3 years ago

Cyclic Poly(l-lactide) via Ring-Expansion Polymerization by Means of Dibutyltin 4-Tert-Butylcatecholate

Cyclic Poly(l-lactide) via Ring-Expansion Polymerization by Means of Dibutyltin 4-Tert-Butylcatecholate
Hans R. Kricheldorf, Steffen M. Weidner, Felix Scheliga
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. Dibutyltin derivatives of catechols catalyze ring-expansion polymerization of l-lactide yielding cyclic poly(l-lactide)s free of racemization and with high molecular weights. At relatively low temperatures, odd-numbered cycles are preferentially formed. The new tin catechol compounds also catalyze alcohol-initiated polymerizations that yield linear poly(l-lactide)s free of cycles.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/macp.201700274

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