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Autor

  • Kricheldorf, Hans R. (3)
  • Weidner, Steffen (3)
  • Scheliga, Felix (1)

Erscheinungsjahr

  • 2018 (1)
  • 2017 (2)

Referierte Publikation

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  • Ring-opening polymerization (2)
  • Catalysts (1)
  • Cyclisation (1)
  • Equilibration (1)
  • Lactides (1)
  • MALDI TOF MS (1)
  • MALDI-TOF MS (1)
  • Mass spectrometry (1)
  • Morphology (1)
  • Polyester (1)
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Organisationseinheit der BAM

  • 1 Analytische Chemie; Referenzmaterialien (3)
  • 1.3 Strukturanalytik (3)

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Transesterification in the solid state of cyclic and linear poly(l-lactide)s (2017)
Weidner, Steffen ; Kricheldorf, Hans R.
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 intermolecular transesterification is even observed at 100 and 80 °C in the solid state. However, cyclic tin mercaptide catalysts transform the initial most probable distribution into a MWD with maxima, which display a conspicuous fine structure due to a preferential crystallization of certain ring sizes. The optimum ring sizes for the crystallization are provided by ring-ring equilibration. The gradual formation of a special morphology shifts the melting temperature to values up to 187 °C. Annealing of commercial poly(l-lactide) with a cyclic tin catalyst also yields a distribution of mass peaks with a maximum showing the characteristic fine structure.
Ring-expansion polymerization of meso-lactide catalyzed by dibutyltin derivatives (2018)
Kricheldorf, Hans R. ; Weidner, Steffen
Meso-Lactide was polymerized in bulk at 60, 80, and 100 °C by means of three different types of catalysts: dibutyltinsulfides (2,2-dibutyl-2-stanna-1,3-dithiolane and 2,20-dibutyl-2-stanna-1,3-dithiane), dibutyltin derivatives of substituted cate-chols (BuCa, CyCa, and BzCa), and dibutyltin derivatives of2,2 dihydroxybiphenyl (SnBi) and 2,2-dihydroxy-1,10-binaphthyl(SnNa. Only the latter two catalysts were active at 60 °C. The architecture of the resulting polylactides depends very much on the structure of the catalyst and on the temperature. At the lowest temperature (60 °C), SnBi and SnNa mainly yielded even-numbered linear chains, but SnNa also yielded even-numbered cycles at 100 °C and short reaction times. In contrast,BuCa, CyCa, and BzCa mainly yielded odd-numbered cycles, although the same catalysts yielded even-numbered linear chains when benzylalcohol was added.
Cyclic poly(l-lactide) via ring-expansion polymerization by means of dibutyltin 4-tert-butylcatecholate (2017)
Kricheldorf, Hans R. ; Weidner, Steffen ; Scheliga, Felix
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 bisalkoxides, neat BuCa yields cyclic poly(l-lactide)s via a fast ring-expansion polymerization. Under certain conditions, a high-melting crystalline phase (Tm = 191 °C) is obtained. At 160 °C and short reaction times even-numbered cycles are slightly prevailing, but, surprisingly, at 120 °C, odd-numbered cycles are predominantly formed. These results definitely prove that a ring-expansion mechanism is operating.
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