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Cyclic Poly( l ‐lactide) via Ring‐Expansion Polymerization by Means of Dibutyltin 4‐ Tert ‐Butylcatecholate
Author(s) -
Kricheldorf Hans R.,
Weidner Steffen M.,
Scheliga Felix
Publication year - 2017
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.201700274
Subject(s) - catechol , polymerization , polymer chemistry , chemistry , benzyl alcohol , catalysis , ring opening polymerization , ring (chemistry) , medicinal chemistry , organic chemistry , polymer
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 ( T m = 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.