Polymerization of epoxide monomers promoted by tBuP4 phosphazene base: a comparative study of kinetic behavior

Abstract

The kinetics of the anionic ring-opening polymerizations (AROP) of epoxide monomers, 1,2-epoxybutane (BO), 1,2-epoxypropane (PO), tert-butyl glycidyl ether (tBuGE), allyl glycidyl ether (AGE), benzyl glycidyl ether (BnGE), and ethoxyethyl glycidyl ether (EEGE), was investigated using benzyl alcohol/tBuP₄ as the initiating system. All the polymerizations proceed in a controlled manner following a first order kinetics with respect to the monomer. The influence of the side chains borne by the oxirane ring was evidenced. Propagating centers derived from epoxide bearing heretoatom-containing side chains display higher reactivities and propagation rates. A reactivity scale has been established and is as follows, k_p,BnGE > k_p,AGE > k_p,EEGE ≫ k_p,tBuGE ≈ k_p,PO > k_p,BO. Using BO as the model monomer and different initiator concentrations, the nature of the propagating species has been identified as ion pairs. The influence of a Lewis acid addition on the monomer reactivities and on the control of the polymerization was also investigated. In the presence of triisobutylaluminum (iBu₃Al), polymerization kinetics was faster but led to a broadening of the molar mass distributions. The monomer reactivity scale was also strongly modified with k_p,PO > k_p,BO > k_p,EEGE ≈ k_p,AGE > k_p,BnGE ≈ k_p,tBuGE. The polymerizations of PO, BO and tBuGE follow zero order kinetics which is not the case for the other oxirane monomers.