SnOct2-Catalyzed Syntheses of Cyclic Poly(l-lactide)s with Catechol as Low-Toxic Co-catalyst
- 10 Downloads
Polymerizations of l-lactide in bulk at 160 or 180 °C were performed with 1/1 mixtures of catechol (CA) or 4-tert-butylcatechol (BuCA) and tin(II)-2-ethylhexanoate (SnOct2) as catalysts and a variation of the Lac/Cat ratio. Weight average molar masses (Mw) up to 170,000 g mol−1 were obtained with CA and up to 120,000 g mol−1 with BuCA. The cyclic structure of the resulting poly(l-lactide)s was proven by MALDI-TOF mass spectrometry and by comparison of their hydrodynamic volumes with those of commercial linear poly(l-lactide)s. The predominance of even-numbered cycles increased with lower temperatures and shorter polymerization times. This finding indicates that the cyclic architecture is the results of a ring-expansion polymerization mechanism. Addition of silylated BuCA as co-catalyst was less favorable than addition of free BuCA.
KeywordsPolylactides Cycles Catechol Ring-expansion polymerization MALDI-TOF mass spectrometry
We wish to thank Profs G. Luinstra and H.-U. Moritz (TMC, Hamburg) and BAM (Berlin) for technical support. Furthermore, we thank Mrs. Rosemarie Laging (BAM, Berlin) for the SEC measurements.
Compliance with Ethical Standards
Conflict of interest
The authors declare no competing or financial interests.
- 1.EthiconInc, Offen. G, 2162900. (1973) Chemical Abstracts 76:73051wGoogle Scholar
- 2.Kanesh GB, Sanchez-Riem F, Svenson DK (1994) Polymers of lactic acid. In: Mobley DP (ed) Plastics from Microbs. Hanser, München, p 1994Google Scholar
- 8.Schmitt EE, Polistina RA, (1967), Cyanamide A, US, 32397033/3463158Google Scholar
- 24.Weidner SM, Kricheldorf HR (2017) The role of transesterification in SnOct2-catalyzed polymerizations of lactides. Macromol Chem Phys 218:1600Google Scholar
- 29.Bigg DM (1996) Annual Technical Conference—Society of Plastic Engineers 30:2028Google Scholar