Yttrium-Mediated Ring-Opening Copolymerization of Oppositely Configurated 4-Alkoxymethylene-β-Propiolactones: Effective Access to Highly Alternated Isotactic Functional PHAs.

The ring-opening copolymerization (ROCOP) of functional 4-alkoxymethylene-β-propiolactones (BPLOR s) by yttrium-bisphenolate complexes was investigated. The ROCOP of equimolar mixtures of BPLOR s of opposite configurations, namely (R)-BPLOR1 /(S)-BPLOR2 [R1 , R2 =OMe, OAllyl, OCH2 Ph (=OBn), OSiMe2 tBu (=OTBDMS)], by the syndioselective Y{ONOOcum }/iPrOH catalyst/initiator system affords P(HBOR1 -alt-HBOR2 ) copolymers with high alternation degrees (altern.=89-94 %), as determined by comprehensive kinetic, 13 C{1 H} NMR spectroscopy, MALDI-ToF MS and ESI MS/MS fragmentation studies. The ROCOP of the (R)-BPLOMe /(S)-BPLOTBDMS combination, featuring a large difference in the substituents' bulkiness, constitutes the only observed exception to this trend (altern.=64 %). On the other hand, the isoselectivity of the Y{ONNOCl }/iPrOH catalyst/initiator system has been exploited to generate, in a one-pot/one-step procedure, original mixtures of isotactic poly(hydroxyalkanoate)s (PHAs). This system efficiently transforms equimolar mixtures of (R)-BPLOAll /(S)-BPLOMe into a 1:1 mixture of the corresponding isotactic iso-(R)-PHBOAll and iso-(S)-PHBOMe homopolymers; almost no copolymerization defects are observed. This new approach has been extended successfully to the ROCOP of equimolar mixtures of racemic monomers, rac-BPLOAll /rac-BPLOMe .