PMLABe Diol Synthesized by Ring‐Opening Polymerization of Racemic Benzyl β‐Malolactonate Initiated by Rare‐Earth Trisborohydride Complexes: An Experimental and DFT Study

Abstract

Polymer diols are a class of polymeric building blocks of high interest for the synthesis of complex macromolecular edifices. Rare-earth borohydride complexes are known as efficient initiators for the ring-opening polymerization (ROP) of cyclic esters, directly affording α,ω-dihydroxy-telechelic polyesters. Here, were report the direct synthesis of poly(benzyl β-malolactonate) (PMLABe) diols, from the ROP of racemic (benzyl β-malolactonate) (rac-MLABe), a valuable and renewable monomer, initiated by the homoleptic [Ln(BH4 )3 (thf)3 ] (Ln=La, Nd, and Sm) complexes. These initiators enabled the controlled ROP of this β-lactone, affording well-defined syndiotactic-enriched (Pr ≈0.83) PMLABes (Mn up to 21 300 g mol(-1) , ÐM ≈1.5) as evidenced by size exclusion chromatography, (1) H and (13) C NMR spectroscopy, and MALDI-ToF mass spectrometry analyses. The first and second insertions of rac-MLABe, as assessed by DFT calculations, revealed more favorable stationary front-side than migratory back-side insertions, the thermodynamically and kinetically competitive ROP on two distinct arms with that on a one arm-only, and the thermodynamically slightly favored formation of syndiotactic-enriched PMLABes.

Highly Stereocontrolled Ring‐Opening Polymerization of Racemic Alkyl β‐Malolactonates Mediated by Yttrium [Amino‐alkoxy‐bis(phenolate)] Complexes

“…This result can be rationalized by competitive coordination of THF versus monomer onto the metallic center. Such behavior has previously been reported in the ROP of alike polar cyclic ester monomers …”

Coordination Ring-Opening Polymerization of Cyclic Esters: A Critical Overview of DFT Modeling and Visualization of the Reaction Mechanisms

“…Only a few publications have focused on quantum-chemical modeling of polymerization of β-lactones (Figure 2a). The first study on the DFT modeling of βBL polymerization considered the chromium complex 1 [35], but the most of the catalysts studied are rare-earth metal complexes represented by compounds 2 – 6 [36,37,38,39,40,41,42,43] (Figure 2b).…”

Highly Syndiotactic or Isotactic Polyhydroxyalkanoates by Ligand‐Controlled Yttrium‐Catalyzed Stereoselective Ring‐Opening Polymerization of Functional Racemic β‐Lactones

“…Reactivity of the catalyst systems in THF was significantly lower, [14] most likely as the result of competitive coordination of THF vs. monomer onto the metallic center; such a behavior has been previously observed in the ROP of alike polar cyclic ester monomers. [10,15] The reactions proceeded with a fair control over the PHB OR s molar masses. This is evidenced by (i) the quite good agreement between experimental molar mass values (Mn,NMR) and theoretical ones (Mn,theo), as determined by 1 H NMR analyses (from the isopropoxycarbonyl end-group and main-chain resonances), and monomer-to-initiator along with BPL OR conversion, respectively, (ii) the linear growth of experimental molar masses (e.g., Mn,NMR) as a function of monomer conversion as illustrated with BPL OAll (Figure S3), as well as (iii) the rather narrow dispersity values (1.07 < ÐM < 1.23) as determined by SEC analysis.…”