Abstract
Chiral 4,8-diphenyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (DiPh-TBD) was synthesized and applied to a ring-opening polymerization of rac-lactide (rac-LA). The chiral DiPh-TBD promoted the synthesis of isotactic enriched polylactides (PLAs) with controlled molecular weight and narrow molecular weight distributions under mild, metal-free conditions. When the [rac-LA]/[Cat.] ratio was 100/1, full monomer conversion was achieved within only 1 min and a moderate probability of 0.67 meso dyads (Pm) was obtained at room temperature. A chain-end control mechanism (CEC) was found to be responsible for the isoselectivity based on the homodecoupled 1H NMR spectrum, the chiral HPLC measurement, and kinetic studies.
Highlights
Compared with many commercial synthetic polymers, polylactides (PLAs) have gained significant recognition due to their divergent properties of biodegradability and biocompatibility, and have found a wide range of applications in textile, pharmaceutical, packing, electronic, and biomedical fields [1,2]
Few studies have reported the synthesis of isotactic PLAs directly from rac-LA using either achiral or chiral organocatalysts [12,13,14,15,16,17,18,19,20,21,22,23]
Two methods are involved in controlling the stereoselectivity of the ring-opening polymerization (ROP) of rac-LA: a chain-end control (CEC) mechanism or an enantiomorphic site control (ESC) mechanism
Summary
Compared with many commercial synthetic polymers, polylactides (PLAs) have gained significant recognition due to their divergent properties of biodegradability and biocompatibility, and have found a wide range of applications in textile, pharmaceutical, packing, electronic, and biomedical fields [1,2]. Crowded catalysts with a chiral rac-LA and achieved isotactic enriched PLAs with a Pm of 0.88 at 25 ◦ C [17] In this field, densely center offer highly stereoselective polymers in the aforementioned organocatalysts for the substituted chiral amino acids (Figure 1C) appeared as robust catalysts for the stereocontrolled ROP stereoselective ROP of rac‐LA. Densely center offer highly stereoselective polymers in the aforementioned organocatalysts for the substituted chiral amino acids (Figure 1C) appeared as robust catalysts for the stereocontrolled ROP stereoselective ROP of rac‐LA To further explore these factors, we anticipated that the introduction of rac-LA, as reported by Cossío et al In 2017.
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