Mechanistic studies for the polymerization of 2,6-dimethylphenol to poly(2,6-dimethyl-1,4-phenylene ether): LC-MS analyses showing rearrangement and redistribution products

For a detailed investigation of the mechanism of the oxidative coupling polymerization of 2,6-dimethylphenol (DMP) to poly(2,6-dimethyl-1,4-phenylene ether) (PPE), reactions were carried out with a mixture of 4-(2',6'-dimethylphenoxy)-2,6-dimethylphenol (DMP-dimer) and 2,4,6-trimethylphenol, under a dioxygen atmosphere using a copper(II)-NMeim catalyst (NMeim = N-methylimidazole). Oxidative coupling experiments were performed for very short reaction times in order to detect any intermediate or hybrid compounds (i.e. when starting from mixtures of the parent phenols) generated during the early stages of the polymerization process. The LC-MS chromatograms of the samples collected reveal peaks which indicate the formation of (i) DMP-monomer; (ii) dimer which is a hybrid of the parent phenols; (iii) DMP-trimer; (iv) trimer which is a hybrid of parent phenols. Formation of DMP monomer and these oligomers are in support of the formation of a quinone-ketal during the reaction. The phenol-ketal further undergoes redistribution (to form monomer and hybrid dimer) and rearrangement (to form trimers). So, these studies further corroborate the formation of a quinone-ketal already during the first steps of the polymerization process. (c) 2006 Elsevier B.V. All rights reserved.