Polymerization of epoxide monomers promoted by tBuP4 phosphazene base: a comparative study of kinetic behavior†
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, kp,BnGE > kp,AGE > kp,EEGE ≫ kp,tBuGE ≈ kp,PO > kp,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 kp,PO > kp,BO > kp,EEGE ≈ kp,AGE > kp,BnGE ≈ kp,tBuGE. The polymerizations of PO, BO and tBuGE follow zero order kinetics which is not the case for the other oxirane monomers.