Polylactides - synthesis,characterization and medical application

Polymerizations of lactides via cationic, anionic, and insertion mechanisms are described. The usefulness of these three mechanisms for preparative purposes is evaluated. The polymerization mechanisms initiated by Al-alkoxides or Sn(II)-2-ethylhexanoate are discussed in more detail. Furthermore, the usefulness of ¹³C NMR spectroscopy for the sequence analysis of copolylactones is demonstrated. Copolyesters of D,L-lactide and ϵ-caprolactone with T_g's around 35°C and high transparency were synthesized. Films of these copolylactones were characterized by various methods and their usefulness as resorbable wound dressing was evaluated. More than 30 patients were successfully treated with this novel wound dressings.     

Anionic and pseudoanionic polymerization of lactones - a comparison

Polymerization via anionic mechanisms or insertion mechanisms (pseudoanionic mechanisms) are compared for β-lactones and L-lactide. The following aspects are discussed: initiation and deprotonation of β-lactones, back-biting degradation, stereosequences of poly(β-D,L-butyrolactone), racemization of L-lactide, systematic variation of endgroups including synthesis of macromers.     

Beitrag zum röntgenographischen Nachweis von Phasen mit geringen Volumenanteilen

Following quantum counting statistical considerations relations were derived which enable to estimate the error of integral intensity measurements of weak interferences and the minimal detectable volume parts of minority phases as a function of the measuring conditions and of the given error limits, and to optimize the choice of radiation and monochromatization conditions for the X-ray analysis of minority phases.     

f-block MOFs: A Pathway to Heterometallic Transuranics

A novel series of heterometallic f-block-frameworks including the first examples of transuranic heterometallic ²³⁸U/²³⁹Pu-metal–organic frameworks (MOFs) and a novel monometallic ²³⁹Pu-analog are reported. In combination with theoretical calculations, we probed the kinetics and thermodynamics of heterometallic actinide(An)-MOF formation and reported the first value of a U-to-Th transmetallation rate. We concluded that formation of uranyl species could be a driving force for solid-state metathesis. Density of states near the Fermi edge, enthalpy of formation, band gap, proton affinity, and thermal/chemical stability were probed as a function of metal ratios. Furthermore, we achieved 97 % of the theoretical maximum capacity for An-integration. These studies shed light on fundamental aspects of actinide chemistry and also foreshadow avenues for the development of emerging classes of An-containing materials, including radioisotope thermoelectric generators or metalloradiopharmaceuticals.     

Resorbable initiators for polymerizations of lactones

Numerous nontoxic (resorbable) salts were prepared from cations and anions belonging to the human metabolism, such as Na, K, Mg, Ca, Zn and Fe in combination with chloride, iodide, hydroxide, carbonate, acetate, stearate, glycolate, L‐lactate, D‐mandelate and various N‐substituted α‐amino acids. All these salts were used as initiators for polymerizations of L‐lactide in bulk at 100–180°C. Furthermore, Grignard reagents, hemin and hematin were included in this study. Zn L‐lactate was found to be the most useful initiator in terms of reactivity, maximum molecular weight of the isolated poly(L‐lactide) and its optical purity. Zn L‐lactate initiated copolymerizations of L‐lactide and glycolid or L‐lactide and ϵ‐caprolactone were also studied. Finally, first studies of the polymerization mechanism of zinc stearate and zin 2‐ethylhexanoate were performed. They suggest that zinc carboxylates combined with an alcohol as coinitiator form reactive zinc alkoxides which are the true initiators at temperatures < 150°C.