Pierre J. Lutz

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.

Polymerization of ethylene oxide under controlled monomer addition via a mass flow controller for tailor made polyethylene oxides

The synthesis of polymers with controlled molecular and structural parameters is challenging due to the required purity of the chemicals and the exclusion of protic impurities and oxygen in particular in the case of an anionic process as shown here. In addition, a pressure build-up in the case of gaseous monomers must be considered as well as other safety requirements regarding explosive and very toxic materials. In the present work, ethylene oxide was used as the monomer and converted to polyethylene oxide (PEO), and subsequently polyethylene glycol (PEG) via the anionic ring opening polymerization technique (AROP). Thereby, different homopolymers with a varying chain length were successfully synthesized with narrow molar mass dispersities (Đ between 1.03 up to 1.09). An important aspect to mention is that the obtained molar mass of the final products matches nicely with the theoretically calculated values by the application of a customized mass flow controller suitable for liquids and gases. Two of them were recently integrated into the existing equipment together with an automation and control system, enabling the exact and controlled addition of any monomer down to 0.1 g h−1 and up to 200 g h−1, even against higher pressure and at different temperatures. Since the automation can be controlled online, no person has to be present during the monomer addition, which leads to improved safeness for the operator. Together with online monitoring, e.g. with FT-IR or UV/Vis, polymerizations were performed more efficiently and faster to yield, e.g., PEG/PEO, which is nowadays an important polymer used in personal, home and health care applications due to the water solubility of low molar mass PEG/PEO in combination with a very low toxicity (for molar masses above 400 g mol−1).

Crystallization-Induced Confinement Enhances Glassy Dynamics in Star-Shaped Polyhedral Oligomeric Polysilesquioxane–Isotactic Polystyrene (POSS–iPS) Hybrid Material

In semicrystalline polymers, the segments around the crystallites typically relax significantly slower than in the purely amorphous phase. This results in an, on average, slower dynamics. Here we present a contrary effect in a star-shaped polymer based on a polyhedral oligomeric silesquioxane (POSS) molecule as center and isotactic polystyrene arms. Measurements by means of broadband dielectric spectroscopy reveal a reduction of the mean relaxation time by up to 1 decade. Analyzing the relaxation time distribution unravels three moieties of different dynamics beyond the crystalline fraction. These are assumed to form respective domains: a rigid amorphous fraction around crystallites, a mobile amorphous fraction, and a confined amorphous fraction of enhanced dynamics presumably located around the POSS centers. Probably, the crystallites in combination with the starlike architecture stabilize the average volume which balances the higher density of the growing crystallites by an increase in free volume in th...