493025-70-0Relevant academic research and scientific papers
Single-site β-diiminate zinc catalysts for the ring-opening polymerization of β-butyrolactone and β-valerolactone to poly(3-hydroxyalkanoates)
Rieth, Lee R.,Moore, David R.,Lobkovsky, Emil B.,Coates, Geoffrey W.
, p. 15239 - 15248 (2002)
Polymerization of β-butyrolactone (BBL) and β-valerolactone (BVL) using the zinc alkoxide initiator (BDI-1)ZnO/Pr [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] proceeds very rapidly under mild conditions to produce poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyvalerate) (PHV), respectively. For the monomer-to-initiator ratio 2001, PHB number-average molecular weights (Mn) are proportional to conversion throughout the reaction and polydispersity indices (PDIs) are narrow, consistent with a living polymerization. Higher monomer-to-initiator ratios can be used to achieve high molecular weight PHB (Mn > 100 000). End-group analysis verifies that the polymerization of BBL follows a coordination-insertion mechanism, where complexes of the form (BDI-1)ZnOCH(Me)CH2-1)ZnOCH(Me)CH2-CO2R are the active species. Variable temperature NMR experiments show that (BDI-1)ZnO/Pr is monomeric in benzene-d6 solution. In contrast, (BDI-2)ZnO/Pr [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene] is a poor initiator at room temperature because it prefers to form a bis-μ-isopropoxide dimer in solution. According to kinetic studies, propagation by (BDI-1)ZnO/Pr is first order in both monomer as well as (BDI-1)ZnO/Pr concentration. These results lead us to propose a monometallic active species. Several results suggest that elimination side reactions are slowly catalyzed by zinc alkoxides, leading to degradation of the polymer.
