title: Coupling of propylene oxide and lactide at a porphyrin chromium(III) center.
abstract: 5,10,15,20-Tetraphenylporphyrin chromium chloride (TPPCrCl) with added [Ph3P═N═PPh3](+)Cl(-) (PPN(+)Cl(-)) selectively polymerizes lactide (L and rac) dissolved in neat propylene oxide (PO) to yield polylactide (PLA) terminated by the -OCHMeCH2Cl group. At 0 °C and below, rac-LA yields polymers highly enriched in isotactic tetrads (iii). At 25 °C, some stereoselectivity is lost as transesterification becomes significant, and at 60 °C and above, enchainment of PO leads to the formation of 3,6-dimethyl-1,4-dioxan-2-one by a backbiting mechanism. At 0 °C, after the enchainment of L-(S,S)-LA in neat (R)-(+)-PO, the formation of (3S,6R)-3,6-dimethyl-1,4-dioxan-2-one occurs, while at higher temperatures the ratio of (3S,6R)-3,6-dimethyl-1,4-dioxan-2-one to (3R,6R)-3,6-dimethyl-1,4-dioxan-2-one falls to 3:2.
authors: Department of Chemistry and Biochemistry, The Ohio State University , 100 West 18th Avenue, Columbus, Ohio 43210, United States.
authors: Vagulejan
authors: V
authors: Balasanthiran
authors: Chandrani
authors: C
authors: Chatterjee
authors: Malcolm H
authors: MH
authors: Chisholm
authors: Nicole D
authors: ND
authors: Harrold
authors: T V
authors: TV
authors: RajanBabu
authors: Grant A
authors: GA
authors: Warren
mesh_terms: D002857:Chromium / Q000737:chemistry*; D004146:Dioxanes / Q000737:chemistry*; D004852:Epoxy Compounds / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*
chemical_list: D004146:Dioxanes; D004852:Epoxy Compounds; D008665:Metalloporphyrins; D002857:Chromium; C091880:dilactide; C009068:propylene oxide