Iodine: A ring opening polymerization catalyst for tetrahydrofuran

Abstract

Tetrahydrofuran (THF) undergoes ring opening polymerization when treated with iodine at a molar ratio ( THF I 2 ) ranging from 30:1 to 9:1. The polymer obtained is high molecular weight polyTHF with a viscosimetric molecular weight ranging from 100,000 to 800,000 Dalton. The structure of the polymer obtained was elucidated by means of FTIR and 1H-NMR spectroscopy in comparison with an authentic sample of polyTHF. The interaction between THF and iodine at early stages of polymerization was investigated by means of electronic spectroscopy which shows that there is a charge transfer interaction with formation of THF oxonium ions and both I 3 − and I 5 − counterions. The propagation mechanism involving oxonium ions (already proposed also in the presence of other initiators) seems to work also in this system. Other potential initiators such as the interhalides IBr, ICl 3 and an iodine-pyridine complex have also been tested and found ineffective as initiators of THF polymerization. The thermal properties of the high molecular weight polyTHF obtained with iodine as catalyst were studied by DSC and found to be as follows: T g = −80.8 ° C, T m = +44 ° C, ΔH m = 1.69 kcal mol , ΔS m = 5.33 cal k mol . It is outlined that iodine could be a convenient initiator from the industrial standpoint for THF polymerization since it is completely recoverable at the end of each batch and can be re-used for new productive batches.