A new route for the preparation of enriched iso-polylactide from rac-lactide via a Lewis acid catalyzed ring-opening of an epoxide

Tetraphenylporphyrin aluminum(iii) salts, TPPAlX, where X = Me, OEt, OiPr, OCHMeCH Cl, and Cl, and bis(triphenylphosphine)imminium chloride, PPN Cl (1 : 1) react with rac-lactide, rac-LA, in neat propylene oxide, PO, to yield chains of enriched isotactic polylactide, PLA, with end groups of PO-Cl and with time these yield cyclic polymers (PO) (PLA) where n = 2 or 3 and even higher. There is no reaction between TPPAlOR (R = Et or Pr), PPN Cl , and rac-LA in neat THF at 25 °C even though TPPAlOR (R = Et or Pr) and PPN Cl in neat PO yields polypropylene oxide with a terminal OR group, H(PO) OR. Taken together, Al(iii) acts as a Lewis acid in the ring-opening of PO, in which PPN Cl is present and the incipient ClCH CHMeO initiates the ROP of LA to yield anion chains of [(PLA)-OCHMeCH Cl] , and then the ring-opening of PO yields cycles, (PO) (PLA), with the liberation of Cl . The polymer was isolated by the addition of MeOH/HCl and end group analysis by mass spectrometry.