Organocatalytic Ring-Opening Polymerization of Morpholinones: New Strategies to Functionalized Polyesters

Abstract

The oxidative lactonization of N-substituted diethanolamines with the Pd catalyst [LPd­(OAc)]₂²⁺[OTf^–]₂ generates N-substituted morpholin-2-ones. The organocatalytic ring-opening polymerization of <i>N</i>-acyl morpholin-2-ones occurs readily to generate functionalized poly­(aminoesters) with <i>N</i>-acylated amines in the polyester backbone. The thermodynamics of the ring-opening polymerization depends sensitively on the hybridization of the nitrogen of the heterocyclic lactone. <i>N</i>-Acyl morpholin-2-ones polymerize readily to generate polymorpholinones, but the <i>N</i>-aryl or <i>N</i>-alkyl substituted morpholin-2-ones do not polymerize. Experimental and theoretical studies reveal that the thermodynamics of ring opening correlates to the degree of pyramidalization of the endocyclic N-atom. Deprotection of the poly­(<i>N</i>-Boc-morpholin-2-one) yields a water-soluble, cationic polymorpholinone