Cyclic Poly( sc xmlns='http://www.wiley.com/namespaces/wiley'l/scl ‐lactide) via Ring‐Expansion Polymerization by Means of Dibutyltin 4‐ i xmlns='http://www.wiley.com/namespaces/wiley'Tert/iTert ‐Butylcatecholate

摘要

Abstract 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.