This Perspective article summarizes efforts paid in our group to develop efficient metal-based catalysts for the immortal ring-opening polymerization (iROP) of cyclic esters in the presence of large amounts of alcohols (ROH) as chain transfer agents. The catalyst systems reviewed include discrete organometallic complexes based on rare earths, magnesium, calcium and more specifically zinc, as well as simple systems employing metal triflate salts, notably Al(OTf)(3), for the (stereo)controlled iROP of lactide (LA), beta-butyrolactone (BBL) and trimethylenecarbonate (TMC). Special emphasis is given to systems that allow the use of minute amounts of metal catalysts and large loadings of both monomer and alcohol for the rapid and productive formation of functional polyesters (H-Pol-OR) with controlled molecular features.

International audienceThe controlled ring-opening polymerization of racemic allyl-β-butyrolactone (rac-BLallyl) in toluene or in bulk, catalyzed by the discrete β-diiminate zinc amido [(BDIiPr)Zn(N(SiMe3)2)] (1) or {amino-methoxy-bis(phenolate)}yttrium amido [(ONOOtBu)Y(N(SiHMe2)2)(THF)] (2) complexes, in association with an alcohol, gave poly(β-hydroxyalkanoate)s (PHAs) with allylic side chains. These PHAsallyl exhibit either a slightly isotactic-enriched (Pm = 0.61) or highly syndiotactic-enriched (Pr = 0.82) backbone structure, respectively, with high molar mass (Mn up to 21,100 g mol−1) and narrow molar mass distribution values (1.05 < Mw/Mn < 1.28), as evidenced by detailed 13C NMR and size exclusion chromatography analyses. Postpolymerization rhodium-catalyzed hydroboration of the resulting PHAsallyl with pinacolborane quantitatively afforded the corresponding PHAsboron. Introduction of boron into the pendant chains did not alter neither the structure of the polymer backbone nor the macromolecular features (Mn, Mw/Mn, and stereoregularity). However, differential scanning calorimetry analyses revealed a significant increase of the glass transition temperature on modifying the allyl for the boron function in these PHAs