Immortal ring-opening polymerization of β-butyrolactone with zinc catalysts: Catalytic approach to poly(3-hydroxyalkanoate)

The zinc alkoxide complex prepared in situ from the reaction of (BDI)Zn(N(SiMe3)2) (BDI = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene) with ROH (R = iPr or Bn = CH2Ph) is an efficient catalyst for both the solution and bulk ring-opening polymerization (ROP) of racemic-β-butyrolactone (BBL). The controlled “immortal” ROP of BBL using the binary catalytic system (BDI)Zn(N(SiMe3)2)/BnOH, where the alcohol acts both as co-initiator and chain transfer agent, proceeds smoothly under mild conditions (solution or bulk, 23-90 °C) to produce atactic poly(3-hydroxybutyrate) with moderate to high molar mass. For the first time, PHBs could be prepared from very small loadings of a metallic catalyst (100 ppm) via an “immortal” procedure, thereby allowing the growth of as many as 50-200 PHBs chains per metal center. Well-defined α-hydroxy,ω-alkoxy ester telechelic PHBs, of molar mass ranging up to M¯n=42,600gmol−1 were thus quantitatively obtained and fully characterized by NMR, MALDI-TOF MS and SEC analyses.

α-hydroxy,ω-alkoxy ester telechelic atactic poly(3-hydroxybutyrate), H-PHB-OR, of moderate to high molar mass (M¯nSEC≤42600g.mol−1) was synthesized from the controlled “immortal” ring-opening polymerization of β-butyrolactone (BBL) under mild conditions (solution or bulk, 23-90 °C) using [(BDI)Zn(N(SiMe3)2)] (BDI = CH(CMeNC6H3-2,6-iPr2)2) as catalyst precursor in the presence of an alcohol ROH (R = CHMe2 or CH2C6H5) acting both as co-initiator and chain transfer agent.