High-speed organocatalytic polymerization of a renewable methylene butyrolactone by a phosphazene superbase
KAUST DepartmentKAUST Catalysis Center (KCC)
Physical Sciences and Engineering (PSE) Division
Chemical Science Program
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AbstractThe organic phosphazene superbase, 1-tert-butyl-4,4,4-tris(dimethylamino)- 2,2-bis[tris(dimethylamino)phosphoranylid-enamino]-2λ5, 4λ5-catenadi(phosphazene) (t-Bu-P4), is found to directly initiate high-speed polymerization of the biomass-derived renewable γ-methyl-α-methylene-γ-butyrolactone (MMBL), in contrast to other polymerization systems using t-Bu-P4 which typically require addition of an organic acid or a nucleophile as a co-initiating component. This MMBL polymerization by t-Bu-P4 alone is extremely rapid; even with a low t-Bu-P4 loading of 0.1 mol% or 0.02 mol%, quantitative monomer conversion is achieved in 20 s or 1 min, respectively, affording medium to high molecular weight PMMBL bioplastics in a catalytic fashion. The combined experimental and theoretical/computational studies have yielded mechanisms of chain initiation through abstraction of a proton from a monomer by t-Bu-P 4, essentially barrier-less chain propagation through rapid conjugate addition of the enolate anion stabilized by the nano-size cation [t-Bu-P 4H]+ to the monomer, and chain termination through chain transfer to the monomer which generates a saturated termination chain end and the [t-Bu-P4H]+-stabilized anionic active species that starts a new chain. This journal is © the Partner Organisations 2014.
SponsorsThis work was supported by the US National Science Foundation (NSF-1300267) for the study carried out at Colorado State University. We thank Dr Yuetao Zhang for some initial experiments. LC thanks the HPC team of Enea (http://www.enea.it) for using the ENEA-GRID and the HPC facilities CRESCO (http://www.cresco.enea.it) in Portici, Italy.
PublisherRoyal Society of Chemistry (RSC)