Benzyl bispidine as an efficient replacement for (−)-sparteine in ring opening polymerisation

The synthesis and application of a dibenzyl-functionalized bispidine, in combination with 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexylthiourea (TU) co-catalyst, has been demonstrated to be an excellent catalyst for the controlled ring-opening polymerisation (ROP) of lactide and cyclic carbonate monomers. Notably, the polymerisation proceeds with negligible transesterification or epimerisation, with the polymerisation of stereopure L-lactide affording highly crystalline poly(lactide) with a Tm of 156 °C. ROP of racemic lactide results in the observation of a modest degree of stereocontrol such that the probability of isotactic enchainment, Pm = 0.74. Comparison of a range of alternative hydrogen bond donor co-catalysts revealed that TU displayed the highest polymerisation rates in combination with the dibenzyl-functionalized bispidine.