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  • Weidner, Steffen (2)
  • Kricheldorf, H. (1)
  • Kricheldorf, Hans R. (1)
  • Scheliga, F. (1)
  • Scheliga, Felix (1)

Erscheinungsjahr

  • 2019 (1)
  • 2017 (1)

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  • MALDI TOF MS (2) (entfernen)

Organisationseinheit der BAM

  • 1.3 Strukturanalytik (2) (entfernen)

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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.
Cyclic poly(lactide)s via the ROPPOC method catalyzed by alkyl- or aryltin chlorides (2019)
Kricheldorf, H. ; Weidner, Steffen ; Scheliga, F.
A comparison of tributyltin chloride, dibutyltin dichloride,and butyltin trichloride as catalysts of ring-opening polymerizations(ROPs) of l-lactides at 160°C in bulk reveals increasing reactivity in the above order, but only the least reactive catalysts, Bu3SnCl, yield a uniform reaction product, namely cyclic poly(L-lactide)s with weight average molecular weights (Mw ́s) in the range of 40,000–80,000. A comparison of dimethyltin , dibutyltin , and diphenyltin dichlorides resulted in the following order of reactivity: Me2SnCl2<Bu2SnCl2<<Ph2SnCl2. In this series also, the most reactive catalyst yields cyclic polylactides, but the extent of cyclization varies with the molecular weight. The formation of cyclic polylactides is explained by ROP combined with simultaneous polycondensation involving end-to-end cyclization (ROPPOC method). ROP of meso-lactide at 80 or 60°C yields even-numbered linear chains as main products, a result supporting the ROPPOC mechanism.
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