46498 2018 eng 2730 2738 24 56 article Wiley Periodicals 1 -- -- -- Spirocyclic phenoxides of germanium, zirconium, and tin were prepared from 2,20-dihydroxybiphenyl and 2,20-dihydroxy-1,10-binaphthyl. Ring-expansion polymerizations of L-lactide are mainly studied at 160 or 180 °C. The reactivity of the catalysts increases in the order: Zr < Ge < Sn. Regardless of catalyst, the weight-average molecular weights (Mw) never exceed 50,000 g mol−1. The resulting poly(L-lactide)s are optically pure and have a cyclic architecture. Decreasing temperature and time favor Formation of even-numbered cycles, and at 102 ° cyclics, almost free of odd-numbered rings are obtained. Analogous polymerizations of meso-lactide give similar results >120 °C, but different results at 100 or 80 °C. Surprisingly, bell-shaped narrow molecular weight distributions are obtained <140 °C, resembling the pattern of living polymerizations found for alcohol-initiated polymerizations. An unusual transesterification mechanism yielding narrow distributions of odd-numbered cycles is discovered too. Journal of Polymer Science A: Polymer Chemistry 10.1002/pola.29259 0887-624X 1099-0518 30.11.2018 Steffen Weidner H. R. Kricheldorf eng uncontrolled Cyclization eng uncontrolled Polylactides eng uncontrolled MALDI-TOF MS eng uncontrolled Ring-opening polymerization eng uncontrolled Spirocyclic Ingenieurwissenschaften und zugeordnete Tätigkeiten Verlagsliteratur Datei im Netzwerk der BAM verfügbar ("Closed Access")