Syntheses of cyclic poly(lactones) by zwitterionic ring opening polymerization catalyzed by N‐heterocyclic carbene

Abstract

Synthesis of cyclic biopolymers from renewable monomers remains a big challenge because of lack of efficient catalysts. The organocatalyst of N‐heterocyclic carbene (NHC), (+)‐1‐methyl‐3‐menthoxymethyl imidazol‐2‐ylidene, is used to prepare cyclic polylactones including poly(ε‐caprolactone) (poly(ε‐CL)), poly(δ‐valearolactone) (poly(δ‐VL)), and poly(ε‐caprolactone‐co‐δ‐valearolactone) (poly(ε‐CL‐co‐δ‐VL)) via zwitterionic ring opening polymerization. The NHC catalyst is founded a highly efficient organic catalyst for the polymerization. The resulting cyclic polymers show a melting temperature (Tm) in a range of 20–60°C, which is dramatically lower than the Tm of cyclic poly(lactide) (Tm = 120–150°C). The resulting copolymer, cyclic poly(ε‐CL‐co‐δ‐VL) owns high molecular weight comparing with corresponding linear poly(ε‐CL‐co‐δ‐VL) produced by other catalysts. The synthesized cyclic homo and copolymers were characterized by 1H‐, 13C‐NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry–thermogravimetric analysis and matrix‐assisted laser desorption ionization‐time of flight mass spectrometry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Advanced Developments in Cyclic Polymers: Synthesis, Applications, and Perspectives

“…Considering the depletion of fossil‐based material resources and the ultimate fate of the large‐scale commodity polymers, synthesis of cyclic polymers from renewable resources has become increasingly important. Therefore, within the reported cyclic polymers, cyclic polyesters from biodegradable monomers, such as lactide and ɛ‐caprolactone, have attracted more interest within the community . The use of metal‐coordination initiators catalyzing ROP of cyclic ester monomers is widely recognized as an efficient process to produce linear polyesters with well‐controlled molecular weights, compositions, and microstructures .…”

“…NHC catalysts are generally air and moisture sensitive, and that makes it inconvenient to scale up the process. Zhu, et al have reported that an NHC catalyst produced in situ from 1‐methyl‐3‐menthoxymethyl imidazolium chloride (Figure ) is relatively robust and highly active for the ROP to produce polylactones . The NHC precursor is much cheaper and more active in comparison with the commonly used 1,3‐bisarylimidazolium chloride (Figure .…”

“…Therefore, within the reported cyclic polymers, cyclic polyesters from biodegradable monomers, such as lactide and e-caprolactone, have attracted more interestw ithin the community. [94][95][96][97] The use of metal-coordination initiators catalyzing ROP of cyclic ester monomers is widely recognized as an efficient process to produce linear polyesters with well-controlledm olecular weights, compositions, and microstructures. [98,99] However,t he residual metal impuritiesw hich are cytotoxic, may limit the wide applicationso f the derived polymers, particularly pharmaceutical andbiomedical.…”

“…Zhu,e ta lh ave reported that an NHC catalystp roduced in situ from 1-methyl-3-menthoxymethyl imidazolium chloride (Figure 15) is relativelyr obust and highly activef or the ROP to produce polylactones. [95][96][97] The NHC precursor is much cheaper and more active in comparison with the commonly used 1,3-bisarylimidazolium chloride (Figure 15. It was first reported that NHC carbene derived from enantiomeric forms of (+ +)-1-methyl-3-menthoxymethyl imidazolium chloride precursor displayed higher activity towards llactide (l-LA, with ap roduct yield of 80 wt %, molecular weight (M w )o f6 9404 and molecular weight density (MWD) of 1.89) than d-lactide( d-LA, with ap roduct yield 40 wt %, M w of 27 224 and MWD of 1.64) with significantly highm olecular weight.…”

The use of stable carbene‐CO2 adducts for the polymerization of trimethylene carbonate

“…Since the 19th century, synthetic polymers have become an important material class. While some polymers are widely used industrially, there are still means to improve and develop macromolecular materials . Especially in the biomedical field, polymers are promising materials for stents, tissue replacement, drug delivery, or suture material .…”