Cyclo-depolymerisation of poly(ethylene naphthalene-2,6-dicarboxylate) andring-opening polymerisations of the cyclic oligomers obtained

Commercial poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) was cyclo-dep olymerised by treatment of a suspension in 1,2-dichlorobenzene at 180 degre es C with 3 mol% of di-n-butyltin oxide as a catalyst. The cyclic oligomers , produced in up to 93% yield, were characterised by gel permeation chromat ography, H-1 NMR spectroscopy and mass spectrometry. The products contained cyclic oligomers ranging from the dimer up to at least the nonamer, with t he trimer being the most abundant. Careful column chromatography of the mix ture allowed pure samples of the cyclic trimer and tetramer to be isolated. Ring-opening polymerisation of the mixture of cyclic oligomers could be ac hieved by heating the mixture with a catalytic amount of di-n-butyltin oxid e at 350 degrees C for 10 min. These interconversions of PEN and the corres ponding cyclic oligomers form the basis of a potential method to recycle th is valuable commercial polymer. Cyclic oligomers were similarly prepared fr om commercial poly(ethylene terephthalate) (PET) and these were then homopo lymerised and copolymerised with the cyclic oligomers from PEN.