Ring-opening polymerisation of E⟩-caprolactone catalysed by Bronsted acids

Two new Bronsted acids [2,2'-ethylidene-bis (4,6-di-tert-butylphenol)] phosphoric acid (EDBPPOOH) and (3,3',5,5'-tetra-tert-butylbiphenyl-2,2'-diol) phosphoric acid (TBPO-POOH) were synthesised and fully characterised by H-1 NMR and C-13 NMR spectra and mass spectra. The ringopening polymerisation (ROP) of E >-caprolactone (E >-CL) catalysed by the two Bronsted acids proceeded at 110A degrees C without a solvent or at ambient temperature in toluene. Experimental results indicated that the two Bronsted acids were efficient catalysts for the ROP of E >-CL with moderate number-average molar mass (Mn) and narrow polydispersity indices (PDI). The catalytic activity of TBPO-POOH is higher than EDBP-POOH in the ROP of E >-CL. After benzyl alcohol was added, it was able to accelerate the polymerisation process. The polymerisation can also occur with the addition of water with a monomer/catalyst/initiator mole ratio of 100: 1: 1. The living polymerisation was ascertained by the linear relationships of the Mn vs. monomer conversion, then it was further confirmed by a second-feed experiment of a double monomer producing double Mn. A kinetic study of the relationships between monomer concentration and time revealed a first-order dependence on monomer concentration in the polymerisation. End-group analysis of H-1 NMR spectra and electrospray-ionisation mass spectra suggests that the two Bronsted acids are capable of catalysing and initiating the ROP of E >-CL. (C) 2014 Institute of Chemistry, Slovak Academy of Sciences