About formation of cycles in Sn(II) octanoate‐catalyzed polymerizations of lactides. Issue 17 (9th August 2018)

• Record Type: Journal Article
• Authors: Kricheldorf, Hans R.; Weidner, Steffen M.; Scheliga, Felix
• Is Part Of: Journal of polymer science. Volume 56:Issue 17(2018)
• Page Start: 1915
• Page End: 1925
• Publication Date: 2018-08-09
• Subjects: cyclization -- MALDI TOF mass spectrometry -- polyester -- ring‐opening polymerization -- transesterification; 547
• DOI: 10.1002/pola.29077
• Languages: English
• ISSNs: 0887-624X

Abstract

ABSTRACT: At first, formation of cycles in commercial poly(l ‐lactide)s is discussed and compared with benzyl alcohol‐initiated polymerizations performed in this work. This comparison was extended to polymerizations initiated with 4‐cyanophenol and pentafluorothiophenol which yielded cyclic polylactides via end‐biting. The initiator/catalyst ratio and the acidity of the initiator were found to be decisive for the extent of cyclization. Further polymerizations ofl ‐lactide were performed with various diphenols as initiators/co‐catalysts. With most diphenols, cyclic polylactides were the main reaction products. Yet, only catechols yielded even‐numbered cycles as main reaction products, a result which proves that their combination with SnOct2 catalyzed a ring‐expansion polymerization (REP). The influence of temperature, time, co‐catalyst, and catalyst concentrations was studied. Four different transesterification reactions yielding cycles were identified. For the cyclic poly(l ‐lactide)s weight average molecular weights ( M w 's) up to 120, 000 were obtained, but 1 H NMR end group analyses indicated that the extent of cyclization was slightly below 100%. The influence of various parameters like structure of initiator and catalyst and temperature on the formation of cyclic poly(l ‐lactide)s has been investigated. Depending on the chosen conditions, the course of the polymerization can be varied from a process yielding exclusively linear polylactides to mainly cyclic polylactides. Three different reaction pathways for cyclization reactions have been identified. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2018, 56, 1915–1925 Abstract : The influence of various parameters like structure of initiator and catalyst and temperature on the formation of cyclic poly(l ‐lactide)s has been investigated. Depending on the chosen conditions, the course of the polymerization can vary from a process yielding exclusively linear polylactides to mainly cyclic polylactides. Three different reaction pathways for cyclization reactions have been identified.