Issue 21, 2016

Depolymerization of 1,4-polybutadiene by metathesis: high yield of large macrocyclic oligo(butadiene)s by ligand selectivity control

Abstract

Herein, we demonstrate a practical high yield preparation of large macrocyclic oligo(butadiene)s, preferably the C16 to C44 fraction, from commercial 1,4-polybutadiene by exploring intramolecular backbiting using a series of commercially available Ru catalysts. Product contamination with linear fragments is restricted by using high molecular weight 1,4-polybutadiene with a low content of 1,2-constructs (vinyl groups). The distribution of the cyclic compounds is largely dependent on the nature of the ligand structure of the Ru catalyst. Kinetic inspection of the reaction reveals a two-step mechanism involving (i) backbiting of the linear polymer with initial formation of large macrocycles followed by (ii) tandem ring-opening ring-closing metathesis predominantly leading to thermodynamically favorable t,t,t-cyclododecatriene (CDT). In particular, second-generation Ru catalysts with N-heterocyclic carbene (NHC) ligands favor undesired CDT formation. First-generation catalysts, presumably due to their high barriers for formation of the intermediate metallacyclobutane, selectively form the C16 to C44 macrocyclic oligo(butadiene) fraction. For example, reaction of (HMW, 98% cis)-polybutadiene with a first-generation Ru catalyst almost yields 90% C16–C44 cyclic oligo(butadiene)s.

Graphical abstract: Depolymerization of 1,4-polybutadiene by metathesis: high yield of large macrocyclic oligo(butadiene)s by ligand selectivity control

Supplementary files

Article information

Article type
Paper
Submitted
28 Apr 2016
Accepted
20 Jun 2016
First published
20 Jun 2016

Catal. Sci. Technol., 2016,6, 7708-7717

Depolymerization of 1,4-polybutadiene by metathesis: high yield of large macrocyclic oligo(butadiene)s by ligand selectivity control

A. Dewaele, T. Renders, B. Yu, F. Verpoort and B. F. Sels, Catal. Sci. Technol., 2016, 6, 7708 DOI: 10.1039/C6CY00933F

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