Issue 9, 2014

High-speed organocatalytic polymerization of a renewable methylene butyrolactone by a phosphazene superbase

Abstract

The 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-P4, essentially barrier-less chain propagation through rapid conjugate addition of the enolate anion stabilized by the nano-size cation [t-Bu-P4H]+ 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.

Graphical abstract: High-speed organocatalytic polymerization of a renewable methylene butyrolactone by a phosphazene superbase

Article information

Article type
Paper
Submitted
09 Nov 2013
Accepted
09 Dec 2013
First published
28 Jan 2014

Polym. Chem., 2014,5, 3261-3270

High-speed organocatalytic polymerization of a renewable methylene butyrolactone by a phosphazene superbase

M. Schmitt, L. Falivene, L. Caporaso, L. Cavallo and E. Y.-X. Chen, Polym. Chem., 2014, 5, 3261 DOI: 10.1039/C3PY01579C

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