measured styrene and isoprene co- and homopolymers. First, the method was applied to homopolymer spectra. Subsequently, the copolymer fingerprint was computed from the copolymer MALDI mass spectra and the correcting function applied. The changes in the composition are plausible, indicating that correction of copolymer abundances was reasonable. CONCLUSIONS Our computational method may help to avoid erroneous conclusions when analyzing copolymer MS spectra. The software is freely available and represents a step towards comprehensive computational support in polymer science. Copyright